CA1063839A - Lubricants for powdered metals - Google Patents
Lubricants for powdered metalsInfo
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- CA1063839A CA1063839A CA206,086A CA206086A CA1063839A CA 1063839 A CA1063839 A CA 1063839A CA 206086 A CA206086 A CA 206086A CA 1063839 A CA1063839 A CA 1063839A
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Abstract
ABSTRACT OF THE DISCLOSURE
Discrete pressure-rupturable microcapsules for lubrication in powder metallurgy are disclosed comprising a core and a solid shell surrounding said core; the core comprises an organic liquid lubricant able to wet powdered metals, the shell comprises a thin non-atmospherically degradable polymeric material; the microcapsules may be used as the sole lubricant in the manufacture of sintered metal parts or may be used in admixture with other solid lubricants to produce beneficial synergistic effects.
Discrete pressure-rupturable microcapsules for lubrication in powder metallurgy are disclosed comprising a core and a solid shell surrounding said core; the core comprises an organic liquid lubricant able to wet powdered metals, the shell comprises a thin non-atmospherically degradable polymeric material; the microcapsules may be used as the sole lubricant in the manufacture of sintered metal parts or may be used in admixture with other solid lubricants to produce beneficial synergistic effects.
Description
This invention relates to lubricants for powder metallurgy and to the manufacture and use of lubricants.
More particularly the lubricant comprises a micro-capsule comprising a core of a liquid lubricant enclosed by a solid shell~
Powdered metals, for example, powdered iron, are used to make small, fairly intricate parts, for example, gears. The fabrication of such metallic parts by powdered metal technology involves the following steps:
a) the powdered metal is blended with a lubricant and other additives to form a mixture, b) the mixture is poured into a mould, -c) the mixture is compacted in the mould to form a part uxing a high pressure, usually of the order of 30 tons per square inch, d) after compaction the part is ejected from the mould, e) the ejected part is subject:ed to a high temperature ~ -;
to decompose and remove the-lubricant, ;
f) the part i~ heated to a higher temparature to cause all the particles of metal in the part to sint~r together and g) the part is cooled, after which it is ready for use, Commonly used lubricants include zinc stearate and lithium stearate. ` `;
The lubricant is added to the powdered metal for several reasons, it increases the bulk density of the uncom-pacted powdered metal. Thi~ means that the moulds can be ;
shallower, for a given thickness of the final part. The bulk density is generally referred to as the "apparent density".
The lubricant allows the compacting pressure to be reduced to attain a specified density before sintering. This is very important because it means that for a given pressure a ~ - 1- ~ :
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larger part can be made. Because of the very large pressures required to compact powdered metal, only relatively small parts are made. The density of the compacted part is called the "green density".
The ejection force to remove the compacted part from the mould is much lower when a lubricant is present and this - lower force results in less mould wear.
Unfortunately, the lubricant also has a few adverse - effects; it often reduces the flow rate of the powdered metal and therefore the rate at which a mould can be filled; it reduces the strength of the compacted part, referred to as the "green strength"; further, it can cause an unattractive surface finish on the sintered part. Zinc stearate is commonly used as a lubricant and slowly deposits a thin coating of zinc on the walls of the oven used to burn off the lubricant or on the walls of the sintering oven.
This last disadvantage is often serious, and because of it a wax is sometimes used instead of zinc stearate. The most commonly used wax is ethylenebisstearamide; however, it is not as good a lubricant as zinc stearate, especially with regard to compressi~ility, i.e., it gives a lower green density for a given compacting pressure, It can only provide tha same compressibility as zinc stearate if it is ground to a very fine powder using a special grinding mill which is expensive and consumes a great deal of energy.
A further disadvantage to customarily used lubricants is that they are dusty. ~ -The present invention provides an entirely or almost entirely organic lubricant for powder metallurgy which is com parable to zinc stearate, with respect to compressibility of the lubricant-metal mixture, as well as with respect to other pro-perties of the mixture and of parts produced therefrom.
More particularly the lubricant comprises a micro-capsule comprising a core of a liquid lubricant enclosed by a solid shell~
Powdered metals, for example, powdered iron, are used to make small, fairly intricate parts, for example, gears. The fabrication of such metallic parts by powdered metal technology involves the following steps:
a) the powdered metal is blended with a lubricant and other additives to form a mixture, b) the mixture is poured into a mould, -c) the mixture is compacted in the mould to form a part uxing a high pressure, usually of the order of 30 tons per square inch, d) after compaction the part is ejected from the mould, e) the ejected part is subject:ed to a high temperature ~ -;
to decompose and remove the-lubricant, ;
f) the part i~ heated to a higher temparature to cause all the particles of metal in the part to sint~r together and g) the part is cooled, after which it is ready for use, Commonly used lubricants include zinc stearate and lithium stearate. ` `;
The lubricant is added to the powdered metal for several reasons, it increases the bulk density of the uncom-pacted powdered metal. Thi~ means that the moulds can be ;
shallower, for a given thickness of the final part. The bulk density is generally referred to as the "apparent density".
The lubricant allows the compacting pressure to be reduced to attain a specified density before sintering. This is very important because it means that for a given pressure a ~ - 1- ~ :
.
larger part can be made. Because of the very large pressures required to compact powdered metal, only relatively small parts are made. The density of the compacted part is called the "green density".
The ejection force to remove the compacted part from the mould is much lower when a lubricant is present and this - lower force results in less mould wear.
Unfortunately, the lubricant also has a few adverse - effects; it often reduces the flow rate of the powdered metal and therefore the rate at which a mould can be filled; it reduces the strength of the compacted part, referred to as the "green strength"; further, it can cause an unattractive surface finish on the sintered part. Zinc stearate is commonly used as a lubricant and slowly deposits a thin coating of zinc on the walls of the oven used to burn off the lubricant or on the walls of the sintering oven.
This last disadvantage is often serious, and because of it a wax is sometimes used instead of zinc stearate. The most commonly used wax is ethylenebisstearamide; however, it is not as good a lubricant as zinc stearate, especially with regard to compressi~ility, i.e., it gives a lower green density for a given compacting pressure, It can only provide tha same compressibility as zinc stearate if it is ground to a very fine powder using a special grinding mill which is expensive and consumes a great deal of energy.
A further disadvantage to customarily used lubricants is that they are dusty. ~ -The present invention provides an entirely or almost entirely organic lubricant for powder metallurgy which is com parable to zinc stearate, with respect to compressibility of the lubricant-metal mixture, as well as with respect to other pro-perties of the mixture and of parts produced therefrom.
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The invention further provides an organic powdered metal lubricant which is cheap, dustless, non-toxic, and which - can be used in quantities no greater than now used for existing lubricants, for example, zinc stearate, lithium stearate and waxes.
The in~ention further provides a lubricant composition which comprises a synergistic mixture of microencapsulated lubricant and unencapsulated solid lubricant. -~
The invention further provides a process by which the 10 microencapsulated lubricant can be manufactured. ~
The invention further provides a method of pro- ~-ducing a sintered metal part using the lubricant of the in-vention.
It has been found that small capsules called micro-capsules consisting of a liquid lubricant surrounded by a solid shell material, having certain properties, provide an excellent lubricant for powdered metals.
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The addition of a liquid lubricant to powdered metal results in high compressibility and low ejection pressure, however, it also causes very poor flow and very low apparent density which are unacceptable.
When the liquid lubricant is encapsulated, however, according to the present invention,it does not have an ~-~
opportunity to reduce the flow rate or the apparent density of the powdered metal; however, when the mixture of powdered metal and encapsulated lubricant is subjected to high pressure during the compaction stage, the shell of the capsule is ruptured or broken and the liquid lubri~ant is released to coat the particles of powdered metal and the die wall, and there-;~ 30 by results in high compressibility and low ejection pressure.
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/ - -According to one aspect of the invention there is pro-vided discrete pressure-rupturable microcapsules for lubrication in powder metallurgy comprising a core and a solid shell sur-rounding said core, said core comprising a non-corrosive organic liquid lubricant able to wet powdered metals, and said shell comprising a thin non-atmospherically-degradable polymeric mate-: rial, said shell being impermeable to said lubricant and having .
a smooth, slippery, non-tacky, outer surface resistant to abrasion by sinterable powdered metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant said shell being rupturable, when said microcapsules are in admixture with sinterable powdered metal and are subjected to powder metallurgy compacting pres- .
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sures, said lubricant and said shell being heat decomposable to ~ gaseous products which are non-corrosive to sinterable metal with a low residùe of carbon at elevated temperatures below the sintering temperature of a powdered metal to be sintered.
. According to another aspect of the invention there is provided a free-flowing lubricant composition for powder metallurgy lubrication ~omprising the discrete pressure-rupturable microcapsules defined above in admixture with a ..
solid particulate lubricant for example an amide wax or a - ~ :
metal stearate, such mixtures exhibit beneficial synergistic effacts.
According to another aspect of the invention the~e is provided a method of producing a sintered metal part from powdered metal comprising: blending said powdered metal with a lubricant comprising discrete pressure-rup~urable microcapsules comprising a core of a non-corrosive liquid organic lubricant able to wet said powdered metal, and surrounding said core a thin polymeric solid shell, to form an intimate mixture, compacting said mixture in a mould at a pressure effective to rupture said ~`t
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The invention further provides an organic powdered metal lubricant which is cheap, dustless, non-toxic, and which - can be used in quantities no greater than now used for existing lubricants, for example, zinc stearate, lithium stearate and waxes.
The in~ention further provides a lubricant composition which comprises a synergistic mixture of microencapsulated lubricant and unencapsulated solid lubricant. -~
The invention further provides a process by which the 10 microencapsulated lubricant can be manufactured. ~
The invention further provides a method of pro- ~-ducing a sintered metal part using the lubricant of the in-vention.
It has been found that small capsules called micro-capsules consisting of a liquid lubricant surrounded by a solid shell material, having certain properties, provide an excellent lubricant for powdered metals.
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The addition of a liquid lubricant to powdered metal results in high compressibility and low ejection pressure, however, it also causes very poor flow and very low apparent density which are unacceptable.
When the liquid lubricant is encapsulated, however, according to the present invention,it does not have an ~-~
opportunity to reduce the flow rate or the apparent density of the powdered metal; however, when the mixture of powdered metal and encapsulated lubricant is subjected to high pressure during the compaction stage, the shell of the capsule is ruptured or broken and the liquid lubri~ant is released to coat the particles of powdered metal and the die wall, and there-;~ 30 by results in high compressibility and low ejection pressure.
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/ - -According to one aspect of the invention there is pro-vided discrete pressure-rupturable microcapsules for lubrication in powder metallurgy comprising a core and a solid shell sur-rounding said core, said core comprising a non-corrosive organic liquid lubricant able to wet powdered metals, and said shell comprising a thin non-atmospherically-degradable polymeric mate-: rial, said shell being impermeable to said lubricant and having .
a smooth, slippery, non-tacky, outer surface resistant to abrasion by sinterable powdered metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant said shell being rupturable, when said microcapsules are in admixture with sinterable powdered metal and are subjected to powder metallurgy compacting pres- .
.
sures, said lubricant and said shell being heat decomposable to ~ gaseous products which are non-corrosive to sinterable metal with a low residùe of carbon at elevated temperatures below the sintering temperature of a powdered metal to be sintered.
. According to another aspect of the invention there is provided a free-flowing lubricant composition for powder metallurgy lubrication ~omprising the discrete pressure-rupturable microcapsules defined above in admixture with a ..
solid particulate lubricant for example an amide wax or a - ~ :
metal stearate, such mixtures exhibit beneficial synergistic effacts.
According to another aspect of the invention the~e is provided a method of producing a sintered metal part from powdered metal comprising: blending said powdered metal with a lubricant comprising discrete pressure-rup~urable microcapsules comprising a core of a non-corrosive liquid organic lubricant able to wet said powdered metal, and surrounding said core a thin polymeric solid shell, to form an intimate mixture, compacting said mixture in a mould at a pressure effective to rupture said ~`t
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shell and release said liquid lubricant and to form said mixture into a self-supporting shaped body, removing said body from ~:
said mould, heating said body to decompose and remove organic material, and sintering said metal particles.
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According to yet another aspect of the invention there is provided a process for producing solid lubricant coated dis-crete pressure rupturable microcapsules, comprising a core of a liquid organic lubricant and a solid polymeric shell surrounding -~said core comprising forming a mixture of the liquid lubricant and a polymerizable monomer soluble therein, forming an emulsion of the mixture with a polar solvent immiscible with said liquid lubricant, reacting said monomer with a polar solvent-soluble monomer or catalyst to produce microcapsules comprising a core of said liquid lubricant and a shell of polymerized monomer or monomers, mixing the microcapsules with the solid lubricant at a temperature above the melting point of the solid lubricant to coat the microcapsules and recovering coated microcapsules.
Liquid Lubricant ~
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With regard to the physical properties of the lubricant it should be liquid at the temperatures at which it is used, the melting point should be below room temperature, or more precisely, below the temperature of the powdered metal when it is compacted. It should have a low enough viscosity so 20 that when the shell is ruptured the lubricant will rapidly flow out and envelop the particles of powdered metal. A viscosity below 300 cp should suffice.
The liquid lubricant must have the ability of wetting the powdered metal. This is generally dependent on the sur~ace tension properties and generally if the surface tension of the lubricant is below about 40 dynes/cm., good wetting should occur.
The liquid lubricant should not dissolve the shell material or it will tend to slowly diffuse through the shell.
Since lubricants are frequently burned off at 800F. prior to sintering, almost all the liquid should desirably volatilize below this temperature. The remaining lubricant should completely burn off in the sintering oven so that very little _ 5 _ ~ ~ :
black soot is deposited on the surface of the sintered part.
With regard to ch~mical properties the liquid ~ `
lubricant should not be corrosive, and should not yield corrosive degradation products or yield degradation products which adversely affect the lining of the sintering furnace or the properties of the sintered metal parts. These requirements eliminate such lubricants as chlorinated and sulphonated fats and oils. ~ ;
Liquid lubricants which have been found to be suitable are animal and vegetable fats and oils which have the required low melting points. Examples are rapeseed oil, soya-bean oil, -peanut oil and coconut oil. Fatty acids and fatty acid esters are also suitable, provided they have low enough melting points.-Examples are:oleic acid; methyl laurate and the methyl ester of lard oil, epoxidized fats and oils which are liquids, such as epoxidized soya-bean oil. Mineral oils and low melting point polyethylene glycols and polypropylene glycols can also be used, but are less preferred.
Small amounts of special additives may be mixed with ;
the liquid lubricant, even though if present in large amounts they would be deleterious. Examples o~ these are chlorinated ~-oils, sulphonated oils, tricresyl phosphate, zinc dithiodi-al~ylphosphates and sodium nitrite. -The lubricant may also contain small amounts of solid lubricants, for example, molybdenum disulphide.
The amount of liquid lubricant present in the micro-capsules should be as great as possible, because the shell material itself is not a good lubricant. Large amounts may be ' employed, provided difficulties are not encountered in the form-a~ion of a continuous shell and the shell is sufficiently strong.
Usually the lubricant content varies between 5~/O and 85% by weight. ,~ ;
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Shell The chemical properties required of the shell material are the same as for the liquid lubricant. With regard to physical properties the shell material must satisfy several ; criteria. The shell should be impermeable to the liquid lubricant. The surface of the shell must be sufficiently smooth and slippery so that a good flow rate and apparent density is obtained for the mixture of powdered metal, lubricants and other additives Neither moisture in the air nor oxygen should degrade the shell.
The shell material should be sufficiently abrasion resistant so that the microcapsules can be thoroughly mixed with the powdered metal without release of the liquid lubricant. During this mixing operation the temperature may reach as high as 130F. and therefore the shell should be able to withstand this temperature. A further and rather obvious requirement, is that the shell should rupture when subjected to the pressure exerted during com-paction, It is also desirable that the shell material be such that thin shells can be utilized so that the percentage of - liquid l~bricant is high.
Microcapsule The size, shape and colour of the microcapsules are important. If the microcapsules are too large they will segregate from the powdered metal. If all of the microcapsules pass through a 140 mesh sieve there is no danger of segregation.
Generally, it is preferable to have the microcapsules as fine as possible, for example, 5 microns in diameter.
Coarser microcapsules frequently lead to lower apparent densities and lower green densities, However, they also lead to higher flow rates, therefore, when a high flow rate is paramount, coarse particles should be used, for example, ~6;~3~ ~
50 microns in diameter. Generally the microcapsule will have a size in the range of about 1 to 200, particularly 5 to 100, microns;
however, the most suitable microcapsule size is also dependent on the particular grade of iron or non-ferrous metal powder.
A spherical shape is the most desirable, because this leads to the highest ~low rate and apparent density. A black or grey colour is undesirable, particularly when the powdered metal is iron powder, because it is then impossible to deter-mine whether the microcapsules have been thoroughly mixed with the powdered metal; white is the preferred colour.
In one embodiment of the invention the shell of the microcapsules is coated with a thin layer of a solid which is a good lubricant for powdered metals, for example, stearic acid or carnauba wax. This coating can result in an improvement in the apparent density and flow rate, without harming the ; other properties. Preferably, the coating constitutes between 5% and 15% of the total weight of the microcapsules. If it is much less, the coating will not completely cover the shell;
if it is much more, the beneficial effects of the encapsulated ' 20 liquid lubricant will be reduced.
In another embodiment o~ the invention the micro-.. . -encapsulated lubricant is mixed with an unencapsulated solid particulate lubricant because ~ynergism occurs with respect to '~
certain properties. For example, the ~ompressibility may reach a maximum at a particular concentration of microcapsules, and the ejection force may reach a minimum at another, usually different, concentration of microcapsules; the values of these concentrations depend upon the particle size and the composition of the micro-capsules and of the unencapsulated solid particulate lubricant.
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, ~ ' , ; . ' , , , : . , Suitable solid particulate lubricants include waxes, for example, ethylenebisstearamidewax, Carnauba wax, Fischer-Tropsch wax, fatty acids, zinc stearate and lithium stearate.
Microcapsule Production There are several methods of microencapsulating a liquid and most of these can be applied to the microencapsulation of `-liquid lubricants. U.S. patents 2,800,457, 3,041,288 and 3,201,353 involve the formation of a shell by the precipitation - of gelatin; in U.S. patent 3,137,631 other proteins are used to form the shell. Precipitation of synthetic polymers is employed in U.S. patent 3,173,878 to produce a shell. U.S.
patent 2,969,330 entails shell formation by the polymerization of a monomer at the interface of the oil and water in which the oil i~ emulsified. In U.S.~patent 3,796,669 the shell formation is by the copolymeriæation of two monomers in an emul~ion of an oil and water.
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~ lthough encapsulation methods using gelatin are the most popular and have been thoroughly investigated, they are not particularly suitable for the present application because, in addition to other reasons, the gelatin shells are moisture sensitive and the surfaces are often tacky; a tacky surface causes low flow rates and low apparent densities.
U.K. patent 950,443 involves a method which is similar to that preferred in the present invention. In this case, microcapsules are formed by a condensation polymerization reaction between a monomer which is soluble in a water phase and a monomer soluble in a water immiscible phase.
The microcapsules may be manufactured by a method ~
comprising the following steps: (1) If necessary, mix an emulsifying agent with either the liquid lubricant, the water ` phase, or both; (2) mix a lubricant soluble monomer with the liquid lubricant, (3) add the resulting mixture to the water phase, (4) mix at room temperature usin~ vigorous agitation to form an emulsion of the desired fine droplet size, (5) to the emulsion add, with mixing, a water soluble monomer react1ve with the lubricant soluble monomer or a polymerizationicatalyst for the lubricant soluble monomer, (6) mix, but not so vigorously that the capsules are destroyed, for several hours with heating - to about 80C. to accelerate the reaction, (7) filter the mixture to separate the microcapsules from the water, (8) wash the micro-capsules to remove emulsifying agent and any excess water soluble monomer and (9) dry the microcapsules. -.''':
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The liquid lubricant should, of course, be inert to and not interfere with the polymerization.
In this respect fatty acids should be avoided as the liquid lubricant when the isocyanate/amine reaction is employed because the fatty acids and amines tend to react together preventing or hindering the formation of microcapsules and the fatty acid can also react with the isocyanate.
To coat the microcapsules with a thin layer of a solid lubricant, the mass of dried microcapsules is heated to a temperature a little above the melting point of the solid lubricant, the solid lubricant is then added, preferably as a fine powder, and the mixture is mixed gently for about an hour while the temperature is held constant. Finally, with continuous mixing, the temperature is allowed to slowly decrease to that of the room. It is generally found that several aggregates of microcapsules have formed during this process because of the bonding nature of the solid lubricant.
These can easily and completely be broken by grinding lightly in a hammer mill.
In the preferred method a di- or polyfunctional i~ocyanate is dissolved in the liquid lubricant; the resulting solution is emulsified in water containing an appropriate emulsifying agent, and an aqueous solution of a di- or poly-functional amine is added. Among the isocyanates that can ~e used there may be mentioned: -toluene diisocyanate dianisidine diisocyanate xylylene diisocyanate bitolylene diisocyanate hexamethylene diisocyanate o,m and p-phenyléne diisocyanate methylene bisphenylisocyanate B` ~
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polymethylene polyphenylisocyanate 1, 6- hexamethylene diisocyanate methylcyclohex~lene diisocyanate -. trimethylhexamethylene diisocyanate .
Examples of amines that can be used in the method are the following~
. ethylene diamine methane diamine .~ 1,3 diaminocyclohexane m-xylylenediamine diethylenetriamine iminobispropylamine ~, propylenediamine trieth~lenetetramine tetraethylenepentamine m-phenylenediamine ::
. 4,4'-methylenedianiline Examples o~ liquid lubricants which can be used in the : preferred encapsulation method are as follows:
rapeseed oil .~ :
soyabean oil ; :
epoxidized soyabean oil . -methyl lardate methyl laurate -:
peanut oil methyl oleate ~
corn oil .
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- When mixed with metal powders, the concentration of the microcapsules or of microcapsules plus unencapsulated solid lubricants, is suitably in the range of 0.1% to 5% by ~ weight, preferably from 0.3% to 1% by weight.
- Test data on lubricant compositions of the invention are illustrated with reference to the accompanying drawings in which FIGURE 1 shows graphically the variation in flow time, green density, apparent density and ejection pressure for : iron powder (MP-32, trademark) ; containing 1% by weight of lubricant comprising microcapsules admixed with particulate ethylene-bisstearamide, with microcapsule concentration, for the micro-capsule of Example IV.
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FIGURE 2 shows graphically the variations in ejection pressure, apparent density and green density for iron powder (MP-32, trade~
mark) containing 1% by weight of lubricant comprising microcapsules admixed with ethylene-bisstearamide, with microcapsule concentration, for the microcapsules of Example VIII.
FIGURE 3 shows graphically the variation in ejection pressure, apparent density and green density for iron powdex (Atomet 29, trademark) containing 1% by weight of lubricant comprising microcapsules . .- . .
admixed with ethylenebisstearamide, with ~-microcapsule concentration, for the micro-capsules of Example X, and FIGURE 4 shows graphically the variation in ejection pressure, apparent density and green density for brass powder (CZ-2, trademark) containing 1% by weight of lubricant comprising micro-capsules admixed with ethylenebisstearamide, with microcapsule concentration, for the -~
microcapsules of Example VIII.
The following examples serve to illustrate the invention, but they are not intended to limit it thereto. - -.
~ EXAMæLE I Rapeseed oil encapsulated in the reaction ; product from eth~lene diamine and toluene diisocyanate.
30 g. of toluene diisocyanate (Nacconate 80, trade-mark from Allied Chemical) was dissolved in 120 g. of refined rapeseed oil. This solution was added with stirring to a - solution of 3 g. of Siponic 218 ( trademark for a polyoxyethylene thioether from Alcolac, Inc.) in 700 g. of water. When the emulsification was complete, the stirring rate was reduced and ~ i ' .. .. . . . . . .
30 g. of ethylene diamine dissolved in 70 g. of water was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The resulting dispersion of microcapsules in water was filtered and the microcapsules dried at 60C. Aggregates of microcapsules were broken by light grinding through a hammer mill.
The microcapsules were white, spherical, free flowing, had an average particle size of about 50 microns and contained about 66% by weight of rapeseed oil.
EXAMPLE II Methyl oleate encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
30 g. of toluene diisocyanate was dissolved in 120 g.
of methyl oleate~ This solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
When the emulsification was complete the stirring rate was reduced and 30 g. of ethylene diamine dissolved in 70 g. of water was added. The temperature was increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated ~rom the water by filtration and then dried at 60C. Aggregates of dried microcapsules were broken by light grinding with a hammer mill.
The microcapsules were white, spherical, free flowing, :. .
had an average particle size of about 50 microns, and contained about 66% by weight methyl oleate.
EXAMPLE III Testing of Microcapsules prepared in Examplès I and II.
The microcapsules prepared in Examples I and II were tested as lubricants for two different powdered metals using the following formulations: ~
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Formulation A Formul_tion B
Iron Powder Iron Powder (QMP's Atomet 29*) 95.10~/o (Domtar s MP32*) 96~28%
Graphite (South~ Graphite (South-western's 1845*) 0.94% western's 1845*) 0~9~/O -Copper (Alcan's Copper (Alcan's MD151*) 2~96~/o MD151*) 1.98%
Lubricant 1. 0~/o Lubricant 0~75%
Standard test methods were used to deter~ine the effects of the lubricant, namely apparent density by ASTM B212-48, compressibillty by ASTM B331-64~ green strength by ASTM
B312-64~ transverse rupture strength by ASTM B528-70 and tensile strength by ASTM E8.
A compacting pressure of 27.5 tons/sq.in. was used to prepare specimens of Formulation A for tensile strength deter-minations and of 30 tons/sq.in. for transverse rupture. A
compacting pressure of 25 tons/sq.in. was used to prepare specimens of Formulation B for tensile and transverse rupture strength determinations.
Following compaction the samples were subjected to 1000F. in a pure hydrogen atmosphere for 20 minutes to burn off the lubricant, and subsequently to 2050F. for 30 minutes -to sinter the metal.
Tables I and II present the results, along with the corresponding results for two commercially used lubricants, zinc stearate and ethylenebisstearamide wax. It can be seen that compared to the stearate and the wax the use of micro-capsules leads to much lower ejection force, to lower apparent ` density and to greater shrinkage. With regard to the other parameters the results are comparable. ~ high shrinkage is frequently desirable, and although the tensile strength obtained using encapsulated rapeseed oil is low, it is still `~
acceptable. `~
* trademark - 15 ~
` . . ~ ' : . : , -TABLE I
Comparison Between Effects of Standard Lubricants and Microcapsul0 Lubricants for Formulation A
Zinc Ethylenebis- Microcapsules from Stearate stearamide Wax Example I Example II
Apparent Density in g/cc 3.08 2.66 2.30 2.37 Ejection Force in t.s.i. 4.2 4.9 4.2 4,0 Green Density ; in g/cc 6.S7 6.53 6.49 6.49 Shrinkage in in./in. X 10 Length 7 13 24 39 Width 6 10 24 36 Thickness 29 26 55 93 Tensile Strength in p.s.i. 54,140 61,050 57,00056,390 j 20 Transverse Rupture Strength in p.s.i. 111,130 111,180 111,080 121,230 -~
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TABLE II
Comparison Between Effects of Standard Lubricants and Microcapsule Lubricants for Formulation B
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Zinc Ethylenebis- Microcapsules from Stearate stearamide Wax Example I Example II
Apparent Density in g/cc 2.73 2.57 2.15 2.25 Ejection Force -in t~.s.i. 4.3 4.8 3.2 306 ` Green Density in g/cc 6.35 6.30 6.30 6.28 Shrinkages in in./in. X 10-4 Length 20 6 6 16 Width 12 6 4 14 Thickness 23 13 43 60 Tensile Strength in p.s.i. 37,890 , 37,260 28,640 37,730 - Transverse Rupture Strength - in p.s.i. 77,410 80,360 74,930 79,290 EXAMPLE IV Soyabean oil encapsulated in the reaction product from Ethylenediamine and toluene ~ diisocyanate.
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30 g. of toluene diisocyanate was dissolved in 60 g.
of soyabean oil (from Canlin Limited). This solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water. When the emulsification was complete, the . . .
~ stirring rate was reduced and 30 g. of ethylene diamine dissolved .
in 70 g. of water-was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred -~
for 4 hours.
The microcapsules were separated from the water by filtration and then dried at 60C. Aggregates of dried micro-capsules were broken by lightly grinding in a hammer mill.
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by weight soyabean oil.
EXAMPLE V Soyabean oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
The same procedure was followed as in Example IV
except that more soyabean oil was added so that the microcap-sules contained about 75% by weight oil.
EXAMPLE VI Effect of mixtures of ethylenebisstearamide - wax and microcapsules from Examples IV and V
on Iron Powder.
Rather than using only microcapsules as a lubricant for ~ ' powdered metals, blends of microcapsules with customary lubricants can be used. Figure 1 gives the results for blends of ethylene-bisstearamide wax (from H. L. Blachford, Limited) with micro~
capsules from Example IV where the total concentration of lubri-', cant system is kept constant at 1% and the powdered metal is iron powder MP-32 (trademark) from Domtar. It is surprising to see that ~, the curve for green density shows a maximum, which occurs at ~ ' , approximately 20% microcapsule content. Similarly, the curve for '' --~
' ejection force shows a minimum, which occurs at approximately 75%
,, microcapsule content. These two separate synergistic effects are beneficial, because a high green density and a low ejection force ', -~
are desirable.
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Blends were also prepared using microcapsules from ~;
Example V to determine the effect of increasing the oil content from 50% to 75% by weight. Although the results are not shown in Figure 1, it was found that with the microcapsules containing ' more oil the apparent densities, flow rates, and ejection pressures were lower, but, the green densities were higher. ,' '`
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EXAMPLE VII Soyabean oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate The same procedure was followed as in Example IV
except that the amount of soyabean oil was increased to 120 g.
so that the microcapsules contained about 66% by weight oil.
- EXAMPLE VIII Soyabean oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
30 y. of toluene diisocyanate was dissolved in 120 g.
of soyabean oil. The solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
The resulting coarse emulsion was then mixed very vigorously in a high intensity colloid mill to produce an emulsion containing very fine droplets of oil. The stirring rate was then reduced and 30 g. of ethylene diamine in 70 g. of water was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated from the water by filtration and dried at 60C. Aggregates of dried micro-capsules were broken by gentle grinding.
The microcapsules were white, spherical, free flowing, - had an average diameter of 5 microns and contained about 66%
by weight oil.
EXAMPLE IX Effect of mixtures of ethylenebisstearamide wax and microcapsules from Examples VII and VIII
on iron powder.
Rather than using only microcapsules as a lubricant for powdered metals, blends of microcapsules with customary lubricants can be employed. Figure 2 gives the results for blends of ethylenebisstearamide wax with the fine particle size capsules from Example VIII. The total concentration of lubricant was held at 1% and the powdered metal was iron powder MP-32 (trademark) from Domtar. It is surprising to see that the curve for green density shows a maximum, which occurs at microcapsule content of .
approximately 50% by weight. The results show that synergism occurs between the two different kinds of lubricant.
Blends were also prepared and tested using micro-capsules from Example VII to determine the effect of micro-capsule particule size. Although the results are not shown, it was found that using the coarser microcapsules resulted in a maximum in the green density, but it occurred at around 3~/O by weight microcapsule content, rather than 5~O by weight as with the finer microcapsules. Furthermore, the apparent densities were lower. The ejection pressures were lower at low con- - -centrations of microcapsules, but higher at high concentrations. ~ ~;
EXAMPLE X Rapeseed oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
The same procedure was used as in Example VIII, except that rapeseed oil was used in place oE soyabean oil. The microcapsules formed had an average diameter of approximately 5 microns and contained 66% by weight oil. ;
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EXAMPLE XI Effect of Mixtures of ethylenebisstearamide wax and microcapsules from Examples I and X on iron powder.
Blends of microcapsules and a conventional lubricant were prepared and tested in iron powder Atomet 29 ttrademark), from Quebec Metal Powder Company. Figure 3 gives the results ~or blends of ethylenebisstearamide wax with the fine particle size capsules from Example X. The total concentration of lubricant was kept constant at 1% by weight. The results are similar to - those given in Examples VI and VIII. A maximum green density occurs at a microcapsule concentration of approximately 40% by weight. As in Example VI there is a minimum in the curve for ejection pressure. Beneficial synergism occurs here also, with regard to both green density and ejection pressure.
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Blends were also prepared and tested using micro-capsules from Example I. These capsules are identical to those from Example X, except that khey are much larger. Although the results are not shown, it was found that the green density reaches a maximum at a lower microcapsule concentration. The ejection pressures and apparent densities are higher.
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EXAMPLE ~II Coating of microcapsules from Example VIII with thin layers of lubricants.
A 166 g. sample of fine microcapsules from Example -VIII was heated to 150F. and to half of this was added, with mixing, 17 g. of double pressed stearic acid and to the other half was added, with mixing, 17 g. of a Fischer-Tropsch Wax (Paraflint - trademark). The samples were held at 150F.
and mixed for 30 minutes. The heat source was then removed and the samples allowed to cool to room temperature, at which point the mixing was stopped. The aggregates that had formed as a result of this treatment were broken by light grinding.
I'he coated microcapsules were tested as lubricants for iron powder, Atomet 29 (trademark) using a lubricant con-centration o 0.75~/~ by weight.
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TABLE III
Effect of Thin Coating on Lubricant Properties -EthyIene Coated Capsules Zinc bissteara- Uncoated Stearic : -Stearate mide Capsules Acid Wax Flow Rate in sec./50 g, 34~5 41.0 no flow no flow no flow Apparent Density -in g./cc 3,24 2.94 2.58 2.95 2.6~ - -Green Density in g./cc 6.60 6.55 6.55 6.60 6.52 ~-~
Ejection Force in t.s.i. 5.4 6.4 5.6 4.9 5.7 ~ ~ -Green Strength in p.s.i. 1664 2218 1437 1175 1423 . . _ . . .
The results show that the stearic acid coated micro-capsules give higher apparent densities and green densities than ~o the uncoated.
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EXAMPLE XIII Coating of microcapsules from Example VII with thin layers of lubricants.
Four samples, each weighing 83 g., of coarse micro-capsules from Example VII were heated to 150F. and to each was added 17 g. of a coating material. Four materials were used: double pressed stearic acid, Fischer Tropsch Wax, hydrogenated castor fatty acid and carnauba wax. The samples were held at 150F. and mixed for 30 minutes. They were then ~allowed to cool at room temperature with constant mixing. Any aggregates of coated microcapsules that had formed were broken by light grinding.
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and 0.75% by weight. Table IV presents the results along with -~-those for customarily used lubricants.
The results show that when coarse microcapsules are coated there is a spectacular improvement in the flow rate and apparent density. Although no results are shown, it was found that coating the capsules increased the green strength, but had no significant effect on other properties.
Effect of Various Coatings on Lubricant Properties . . ., _ _ .
Concentration Flow Rate Apparent Density of Lubricant in sec./50 G. in g./cc.
Ethylene 0.50/O 32.0 2 73 Bisstearamide 0.75% 35.0 2 62 ~ -Uncoated 0.50/0no flow 2.38 Micro-capsules 0.75% no flow -Stearic Acid 0.50/0 39.5 2.71 Coated Capsules~ 0.75% 37,5 2,67 Fischer Tropsch 0.50O/o30.5 2.61 Wax Coated Capsules 0,75% 35,0 2.54 Castor Fatty 0.50/0 Acid Coated Capsules 0.75% 38.5 2.60 Carnauba Wa~ 0.50/0 - - -Coated 0.75% 37.0 2.61 EXAMPLE XIV Methyl Lardate encapsulated in the reaction product from Ethylene Diamine and Trimethyl ~ -Hexamethylene Diisocyanate~
30 g. of trimethyl hexamethylene diisocyanate was dissolved in 120 g. of methyl lardate. This solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water. When the emulsification was complete, ; the stirring rate was reduced and 30 g. of ethylene diamine - dissolved in 70 g. of water was added. The temperature was 10 then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The resulting dispersion of microcapsules in water was filtered and the microcapsules dried at 60C. Aggregates of microcapsules were broken by light grinding.
The microcapsules were white, spherical, free flowing, had an average particle size of 50 microns and contained ; approximately 66% by weight methyl lardate.
EXAMPLE XV Methyl lardate encapsulated in the reaction product ~rom propylenediamine and trimethyl hexamethylene diisocyanake.
.. , The same procedure was followed as in Example XIV
except that 32 g. of propylene diamine were used instead of 30 g. of ethylenediamine. ~ -The resulting microcapsules were white, spherical, free flowing, had an average particle size of 50 microns and -contained approximately 66% methyl lardate.
EXAMPLE X~I Rapeseed oil encapsulated in polymerized divinylbenzene.
- 25 g~ of divinylbenzene were dissolved in 60 g. of rapeseed oil. This solution was added with vigorous stirring to a solution of 0.5 g. of Siponic 218 in 700 g. of water.
When the emulsification was complete, the stirring rate was reduced and the temperature raised to 80C. Then, 2 g. of .. . .
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potassium persulphate were added and the mixture stirred at 80C. for 6 hours. The temperature was allowed to drop to 25C, At this point, the mixture was filtered, and the microcapsules washed and then dried at 45~C. The dried capsules were gently ground to break any aggregates.
The final microcapsules were white, spherical, free flowing, had an average particle size of 20 microns and contained approximately 7~/0 by weight rapeseed oil.
EXAMPLE XVII Isostearic acid encapsulated in polymerized divinylbenzene.
The same procedure was followed as in Example XVI,-except that 60 g. of isostearic acid was used instead of 60 g.
of rapeseed oil.
The resulting microcapsules were white, spherical, free flowing, had an average particles size of 20 microns and con-tained approximately 70/0 by weight isostearic acid.
EXAMPLE XVIII Effect of mlxtures of ethylenebisstearamide wax and microcapsules from Example VIII on bxass powder.
Blends of microcapsules and a conventional lubricant ~; 20 were prepared and tested using CZ-2 (trademark) brass powder (from Canada Metals Limited). Figure 4 gives the results for ; blends of ethylenebisstearamide wax with the fine particle siæe microcapsules prepared in Example VIII. The total concentration of lubricant was he~d constant at 1% by weight. Here again synergism occurs and there is a maximum in the green density, which in this case occurs at a concentration of microcapsules of approximately 60% by weight. In contrast to the results for iron powders, the-ejection pressure increases with the addition of microcapsules.
EXAMPLE XIX Epoxidized soyabean oil encapsulated in the reaction product from ethylene diamine and polymethylene polyphenylisocyanate.
13.5 g. of polymethylene polyphenylisocyanate (Mondur MRS, trademark from Mobay Chemical Company) was dissolved in 76.5 g. of epoxidized soyabean oil (Paraplex G-62, trademark -from Ro~n and Haas). The solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
The resulting coarse emulsion was then mixed very vigorously in a high intensity colloid mill to produce an emulsion containing very fine droplets of oil. The stirring rate was then reduced and 3~5 g. of ethylene diamine in 10 g. of water was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated from the water by filtration and dried at 60C. Aggregates of dried microcapsules were broken by gentle grinding.
The microcapsules were white, spherical, free flowing, -had an average diameter of 5 microns and contained 85% oil.
When tested as lubricants for powdered metals they gave results similar to those obtained with unepox:idized soyabean oil. ;
; EXAMPLE XX Effect of mixtures of zinc s-tearates and microcapsules from Example VIII on iron powder.
Blends of zinc stearate (from H. L. Blachford, Limited) and microcapsules from Example VIII were prepared and tested - using Atomet 29 (trademark) from Quebec Metal Powder Company.
The total concentra-tion of lubricant was held constant at 1%
by weight. Although, no maximum occurred in the plot for green density, a minimum occurred in the ejection force at approximately 60% microcapsule content, showing once again the existence of ~;~ synergism.
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. - ., SUPPLEMENTARY DISCLOSURE
This disclosure and the original disclosure are concerned with lubricants for powder metallurgy and with the manufacture and use of such lubricants; and more ~ especially are concerned with microencapsulated lubricants.
- As described in the original disclosure the microcapsules of the invention comprise a core and a solid shell surrounding the core.
Liquid _ubricant The core comprises a liquid lubricant. The lubricant should have a low enough viscosity that when the shell is ruptured, the lubricant will rapidly flow out and envelop the particles of powdered metal.
In this respect the viscosity is suitably less than 1500 centipoises, preferably less than 600 centipoises and most suitably below 300 centipoises.
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Generally the surface tension of the lubricant is below about 50 and preferably below about 40 dynes/cm so as to achieve good wetting of the powdered metal.
Lubricants are frequently burned off at about 1200F
or below prior to sintering and so in general it is ~, appropriate that at least 90% of the liquid should volatize or decompose below 1200F.
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; Examples of specific liquid lubricants in the invention, in addition to those mentioned in the original disclosure include fatty acid esters of polyols such as glycerol, trimethylolpropane, pentaerythritol, poly-ethylene glycols, (for example polyethylene glycol dioleate), polypropylene glycols, and copolymers formed by addition of ethylene oxide and propylene oxide to a glycol or amine base. Generally synthetic fatty acid esters or ~J ' , :; :
mixtures of synthetic fatty acid esters or mixtures of `
synthetic and natural fatty acid esters are preferred~
Mineral oils and low melting point polyethylene glycols and polypropylene glycols can also be used, but are less preferred.
An antioxidant may be included in admixture with the liquid lubricant as a special additive.
Usually the lubricant content of the micro-capsule varies between 50% and 90%, preferably 50% to 85%, by weight, of the microcapsule.
Shell The chemical properties required of the shell material are similar to those for the liquid lubricant.
; The surface of the shell must be sufficiently smooth `
and non-tacky so that a good flow rate and apparent ' density is obtained for the mixture of powdered metal, ; lubricants and other additives. The flow rate and apparent density are desirably at least ninety percent of the correspondin~ values for the powder without lubricant, and should preferably be greater. Desirably in obtaining the best results the shell should have a smooth, non-tacky outer surface such that the flow rate and apparent density of a mixture of the microcapsules and powdered ferrous .~ ~ . . .
`~ metal which mixturecomprises the microcapsules in an -~
amount of 0.1% to 1%, by weight, are at least 90% of the corresponding values for the free powdered ferrous metals. Values less than 90% may be satisfactory for some ` -;
purposes although less preferred. -The shell-should rupture when subjected to the pressure exerted during compaction. This pressure can range from as low as one t.s.i. (tons per square inch) , ~
; . . ', . ', ,. ' . :' ~ : '' : . , .' , to as high as one hundred t.s.i., and even slightly above this at times. For iron and steel pressures of 20 - 60 t.s.i. are most commonly used, while for brass and bronze - somewhat lower pressures are generally used, and for aluminum the usual range is 10 - 30 t.s.i. It is also desirable that the shell material be such that thin shells can be utilized so that the percentage of liquid lubricant is high. Shell thick-ness is usually in the range 0.01 to 50 microns, preferably 0.1 to 20 microns, depending on capsule size.
Microcapsule Fine capsules are not always preferable since they fit more easily into interstices between the metal -particles and a greater degree of compaction is re~uired before they break. Also, in capsules prepared by the inter-facial method, the wall thickness is proportional to the capsule diameter, so smaller capsules are less resistant ~`~` to abrasion.
- In the synergistic mixtures of microcapsules and unencapsulated solid particulate lubricant the optimum microcapsule concentration is dependent upon the particle size and the composition of the microcapsules and of the un-encapsulated solid particulate lubricant. The compositions giving optimum properties can vary over a wide range, depend-ing on the property considered and the powder used, but usually the microcapsule content is from 1 to 99, preferably 5 to 95, percent.
Microcapsule Production As described in the original disclosure the microcapsules may be manufactured by a method comprising the following steps~ If necessary, mix an emulsifying agent with either the liquid lubricant, the water phase, :
or both. (2) Mix a lubricant soluble monomer with the liquid lubicant. (3) Add the resulting mixture to the water phase.
shell and release said liquid lubricant and to form said mixture into a self-supporting shaped body, removing said body from ~:
said mould, heating said body to decompose and remove organic material, and sintering said metal particles.
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According to yet another aspect of the invention there is provided a process for producing solid lubricant coated dis-crete pressure rupturable microcapsules, comprising a core of a liquid organic lubricant and a solid polymeric shell surrounding -~said core comprising forming a mixture of the liquid lubricant and a polymerizable monomer soluble therein, forming an emulsion of the mixture with a polar solvent immiscible with said liquid lubricant, reacting said monomer with a polar solvent-soluble monomer or catalyst to produce microcapsules comprising a core of said liquid lubricant and a shell of polymerized monomer or monomers, mixing the microcapsules with the solid lubricant at a temperature above the melting point of the solid lubricant to coat the microcapsules and recovering coated microcapsules.
Liquid Lubricant ~
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With regard to the physical properties of the lubricant it should be liquid at the temperatures at which it is used, the melting point should be below room temperature, or more precisely, below the temperature of the powdered metal when it is compacted. It should have a low enough viscosity so 20 that when the shell is ruptured the lubricant will rapidly flow out and envelop the particles of powdered metal. A viscosity below 300 cp should suffice.
The liquid lubricant must have the ability of wetting the powdered metal. This is generally dependent on the sur~ace tension properties and generally if the surface tension of the lubricant is below about 40 dynes/cm., good wetting should occur.
The liquid lubricant should not dissolve the shell material or it will tend to slowly diffuse through the shell.
Since lubricants are frequently burned off at 800F. prior to sintering, almost all the liquid should desirably volatilize below this temperature. The remaining lubricant should completely burn off in the sintering oven so that very little _ 5 _ ~ ~ :
black soot is deposited on the surface of the sintered part.
With regard to ch~mical properties the liquid ~ `
lubricant should not be corrosive, and should not yield corrosive degradation products or yield degradation products which adversely affect the lining of the sintering furnace or the properties of the sintered metal parts. These requirements eliminate such lubricants as chlorinated and sulphonated fats and oils. ~ ;
Liquid lubricants which have been found to be suitable are animal and vegetable fats and oils which have the required low melting points. Examples are rapeseed oil, soya-bean oil, -peanut oil and coconut oil. Fatty acids and fatty acid esters are also suitable, provided they have low enough melting points.-Examples are:oleic acid; methyl laurate and the methyl ester of lard oil, epoxidized fats and oils which are liquids, such as epoxidized soya-bean oil. Mineral oils and low melting point polyethylene glycols and polypropylene glycols can also be used, but are less preferred.
Small amounts of special additives may be mixed with ;
the liquid lubricant, even though if present in large amounts they would be deleterious. Examples o~ these are chlorinated ~-oils, sulphonated oils, tricresyl phosphate, zinc dithiodi-al~ylphosphates and sodium nitrite. -The lubricant may also contain small amounts of solid lubricants, for example, molybdenum disulphide.
The amount of liquid lubricant present in the micro-capsules should be as great as possible, because the shell material itself is not a good lubricant. Large amounts may be ' employed, provided difficulties are not encountered in the form-a~ion of a continuous shell and the shell is sufficiently strong.
Usually the lubricant content varies between 5~/O and 85% by weight. ,~ ;
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Shell The chemical properties required of the shell material are the same as for the liquid lubricant. With regard to physical properties the shell material must satisfy several ; criteria. The shell should be impermeable to the liquid lubricant. The surface of the shell must be sufficiently smooth and slippery so that a good flow rate and apparent density is obtained for the mixture of powdered metal, lubricants and other additives Neither moisture in the air nor oxygen should degrade the shell.
The shell material should be sufficiently abrasion resistant so that the microcapsules can be thoroughly mixed with the powdered metal without release of the liquid lubricant. During this mixing operation the temperature may reach as high as 130F. and therefore the shell should be able to withstand this temperature. A further and rather obvious requirement, is that the shell should rupture when subjected to the pressure exerted during com-paction, It is also desirable that the shell material be such that thin shells can be utilized so that the percentage of - liquid l~bricant is high.
Microcapsule The size, shape and colour of the microcapsules are important. If the microcapsules are too large they will segregate from the powdered metal. If all of the microcapsules pass through a 140 mesh sieve there is no danger of segregation.
Generally, it is preferable to have the microcapsules as fine as possible, for example, 5 microns in diameter.
Coarser microcapsules frequently lead to lower apparent densities and lower green densities, However, they also lead to higher flow rates, therefore, when a high flow rate is paramount, coarse particles should be used, for example, ~6;~3~ ~
50 microns in diameter. Generally the microcapsule will have a size in the range of about 1 to 200, particularly 5 to 100, microns;
however, the most suitable microcapsule size is also dependent on the particular grade of iron or non-ferrous metal powder.
A spherical shape is the most desirable, because this leads to the highest ~low rate and apparent density. A black or grey colour is undesirable, particularly when the powdered metal is iron powder, because it is then impossible to deter-mine whether the microcapsules have been thoroughly mixed with the powdered metal; white is the preferred colour.
In one embodiment of the invention the shell of the microcapsules is coated with a thin layer of a solid which is a good lubricant for powdered metals, for example, stearic acid or carnauba wax. This coating can result in an improvement in the apparent density and flow rate, without harming the ; other properties. Preferably, the coating constitutes between 5% and 15% of the total weight of the microcapsules. If it is much less, the coating will not completely cover the shell;
if it is much more, the beneficial effects of the encapsulated ' 20 liquid lubricant will be reduced.
In another embodiment o~ the invention the micro-.. . -encapsulated lubricant is mixed with an unencapsulated solid particulate lubricant because ~ynergism occurs with respect to '~
certain properties. For example, the ~ompressibility may reach a maximum at a particular concentration of microcapsules, and the ejection force may reach a minimum at another, usually different, concentration of microcapsules; the values of these concentrations depend upon the particle size and the composition of the micro-capsules and of the unencapsulated solid particulate lubricant.
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Microcapsule Production There are several methods of microencapsulating a liquid and most of these can be applied to the microencapsulation of `-liquid lubricants. U.S. patents 2,800,457, 3,041,288 and 3,201,353 involve the formation of a shell by the precipitation - of gelatin; in U.S. patent 3,137,631 other proteins are used to form the shell. Precipitation of synthetic polymers is employed in U.S. patent 3,173,878 to produce a shell. U.S.
patent 2,969,330 entails shell formation by the polymerization of a monomer at the interface of the oil and water in which the oil i~ emulsified. In U.S.~patent 3,796,669 the shell formation is by the copolymeriæation of two monomers in an emul~ion of an oil and water.
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~ lthough encapsulation methods using gelatin are the most popular and have been thoroughly investigated, they are not particularly suitable for the present application because, in addition to other reasons, the gelatin shells are moisture sensitive and the surfaces are often tacky; a tacky surface causes low flow rates and low apparent densities.
U.K. patent 950,443 involves a method which is similar to that preferred in the present invention. In this case, microcapsules are formed by a condensation polymerization reaction between a monomer which is soluble in a water phase and a monomer soluble in a water immiscible phase.
The microcapsules may be manufactured by a method ~
comprising the following steps: (1) If necessary, mix an emulsifying agent with either the liquid lubricant, the water ` phase, or both; (2) mix a lubricant soluble monomer with the liquid lubricant, (3) add the resulting mixture to the water phase, (4) mix at room temperature usin~ vigorous agitation to form an emulsion of the desired fine droplet size, (5) to the emulsion add, with mixing, a water soluble monomer react1ve with the lubricant soluble monomer or a polymerizationicatalyst for the lubricant soluble monomer, (6) mix, but not so vigorously that the capsules are destroyed, for several hours with heating - to about 80C. to accelerate the reaction, (7) filter the mixture to separate the microcapsules from the water, (8) wash the micro-capsules to remove emulsifying agent and any excess water soluble monomer and (9) dry the microcapsules. -.''':
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The liquid lubricant should, of course, be inert to and not interfere with the polymerization.
In this respect fatty acids should be avoided as the liquid lubricant when the isocyanate/amine reaction is employed because the fatty acids and amines tend to react together preventing or hindering the formation of microcapsules and the fatty acid can also react with the isocyanate.
To coat the microcapsules with a thin layer of a solid lubricant, the mass of dried microcapsules is heated to a temperature a little above the melting point of the solid lubricant, the solid lubricant is then added, preferably as a fine powder, and the mixture is mixed gently for about an hour while the temperature is held constant. Finally, with continuous mixing, the temperature is allowed to slowly decrease to that of the room. It is generally found that several aggregates of microcapsules have formed during this process because of the bonding nature of the solid lubricant.
These can easily and completely be broken by grinding lightly in a hammer mill.
In the preferred method a di- or polyfunctional i~ocyanate is dissolved in the liquid lubricant; the resulting solution is emulsified in water containing an appropriate emulsifying agent, and an aqueous solution of a di- or poly-functional amine is added. Among the isocyanates that can ~e used there may be mentioned: -toluene diisocyanate dianisidine diisocyanate xylylene diisocyanate bitolylene diisocyanate hexamethylene diisocyanate o,m and p-phenyléne diisocyanate methylene bisphenylisocyanate B` ~
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polymethylene polyphenylisocyanate 1, 6- hexamethylene diisocyanate methylcyclohex~lene diisocyanate -. trimethylhexamethylene diisocyanate .
Examples of amines that can be used in the method are the following~
. ethylene diamine methane diamine .~ 1,3 diaminocyclohexane m-xylylenediamine diethylenetriamine iminobispropylamine ~, propylenediamine trieth~lenetetramine tetraethylenepentamine m-phenylenediamine ::
. 4,4'-methylenedianiline Examples o~ liquid lubricants which can be used in the : preferred encapsulation method are as follows:
rapeseed oil .~ :
soyabean oil ; :
epoxidized soyabean oil . -methyl lardate methyl laurate -:
peanut oil methyl oleate ~
corn oil .
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- When mixed with metal powders, the concentration of the microcapsules or of microcapsules plus unencapsulated solid lubricants, is suitably in the range of 0.1% to 5% by ~ weight, preferably from 0.3% to 1% by weight.
- Test data on lubricant compositions of the invention are illustrated with reference to the accompanying drawings in which FIGURE 1 shows graphically the variation in flow time, green density, apparent density and ejection pressure for : iron powder (MP-32, trademark) ; containing 1% by weight of lubricant comprising microcapsules admixed with particulate ethylene-bisstearamide, with microcapsule concentration, for the micro-capsule of Example IV.
.. .
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... . .
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FIGURE 2 shows graphically the variations in ejection pressure, apparent density and green density for iron powder (MP-32, trade~
mark) containing 1% by weight of lubricant comprising microcapsules admixed with ethylene-bisstearamide, with microcapsule concentration, for the microcapsules of Example VIII.
FIGURE 3 shows graphically the variation in ejection pressure, apparent density and green density for iron powdex (Atomet 29, trademark) containing 1% by weight of lubricant comprising microcapsules . .- . .
admixed with ethylenebisstearamide, with ~-microcapsule concentration, for the micro-capsules of Example X, and FIGURE 4 shows graphically the variation in ejection pressure, apparent density and green density for brass powder (CZ-2, trademark) containing 1% by weight of lubricant comprising micro-capsules admixed with ethylenebisstearamide, with microcapsule concentration, for the -~
microcapsules of Example VIII.
The following examples serve to illustrate the invention, but they are not intended to limit it thereto. - -.
~ EXAMæLE I Rapeseed oil encapsulated in the reaction ; product from eth~lene diamine and toluene diisocyanate.
30 g. of toluene diisocyanate (Nacconate 80, trade-mark from Allied Chemical) was dissolved in 120 g. of refined rapeseed oil. This solution was added with stirring to a - solution of 3 g. of Siponic 218 ( trademark for a polyoxyethylene thioether from Alcolac, Inc.) in 700 g. of water. When the emulsification was complete, the stirring rate was reduced and ~ i ' .. .. . . . . . .
30 g. of ethylene diamine dissolved in 70 g. of water was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The resulting dispersion of microcapsules in water was filtered and the microcapsules dried at 60C. Aggregates of microcapsules were broken by light grinding through a hammer mill.
The microcapsules were white, spherical, free flowing, had an average particle size of about 50 microns and contained about 66% by weight of rapeseed oil.
EXAMPLE II Methyl oleate encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
30 g. of toluene diisocyanate was dissolved in 120 g.
of methyl oleate~ This solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
When the emulsification was complete the stirring rate was reduced and 30 g. of ethylene diamine dissolved in 70 g. of water was added. The temperature was increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated ~rom the water by filtration and then dried at 60C. Aggregates of dried microcapsules were broken by light grinding with a hammer mill.
The microcapsules were white, spherical, free flowing, :. .
had an average particle size of about 50 microns, and contained about 66% by weight methyl oleate.
EXAMPLE III Testing of Microcapsules prepared in Examplès I and II.
The microcapsules prepared in Examples I and II were tested as lubricants for two different powdered metals using the following formulations: ~
;. :
, ., . , .
, . :: ,. . . ...
. . .
Formulation A Formul_tion B
Iron Powder Iron Powder (QMP's Atomet 29*) 95.10~/o (Domtar s MP32*) 96~28%
Graphite (South~ Graphite (South-western's 1845*) 0.94% western's 1845*) 0~9~/O -Copper (Alcan's Copper (Alcan's MD151*) 2~96~/o MD151*) 1.98%
Lubricant 1. 0~/o Lubricant 0~75%
Standard test methods were used to deter~ine the effects of the lubricant, namely apparent density by ASTM B212-48, compressibillty by ASTM B331-64~ green strength by ASTM
B312-64~ transverse rupture strength by ASTM B528-70 and tensile strength by ASTM E8.
A compacting pressure of 27.5 tons/sq.in. was used to prepare specimens of Formulation A for tensile strength deter-minations and of 30 tons/sq.in. for transverse rupture. A
compacting pressure of 25 tons/sq.in. was used to prepare specimens of Formulation B for tensile and transverse rupture strength determinations.
Following compaction the samples were subjected to 1000F. in a pure hydrogen atmosphere for 20 minutes to burn off the lubricant, and subsequently to 2050F. for 30 minutes -to sinter the metal.
Tables I and II present the results, along with the corresponding results for two commercially used lubricants, zinc stearate and ethylenebisstearamide wax. It can be seen that compared to the stearate and the wax the use of micro-capsules leads to much lower ejection force, to lower apparent ` density and to greater shrinkage. With regard to the other parameters the results are comparable. ~ high shrinkage is frequently desirable, and although the tensile strength obtained using encapsulated rapeseed oil is low, it is still `~
acceptable. `~
* trademark - 15 ~
` . . ~ ' : . : , -TABLE I
Comparison Between Effects of Standard Lubricants and Microcapsul0 Lubricants for Formulation A
Zinc Ethylenebis- Microcapsules from Stearate stearamide Wax Example I Example II
Apparent Density in g/cc 3.08 2.66 2.30 2.37 Ejection Force in t.s.i. 4.2 4.9 4.2 4,0 Green Density ; in g/cc 6.S7 6.53 6.49 6.49 Shrinkage in in./in. X 10 Length 7 13 24 39 Width 6 10 24 36 Thickness 29 26 55 93 Tensile Strength in p.s.i. 54,140 61,050 57,00056,390 j 20 Transverse Rupture Strength in p.s.i. 111,130 111,180 111,080 121,230 -~
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TABLE II
Comparison Between Effects of Standard Lubricants and Microcapsule Lubricants for Formulation B
_ . . . . . .. .... .
Zinc Ethylenebis- Microcapsules from Stearate stearamide Wax Example I Example II
Apparent Density in g/cc 2.73 2.57 2.15 2.25 Ejection Force -in t~.s.i. 4.3 4.8 3.2 306 ` Green Density in g/cc 6.35 6.30 6.30 6.28 Shrinkages in in./in. X 10-4 Length 20 6 6 16 Width 12 6 4 14 Thickness 23 13 43 60 Tensile Strength in p.s.i. 37,890 , 37,260 28,640 37,730 - Transverse Rupture Strength - in p.s.i. 77,410 80,360 74,930 79,290 EXAMPLE IV Soyabean oil encapsulated in the reaction product from Ethylenediamine and toluene ~ diisocyanate.
.
30 g. of toluene diisocyanate was dissolved in 60 g.
of soyabean oil (from Canlin Limited). This solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water. When the emulsification was complete, the . . .
~ stirring rate was reduced and 30 g. of ethylene diamine dissolved .
in 70 g. of water-was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred -~
for 4 hours.
The microcapsules were separated from the water by filtration and then dried at 60C. Aggregates of dried micro-capsules were broken by lightly grinding in a hammer mill.
... . .
"': '' , The microcapsules were white, spherical, free fl,owing had an average diameter of 50 microns, and contained about 50%
by weight soyabean oil.
EXAMPLE V Soyabean oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
The same procedure was followed as in Example IV
except that more soyabean oil was added so that the microcap-sules contained about 75% by weight oil.
EXAMPLE VI Effect of mixtures of ethylenebisstearamide - wax and microcapsules from Examples IV and V
on Iron Powder.
Rather than using only microcapsules as a lubricant for ~ ' powdered metals, blends of microcapsules with customary lubricants can be used. Figure 1 gives the results for blends of ethylene-bisstearamide wax (from H. L. Blachford, Limited) with micro~
capsules from Example IV where the total concentration of lubri-', cant system is kept constant at 1% and the powdered metal is iron powder MP-32 (trademark) from Domtar. It is surprising to see that ~, the curve for green density shows a maximum, which occurs at ~ ' , approximately 20% microcapsule content. Similarly, the curve for '' --~
' ejection force shows a minimum, which occurs at approximately 75%
,, microcapsule content. These two separate synergistic effects are beneficial, because a high green density and a low ejection force ', -~
are desirable.
! . ' . .
Blends were also prepared using microcapsules from ~;
Example V to determine the effect of increasing the oil content from 50% to 75% by weight. Although the results are not shown in Figure 1, it was found that with the microcapsules containing ' more oil the apparent densities, flow rates, and ejection pressures were lower, but, the green densities were higher. ,' '`
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EXAMPLE VII Soyabean oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate The same procedure was followed as in Example IV
except that the amount of soyabean oil was increased to 120 g.
so that the microcapsules contained about 66% by weight oil.
- EXAMPLE VIII Soyabean oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
30 y. of toluene diisocyanate was dissolved in 120 g.
of soyabean oil. The solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
The resulting coarse emulsion was then mixed very vigorously in a high intensity colloid mill to produce an emulsion containing very fine droplets of oil. The stirring rate was then reduced and 30 g. of ethylene diamine in 70 g. of water was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated from the water by filtration and dried at 60C. Aggregates of dried micro-capsules were broken by gentle grinding.
The microcapsules were white, spherical, free flowing, - had an average diameter of 5 microns and contained about 66%
by weight oil.
EXAMPLE IX Effect of mixtures of ethylenebisstearamide wax and microcapsules from Examples VII and VIII
on iron powder.
Rather than using only microcapsules as a lubricant for powdered metals, blends of microcapsules with customary lubricants can be employed. Figure 2 gives the results for blends of ethylenebisstearamide wax with the fine particle size capsules from Example VIII. The total concentration of lubricant was held at 1% and the powdered metal was iron powder MP-32 (trademark) from Domtar. It is surprising to see that the curve for green density shows a maximum, which occurs at microcapsule content of .
approximately 50% by weight. The results show that synergism occurs between the two different kinds of lubricant.
Blends were also prepared and tested using micro-capsules from Example VII to determine the effect of micro-capsule particule size. Although the results are not shown, it was found that using the coarser microcapsules resulted in a maximum in the green density, but it occurred at around 3~/O by weight microcapsule content, rather than 5~O by weight as with the finer microcapsules. Furthermore, the apparent densities were lower. The ejection pressures were lower at low con- - -centrations of microcapsules, but higher at high concentrations. ~ ~;
EXAMPLE X Rapeseed oil encapsulated in the reaction product from ethylene diamine and toluene diisocyanate.
The same procedure was used as in Example VIII, except that rapeseed oil was used in place oE soyabean oil. The microcapsules formed had an average diameter of approximately 5 microns and contained 66% by weight oil. ;
,.:
EXAMPLE XI Effect of Mixtures of ethylenebisstearamide wax and microcapsules from Examples I and X on iron powder.
Blends of microcapsules and a conventional lubricant were prepared and tested in iron powder Atomet 29 ttrademark), from Quebec Metal Powder Company. Figure 3 gives the results ~or blends of ethylenebisstearamide wax with the fine particle size capsules from Example X. The total concentration of lubricant was kept constant at 1% by weight. The results are similar to - those given in Examples VI and VIII. A maximum green density occurs at a microcapsule concentration of approximately 40% by weight. As in Example VI there is a minimum in the curve for ejection pressure. Beneficial synergism occurs here also, with regard to both green density and ejection pressure.
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Blends were also prepared and tested using micro-capsules from Example I. These capsules are identical to those from Example X, except that khey are much larger. Although the results are not shown, it was found that the green density reaches a maximum at a lower microcapsule concentration. The ejection pressures and apparent densities are higher.
.
EXAMPLE ~II Coating of microcapsules from Example VIII with thin layers of lubricants.
A 166 g. sample of fine microcapsules from Example -VIII was heated to 150F. and to half of this was added, with mixing, 17 g. of double pressed stearic acid and to the other half was added, with mixing, 17 g. of a Fischer-Tropsch Wax (Paraflint - trademark). The samples were held at 150F.
and mixed for 30 minutes. The heat source was then removed and the samples allowed to cool to room temperature, at which point the mixing was stopped. The aggregates that had formed as a result of this treatment were broken by light grinding.
I'he coated microcapsules were tested as lubricants for iron powder, Atomet 29 (trademark) using a lubricant con-centration o 0.75~/~ by weight.
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TABLE III
Effect of Thin Coating on Lubricant Properties -EthyIene Coated Capsules Zinc bissteara- Uncoated Stearic : -Stearate mide Capsules Acid Wax Flow Rate in sec./50 g, 34~5 41.0 no flow no flow no flow Apparent Density -in g./cc 3,24 2.94 2.58 2.95 2.6~ - -Green Density in g./cc 6.60 6.55 6.55 6.60 6.52 ~-~
Ejection Force in t.s.i. 5.4 6.4 5.6 4.9 5.7 ~ ~ -Green Strength in p.s.i. 1664 2218 1437 1175 1423 . . _ . . .
The results show that the stearic acid coated micro-capsules give higher apparent densities and green densities than ~o the uncoated.
.. ~ .
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EXAMPLE XIII Coating of microcapsules from Example VII with thin layers of lubricants.
Four samples, each weighing 83 g., of coarse micro-capsules from Example VII were heated to 150F. and to each was added 17 g. of a coating material. Four materials were used: double pressed stearic acid, Fischer Tropsch Wax, hydrogenated castor fatty acid and carnauba wax. The samples were held at 150F. and mixed for 30 minutes. They were then ~allowed to cool at room temperature with constant mixing. Any aggregates of coated microcapsules that had formed were broken by light grinding.
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, ,: . . . -The coated microcapsules were tested as lubricants for iron powder Atomet 29 (trademark) using concentrations of 0.50%
and 0.75% by weight. Table IV presents the results along with -~-those for customarily used lubricants.
The results show that when coarse microcapsules are coated there is a spectacular improvement in the flow rate and apparent density. Although no results are shown, it was found that coating the capsules increased the green strength, but had no significant effect on other properties.
Effect of Various Coatings on Lubricant Properties . . ., _ _ .
Concentration Flow Rate Apparent Density of Lubricant in sec./50 G. in g./cc.
Ethylene 0.50/O 32.0 2 73 Bisstearamide 0.75% 35.0 2 62 ~ -Uncoated 0.50/0no flow 2.38 Micro-capsules 0.75% no flow -Stearic Acid 0.50/0 39.5 2.71 Coated Capsules~ 0.75% 37,5 2,67 Fischer Tropsch 0.50O/o30.5 2.61 Wax Coated Capsules 0,75% 35,0 2.54 Castor Fatty 0.50/0 Acid Coated Capsules 0.75% 38.5 2.60 Carnauba Wa~ 0.50/0 - - -Coated 0.75% 37.0 2.61 EXAMPLE XIV Methyl Lardate encapsulated in the reaction product from Ethylene Diamine and Trimethyl ~ -Hexamethylene Diisocyanate~
30 g. of trimethyl hexamethylene diisocyanate was dissolved in 120 g. of methyl lardate. This solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water. When the emulsification was complete, ; the stirring rate was reduced and 30 g. of ethylene diamine - dissolved in 70 g. of water was added. The temperature was 10 then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The resulting dispersion of microcapsules in water was filtered and the microcapsules dried at 60C. Aggregates of microcapsules were broken by light grinding.
The microcapsules were white, spherical, free flowing, had an average particle size of 50 microns and contained ; approximately 66% by weight methyl lardate.
EXAMPLE XV Methyl lardate encapsulated in the reaction product ~rom propylenediamine and trimethyl hexamethylene diisocyanake.
.. , The same procedure was followed as in Example XIV
except that 32 g. of propylene diamine were used instead of 30 g. of ethylenediamine. ~ -The resulting microcapsules were white, spherical, free flowing, had an average particle size of 50 microns and -contained approximately 66% methyl lardate.
EXAMPLE X~I Rapeseed oil encapsulated in polymerized divinylbenzene.
- 25 g~ of divinylbenzene were dissolved in 60 g. of rapeseed oil. This solution was added with vigorous stirring to a solution of 0.5 g. of Siponic 218 in 700 g. of water.
When the emulsification was complete, the stirring rate was reduced and the temperature raised to 80C. Then, 2 g. of .. . .
: . .. . .
potassium persulphate were added and the mixture stirred at 80C. for 6 hours. The temperature was allowed to drop to 25C, At this point, the mixture was filtered, and the microcapsules washed and then dried at 45~C. The dried capsules were gently ground to break any aggregates.
The final microcapsules were white, spherical, free flowing, had an average particle size of 20 microns and contained approximately 7~/0 by weight rapeseed oil.
EXAMPLE XVII Isostearic acid encapsulated in polymerized divinylbenzene.
The same procedure was followed as in Example XVI,-except that 60 g. of isostearic acid was used instead of 60 g.
of rapeseed oil.
The resulting microcapsules were white, spherical, free flowing, had an average particles size of 20 microns and con-tained approximately 70/0 by weight isostearic acid.
EXAMPLE XVIII Effect of mlxtures of ethylenebisstearamide wax and microcapsules from Example VIII on bxass powder.
Blends of microcapsules and a conventional lubricant ~; 20 were prepared and tested using CZ-2 (trademark) brass powder (from Canada Metals Limited). Figure 4 gives the results for ; blends of ethylenebisstearamide wax with the fine particle siæe microcapsules prepared in Example VIII. The total concentration of lubricant was he~d constant at 1% by weight. Here again synergism occurs and there is a maximum in the green density, which in this case occurs at a concentration of microcapsules of approximately 60% by weight. In contrast to the results for iron powders, the-ejection pressure increases with the addition of microcapsules.
EXAMPLE XIX Epoxidized soyabean oil encapsulated in the reaction product from ethylene diamine and polymethylene polyphenylisocyanate.
13.5 g. of polymethylene polyphenylisocyanate (Mondur MRS, trademark from Mobay Chemical Company) was dissolved in 76.5 g. of epoxidized soyabean oil (Paraplex G-62, trademark -from Ro~n and Haas). The solution was added with stirring to a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
The resulting coarse emulsion was then mixed very vigorously in a high intensity colloid mill to produce an emulsion containing very fine droplets of oil. The stirring rate was then reduced and 3~5 g. of ethylene diamine in 10 g. of water was added. The temperature was then increased to 80C. and maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated from the water by filtration and dried at 60C. Aggregates of dried microcapsules were broken by gentle grinding.
The microcapsules were white, spherical, free flowing, -had an average diameter of 5 microns and contained 85% oil.
When tested as lubricants for powdered metals they gave results similar to those obtained with unepox:idized soyabean oil. ;
; EXAMPLE XX Effect of mixtures of zinc s-tearates and microcapsules from Example VIII on iron powder.
Blends of zinc stearate (from H. L. Blachford, Limited) and microcapsules from Example VIII were prepared and tested - using Atomet 29 (trademark) from Quebec Metal Powder Company.
The total concentra-tion of lubricant was held constant at 1%
by weight. Although, no maximum occurred in the plot for green density, a minimum occurred in the ejection force at approximately 60% microcapsule content, showing once again the existence of ~;~ synergism.
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. - ., SUPPLEMENTARY DISCLOSURE
This disclosure and the original disclosure are concerned with lubricants for powder metallurgy and with the manufacture and use of such lubricants; and more ~ especially are concerned with microencapsulated lubricants.
- As described in the original disclosure the microcapsules of the invention comprise a core and a solid shell surrounding the core.
Liquid _ubricant The core comprises a liquid lubricant. The lubricant should have a low enough viscosity that when the shell is ruptured, the lubricant will rapidly flow out and envelop the particles of powdered metal.
In this respect the viscosity is suitably less than 1500 centipoises, preferably less than 600 centipoises and most suitably below 300 centipoises.
:
Generally the surface tension of the lubricant is below about 50 and preferably below about 40 dynes/cm so as to achieve good wetting of the powdered metal.
Lubricants are frequently burned off at about 1200F
or below prior to sintering and so in general it is ~, appropriate that at least 90% of the liquid should volatize or decompose below 1200F.
. .
; Examples of specific liquid lubricants in the invention, in addition to those mentioned in the original disclosure include fatty acid esters of polyols such as glycerol, trimethylolpropane, pentaerythritol, poly-ethylene glycols, (for example polyethylene glycol dioleate), polypropylene glycols, and copolymers formed by addition of ethylene oxide and propylene oxide to a glycol or amine base. Generally synthetic fatty acid esters or ~J ' , :; :
mixtures of synthetic fatty acid esters or mixtures of `
synthetic and natural fatty acid esters are preferred~
Mineral oils and low melting point polyethylene glycols and polypropylene glycols can also be used, but are less preferred.
An antioxidant may be included in admixture with the liquid lubricant as a special additive.
Usually the lubricant content of the micro-capsule varies between 50% and 90%, preferably 50% to 85%, by weight, of the microcapsule.
Shell The chemical properties required of the shell material are similar to those for the liquid lubricant.
; The surface of the shell must be sufficiently smooth `
and non-tacky so that a good flow rate and apparent ' density is obtained for the mixture of powdered metal, ; lubricants and other additives. The flow rate and apparent density are desirably at least ninety percent of the correspondin~ values for the powder without lubricant, and should preferably be greater. Desirably in obtaining the best results the shell should have a smooth, non-tacky outer surface such that the flow rate and apparent density of a mixture of the microcapsules and powdered ferrous .~ ~ . . .
`~ metal which mixturecomprises the microcapsules in an -~
amount of 0.1% to 1%, by weight, are at least 90% of the corresponding values for the free powdered ferrous metals. Values less than 90% may be satisfactory for some ` -;
purposes although less preferred. -The shell-should rupture when subjected to the pressure exerted during compaction. This pressure can range from as low as one t.s.i. (tons per square inch) , ~
; . . ', . ', ,. ' . :' ~ : '' : . , .' , to as high as one hundred t.s.i., and even slightly above this at times. For iron and steel pressures of 20 - 60 t.s.i. are most commonly used, while for brass and bronze - somewhat lower pressures are generally used, and for aluminum the usual range is 10 - 30 t.s.i. It is also desirable that the shell material be such that thin shells can be utilized so that the percentage of liquid lubricant is high. Shell thick-ness is usually in the range 0.01 to 50 microns, preferably 0.1 to 20 microns, depending on capsule size.
Microcapsule Fine capsules are not always preferable since they fit more easily into interstices between the metal -particles and a greater degree of compaction is re~uired before they break. Also, in capsules prepared by the inter-facial method, the wall thickness is proportional to the capsule diameter, so smaller capsules are less resistant ~`~` to abrasion.
- In the synergistic mixtures of microcapsules and unencapsulated solid particulate lubricant the optimum microcapsule concentration is dependent upon the particle size and the composition of the microcapsules and of the un-encapsulated solid particulate lubricant. The compositions giving optimum properties can vary over a wide range, depend-ing on the property considered and the powder used, but usually the microcapsule content is from 1 to 99, preferably 5 to 95, percent.
Microcapsule Production As described in the original disclosure the microcapsules may be manufactured by a method comprising the following steps~ If necessary, mix an emulsifying agent with either the liquid lubricant, the water phase, :
or both. (2) Mix a lubricant soluble monomer with the liquid lubicant. (3) Add the resulting mixture to the water phase.
(4) Mix at room temperature uslng vigorous agi~ation to form an emulsion of the desired droplet size, as discussed above. (5) To the emulsion add, with mixing, a water soluble monomer reactive wiih the lubricant soluble monomer or a polymerization catalyst for the lubricant soluble monomer. (6) Mix, but not so vigourously that the capsules are destroyed, for several hours, with heating to about 80C. if desired, to accelerate the reaction. (7) Filter the mixture to separate the microcapsules from the water. t8) Wash t'ne microcapsules to remove emulsify-. .
ing agent and any excess water soluble monomer and (9) dry the microcapsules.
'! I As llndicated in the original disclosure polyurea shells derived from the polymerization of a di- or polyisocyanate with a di- or polyamine are especially preferred.
In particular it is preferred to employ a shell de-; rived from the polymerization of a polyisocyanate with a poly- ~ ;
amine' such shells are found to be stronger and to provide better flow characteristics. -. .
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The microcapsules themselves represent a total lubricant system in that not only does the core act as a lubricant on rupture of the microcapsules but the unbroken microcapsules themselves act as lubricant. When the microcapsules are mixed with a powdered metal, for example powdered iron, the bulk density (i.e. the apparent density, as it is generally called) of the iron powder/microcapsule mixture is greate~ than that bf the iron powder alone; this is in spite of the fact that the specific gravity of the microcapsules is much lower than that of the iron.
; The apparent density is directly related to the ease with which the particles of iron powder can slide over one another. The more easily that the iron particles slide over one another, the higher the apparent density will be, because of the greater extent to which the particles of iron can be packed or nested together. One advantage of the microcapsules is that they produce an increase in the bulk density of the uncompacted powdered metal. This means that the molds can be shallower, for a given thick-ness of the final part.
Thus, not only does the core of the microcapsule provide a lubricant on rupture of the microcapsule, but also the smooth non-tacky shell of the microcapsule acts as a lubricant prior to rupture of the microcapsules.
- 31 - ~
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-3~ .
A further importantcriterion of the microcapsules of the present invention which is important to the utility in powder metallurgy is that the outer surface of the micro-capsules must be resistant to abrasion by sinterable powdered metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without any substantial release of lubricant: at the same time the shell must be rupturable when the mixture is subjected to powder metallurgy compacting pressures. The abrasion resistance required of the microcapsules is very high.
Particles of iron powder are angular and have sharp - -edges and are very heavy having a specific gravity of about 7.9. It is surprising that microcapsules could be developed which withstand the abrasive treatment received, when being mixed with iron powder.
Before compaction of the mixture, there are two important properties of the powdered metal-lubricant mixture which are greatly affected by the lubricant. One is the apparent density, and the other is the flow rate. Customarily used lubricants such as zinc stearate and ethylenebisstear- ;
amidewaxalmost always reduce the flow rate to a ~mall ~ ' . ', .
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.. .
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:, extent. If more than a very small amount of a liquid lubricant is added directly to a powdered metal, the flow rate is substantially reduced and this is a very serious disadvantage because it then becomes impossible to fill the mold completely. A great many different materials have been tested which give good lubrication as far as, say, apparent density and compressibility and maybe also ejection pressure are concerned, which materials fail completely with regard to flow rate because they reduce the flow rate drastically. The microcapsules of the invention do not reduce the flow rate drastically and indeed sometimes they improve it. When they do reduce it, the reduction is less than with zinc stearate or ethylenebisstearamide wax, which are the materials conventionally employed as lubricants in powder metallurgy techniques.
This latter feature of the microcapsules is illustrated later in Table V from which can be compared the flow time of powdered metals containing microcapsules of the invention with powder metal mixtures con-taining zinc stearate and ethylenebisstearamide wax, respectively, as the lubricant. It will be seen that in each case the flow time for the mixture containing microcapsules of the invention is lower than the flow time for the mixtures containing zinc stearate or ethylenebis-stearamide wax; indeed the microcapsules of the present invention,which can be considered an organic lubricant, produce a flow time considerably faster than the conven-tional organic lubricant, namely ethylenebisstearamide.
Further, the flow time for each of the mixtures containing microcapsules in Table V is less than that for the powdered metals alone. In particular the flow time - 33 _ ,~'\~ , '' :
; ~' for the Atomet 28 by itself is 27.1 seconds and the flow time for Atomet 29 by itself is 24.2 seconds. The corres-ponding figures for the mixtures with microcapsules of the invention are 24.6 and 23.4 seconds respectively.
On the other hand the flow times for the mixtures with zinc stearate and ethylenebisstearamide wax are shown to be higher than the flow times for the powdered metals . .
alone. From this it can be seen that the microcapsules of the invention are superior to zinc stearate and ethylenebisstearamide wax with regard to flow rate.
It is really very surprising, and certainly not obviQus, that microcapsules should produce such good results. This is especially so when one considers that the especially preferred shell material is a polyurea, which is produced by reacting an isocyanate with an'amine, since polyurea is not known as a lubricant.
Production of Sintered Metal Article The microcapsules of the invention or mixtures of the microcapsules with solid particulate lubricants are advantageously employed in the manufacture of sintered . !
metal articles from powdered metal.
In this method the powdered metal is mixed or blended with the microcapsules, or a mixture of the micro-capsules with a conventional solid particulate lubricant, to form an intimate mixture.
The mixture is compacted in a mould at a pressure effective to rupture the shell of the microcapsules and release the liquid lubricant, and to form the mixture into a self-supporting shaped body. The compacting pressure will depend too on the particular metal powder and may be from 1 t.s.i. to 100 t.s.i. or even higher; generally compacting pressures of 10 t.s.i. to 75 t.s.i. will be *trademark - 34 -.~ ~ ;.
'~ ,. .
satisfactory.
The self supporting body is removed from the mould and is heated to decompose and remove the lubricant and shell and to sinter the metal particles. This heating operation may take place in two separate stages, most of the lubricant and shell and any solid particulate lubricant being removed in a first heating stage and any residual material subsequently being removed in the sintering furnace. The lubricant and shell could be removed entirely in the sintering furnace but this results in deposits on the interior of the sintering furnace which may serve to decrease the efficiency of the furnace over à period of time.
When mixed with metal powders, the concentration of the microcapsules or of microcapsulès plus unencapsulated solid lubricants is suitably in the range of 0.1% to 5%
by weight, preferably from 0.3% to 2% more preferably 0.~/0 to 1% by weight.
The method can be employed in the manufacture of sintered metal parts from a variety of powdered sinterable metals including ferrous metals, for example, iron and steel,and non-ferrous metals, for example, aluminium, copper and zinc, as well as mixtures of metal powders, for example mixtures of iron and copper, and powdered alloys, for example, brass powder. It will be understood that such sinterable metal powders may also include conventional additives, for example, graphite, which is often employed in admixture with iron.
The microcapsules may also be employed in the manufacture of sintered parts from sinterable metal oxides, . ~ , . .
and sinterable metal salts, for example, uranium oxide `
and barium ferrite.
. . , ::
~ :; . ::
., -In a further aspect of the invention there is provided a novel composition of matter for the -manufacture of sintered iron articles comprising a sinterable mixture comprising powdered metal, for example iron, and discrete pressure rupturable microcapsules of the invention.
The invention is further illustrated by reference to the following examples directed to particular and preferred embodiments. ;
EXAMPLE XXI
Epoxidized soyabean oil encapsulated in the reaction product -from triethylene-tetramine and polymethylene p~lyphenyl-isocyanate. ~-19.6 g of polymethylene polyphenylisocyanate (Mondur MRS, trademark, from Mobay Chemical Company), was dissolved in 75.0 g of epoxidized soyabean oil (Plasto-lein 9232, trademar~ from Emery Industries, Inc~) together with 3.0 g~ of a tallow fatty acid diester of polyethylene ; glycol of molecular weight 600. The solution was added with vigorous stirring to 700 ml. of water. When the emulsification was complete, the stirring rate was reduced and 10.0 g of triethylenetetramine dissolved in 100 ml. of water was added. The mixture was heated to 80C. for two hours with continued stirring, cooled, and filtered. The - microcapsules were dried at 60C. and disaggregated by sieving through a 60 mesh sieve. They were white, spherical, free-flowing, had an average diameter of about 70 microns, and contained about 75% by weight of oil.
EXAMPLE XXII
Testing of microcapsules prepared in ~ -Example XXI.
The microcapsules of Example XXI were tested in the iron powders Atomet 28 (trademark, from Quebec Metal ;
) ., ~ -;
,~ . , Powder Co.) and Atomet 29, and results were compared with those obtained for zinc stearate and ethylenebisstear-amide wax. Lubricant and iron powder were thoroughly mixed and transverse rupture specimens pressed using a pressure of 67200 psi. The parts were subjected to lubricant burn-off at 1000F. for 30 minutes in an atmosphere of hydrogen-nitrogen (50:50), followed by sintering at 2050F.
for 30 minutes. Properties were measured according to standard ASTM procedures and are shown in Table V.
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ing agent and any excess water soluble monomer and (9) dry the microcapsules.
'! I As llndicated in the original disclosure polyurea shells derived from the polymerization of a di- or polyisocyanate with a di- or polyamine are especially preferred.
In particular it is preferred to employ a shell de-; rived from the polymerization of a polyisocyanate with a poly- ~ ;
amine' such shells are found to be stronger and to provide better flow characteristics. -. .
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The microcapsules themselves represent a total lubricant system in that not only does the core act as a lubricant on rupture of the microcapsules but the unbroken microcapsules themselves act as lubricant. When the microcapsules are mixed with a powdered metal, for example powdered iron, the bulk density (i.e. the apparent density, as it is generally called) of the iron powder/microcapsule mixture is greate~ than that bf the iron powder alone; this is in spite of the fact that the specific gravity of the microcapsules is much lower than that of the iron.
; The apparent density is directly related to the ease with which the particles of iron powder can slide over one another. The more easily that the iron particles slide over one another, the higher the apparent density will be, because of the greater extent to which the particles of iron can be packed or nested together. One advantage of the microcapsules is that they produce an increase in the bulk density of the uncompacted powdered metal. This means that the molds can be shallower, for a given thick-ness of the final part.
Thus, not only does the core of the microcapsule provide a lubricant on rupture of the microcapsule, but also the smooth non-tacky shell of the microcapsule acts as a lubricant prior to rupture of the microcapsules.
- 31 - ~
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A further importantcriterion of the microcapsules of the present invention which is important to the utility in powder metallurgy is that the outer surface of the micro-capsules must be resistant to abrasion by sinterable powdered metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without any substantial release of lubricant: at the same time the shell must be rupturable when the mixture is subjected to powder metallurgy compacting pressures. The abrasion resistance required of the microcapsules is very high.
Particles of iron powder are angular and have sharp - -edges and are very heavy having a specific gravity of about 7.9. It is surprising that microcapsules could be developed which withstand the abrasive treatment received, when being mixed with iron powder.
Before compaction of the mixture, there are two important properties of the powdered metal-lubricant mixture which are greatly affected by the lubricant. One is the apparent density, and the other is the flow rate. Customarily used lubricants such as zinc stearate and ethylenebisstear- ;
amidewaxalmost always reduce the flow rate to a ~mall ~ ' . ', .
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:, extent. If more than a very small amount of a liquid lubricant is added directly to a powdered metal, the flow rate is substantially reduced and this is a very serious disadvantage because it then becomes impossible to fill the mold completely. A great many different materials have been tested which give good lubrication as far as, say, apparent density and compressibility and maybe also ejection pressure are concerned, which materials fail completely with regard to flow rate because they reduce the flow rate drastically. The microcapsules of the invention do not reduce the flow rate drastically and indeed sometimes they improve it. When they do reduce it, the reduction is less than with zinc stearate or ethylenebisstearamide wax, which are the materials conventionally employed as lubricants in powder metallurgy techniques.
This latter feature of the microcapsules is illustrated later in Table V from which can be compared the flow time of powdered metals containing microcapsules of the invention with powder metal mixtures con-taining zinc stearate and ethylenebisstearamide wax, respectively, as the lubricant. It will be seen that in each case the flow time for the mixture containing microcapsules of the invention is lower than the flow time for the mixtures containing zinc stearate or ethylenebis-stearamide wax; indeed the microcapsules of the present invention,which can be considered an organic lubricant, produce a flow time considerably faster than the conven-tional organic lubricant, namely ethylenebisstearamide.
Further, the flow time for each of the mixtures containing microcapsules in Table V is less than that for the powdered metals alone. In particular the flow time - 33 _ ,~'\~ , '' :
; ~' for the Atomet 28 by itself is 27.1 seconds and the flow time for Atomet 29 by itself is 24.2 seconds. The corres-ponding figures for the mixtures with microcapsules of the invention are 24.6 and 23.4 seconds respectively.
On the other hand the flow times for the mixtures with zinc stearate and ethylenebisstearamide wax are shown to be higher than the flow times for the powdered metals . .
alone. From this it can be seen that the microcapsules of the invention are superior to zinc stearate and ethylenebisstearamide wax with regard to flow rate.
It is really very surprising, and certainly not obviQus, that microcapsules should produce such good results. This is especially so when one considers that the especially preferred shell material is a polyurea, which is produced by reacting an isocyanate with an'amine, since polyurea is not known as a lubricant.
Production of Sintered Metal Article The microcapsules of the invention or mixtures of the microcapsules with solid particulate lubricants are advantageously employed in the manufacture of sintered . !
metal articles from powdered metal.
In this method the powdered metal is mixed or blended with the microcapsules, or a mixture of the micro-capsules with a conventional solid particulate lubricant, to form an intimate mixture.
The mixture is compacted in a mould at a pressure effective to rupture the shell of the microcapsules and release the liquid lubricant, and to form the mixture into a self-supporting shaped body. The compacting pressure will depend too on the particular metal powder and may be from 1 t.s.i. to 100 t.s.i. or even higher; generally compacting pressures of 10 t.s.i. to 75 t.s.i. will be *trademark - 34 -.~ ~ ;.
'~ ,. .
satisfactory.
The self supporting body is removed from the mould and is heated to decompose and remove the lubricant and shell and to sinter the metal particles. This heating operation may take place in two separate stages, most of the lubricant and shell and any solid particulate lubricant being removed in a first heating stage and any residual material subsequently being removed in the sintering furnace. The lubricant and shell could be removed entirely in the sintering furnace but this results in deposits on the interior of the sintering furnace which may serve to decrease the efficiency of the furnace over à period of time.
When mixed with metal powders, the concentration of the microcapsules or of microcapsulès plus unencapsulated solid lubricants is suitably in the range of 0.1% to 5%
by weight, preferably from 0.3% to 2% more preferably 0.~/0 to 1% by weight.
The method can be employed in the manufacture of sintered metal parts from a variety of powdered sinterable metals including ferrous metals, for example, iron and steel,and non-ferrous metals, for example, aluminium, copper and zinc, as well as mixtures of metal powders, for example mixtures of iron and copper, and powdered alloys, for example, brass powder. It will be understood that such sinterable metal powders may also include conventional additives, for example, graphite, which is often employed in admixture with iron.
The microcapsules may also be employed in the manufacture of sintered parts from sinterable metal oxides, . ~ , . .
and sinterable metal salts, for example, uranium oxide `
and barium ferrite.
. . , ::
~ :; . ::
., -In a further aspect of the invention there is provided a novel composition of matter for the -manufacture of sintered iron articles comprising a sinterable mixture comprising powdered metal, for example iron, and discrete pressure rupturable microcapsules of the invention.
The invention is further illustrated by reference to the following examples directed to particular and preferred embodiments. ;
EXAMPLE XXI
Epoxidized soyabean oil encapsulated in the reaction product -from triethylene-tetramine and polymethylene p~lyphenyl-isocyanate. ~-19.6 g of polymethylene polyphenylisocyanate (Mondur MRS, trademark, from Mobay Chemical Company), was dissolved in 75.0 g of epoxidized soyabean oil (Plasto-lein 9232, trademar~ from Emery Industries, Inc~) together with 3.0 g~ of a tallow fatty acid diester of polyethylene ; glycol of molecular weight 600. The solution was added with vigorous stirring to 700 ml. of water. When the emulsification was complete, the stirring rate was reduced and 10.0 g of triethylenetetramine dissolved in 100 ml. of water was added. The mixture was heated to 80C. for two hours with continued stirring, cooled, and filtered. The - microcapsules were dried at 60C. and disaggregated by sieving through a 60 mesh sieve. They were white, spherical, free-flowing, had an average diameter of about 70 microns, and contained about 75% by weight of oil.
EXAMPLE XXII
Testing of microcapsules prepared in ~ -Example XXI.
The microcapsules of Example XXI were tested in the iron powders Atomet 28 (trademark, from Quebec Metal ;
) ., ~ -;
,~ . , Powder Co.) and Atomet 29, and results were compared with those obtained for zinc stearate and ethylenebisstear-amide wax. Lubricant and iron powder were thoroughly mixed and transverse rupture specimens pressed using a pressure of 67200 psi. The parts were subjected to lubricant burn-off at 1000F. for 30 minutes in an atmosphere of hydrogen-nitrogen (50:50), followed by sintering at 2050F.
for 30 minutes. Properties were measured according to standard ASTM procedures and are shown in Table V.
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EXAMPLE XXIII
Testing of microcapsules prepared in Example XXI
The microcapsules of Example XXI were tested in Iron Powder MH-100 of Hoeganaes to determine the flow time, flow rate and apparent density. The results are tabulated in Table VI.
TABLE VI
MH-100 M~I-100 MH-100 alone + 1% + 5%
microcaps. microcaps.
_ .. ;
Flow time (sec./50 g.) 31.3 25.7 33.9 Flow rate (as % of rate for pure MH-100) 100% 122~ 92%
Apparent density (g./cm. ) 2.582 2.603 2.283 Apparent density (as % of - apparent density for pure , MH-100) 100% 101% 88%
".
The results demonstrate that 0ven with higher concentrations of microcapsules of the invention satisfactory flow rate and apparent density values were ob~ained.
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EXAMPLE XXIII
Testing of microcapsules prepared in Example XXI
The microcapsules of Example XXI were tested in Iron Powder MH-100 of Hoeganaes to determine the flow time, flow rate and apparent density. The results are tabulated in Table VI.
TABLE VI
MH-100 M~I-100 MH-100 alone + 1% + 5%
microcaps. microcaps.
_ .. ;
Flow time (sec./50 g.) 31.3 25.7 33.9 Flow rate (as % of rate for pure MH-100) 100% 122~ 92%
Apparent density (g./cm. ) 2.582 2.603 2.283 Apparent density (as % of - apparent density for pure , MH-100) 100% 101% 88%
".
The results demonstrate that 0ven with higher concentrations of microcapsules of the invention satisfactory flow rate and apparent density values were ob~ained.
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Claims (51)
1. Discrete pressure-rupturable microcapsules for lubrication in powder metallurgy comprising a core and a solid shell surrounding said core; said core comprising a non-corrosive organic liquid lubricant able to wet powdered metals, and said shell comprising a thin non-atmospherically-degradable polymeric material, said shell being impermeable to said lubricant and having a smooth, slippery, non-tacky, outer surface resistant to abrasion by sinterable powdered metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant said shell being rupturable, when said microcapsules are in admixture with sinterable powdered metal and are subjected to powder metallurgy compacting pressures; said lubricant and said shell being heat decomposable to gaseous products which are non-corrosive to sinterable metal with a low residue of carbon at elevated temperatures below the sintering temperature of a powdered metal to be sintered.
2. Microcapsules according to claim 1, wherein said liquid lubricant is selected from epoxidized animal and vege-table fats and oils.
3. Microcapsules according to claim 1, wherein said liquid lubricant is selected from animal and vegetable fats and oils.
4. Microcapsules according to claim 1, wherein said liquid lubricant comprises a fatty acid ester.
5, Microcapsules according to claim 4, wherein said liquid lubricant is non-corrosive to iron, has a viscosity below 300 cp and a surface tension below 40 dynes/cm and com-prises 50 to 85% by weight of the microcapsules said lubricant and shell being heat decomposable below 800°F to gaseous pro-ducts which are non-corrosive to iron.
6. Microcapsules according to claim 1, having a size in the range of 1 to 200 microns.
7. Microcapsules according to claim 4 or 5, having a size in the range of 1 to 200 microns.
8. Microcapsules according to claim 1, 4 or 5, wherein said shell has a thin surface coating of a solid lubricant for metal powders.
9. Microcapsules according to claim 1, 2 or 3, having a size in the range of 5 to 100 microns.
10. Microcapsules according to claim 4 or 5, having a size in the range of 5 to 100 microns.
11. Microcapsules according to claim 1, 2 or 3, having a size in the range of 5 to 50 microns.
12. Microcapsules according to claim 4 or 5, having a size in the range of 5 to 50 microns.
13. Microcapsules according to claim 1, 2 or 3, wherein said shell is derived from the polymerization of a di- or poly-isocyanate with a di- or poly-amine.
14. Microcapsules according to claim 4 or 5, wherein said shell is derived from the polymerization of a di- or poly-iso-cyanate with a di- or poly-amine.
15. Microcapsules according to claim 1, 4 or 5, wherein said shell is derived from the polymerization of a di- or poly-isocyanate with a di- or poly-amine and said microcapsules have a size in the range of 1 to 200 microns.
16. Microcapsules according to claim 1, 4 or 5, wherein said shell is derived from the polymerization of a diisocyanate with a diamine, the microcapsules having a size in the range of 5 to 100 microns.
17. Microcapsules according to claim 1, 4 or 5, having a size in the range of 5 to 100 microns wherein said shell is derived from the polymerization of a diamine with a poly-isocyanate.
18. Microcapsules according to claim 1, 4 or 5, having a size in the range of 5 to 100 microns, wherein said shell is derived from the polymerization of a diamine and polymethylene polyphenylisocyanate.
19. A process for producing solid lubricant coated discrete pressure rupturable microcapsules, comprising a core of a liquid organic lubricant and a solid polymeric shell surrounding said core comprising forming a mixture of the liquid lubricant and a poly-merizable monomer soluble therein, forming an emulsion of the mixture with a polar solvent immiscible with said liquid lubricant, reacting said monomer with a polar solvent-soluble monomer or catalyst to produce microcapsules comprising a core of said liquid lubricant and a hell of polymeric material, mixing the microcapsules with a solid lubricant at a temperature above the melting point of the solid lubricant to coat the microcapsules, and recovering solid lubricant coated microcapsules.
20. A method of producing a sintered metal part from powdered metal comprising blending said powdered metal with a lubricant comprising discrete pressure-rupturable microcapsules comprising a core of a non-corrosive liquid organic lubricant able to wet said powdered metal, and surrounding said core a thin polymeric solid shell, to form an intimate mixture, compacting said mixture in a mould at a pressure effective to rupture said shell and release said liquid lubricant and to form said mixture into a self-supporting shaped body, removing said body from said mould, heating said body to decompose and remove organic material, and sintering said metal particles.
21. A method according to claim 20, wherein said lubricant is a synergistic mixture of said microcapsules and a solid unencapsulated particulate powder metallurgy lubricant.
22. A method according to claim 20, wherein said shell has at its outer surface a thin coating of a solid lubricant for metal powders.
23. A method according to claim 20, 21 or 22, wherein said powdered metal is a powdered metal alloy.
24. A method according to claim 20, 21 or 22, wherein said powdered metal is a mixture of metal powders.
25. A method according to claim 20, wherein said powdered metal comprises iron powder.
26. A method according to claim 25, wherein said iron powder contains graphite as an additive.
27. A method according to claim 20, 21 or 22, wherein said liquid organic lubricant comprises a fatty acid ester.
28. A method according to claim 21, wherein said unen-capsulated lubricant is an amide wax.
29. A method according to claim 28, wherein said amide wax is ethylenebisstearamide.
30. A method according to claim 21, wherein said unencapsulated lubricant is a metal stearate.
31. A method according to claim 30, wherein said metal stearate is zinc stearate.
32. A method according to claim 20, wherein said liquid lubricant is non-corrosive to iron, has a viscosity below 300 cp and a surface tension below 40 dynes/cm and comprises 50 to 85% by weight of the microcapsules: said lubricant and shell being heat decomposable below 800°F to gaseous products which are non-corrosive to iron.
33. A method according to claim 32, wherein said lubricant comprises a fatty acid ester.
34. A method according to claim 20, 32 or 33, wherein said shell is derived from the polymerization of a di- or poly-isocyanate with a di- or poly-amine.
CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE
CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE
35. Discrete pressure-rupturable microcapsules for lubrication in powder metallurgy comprising a core and a solid shell surrounding said core; said core comprising an organic liquid lubricant non-corrosive to ferrous metal, having a viscosity below 1500 cp and a surface tension below 50 dynes/cm and being able to wet powdered ferrous metal, said core comprising 50 to 90% by weight, of the microcapsules;
said shell being derived from the polymerization of a di-or poly-isocyanate with a di- or poly-amine, non-degradable by moisture or oxygen, impermeable to said lubricant and having a smooth, non-tacky, outer surface such that the flow rate and apparent density of a mixture of the the microcapsules and powdered ferrous metal comprising microcapsules in an amount of 0.1% to 1%, by weight, are at least 90% of the corresponding values for the free powdered ferrous metal, said outer surface being resistant to abrasion by powdered ferrous metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant, said shell being rupturable when said micro-capsules are in admixture with powdered ferrous metal at a pressure of 20 to 100 t.s.i.; said lubricant and said shell being heat decomposable or volatilizable to gaseous products, which are non-corrosive to powdered ferrous metal, with a low residue of carbon at elevated temperatures below the sintering temperature of the ferrous metal; said micro-capsules being spherical and having a diameter in the range of 1 to 200 microns with a shell thickness of 0.01 to 50 microns.
said shell being derived from the polymerization of a di-or poly-isocyanate with a di- or poly-amine, non-degradable by moisture or oxygen, impermeable to said lubricant and having a smooth, non-tacky, outer surface such that the flow rate and apparent density of a mixture of the the microcapsules and powdered ferrous metal comprising microcapsules in an amount of 0.1% to 1%, by weight, are at least 90% of the corresponding values for the free powdered ferrous metal, said outer surface being resistant to abrasion by powdered ferrous metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant, said shell being rupturable when said micro-capsules are in admixture with powdered ferrous metal at a pressure of 20 to 100 t.s.i.; said lubricant and said shell being heat decomposable or volatilizable to gaseous products, which are non-corrosive to powdered ferrous metal, with a low residue of carbon at elevated temperatures below the sintering temperature of the ferrous metal; said micro-capsules being spherical and having a diameter in the range of 1 to 200 microns with a shell thickness of 0.01 to 50 microns.
36. Microcapsules according to claim 35 wherein said liquid lubricant comprises at least one fatty acid ester.
37. Microcapsules according to claim 35 or 36, wherein said shell is derived from the polymerization of a diisocyanate with a diamine.
38. Microcapsules according to claim 35 or 36, wherein said shell is derived from the polymerization of a polyamine with a polyisocyanate.
39. Microcapsules according to claim 35 or 36, wherein said shell is derived from the polymerization of a polyamine selected from the group consisting of triethylene-tetramine, diethylene triamine or tetraethylene-pentamine with polymethylene poly-phenylisocyanate.
40. Microcapsules according to claim 35 or 36, wherein said shell is derived from the polymerization of triethylene-tetra-mine with a polymethylene polyphenylisocyanate.
41. Microcapsules according to claim 35 or 36, having a diameter in the range of 5 to 100 microns with a shell thickness of 0.1 to 20 microns.
42. Microcapsules according to claim 35 or 36, having a diameter in the range of 5 to 100 microns with a shell thickness of 0.1 to 20 microns, said shell being derived from the poly-merization of a polyamine with a polyisocyanate.
43. Microcapsules according to claim 35 or 36, having a diameter in the range of 5 to 100 microns with a shell thickness of 0.1 to 20 microns, said shell being derived from the poly-merization of a polyamine selected from the group consisting of triethylene-tetramine, diethylene triamine and tetraethylene-pentamine with polymethylene polyphenylisocyanate.
44. Microcapsules according to claim 35 or 36, having a diameter in the range of 5 to 100 microns with a shell thick-ness of 0.1 to 20 microns, said shell being derived from the polymerization of triethylene-tetramine with a polymethylene polyphenylisocyanate.
45. A method according to claim 20, wherein said micro-capsules are blended with said powdered metal in an amount of 0.1% to 5%, by weight; said core comprising an organic liquid lubricant non-corrosive to ferrous metal, having a viscosity below 1500 cp and a surface tension below 50 dynes/cm and being able to wet powdered ferrous metal; said core comprising 50 to 90%, by weight, of the microcapsules; said shell being derived from the polymerization of a di- or poly-isocyanate with a di- or polyamine, non-degradable by moisture or oxygen, impermeable to said lubricant and having a smooth, non-tacky, outer surface such that the flow rate and apparent density of a mixture of the microcapsules and powdered ferrous metal comprising microcapsules in an amount of 0.1%
to 1%, by weight, are at least 90% of the corresponding values for the free powdered ferrous metal, said outer surface being resistant to abrasion by powdered ferrous metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant, said shell being rupturable when said micro-capsules are in admixture with powdered ferrous metal at a pressure of 20 to 100 t.s.i.;
said lubricant and said shell being heat decomposable or volatilizable to gaseous products, which are non-corrosive to powdered ferrous metal, with a low residue of carbon at elevated temperatures below the sintering temperature of the ferrous metal; said microcapsules being spherical and having a diameter in the range of 1 to 200 microns with a shell thickness of 0.01 to 50 microns.
to 1%, by weight, are at least 90% of the corresponding values for the free powdered ferrous metal, said outer surface being resistant to abrasion by powdered ferrous metal to the extent that the microcapsules can be thoroughly mixed with sinterable powdered metal without release of lubricant, said shell being rupturable when said micro-capsules are in admixture with powdered ferrous metal at a pressure of 20 to 100 t.s.i.;
said lubricant and said shell being heat decomposable or volatilizable to gaseous products, which are non-corrosive to powdered ferrous metal, with a low residue of carbon at elevated temperatures below the sintering temperature of the ferrous metal; said microcapsules being spherical and having a diameter in the range of 1 to 200 microns with a shell thickness of 0.01 to 50 microns.
46. A method according to claim 45 wherein said liquid lubricant comprises at least one fatty acid ester.
47. A method according to claim 45 or 46, wherein said shell is derived from the polymerization of a polyamine with a polyisocyanate.
48. A method according to claim 45 or 46 wherein said shell is derived from the polymerization of triethylene-tetramine with a polymethylene polyphenylisocyanate.
49. A novel composition of matter for the manufacture of a sintered metal article comprising a sinterable mixture comprising a powdered metal and microcapsules as defined in claim 35, said microcapsules being present in an amount of 0.1% to 5%, by weight.
50. A composition of matter according to claim 49 wherein said microcapsules are present in an amount of 0.3 to 2%, by weight.
51. A composition of matter according to claim 49 or 50 wherein said powdered metal is ferrous metal and said liquid lubricant comprises at least one fatty acid ester.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA206,086A CA1063839A (en) | 1974-07-31 | 1974-07-31 | Lubricants for powdered metals |
| US05/749,699 US4106932A (en) | 1974-07-31 | 1976-12-10 | Lubricants for powdered metals, and powdered metal compositions containing said lubricants |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA206,086A CA1063839A (en) | 1974-07-31 | 1974-07-31 | Lubricants for powdered metals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1063839A true CA1063839A (en) | 1979-10-09 |
Family
ID=4100810
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA206,086A Expired CA1063839A (en) | 1974-07-31 | 1974-07-31 | Lubricants for powdered metals |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1063839A (en) |
-
1974
- 1974-07-31 CA CA206,086A patent/CA1063839A/en not_active Expired
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