CA1055732A - Sintered blanks for rolling and forging and method of producing same - Google Patents
Sintered blanks for rolling and forging and method of producing sameInfo
- Publication number
- CA1055732A CA1055732A CA216,397A CA216397A CA1055732A CA 1055732 A CA1055732 A CA 1055732A CA 216397 A CA216397 A CA 216397A CA 1055732 A CA1055732 A CA 1055732A
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- Prior art keywords
- metal
- powder
- sintering
- compound
- zinc
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
Sintered blanks for rolling and forging, metal powders used in making such blanks and a method of producing such blanks and powders include the addition of a compound of an alkali metal or an alkaline earth metal to the metal powders before sintering.
Sintered blanks for rolling and forging, metal powders used in making such blanks and a method of producing such blanks and powders include the addition of a compound of an alkali metal or an alkaline earth metal to the metal powders before sintering.
Description
~S~i732 In the art of powder metallurgy, there is a widely known process in which a metal or alloy powder is first compacted to form a "green compact" and then the green compact is heated at a relatively low temperature in a reducing or neutral gaseous atmos-phere so as to obtain a sintered compact. With this method, it is possible to obtain a sintered compact of a material which is usually hard to melt. Furthermore, the inclusion of impurities is minimized as compared with products obtained by more usual melting methods, and hence it is possible to obtain a product having excellent physical and other properties which cannot be expected from the ordinary products formed from molten metal.
This method, however, has the problem that the sintered compact obtained by sintering a green powder compact is porous.
Also, in the case of a metal having high vapor pressure, such as zinc, the component elements tend to volatilize under the sinter-ing heat, so that it is sometimes impossible to obtain a sinter-ed blank of a desired composition. There are also materials that cannot be sintered by using this method. Thus, there has been a certain limitation as to the scope of products obtainable -20 and the scope of use of these products. Such deficiencies have ~-been particularly noticeable in the case of the sintering of high brass.
Therefore, the method generally employed for obtaining high-dPnsity metal-made machine parts is one of cutting solid materials or casting molten materials to the approximata size -of the object product and then machining them into the desired shape. With this conventional method, as adapted for instance to the forming of pressure-proof brass pipe parts as commonly used in industry, first the brass cutting scraps and molten mat-:,, erial are fed into a melting furnace, followed by the addition -1- ~ ~
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thereto of zinc, lead and electrolytic copper to prepare a mol-ten bath of the desired brass composition for forging. This molten bath is then shaped into an ingot, the latter being then rolled into an elongated brass bar of a desired size, and this bar is cut into a desired size to form billets. Then the cut billets are heated to around 700 C, subjected to hot forgin~ in a mold of a predetermined configuration and further passed through the steps of trimming, surface cleaning and machining to - produce a desired pressure-proof pipe part.
In this conventional method, since the shapes of the billets which can be forged are limited, many sections are le~t that require machining after forging, resulting in increased working time and loss of material. The cutting scraps ~rom the machining are later reduced in the melting furnace. When high brass is being used, it is necessary to replenish the zinc com-p~nent of the brass as zinc tends to evaporate during the process.
; This increases the cost of the heat source and consequently the manufacturing cost of the finished article. In many of the cur-rently used methods, the loss in weight of the mat~rial su~fered .:
during the machinin~ of the forged blanks exceeds 50% in the aase ; of pipe parts, as such parts are mostly hollow in shape.
In order to overcome these~disadvantages, some forging machines have been developed which are specifically designed for the forging of hollow parts, but such machines have complicated -die mechanisms, and are also expensive. Consequently, they have not yet found general accepta~nce. -According to the present invention there is provided a~
mlxture for use in producing a;sintered compact comprising at least one metal in-powder form the particles comprlsed in the i~ 30 powder having a coatin~ containlng a metal selected from the .
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group consisting of alkali metals and alkaline earth metals.
According to~a further aspect of the present invention a sintered compact includ~ng at least one metal selected from the yroup consisting of alkali metals and alkaline earth metals.
According to a further aspect of the present invention there is provided a method of producing a sintered product com-prising the steps of adding to a metal powder a compound contain-ing a metal selected from the group consisting of alkali metals and alkaline earth metals, heating the powder and said compound to a temperature higher than the decomposition temperature of the compound, and compacting and sintering the powder and com- ' pound to produce a sintered compact.
An embodiment of the invention will now be described with reference to the accompanying drawings, in which:- ;
Figure 1 is a perspective view showing the shapes of the respective green compacts used for making a valve casing;
Figure 2 is an exploded perspective view showing the re-spective parts of a completed ball valve; ~
Figure 3 is a diagram showing the relation between the ~:
density of a green compact and the compacting pressure exerted on the sintering powder;
Figure 4 is a diagram showing the change in diameter after sintering;
Figure 5 is a diagram showing the loss in the quantity of zinc due to sintering;
Figure 6 is a diagram showing the mechanical properties of the sintered body; and Figure 7 is a diagram showing the relationship between the density ana porosity of the sintered body.
Tn these drawings, reference numeral 1 indicates a valve , "` ~! `
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casing, and 1' the green compact used to make the valve casing,2 indicates a~ end cap and ~' the gxeen compact for making the end cap, while 3 lndicates a ball and 3' the green compact for making the ball.
H.R.B. shows a Rockwell hardness measured by a B
scale.
The process described herein may be used to produce roll-ing and forging blanks by way of a powder metallurgy process.
The concept of producing a machine part by first forming a sintered compact having a shape close to that of the desired product and then subjecting said sintered compact to final work-ing is well known in the art. It has, however, been considered impossible to produce with this process an article having as great a density as is obtained from molten metal because the sin-tered compact is porous and low in density.
The present inventors have undertaken extensive research and study with a view to obtaining a sintered compact that can be forged under pressure in order that a high density product might be obtained by first making a sintered compact having a shape ciose to that of the desired product and then subjecting such sintered compact to pressure forging. The present invention is the successful result of such efforts.
It has been ~ound that the addition of a compound of an alkali metal or alkaline earth metal to a metal powder suited for sintering prior to sintering has resulted in unexpected advantages, particularly if the sintered proauct is subsequently rolled or forged.
The chemical action of a compound of an alkali or alkaline earth metal (hereinaft-er representatively referred to as alkali m~tal) used in the metal powder is not yet definitely known, but B` ~ ~:
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it is considered that the following actions take place. Prior to or during compaction,the compound containing the alkali metal is decomposed by heating into a uniform solid solution in the form of the alkali metal alone or in the ~orm of an oxide on the sur-faces of the metal powder particles to be sintered. In this case, when such solid solution is cooled, a part thereof is again sep-arated out in the form of the alkali metal, and it is considered that such separated alkali metal and the solid solution layer serve in combination to expedite sliding of the metal powder par-ticles relative to each other when pressure is applied duringcompacting, so that a dense green compact may be obtained.
It is considered that the alkali metal separated on the metal powder particle surfaces is in the form of a solid solution at the bonded parts or necks of the metal particles and this pro-motes growth of the necks at a lower temperature to allow easy sintering. It is also considered that the crystal grain boundary of this solid solution layer portion slips easily under forging pressure, making it possible to practice rolling and forging.
It is believed that any metal which forms to some extent -a solid solution with an alkali or alkaline earth metal can be employed to produce the sintered compact. However, better results are obtained when a heavy metal is used, particularly one which is hard to sinter, such as, for example, brass with a high zinc content. A metal such as Si, Al, Sn or Mn, may be added to the brass, usually for the purpose of improving the properties of the product.
Any type of metal powder that has been used heretofore for sintering can be used. Slnce green compacting and sintering can be easily accomplished for the above reasons, it is possible, 3Q to use a metal powder having a particle size in excess of 50 mesh.
.
~O~S~32 The shape of usable powder particles also spans a wide range.
Therefore, in the case of brass, cutting scraps or swarfs obtained from conventional castings can be used as originally produced or after slightly crushing them.
As to the alkali metal compounds to be added to the metal powder, it is preferred to use the type of alkali metal compound which thermally decomposes to leave an alkali metal. For example, carbonates such as lithium carbonate, potassium carbonate or sod-ium carbonate are most practical and economical because they are inexpesnive, but it is also possible to use other organic salts sUch as oxalates or acetates, or inorganic salts such as halides or silicofluorides as shown in Table 1 below.
Any amount of alkali metal compound may be added but pre-ferably there is just enough for the alkali metal to cover very thinly the surface of the metal powder particles for sintering ~ -at heat-treatment. However if too much alkali metal compound is used, in cases such as brass,some alkali may remain after being sintered. Depending on the metal powder being sintered the pre-sence of an alkali metal powder after sintering may cause subse-quent metal corrosion. Consequently in the case of brass the ` amount of additional alkali metal compound is preferable less than 0.1% to a metal powder. In the case of other metals, an amount of alkali metal compound can be added up to 1.0%. In this connection, the pH of the sintered compact when sintered by add-.
ing a brass to barium carbonate, is pH 7 whan the~amount of addi-tional barium carbonate is 0.01 to 0.1% and is pH 10 when it is 0.3~
The amount of alkali metal compound used will depend to ' some extent on the particle size of the metal powder.
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Table 1 - Kinds Or alka~ll metal compounds usable and ef f ects thereof _ . . ~ . .
Compound~ ~dded Kind oY me~al powder used . . ~
. . . _ . . . . . .
Klnd oi' Repr~ent- Cu-Zn Cu-N1-Zn Fe-N1 8 alts at lve : :
compound~
. __ .. _ . . . __ .
Carbonate K2 CO O O O
Ll 2 C~3 3 (~) (~) O
BaC0 3 O O (~) Ox al at e 8 K2 C20 4 O O O . -LI2C204 (~ (~) C) ' - ' BaC24 O O (~) CaC20 4 O O O
A~e t at e 3 CH3 COONa O ~O O
CH 3COOK O O O : .
CH 3COOLl (~) (~) O
( CH3CO2 ) 2Ba O O (~) ( CH 3C02 ) 2 Ca (~) O O
. . . _ .. _ Chloride8 KCl2 O O O
BaC12 O O ' (~) Fluoride8 . . _ 8 o BaF2 (~) (~) Si ll cio- . . . ~
'luoride~ Na2~;iF6 - CaSîF6 ~ (~) C~
. 9a~:1 F~ O O O
_ . . ~ . . - . -Iodlde~ NI O O (~) . CaI 2 - ~---. ~ . - . . `:: "'"~' " ' ,, : ' .:
-.
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~C~55'~32 (Note) Mark ~ indicates excellent sinterability and forgeability, and mark O indicates good sinterability and forgeability.
The alkali metal compound may be added during sintering, but in most cases, it is added during the annealing treatment which is used to improve the compactibility of the metal powder.
The annealing temperature and time may be suitably selected in dependence on the type of alkali metal compound used. The alkali metal compound may be introduced in the form of a powder or may be introduced after dissolving it in a suitable solvent, the lat-ter being volatilized after mixing. It is sufficient to add thealkali metal compound in such an amount that it will cover the surfaces of the metal powder particles. This amount varies ac-cording to the type and particle size of metal used, but in the case of brass, about 0.1~ (by weight) of alkali metal compound is preferably used. In the following discussion, all of the numeri-cal values shown are based on the use of brass (40~Zn-60%Cu).
The metal powder which has been heated and annealed to-gether with thq alkali metal compound as described above is treat-ed with a lubricant according to a known method and then subjected to pressure molding at ambient or elevated temperature in a mold of a predetermined configuration. The green compact so formed may be of a complicated configuration, which is characteristic of -powder metallurgy, but it is preferred to select the shape by taking into account the plastic limit of the sintered compact, if it is next subjected to a forging process. It is also desirable to provide a well-calculated blank configuration to eliminate the extra work such as burring required in the conventional techniques.
The green should pxeferably be molded to a density of more than -about 6.5 g/cm3 The molded green compact i9 then heated and sintered in ;~
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a reducing or neutral gaseous atmosphere conventionally used ~or sintering, sueh as, for example, an atmosphere of decomposed am-monia gas, nitro~en gàs or endothermic gas at a temperature of around 750 to 850 C to obtain a sintered compact of a desired shape. It is desirable to carry out the above-said sintering in such a way that the resulting sintered compact will have a speci- ~ -fic gravity greater than 7.5 g/cm3 to make it possible to employ a subsequent forging step. For this purpose, the sintering tem-perature and time are suitably adjusted according to the density of the green compact.
The sintered compact is then subjected to a forging or rolling step. Forging or rolling of the sintered compact may be conducted immediàtely after completion of sintering, while main-taining the sintering temperature, or after cooling and storing for a certain period of time. Such forging or rolling is usually carried out by heating the compact to abo~t 650 to 750C, but in some cases, this step may be accomplished by warm or cold working.
For forging sintered blanks, a method is known in which the sintered blanks are squeezed into the forging dies from the outer wall. There is also known a method in which the sintered blanks are expanded outwardly from the inside. Sintered blanks produced as described above may be used in both the above methods, and also the pressure used for forging may be more than 20% lower ~-than that requirecl for forging of the material obtained by the conventional melting method. In the case of certain configurations, the heating temperature of the slntered compact may be lowered or the forging work may even be carried out at the ambient tempera-- ture.
A noticeable difference ~rom the conventional forging techniques is that the sintered compact introduced into the forg- ~ ~
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, -9- .. :
~IDSS~732 ing mold may contain a few bubbles and hence, in some cases, de-aeration is required during the forging step. Such deaeration may be accomplished in several ways, such as adjusting the speed of the forging pressure, applying a coating of graphite powder or the like as a deaerating agent to the sintered compact, or reduc-ing pressure in the mold simultaneously with an increase in the externally applied pressure. Any of these methods can be used as appropriate.
It has been found possible to make a sintered compact by using a powder metallurgy process having a shape close to that of the desired product and use the compact as blanks for rolling and forging. Therefore, no burrs are produced during forging and the res7~1ting compact is in the shape of the desired completed product. It is possible to obtain products which can be easily rolled and forged and which have higher physical strength than con-ventional articles by addition of an alkali metal compound, It will be seen from the foregoing discussion that the process is particularly useful as a method of making a rollable and forgeable sintered compact by adding a compound of an alkali or alkaiine earth metal. The process has also been found useful in depressing the vaporization or sublimation of metal during sintering. -Zinc is a metal which undergoes the most vigorous vapori-zation or sublimation during slntering, so that in the following discussion of the sublimation-depressing effect of the present in-vention reference is made to an example which uses a sintering i powder of zinc-containing brass.
The sintering of brass involves many technical problems, most of which are ascribed to the high vapor pressure and the vig-orous sublimation of zinc. When sintering is carried out in the liquid-phase of two components supplied as a mixed powder of aop-~ ' , ' ' ' ' .
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per and zinc, by using the basic techniques of powder metallurgy, the resultant sintered body is poor in compactness, and much eva-poration loss of zinc takes place during the heating-up, so that it is hardly possible to obtain a high-density sintered compact.
Furthermore, such a mixed powder undergoes extensive thermal ex-pansion in the course of the heating-up.
For these reasons, alloy powders have ~een developed and used for the sintering of brass, but since a heating treatment is indispensable for the manufacture of such alloy powders, it is im-possible to obtain brass powder with a high zinc content. Usually,a neutral or weak reducing gas is used for sintering, but as it is impossible to prevent an evaporation loss of the zinc compon-ent, the surface of the sinterad compact i5 roughened by the de-zincing phenomenom. Two methods are known for preventing such surface roughening: a method in which sintering is carried out in ~:
an atmosphere under a pressure higher than the vapor pressure of zinc, and a method in which sintering is carried out in a saturat-ed vapor of zinc. The former method, however, is inefficient, be-cause it cannot be carried out in a continuous heating furnace and :
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must be carried out on a batch basis, while the latter method is uneconomical because the furnace body may be damaged by the zinc vapor. These factors have been an obstacle to the utilization of techniques of powder metallurgy in the sintering of brass type ~ :~
materials.
It has been found that the addition of alkali metal com-pounds provides a sintering method in which the evaporatlon loss of zinc is minimiz~ed and also no specific atmosphere is required.
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It also provides novel powder metallurgical techniques for the utilization of brass alloys (40%Zn-60%Cu) which have high mechani-- 30 cal strength and corrosion resistance, and the production of brass - ~ ' ,.
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alloy powders used for the sintering of such alloys.
A sintering brass powder containing more than 35% zinc/
cannot be obtained by the conventional spraying method or pulveri-zing method in which copper and zinc powders are mixed and sinter ed, because such methods include a sintering or melting step in which an excessive loss of zinc is caused by the sublimation of zinc. Such methods are therefore uneconomical and incapable of producing brass of the desired composition. Therefoxe, a me~hod is employed in which brass containing a predetermined amount of zinc is cast and the casting is then cut and mechanically pulveri-zed. For disintegration, the brass mass is first granulated to -form brass particles of about 12 mesh in size and then these brass particles are further pulverized mechanically. Brass under-goes a change of hardness due to work-hardening in the first stage of pulverization and loses its malleability, so that it becomes easy to pulverize. Any known type of grinding machine -such as a ball mill, rod mill, speed hammer mill, or atomizer can -`~
be used, and desired fines of les`s than 100 meshes can be obtained either by a dry process or by a wet process.
Since this pulverization step involves no heating, there is no evaporation loss of zinc and hence the powder is disinte- -grated without changing the original composition of the powder~
The obtained fines require heating to eliminate work strain as such work strain produced by work-hardening during pulverization will affect the compactness of the sintered compact. An alkali metal compound is added to the ~ines ~ which are then heated at a temperature higher than that `at which the added alkali metal com-pound is dissolved. The heating eliminates work s~rain, and the resulting brass powder is also subjected to an alkali~metal treat- -ment to produce the desired brass powder having a high zinc content.
;5732 In the case of ~rass (30%Zn or 20~iZn) which has been com-monly used for sintering, disintegration can be accomplished either by a spraying step or by a sintering-pulverizing step, and if the powder is subjected to an alkali metal compound treatment before compacting and sintering, it can be sintered with little evaporative loss of ~inc.
The brass mass used for obtaining the powder may be form-ed by melting and casting the mixture of materials blended at a predetermined ratio for each sintering process, but it is also possible to use commercially available brass rods.
The alkali metal compounds used should be ones which are decomposed and vaporized upon being heated and which, when so vaporized, produce inactive gases whlch do not corrode brass, such as SO2 and NO2.
Although the action of the alkali metal compound is not known in detail, it is considered that a small amount of alkali ~
metal is diffused and deposited on the surface of the brass pow- ~ -der by heating and, at the sintering temperature,~such alkali ~ ~~
metal prevents the oxidation of the powder owing to its reducing property and forms an axeotropic mixture with ~inc to prevent evaporation loss of zinc at the sintering temperature, thereby expediting sintering.
The heating treatment is preferably effected by heating the mixturè at a temperature higher than that at which the alkali m tal compound is decomposed, until the decomposition gas ceases to be emitted, but it is also possible to carry out this heating treatment at the annealing temperature so as to concurrently~an--neal the metal. Usually, such treatment is carried~out at a tem-o peraturè of about 550 to 650 C.
As the alkali metal compound treatment is carried out at :
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550 to 560C, the green compact of the brass powder undergoes no expansion with the change of state o~ zinc that takes place as it is heated up to 400 to 500 C, so that the bonds (necks) produced during compacting are stable and in a form permitting the easy progress of sintering. Also, since this powder has good flow and compression rates as well as excellent release characteristics when a lubricant is added, it can be easily compacted by an auto-matic compacting machine of the type generally used in powder metallurgy.
Thus, the products obtained by using the above method are significantly low in manufacturing cost as compared with conven- ~.
tional products, and they also have excellent ~ualities and pro-perties as disclosed by consideration in the following test examples.
Sintered compacts formed by the above described method and those made by a conventional method were prepared, using var~ . .
- .
ious kinds o~ metal powders, and the densities of the respective .
green compacts, sintered compacts and sintered compacts after ap-plication of pressure were measured.
Each of the green compacts was formed by charging lOgr of powder into a die having lOmm (diameter) under a pressure of 5 x 103 kg/cm . The resulting green compacts wera heated in a nitrogen stream at a temperature suited to the respective metals :
therein for 30 minutes to obtain sintered compacts, and then each of these sintered compacts was charged into a die of the same diameter and subjected to a pressure of 7 x 10 kg/cm2 at room tem-. , .
perature. Thereafter, the density of the resulting products was ~ -measured. The results are shown in~Table 2~ Each~numerical 30 figure in the table shows the mean value obtained from measuring ..
' , : -14--~.3 - . . . .. .~ - ... .. . ........ , : , . . . . .
l~SS732 lO pieces of the material being tested.
As is apparent from the results in Table 2, the effect of the addition of an alkali metal is conspicuous when using an alloy consisting of two or more kinds of metals.
In Table 2, the case of a brass containing 40% Zn is des-cribed as a representative example. Sintered compacts of brass powder which are practically used in conventional methods, are sintered compacts containing 30% Zn at the most. When such sinter-ed compacts contain more than 30% Zn, the sublimation of Zn at 10 sintering is too great and a sintered alloy for practical use can -not be obtained or sintering can not be carried out. It will be seen that significant benefits accrue by the use of alkali metal compounds particularly when a brass containing more than 30% Zn is used.
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-~ ~ ~ ~ -Note: Mark (*l indicate that no repressing was made because the sintered compact was of too low ::~
strength.
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Sintered compacts made according to the method described above and those a¢cording to a conventional method were prepared using various types of metal powders, and these sintered compacts were subjected to hot forging at temperatures and under pressures suited to the respective types of metals to obtain disc-shaped forgings having an outer diameter o:E 45 mm and a thickness of 10 mm.
The variation in density and tensilestrength of these forgings were measured, and the results are shown in Table 3.
Each numerical figure in the table indicates the mean value ob-tained from 10 tested specimens.
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A dash~ (-) shows that forging could not be made.
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- ~ - 18-1~i5732 EXA~IPLE 1 .
Cutting scrap~s of free cutting hrass (JIS-H-3422) were degreased, magnetically screened to remove iron impurities, and then pulverized and passed through a 50-mesh sieve. 0.1~ of anhydrous potasslum carbonate was added to the resulting powder and then annealed in a nitrogen stream at 550 to 660C to pro-duce a powder having the properties shown in Table.
~ .... . - - - ._ - v, .
Item Propertiea .. ... _ .. ~ .
Chemlcal Cu 58%, Pb 1.5%, Fe 0~3 composition Sn 0.2~, Zn remalnder _ . . .. ~ ~. .. .
Partlcle slze dl~trl~utlon 50 - 100 mesh 4Q~
100 - 150 mesh 20~
150 - 2~0 me~h 10%
200 - 250 mesh 10%
Creater than 25Q mesh 20~
. . . _ . ._ ~ . ._ . Apparent den-slty (bulk ~pecl~lc 3.6 ~cm3 gravlty) ,,_ _ .: ;
Fluldlty .,:
0.2~ of zinc stea~ate was then added to the above-said ~ -powder, which was~then subjected to a lubricant treatment in a mixing machine and shaped by a~compacting machine to obtain a green compact`l' having a density of 7.5 g/cm and having ~a configuration as shown in Figure 1.
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Then -this green compact was sintered in a decomposed-ammonia gaseous atmosphere (764 mmHg, flowing at the rate of
This method, however, has the problem that the sintered compact obtained by sintering a green powder compact is porous.
Also, in the case of a metal having high vapor pressure, such as zinc, the component elements tend to volatilize under the sinter-ing heat, so that it is sometimes impossible to obtain a sinter-ed blank of a desired composition. There are also materials that cannot be sintered by using this method. Thus, there has been a certain limitation as to the scope of products obtainable -20 and the scope of use of these products. Such deficiencies have ~-been particularly noticeable in the case of the sintering of high brass.
Therefore, the method generally employed for obtaining high-dPnsity metal-made machine parts is one of cutting solid materials or casting molten materials to the approximata size -of the object product and then machining them into the desired shape. With this conventional method, as adapted for instance to the forming of pressure-proof brass pipe parts as commonly used in industry, first the brass cutting scraps and molten mat-:,, erial are fed into a melting furnace, followed by the addition -1- ~ ~
~C~5573Z
thereto of zinc, lead and electrolytic copper to prepare a mol-ten bath of the desired brass composition for forging. This molten bath is then shaped into an ingot, the latter being then rolled into an elongated brass bar of a desired size, and this bar is cut into a desired size to form billets. Then the cut billets are heated to around 700 C, subjected to hot forgin~ in a mold of a predetermined configuration and further passed through the steps of trimming, surface cleaning and machining to - produce a desired pressure-proof pipe part.
In this conventional method, since the shapes of the billets which can be forged are limited, many sections are le~t that require machining after forging, resulting in increased working time and loss of material. The cutting scraps ~rom the machining are later reduced in the melting furnace. When high brass is being used, it is necessary to replenish the zinc com-p~nent of the brass as zinc tends to evaporate during the process.
; This increases the cost of the heat source and consequently the manufacturing cost of the finished article. In many of the cur-rently used methods, the loss in weight of the mat~rial su~fered .:
during the machinin~ of the forged blanks exceeds 50% in the aase ; of pipe parts, as such parts are mostly hollow in shape.
In order to overcome these~disadvantages, some forging machines have been developed which are specifically designed for the forging of hollow parts, but such machines have complicated -die mechanisms, and are also expensive. Consequently, they have not yet found general accepta~nce. -According to the present invention there is provided a~
mlxture for use in producing a;sintered compact comprising at least one metal in-powder form the particles comprlsed in the i~ 30 powder having a coatin~ containlng a metal selected from the .
~ -2- ~ ~
10557;~Z
group consisting of alkali metals and alkaline earth metals.
According to~a further aspect of the present invention a sintered compact includ~ng at least one metal selected from the yroup consisting of alkali metals and alkaline earth metals.
According to a further aspect of the present invention there is provided a method of producing a sintered product com-prising the steps of adding to a metal powder a compound contain-ing a metal selected from the group consisting of alkali metals and alkaline earth metals, heating the powder and said compound to a temperature higher than the decomposition temperature of the compound, and compacting and sintering the powder and com- ' pound to produce a sintered compact.
An embodiment of the invention will now be described with reference to the accompanying drawings, in which:- ;
Figure 1 is a perspective view showing the shapes of the respective green compacts used for making a valve casing;
Figure 2 is an exploded perspective view showing the re-spective parts of a completed ball valve; ~
Figure 3 is a diagram showing the relation between the ~:
density of a green compact and the compacting pressure exerted on the sintering powder;
Figure 4 is a diagram showing the change in diameter after sintering;
Figure 5 is a diagram showing the loss in the quantity of zinc due to sintering;
Figure 6 is a diagram showing the mechanical properties of the sintered body; and Figure 7 is a diagram showing the relationship between the density ana porosity of the sintered body.
Tn these drawings, reference numeral 1 indicates a valve , "` ~! `
~ i l~S573Z
casing, and 1' the green compact used to make the valve casing,2 indicates a~ end cap and ~' the gxeen compact for making the end cap, while 3 lndicates a ball and 3' the green compact for making the ball.
H.R.B. shows a Rockwell hardness measured by a B
scale.
The process described herein may be used to produce roll-ing and forging blanks by way of a powder metallurgy process.
The concept of producing a machine part by first forming a sintered compact having a shape close to that of the desired product and then subjecting said sintered compact to final work-ing is well known in the art. It has, however, been considered impossible to produce with this process an article having as great a density as is obtained from molten metal because the sin-tered compact is porous and low in density.
The present inventors have undertaken extensive research and study with a view to obtaining a sintered compact that can be forged under pressure in order that a high density product might be obtained by first making a sintered compact having a shape ciose to that of the desired product and then subjecting such sintered compact to pressure forging. The present invention is the successful result of such efforts.
It has been ~ound that the addition of a compound of an alkali metal or alkaline earth metal to a metal powder suited for sintering prior to sintering has resulted in unexpected advantages, particularly if the sintered proauct is subsequently rolled or forged.
The chemical action of a compound of an alkali or alkaline earth metal (hereinaft-er representatively referred to as alkali m~tal) used in the metal powder is not yet definitely known, but B` ~ ~:
~5~3;~:
it is considered that the following actions take place. Prior to or during compaction,the compound containing the alkali metal is decomposed by heating into a uniform solid solution in the form of the alkali metal alone or in the ~orm of an oxide on the sur-faces of the metal powder particles to be sintered. In this case, when such solid solution is cooled, a part thereof is again sep-arated out in the form of the alkali metal, and it is considered that such separated alkali metal and the solid solution layer serve in combination to expedite sliding of the metal powder par-ticles relative to each other when pressure is applied duringcompacting, so that a dense green compact may be obtained.
It is considered that the alkali metal separated on the metal powder particle surfaces is in the form of a solid solution at the bonded parts or necks of the metal particles and this pro-motes growth of the necks at a lower temperature to allow easy sintering. It is also considered that the crystal grain boundary of this solid solution layer portion slips easily under forging pressure, making it possible to practice rolling and forging.
It is believed that any metal which forms to some extent -a solid solution with an alkali or alkaline earth metal can be employed to produce the sintered compact. However, better results are obtained when a heavy metal is used, particularly one which is hard to sinter, such as, for example, brass with a high zinc content. A metal such as Si, Al, Sn or Mn, may be added to the brass, usually for the purpose of improving the properties of the product.
Any type of metal powder that has been used heretofore for sintering can be used. Slnce green compacting and sintering can be easily accomplished for the above reasons, it is possible, 3Q to use a metal powder having a particle size in excess of 50 mesh.
.
~O~S~32 The shape of usable powder particles also spans a wide range.
Therefore, in the case of brass, cutting scraps or swarfs obtained from conventional castings can be used as originally produced or after slightly crushing them.
As to the alkali metal compounds to be added to the metal powder, it is preferred to use the type of alkali metal compound which thermally decomposes to leave an alkali metal. For example, carbonates such as lithium carbonate, potassium carbonate or sod-ium carbonate are most practical and economical because they are inexpesnive, but it is also possible to use other organic salts sUch as oxalates or acetates, or inorganic salts such as halides or silicofluorides as shown in Table 1 below.
Any amount of alkali metal compound may be added but pre-ferably there is just enough for the alkali metal to cover very thinly the surface of the metal powder particles for sintering ~ -at heat-treatment. However if too much alkali metal compound is used, in cases such as brass,some alkali may remain after being sintered. Depending on the metal powder being sintered the pre-sence of an alkali metal powder after sintering may cause subse-quent metal corrosion. Consequently in the case of brass the ` amount of additional alkali metal compound is preferable less than 0.1% to a metal powder. In the case of other metals, an amount of alkali metal compound can be added up to 1.0%. In this connection, the pH of the sintered compact when sintered by add-.
ing a brass to barium carbonate, is pH 7 whan the~amount of addi-tional barium carbonate is 0.01 to 0.1% and is pH 10 when it is 0.3~
The amount of alkali metal compound used will depend to ' some extent on the particle size of the metal powder.
.
~,,, , :
.
l~S573Z
Table 1 - Kinds Or alka~ll metal compounds usable and ef f ects thereof _ . . ~ . .
Compound~ ~dded Kind oY me~al powder used . . ~
. . . _ . . . . . .
Klnd oi' Repr~ent- Cu-Zn Cu-N1-Zn Fe-N1 8 alts at lve : :
compound~
. __ .. _ . . . __ .
Carbonate K2 CO O O O
Ll 2 C~3 3 (~) (~) O
BaC0 3 O O (~) Ox al at e 8 K2 C20 4 O O O . -LI2C204 (~ (~) C) ' - ' BaC24 O O (~) CaC20 4 O O O
A~e t at e 3 CH3 COONa O ~O O
CH 3COOK O O O : .
CH 3COOLl (~) (~) O
( CH3CO2 ) 2Ba O O (~) ( CH 3C02 ) 2 Ca (~) O O
. . . _ .. _ Chloride8 KCl2 O O O
BaC12 O O ' (~) Fluoride8 . . _ 8 o BaF2 (~) (~) Si ll cio- . . . ~
'luoride~ Na2~;iF6 - CaSîF6 ~ (~) C~
. 9a~:1 F~ O O O
_ . . ~ . . - . -Iodlde~ NI O O (~) . CaI 2 - ~---. ~ . - . . `:: "'"~' " ' ,, : ' .:
-.
-7- ~-' ";;
~C~55'~32 (Note) Mark ~ indicates excellent sinterability and forgeability, and mark O indicates good sinterability and forgeability.
The alkali metal compound may be added during sintering, but in most cases, it is added during the annealing treatment which is used to improve the compactibility of the metal powder.
The annealing temperature and time may be suitably selected in dependence on the type of alkali metal compound used. The alkali metal compound may be introduced in the form of a powder or may be introduced after dissolving it in a suitable solvent, the lat-ter being volatilized after mixing. It is sufficient to add thealkali metal compound in such an amount that it will cover the surfaces of the metal powder particles. This amount varies ac-cording to the type and particle size of metal used, but in the case of brass, about 0.1~ (by weight) of alkali metal compound is preferably used. In the following discussion, all of the numeri-cal values shown are based on the use of brass (40~Zn-60%Cu).
The metal powder which has been heated and annealed to-gether with thq alkali metal compound as described above is treat-ed with a lubricant according to a known method and then subjected to pressure molding at ambient or elevated temperature in a mold of a predetermined configuration. The green compact so formed may be of a complicated configuration, which is characteristic of -powder metallurgy, but it is preferred to select the shape by taking into account the plastic limit of the sintered compact, if it is next subjected to a forging process. It is also desirable to provide a well-calculated blank configuration to eliminate the extra work such as burring required in the conventional techniques.
The green should pxeferably be molded to a density of more than -about 6.5 g/cm3 The molded green compact i9 then heated and sintered in ;~
,' ' ' ~5573Z
a reducing or neutral gaseous atmosphere conventionally used ~or sintering, sueh as, for example, an atmosphere of decomposed am-monia gas, nitro~en gàs or endothermic gas at a temperature of around 750 to 850 C to obtain a sintered compact of a desired shape. It is desirable to carry out the above-said sintering in such a way that the resulting sintered compact will have a speci- ~ -fic gravity greater than 7.5 g/cm3 to make it possible to employ a subsequent forging step. For this purpose, the sintering tem-perature and time are suitably adjusted according to the density of the green compact.
The sintered compact is then subjected to a forging or rolling step. Forging or rolling of the sintered compact may be conducted immediàtely after completion of sintering, while main-taining the sintering temperature, or after cooling and storing for a certain period of time. Such forging or rolling is usually carried out by heating the compact to abo~t 650 to 750C, but in some cases, this step may be accomplished by warm or cold working.
For forging sintered blanks, a method is known in which the sintered blanks are squeezed into the forging dies from the outer wall. There is also known a method in which the sintered blanks are expanded outwardly from the inside. Sintered blanks produced as described above may be used in both the above methods, and also the pressure used for forging may be more than 20% lower ~-than that requirecl for forging of the material obtained by the conventional melting method. In the case of certain configurations, the heating temperature of the slntered compact may be lowered or the forging work may even be carried out at the ambient tempera-- ture.
A noticeable difference ~rom the conventional forging techniques is that the sintered compact introduced into the forg- ~ ~
.' ~'' .
, -9- .. :
~IDSS~732 ing mold may contain a few bubbles and hence, in some cases, de-aeration is required during the forging step. Such deaeration may be accomplished in several ways, such as adjusting the speed of the forging pressure, applying a coating of graphite powder or the like as a deaerating agent to the sintered compact, or reduc-ing pressure in the mold simultaneously with an increase in the externally applied pressure. Any of these methods can be used as appropriate.
It has been found possible to make a sintered compact by using a powder metallurgy process having a shape close to that of the desired product and use the compact as blanks for rolling and forging. Therefore, no burrs are produced during forging and the res7~1ting compact is in the shape of the desired completed product. It is possible to obtain products which can be easily rolled and forged and which have higher physical strength than con-ventional articles by addition of an alkali metal compound, It will be seen from the foregoing discussion that the process is particularly useful as a method of making a rollable and forgeable sintered compact by adding a compound of an alkali or alkaiine earth metal. The process has also been found useful in depressing the vaporization or sublimation of metal during sintering. -Zinc is a metal which undergoes the most vigorous vapori-zation or sublimation during slntering, so that in the following discussion of the sublimation-depressing effect of the present in-vention reference is made to an example which uses a sintering i powder of zinc-containing brass.
The sintering of brass involves many technical problems, most of which are ascribed to the high vapor pressure and the vig-orous sublimation of zinc. When sintering is carried out in the liquid-phase of two components supplied as a mixed powder of aop-~ ' , ' ' ' ' .
. ~ , .
.
~;573Z :
per and zinc, by using the basic techniques of powder metallurgy, the resultant sintered body is poor in compactness, and much eva-poration loss of zinc takes place during the heating-up, so that it is hardly possible to obtain a high-density sintered compact.
Furthermore, such a mixed powder undergoes extensive thermal ex-pansion in the course of the heating-up.
For these reasons, alloy powders have ~een developed and used for the sintering of brass, but since a heating treatment is indispensable for the manufacture of such alloy powders, it is im-possible to obtain brass powder with a high zinc content. Usually,a neutral or weak reducing gas is used for sintering, but as it is impossible to prevent an evaporation loss of the zinc compon-ent, the surface of the sinterad compact i5 roughened by the de-zincing phenomenom. Two methods are known for preventing such surface roughening: a method in which sintering is carried out in ~:
an atmosphere under a pressure higher than the vapor pressure of zinc, and a method in which sintering is carried out in a saturat-ed vapor of zinc. The former method, however, is inefficient, be-cause it cannot be carried out in a continuous heating furnace and :
.
must be carried out on a batch basis, while the latter method is uneconomical because the furnace body may be damaged by the zinc vapor. These factors have been an obstacle to the utilization of techniques of powder metallurgy in the sintering of brass type ~ :~
materials.
It has been found that the addition of alkali metal com-pounds provides a sintering method in which the evaporatlon loss of zinc is minimiz~ed and also no specific atmosphere is required.
.
It also provides novel powder metallurgical techniques for the utilization of brass alloys (40%Zn-60%Cu) which have high mechani-- 30 cal strength and corrosion resistance, and the production of brass - ~ ' ,.
.`11~ -, ~' -1055'73Z
alloy powders used for the sintering of such alloys.
A sintering brass powder containing more than 35% zinc/
cannot be obtained by the conventional spraying method or pulveri-zing method in which copper and zinc powders are mixed and sinter ed, because such methods include a sintering or melting step in which an excessive loss of zinc is caused by the sublimation of zinc. Such methods are therefore uneconomical and incapable of producing brass of the desired composition. Therefoxe, a me~hod is employed in which brass containing a predetermined amount of zinc is cast and the casting is then cut and mechanically pulveri-zed. For disintegration, the brass mass is first granulated to -form brass particles of about 12 mesh in size and then these brass particles are further pulverized mechanically. Brass under-goes a change of hardness due to work-hardening in the first stage of pulverization and loses its malleability, so that it becomes easy to pulverize. Any known type of grinding machine -such as a ball mill, rod mill, speed hammer mill, or atomizer can -`~
be used, and desired fines of les`s than 100 meshes can be obtained either by a dry process or by a wet process.
Since this pulverization step involves no heating, there is no evaporation loss of zinc and hence the powder is disinte- -grated without changing the original composition of the powder~
The obtained fines require heating to eliminate work strain as such work strain produced by work-hardening during pulverization will affect the compactness of the sintered compact. An alkali metal compound is added to the ~ines ~ which are then heated at a temperature higher than that `at which the added alkali metal com-pound is dissolved. The heating eliminates work s~rain, and the resulting brass powder is also subjected to an alkali~metal treat- -ment to produce the desired brass powder having a high zinc content.
;5732 In the case of ~rass (30%Zn or 20~iZn) which has been com-monly used for sintering, disintegration can be accomplished either by a spraying step or by a sintering-pulverizing step, and if the powder is subjected to an alkali metal compound treatment before compacting and sintering, it can be sintered with little evaporative loss of ~inc.
The brass mass used for obtaining the powder may be form-ed by melting and casting the mixture of materials blended at a predetermined ratio for each sintering process, but it is also possible to use commercially available brass rods.
The alkali metal compounds used should be ones which are decomposed and vaporized upon being heated and which, when so vaporized, produce inactive gases whlch do not corrode brass, such as SO2 and NO2.
Although the action of the alkali metal compound is not known in detail, it is considered that a small amount of alkali ~
metal is diffused and deposited on the surface of the brass pow- ~ -der by heating and, at the sintering temperature,~such alkali ~ ~~
metal prevents the oxidation of the powder owing to its reducing property and forms an axeotropic mixture with ~inc to prevent evaporation loss of zinc at the sintering temperature, thereby expediting sintering.
The heating treatment is preferably effected by heating the mixturè at a temperature higher than that at which the alkali m tal compound is decomposed, until the decomposition gas ceases to be emitted, but it is also possible to carry out this heating treatment at the annealing temperature so as to concurrently~an--neal the metal. Usually, such treatment is carried~out at a tem-o peraturè of about 550 to 650 C.
As the alkali metal compound treatment is carried out at :
~, ' :~ .
~05573Z
550 to 560C, the green compact of the brass powder undergoes no expansion with the change of state o~ zinc that takes place as it is heated up to 400 to 500 C, so that the bonds (necks) produced during compacting are stable and in a form permitting the easy progress of sintering. Also, since this powder has good flow and compression rates as well as excellent release characteristics when a lubricant is added, it can be easily compacted by an auto-matic compacting machine of the type generally used in powder metallurgy.
Thus, the products obtained by using the above method are significantly low in manufacturing cost as compared with conven- ~.
tional products, and they also have excellent ~ualities and pro-perties as disclosed by consideration in the following test examples.
Sintered compacts formed by the above described method and those made by a conventional method were prepared, using var~ . .
- .
ious kinds o~ metal powders, and the densities of the respective .
green compacts, sintered compacts and sintered compacts after ap-plication of pressure were measured.
Each of the green compacts was formed by charging lOgr of powder into a die having lOmm (diameter) under a pressure of 5 x 103 kg/cm . The resulting green compacts wera heated in a nitrogen stream at a temperature suited to the respective metals :
therein for 30 minutes to obtain sintered compacts, and then each of these sintered compacts was charged into a die of the same diameter and subjected to a pressure of 7 x 10 kg/cm2 at room tem-. , .
perature. Thereafter, the density of the resulting products was ~ -measured. The results are shown in~Table 2~ Each~numerical 30 figure in the table shows the mean value obtained from measuring ..
' , : -14--~.3 - . . . .. .~ - ... .. . ........ , : , . . . . .
l~SS732 lO pieces of the material being tested.
As is apparent from the results in Table 2, the effect of the addition of an alkali metal is conspicuous when using an alloy consisting of two or more kinds of metals.
In Table 2, the case of a brass containing 40% Zn is des-cribed as a representative example. Sintered compacts of brass powder which are practically used in conventional methods, are sintered compacts containing 30% Zn at the most. When such sinter-ed compacts contain more than 30% Zn, the sublimation of Zn at 10 sintering is too great and a sintered alloy for practical use can -not be obtained or sintering can not be carried out. It will be seen that significant benefits accrue by the use of alkali metal compounds particularly when a brass containing more than 30% Zn is used.
; : .
:
'`' '', '' ' , , ` 30 ~ ~
`
' -" ' -` -15- ~ ~
i .. . ~ . ~, . . ~_ ~ . .
1 ~ -~ ~3 N
_ _ ~ ~ __ ~ ~ ~. ' __ ~ ~ p~ ~ O ~ O. ~y . , . -~ ~ ~ ~
~1 p~ tQ ~ ~ ~ a~ . 0 co . ~ a),; ` 0 0 ~; ~._. ,. . . ____ _ _ _ _~ . _ h t~
P. ~, ~ ~ ~ ~ u~ Ln o a c~ u~ c.
~; ~ ~ ~ ~ cr~ ~ ~ ~ ~ ~ tt~ ~
s~ u~ g t- r- t- t-- co t~ t-- r- . c- ~ l æ , _ __ ~ _ __ ~ ~ ~ ~, ~ O O O ~ U~ ~ . U~
O ~ ~ ~ ~ 1~ 11~ ~- o N o h O r- t~ ~ t - 1~ t-- ~ ~ t-- C~
- 6~,, .~ ~ - - l~ - - - - - - - -'3 o ~ ~ ' s~ a ~
h C~ ~ C~ C~ ~ . c~ El .,1 O : Q O ~O C:i O O O O
d El ~3 O ~ ~ ~ _ 8 ~ o ~ ~
~ ~ _ ~ _ .. .,~ _ ~ _ . ,.
a N ~Z ~N ~Z; ~3 o ~ . O d ;
- ., . .. , ........ ... _. _ ...... ~ - . _ , .
rl ~ O O - N 8 ~ ~ .. o o C~ ~ . ~
h ~ 0 ~1 ~t IS~
Pl ~ E~ j , ~ I ~ , ~, ~ _ _ __ , . . ._ ~ :~ I--$~,_ . 1_~ I _ ~ h 5:~ ~:: ~1 1:~
. . ~ . ~ ~ S~ O O . ~ O
h ~ ~ ~0 E3 0 O ~ o~ q ~ ~ ~ S~ æ
C~D~ a~ ~ o ~ 0 ~ .
3 ,q ~ ~ m a~ . ~ 0 h Cl rl p4 N V . ~ ~
0 0 tll E~ C!9 p-- N 5Z; ~_ ~ p~ _ ---- i-~ -- ~ --- --C~ - , ~ ' h C . ~ . ~ ~ . ~ o ~ ~;
a) o ~ o ~ O ~
. ~ ~ ~ ~ ~a ~ ,~ .
o o ~l ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ,a . ~ C~ IQ ~ ~ ~ ~ C~ P~ Z~ C~ ~3 æ ~4 ~, -: ,`~-'. r1 ~ ~ -, ' ~n c~ ~ - ~ ~ `
-~ ~ ~ ~ -Note: Mark (*l indicate that no repressing was made because the sintered compact was of too low ::~
strength.
~' 55~3Z
Sintered compacts made according to the method described above and those a¢cording to a conventional method were prepared using various types of metal powders, and these sintered compacts were subjected to hot forging at temperatures and under pressures suited to the respective types of metals to obtain disc-shaped forgings having an outer diameter o:E 45 mm and a thickness of 10 mm.
The variation in density and tensilestrength of these forgings were measured, and the results are shown in Table 3.
Each numerical figure in the table indicates the mean value ob-tained from 10 tested specimens.
: .
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:
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:1~5573Z
~r _ _ ... _ .... .., _ - ~- ~ _..... . __ , _ . _ ~ .
~ h ~ N N Q~ l et l 1~ ~0 O ~1 01 . .
. ~ _ __ _ . . _ 0, ~ o l 0 l ~ 0~ a:~ o r~l~ . . .. _.. _ ___ .---- .
uon~u~ IS~ ~ o ~ c~ I ~ 1.~ -o~ o ..
_ ,. . . . ,, . . ~. .- , __ ._ . -- ._--~D~3 Oo oO Oo .. Oo l Oo 0 :0; 0 ,~ . _ _ _ _ . ` _ ~, . . I
~ 3 h c~ O N O N O 0 O o Ir~ Ir~
~o$ ~d r~ ~ ~ t- ao ~D t- 1- r- r-. . . .. . _ . __ ,,, ___ _ _ :
X 0 O ~ O O _~ O O O O ~ : :
_.___ _ . _ . . . . .~ __ . '~:.
S-l--' . C~ ~1 . ~ . ~_1 N
~O ~ N ~ h ~ - ~: .
O ., _ ~1_ O O O ' ~ ..
3 ~i ~ ~ ~ u~ C ;: 0 8 d ,1 ~ : ~ o o o :-~
O ~ 13 ~ j _ Z :~ _ p.j N O
~ ... ~__ . .. _ . ` 'o~ ............ ~--~ '' ~ ' ;~ ' S: . ~ Lr~
O O O ~ L~ 11~ ~--1 E3 C~ .~ 0~i . . ~D'I
O O ~ ~ ~ P~ .~ ~;
F~ t.) 0 e~ ' ~. I t~ t ..
., 1 7 0 __ . ~. . ,.... ..... _._ ~ ' 0 ~i r~ N r~ ~t : ~ :.
.~ ~ . :~V__ ~ .~ ~.
A dash~ (-) shows that forging could not be made.
'~"
;::
- ~ - 18-1~i5732 EXA~IPLE 1 .
Cutting scrap~s of free cutting hrass (JIS-H-3422) were degreased, magnetically screened to remove iron impurities, and then pulverized and passed through a 50-mesh sieve. 0.1~ of anhydrous potasslum carbonate was added to the resulting powder and then annealed in a nitrogen stream at 550 to 660C to pro-duce a powder having the properties shown in Table.
~ .... . - - - ._ - v, .
Item Propertiea .. ... _ .. ~ .
Chemlcal Cu 58%, Pb 1.5%, Fe 0~3 composition Sn 0.2~, Zn remalnder _ . . .. ~ ~. .. .
Partlcle slze dl~trl~utlon 50 - 100 mesh 4Q~
100 - 150 mesh 20~
150 - 2~0 me~h 10%
200 - 250 mesh 10%
Creater than 25Q mesh 20~
. . . _ . ._ ~ . ._ . Apparent den-slty (bulk ~pecl~lc 3.6 ~cm3 gravlty) ,,_ _ .: ;
Fluldlty .,:
0.2~ of zinc stea~ate was then added to the above-said ~ -powder, which was~then subjected to a lubricant treatment in a mixing machine and shaped by a~compacting machine to obtain a green compact`l' having a density of 7.5 g/cm and having ~a configuration as shown in Figure 1.
~ :
.
3 ~573Z
Then -this green compact was sintered in a decomposed-ammonia gaseous atmosphere (764 mmHg, flowing at the rate of
2~ /min) at 800C for 30 minutes to obtain a sintered compact.
The resulting sintered compact, maintained at 650 C, was charged into a forging mold and forged under a pressure of 4xlO3kg/cm to produce a casing base material for a ball valve.
Thereafter, the surface of the forging was cleaned by shot blasting or pickling and then subjected to machining, such as thread cutting, to obtain a ball valve casing 1 of the shape shown in Figure 2. Practical tests were conducted on this ball valve casing, and yielded the results shown in Table 5. Each numerical figure in the table represents the mean value obtain~
ed from five specimens tested.
;, .
.
: "
.. -, .
-20- ~. .
:, 1~5732 Test Item Te~tlng condltions ¦ R~sults ~ . __ ~ ......................... I .. -, .
Leaka~e te~t 1) Air .
pressure 2 ke/cm2 No leak Alr ~
pres~urc -?0 kgJcm2 NO leak ~lr pressure 50 kg/cm~ No leak _ ~ _ _ _ . r , ~ _ _ . __ Pressure te~t Water pressure 100 kg/cm2 No la~k Water- :
. preasure 200 kg/c~2 No leak . ~ . . . . ~ `,-::
M~rcury te~t JIS-H-3422 No crack . -:
was ob- -: .
~er~red : ~
(~or 15 :
minutes) . . ._ Anunonla test Under pre~sure of 20 kgJcm2 for 90 No hours crack ::-. ~ found _ . . . :
Endurance te~t Le~t under pres~ure No ab-. o~ 100 kg/cm2 ~or normal- .- -. , 60 days . lty : "~.',,'-Note 1) Compressed air of specified pressures was ~ed ~.
into the specimen valve and the valve was left in the state for one minute, and then the sur- -face was examined for alr leakage from the specimens.
" ' , ':
~ ~
: -, :
:: :
, ., ~ -21-~ ~ ~ o 1~5573Z
Note 2) Water pressures (100 kg/cm and 200 kg/cm ) were applied to a flat and regular hexagonal cap nut (measuring 32 mm on a side, and having a 3/4" in-ternal pipe thread with an end wall thickness of 2.60 mm) for one minute, and the end wall portion was examined for any breaks.
The results shown in Table 5 attest to the fact that the valve manufactured by the above described method can well stand practical use as a multi-purpose high pressure valve.
The manufacturing cost of the valve casing as compared with that required for manufacturing the same part according to conve~tional methods, can be reduced more than 30% by virtue of the increased utilization of the raw material. Great improve-ments are also made in machining and manufacturing efficiencies to allow a marked cost reduction.
A valve ball 3 as shown in Figure 2 was made by using the same powder as used in Example 1.
First, a thick cylindrical green compact 3' such 3S ~
20 shown in Figure 1 was formed after the manner of Example 1, and -this green compact was sintered and then forged to obtain a spherica~ body closely akin to the desired ball. The forged , spherical body was then abraded~to increase the surface finish of its spherical surface. Thereafter, a groove or recess for mounting the handle therein was formed by machining, thus obtain ing the desired ball 3. ~ ~
The resulting part was tested as in Example 1, and the test results showed that the product is quite serviceable a3 ~a general-purpose high pressure valve part. ~ ~ ~
Such a part has heretofore~been made by cutting and abrad-, ' ' ' ' ~05S73;~
ing round bar stock without performing any plastic work, so that many man-hours were r~quired, which caused an elevated cost. The manufacturing cost, however, can be markedly reduced by use of the blanks produced by sintering.
It is possible to make an end cap ~, such as shown in Figure 2, in exactly the same way. In this case, a cylindrical green compact 2' having a stepped outer peripheral sur~ace as shown in Figure 1 is sintered and the sintered comp~ct is forged into a shape similar to that of the end product, and then threads are cut by a tapping machine.
In this example an a~ticorrosive ball valve is made by utilizing multi-phase condition sintering of more than two diff~
erent types of metal, which is characteristic of powder metallurgy.
17~ of pure nickel powder and then 0.1% o~ lithium oxalate were added to the free cut brass powder, which was used as a sintering powder in Example 1 and the mixtura was annealed in a ~-nitrogen stream at 550 to 600C for about 30 minutes to obtain a powder having the properti~s shown in Table 6.
, TABLE 6 . . . __ - : :
Ite~ Properties . . . .: . ... .
Chemlcal Cu 4 R . ~, Nl 17 . 5%, composltion Pb 1.25%, (Sn + Fe) 0.0~, Zn remainder ~ .
Partl~le ~lze 50 - lOo mesh OS
dlstrlbution 100 - 150 me~h 17%
150 - 200 mesh 20 200 - 250 mesh 25 250 - me~h ~ 38%
._, ~ ~
Apparent density 3.2 g/cm3 (bulk ~pe~i~lc ~ ~ gravlty) -~ -r ,.-- ~
Fluidi~y 45 sec/50 Rr ~ .
~OSS732 This powder was further subjected to a lubricant treat-ment after the manner~of Example l and a ball valve (consisting of a casing, an end cap and a ball) was made in the same way as Example 1 except for the ~00 C and 30 minutes sintering condi-tions.
This valve was subjected to the same endurance test as Example 1 to obtain satisfactory results. It was also subjected to a 24 houranticorroslon test and salt spray test together with ~-nickel silver of JIS specification (JIS-H-3711) for comparison purposes, but no difference was observed.
Hard chrome plating (5~ thickness) was applied to the ball part of the ball valve obtained in Example 2, and this was put to an endurance test by subjecting it to salt spray and am-monia along with a similar chrome plated part manufactured by a -conventional method. The results showed no difference between - the product formed by sintering and the conventional produc~t.
- - Generally, most of the powder metallurgy products have pinholes piercing the surfaca, and such pinholes are not elimin~
ated perfectly even by coining or forging, so that, usually, sy-nthetic resin is inf~ltrated into the surface and then plating is applied thereover. The products formed by the above described method, owing to their excellent forgeability, are free of pin-holes.
Cu~ting scraps of free cutting brass (40~Zn - 60% Cu) hav- `
ing the composition shown in Table 7 were degreased and the pulverized in a ball mill.
~ ` ~':, ;~
:; : -, ' ~)5573Z
Elements Cu Pb Fe Sn Zn Composition -~ -- -~-- ¦
(%) 58.2 1.5 0.92 0.25 remainder , ~ l To this powder was added sufficient lithium carbonate powder to bring the lithium content of the powder to about 0.1~, and the powder was thoroughly mixed until homogeneous. Then the mixture was heated in a neutral atmosphere a~ a temperature of around 550 to 560C, whereupon the lithium carbonate was decomp-10 osed, releasing carbon dioxide gas, and a small amount of lithium ~ -was diffused, infiltrated and settled on the surfaces of the - -~
brass powder particles. This phenomenon is considered to occur -for the following reason. Although lithium carbonate is ther-mally decomposed at 550 C and divided into lithium oxide and carbon dioxide gas, it is considered that lithium oxide undergoes a certain chemical change in the presence of brass and is bonded -thereto in a stable state.
A sintering brass powder suitable for use in the above ; process-can be obtained in the above-described manner. If the lithium carbonate were added in the form of lithium oxide, the resulting powder would be highly hygroscopic and also exhibit strong alkalinity in the presence of-water, because lithium oxide - has such properties. On the contrary, the powder produced above showed no hygroscopic disposition even if left in the air for a ~ -long time. Also, even when the powder was thrown into water, the hydrogen ion concentration remained almost unchanged. Further, the work strain produced in the pulverizing step has been perfect-ly eliminated. -,~ We will now discuss the green compactability of this brass 30 powder and the properties of the sintered compact. -.
' ' :
~ 25-1~5573;~
The powder was screened into groups of respective par-ticle size ranges, and these were blended in the proportions shown in Table 8. A lubricant was added thereto and the powder mixed in a cone blender with a stirring speed of 20 r.p.m. at the rate of approximately 10 kg/hour to prepare a powder with fluidity of about 30 sec/50 gr, ancl this powder was then com-pacted in a predetermined mold to obtain a green compact.
TAB~E 8 l . _ , _ ~ - -I -Partlcl ~ize Percent by Welght .~ ~
100 - 1~0 20 150 -`200 20 2~0 - 32S 20 32~ - 20 -. _ .. __ .
Apparent d~nslty ml~ed powder 3.4 g/cm3 r _ ___ . . .__.
Figure 3 shows the relationship between the compacting pressure and density of the resulting green compact. The lubri-cant used in the compa~ting step is preferably metal salts of stearic acid, waxing powders or the like of a type generally used in powder metallurgy, Fe powder or Cu-Sn powder. The result-ing green compact has good edge stability and has almost no ten-dency to spring back after compacting.
Thlsgreen compact is heated and sintered in a stream of N2 gas (flowing at the rate o~ abouz 3Q/min3 at 800 C for 40 minutes to obtain a sintered compact. The lubricant separates 30 at a temperature of 400 to 500 C in the course of heating, and ~. . -, ~.
:'~ ' ' ' .
~05S732 thereafter almost no volatile material is produced and the par-ticle necks grow. Substantially the same phenomenon as observed in the ordinary solid-phase sintering mechanism ta]ces place until the temperature reaches the level of 500 to 700 C at which the intra-solid diffusion begins at the crystal grain boundaries, but as the temperature passes the level or vicinity of 700 C, the in-fluence of the added alkali metal becomes conspicuous. That is, growth of the necks advances more and more rapidly and the spaces between the particles shrink and gradually diminish to increase density. The solid-phase sintering is completed at around 800 C.
During this period, no change of composition takes place and also almost no evaporation loss of zinc is suffered. This is probably because the difference in osmotic pressure between the ions of the alkali metal added and the zinc in the brass composite causes an increase in the sublimation temperature of zinc to retard the dezincing which could otherwise be caused by evaporation loss.
Dimensional change tsPring back) after sintering is - -shown in Figure 4 by the relationship between the density and compression rate of the green compact. Figure 5 shows the rate -of loss in weight of zinc during sintering, and Figure 6 shows the physical strength of thie resulting sintered body. The rela-tionship between the density and porosity of the sintered com-pact is shown in Figure 7. As shown by Figures 4 to 7, a gold-colored sintered compact can be obtained which has high physical strength and dimensional accuracy and~which is beautifully lust-rous on its surface.
When a brass powder (40% Zn - 60~ Cu) which has not been -treated with alkali metal is compacted and sintered in the same way as above, thermal expansion takes place at around 550 C. Its rate is 2 to 4% in the diametral direction and 5 to 8% in total :~:
` ` t -27-lOS~732 length. Even if the temperature exceeds 700 C, no densification of the sintered compact takes place with growth of the necks and zinc is lost by evaporation. Also, no shrinkage of the sinter-ed compact is caused at 800 C. This sintered compact is weak in mechanical strength, its tensile strength being less than 10 kg/cm . The loss of zinc by evaporation exceeds 8~.
Although the present invention has been described with respect to a powder consisting of a copper-based alloy having a high zinc content (35 to 45~), it is of course possible to obtain the sintering powder directly from brass. Even when using con-ventional brass (20% Zn or 30% Zn), the loss of zinc by evapora-tion is only about ~ to 5%, and the density of the sintered com-pact is about 7.0 g/cm at its highest.
The properties of the brass sintered compacts manufactur-ed according to the above described process are as shown in Figures 3 to 7. It will thus be appreciated that the above process is an economical brass working method as compared with -the conventional forging-machining processes. The sintered compacts can be highly densified by warm forging to provide pressure-proof parts. Also, when an alkali metal is added to the base powder other metals such, for example, as Fe or Ni may also be added in a suitable amount to produce a friction material. `
Thus, the above process provides not only powders for obtaining the zinc-rich brass sintered parts but also inexpensive matrices for use in powder metallurgy.
i `
.
~' ' .
The resulting sintered compact, maintained at 650 C, was charged into a forging mold and forged under a pressure of 4xlO3kg/cm to produce a casing base material for a ball valve.
Thereafter, the surface of the forging was cleaned by shot blasting or pickling and then subjected to machining, such as thread cutting, to obtain a ball valve casing 1 of the shape shown in Figure 2. Practical tests were conducted on this ball valve casing, and yielded the results shown in Table 5. Each numerical figure in the table represents the mean value obtain~
ed from five specimens tested.
;, .
.
: "
.. -, .
-20- ~. .
:, 1~5732 Test Item Te~tlng condltions ¦ R~sults ~ . __ ~ ......................... I .. -, .
Leaka~e te~t 1) Air .
pressure 2 ke/cm2 No leak Alr ~
pres~urc -?0 kgJcm2 NO leak ~lr pressure 50 kg/cm~ No leak _ ~ _ _ _ . r , ~ _ _ . __ Pressure te~t Water pressure 100 kg/cm2 No la~k Water- :
. preasure 200 kg/c~2 No leak . ~ . . . . ~ `,-::
M~rcury te~t JIS-H-3422 No crack . -:
was ob- -: .
~er~red : ~
(~or 15 :
minutes) . . ._ Anunonla test Under pre~sure of 20 kgJcm2 for 90 No hours crack ::-. ~ found _ . . . :
Endurance te~t Le~t under pres~ure No ab-. o~ 100 kg/cm2 ~or normal- .- -. , 60 days . lty : "~.',,'-Note 1) Compressed air of specified pressures was ~ed ~.
into the specimen valve and the valve was left in the state for one minute, and then the sur- -face was examined for alr leakage from the specimens.
" ' , ':
~ ~
: -, :
:: :
, ., ~ -21-~ ~ ~ o 1~5573Z
Note 2) Water pressures (100 kg/cm and 200 kg/cm ) were applied to a flat and regular hexagonal cap nut (measuring 32 mm on a side, and having a 3/4" in-ternal pipe thread with an end wall thickness of 2.60 mm) for one minute, and the end wall portion was examined for any breaks.
The results shown in Table 5 attest to the fact that the valve manufactured by the above described method can well stand practical use as a multi-purpose high pressure valve.
The manufacturing cost of the valve casing as compared with that required for manufacturing the same part according to conve~tional methods, can be reduced more than 30% by virtue of the increased utilization of the raw material. Great improve-ments are also made in machining and manufacturing efficiencies to allow a marked cost reduction.
A valve ball 3 as shown in Figure 2 was made by using the same powder as used in Example 1.
First, a thick cylindrical green compact 3' such 3S ~
20 shown in Figure 1 was formed after the manner of Example 1, and -this green compact was sintered and then forged to obtain a spherica~ body closely akin to the desired ball. The forged , spherical body was then abraded~to increase the surface finish of its spherical surface. Thereafter, a groove or recess for mounting the handle therein was formed by machining, thus obtain ing the desired ball 3. ~ ~
The resulting part was tested as in Example 1, and the test results showed that the product is quite serviceable a3 ~a general-purpose high pressure valve part. ~ ~ ~
Such a part has heretofore~been made by cutting and abrad-, ' ' ' ' ~05S73;~
ing round bar stock without performing any plastic work, so that many man-hours were r~quired, which caused an elevated cost. The manufacturing cost, however, can be markedly reduced by use of the blanks produced by sintering.
It is possible to make an end cap ~, such as shown in Figure 2, in exactly the same way. In this case, a cylindrical green compact 2' having a stepped outer peripheral sur~ace as shown in Figure 1 is sintered and the sintered comp~ct is forged into a shape similar to that of the end product, and then threads are cut by a tapping machine.
In this example an a~ticorrosive ball valve is made by utilizing multi-phase condition sintering of more than two diff~
erent types of metal, which is characteristic of powder metallurgy.
17~ of pure nickel powder and then 0.1% o~ lithium oxalate were added to the free cut brass powder, which was used as a sintering powder in Example 1 and the mixtura was annealed in a ~-nitrogen stream at 550 to 600C for about 30 minutes to obtain a powder having the properti~s shown in Table 6.
, TABLE 6 . . . __ - : :
Ite~ Properties . . . .: . ... .
Chemlcal Cu 4 R . ~, Nl 17 . 5%, composltion Pb 1.25%, (Sn + Fe) 0.0~, Zn remainder ~ .
Partl~le ~lze 50 - lOo mesh OS
dlstrlbution 100 - 150 me~h 17%
150 - 200 mesh 20 200 - 250 mesh 25 250 - me~h ~ 38%
._, ~ ~
Apparent density 3.2 g/cm3 (bulk ~pe~i~lc ~ ~ gravlty) -~ -r ,.-- ~
Fluidi~y 45 sec/50 Rr ~ .
~OSS732 This powder was further subjected to a lubricant treat-ment after the manner~of Example l and a ball valve (consisting of a casing, an end cap and a ball) was made in the same way as Example 1 except for the ~00 C and 30 minutes sintering condi-tions.
This valve was subjected to the same endurance test as Example 1 to obtain satisfactory results. It was also subjected to a 24 houranticorroslon test and salt spray test together with ~-nickel silver of JIS specification (JIS-H-3711) for comparison purposes, but no difference was observed.
Hard chrome plating (5~ thickness) was applied to the ball part of the ball valve obtained in Example 2, and this was put to an endurance test by subjecting it to salt spray and am-monia along with a similar chrome plated part manufactured by a -conventional method. The results showed no difference between - the product formed by sintering and the conventional produc~t.
- - Generally, most of the powder metallurgy products have pinholes piercing the surfaca, and such pinholes are not elimin~
ated perfectly even by coining or forging, so that, usually, sy-nthetic resin is inf~ltrated into the surface and then plating is applied thereover. The products formed by the above described method, owing to their excellent forgeability, are free of pin-holes.
Cu~ting scraps of free cutting brass (40~Zn - 60% Cu) hav- `
ing the composition shown in Table 7 were degreased and the pulverized in a ball mill.
~ ` ~':, ;~
:; : -, ' ~)5573Z
Elements Cu Pb Fe Sn Zn Composition -~ -- -~-- ¦
(%) 58.2 1.5 0.92 0.25 remainder , ~ l To this powder was added sufficient lithium carbonate powder to bring the lithium content of the powder to about 0.1~, and the powder was thoroughly mixed until homogeneous. Then the mixture was heated in a neutral atmosphere a~ a temperature of around 550 to 560C, whereupon the lithium carbonate was decomp-10 osed, releasing carbon dioxide gas, and a small amount of lithium ~ -was diffused, infiltrated and settled on the surfaces of the - -~
brass powder particles. This phenomenon is considered to occur -for the following reason. Although lithium carbonate is ther-mally decomposed at 550 C and divided into lithium oxide and carbon dioxide gas, it is considered that lithium oxide undergoes a certain chemical change in the presence of brass and is bonded -thereto in a stable state.
A sintering brass powder suitable for use in the above ; process-can be obtained in the above-described manner. If the lithium carbonate were added in the form of lithium oxide, the resulting powder would be highly hygroscopic and also exhibit strong alkalinity in the presence of-water, because lithium oxide - has such properties. On the contrary, the powder produced above showed no hygroscopic disposition even if left in the air for a ~ -long time. Also, even when the powder was thrown into water, the hydrogen ion concentration remained almost unchanged. Further, the work strain produced in the pulverizing step has been perfect-ly eliminated. -,~ We will now discuss the green compactability of this brass 30 powder and the properties of the sintered compact. -.
' ' :
~ 25-1~5573;~
The powder was screened into groups of respective par-ticle size ranges, and these were blended in the proportions shown in Table 8. A lubricant was added thereto and the powder mixed in a cone blender with a stirring speed of 20 r.p.m. at the rate of approximately 10 kg/hour to prepare a powder with fluidity of about 30 sec/50 gr, ancl this powder was then com-pacted in a predetermined mold to obtain a green compact.
TAB~E 8 l . _ , _ ~ - -I -Partlcl ~ize Percent by Welght .~ ~
100 - 1~0 20 150 -`200 20 2~0 - 32S 20 32~ - 20 -. _ .. __ .
Apparent d~nslty ml~ed powder 3.4 g/cm3 r _ ___ . . .__.
Figure 3 shows the relationship between the compacting pressure and density of the resulting green compact. The lubri-cant used in the compa~ting step is preferably metal salts of stearic acid, waxing powders or the like of a type generally used in powder metallurgy, Fe powder or Cu-Sn powder. The result-ing green compact has good edge stability and has almost no ten-dency to spring back after compacting.
Thlsgreen compact is heated and sintered in a stream of N2 gas (flowing at the rate o~ abouz 3Q/min3 at 800 C for 40 minutes to obtain a sintered compact. The lubricant separates 30 at a temperature of 400 to 500 C in the course of heating, and ~. . -, ~.
:'~ ' ' ' .
~05S732 thereafter almost no volatile material is produced and the par-ticle necks grow. Substantially the same phenomenon as observed in the ordinary solid-phase sintering mechanism ta]ces place until the temperature reaches the level of 500 to 700 C at which the intra-solid diffusion begins at the crystal grain boundaries, but as the temperature passes the level or vicinity of 700 C, the in-fluence of the added alkali metal becomes conspicuous. That is, growth of the necks advances more and more rapidly and the spaces between the particles shrink and gradually diminish to increase density. The solid-phase sintering is completed at around 800 C.
During this period, no change of composition takes place and also almost no evaporation loss of zinc is suffered. This is probably because the difference in osmotic pressure between the ions of the alkali metal added and the zinc in the brass composite causes an increase in the sublimation temperature of zinc to retard the dezincing which could otherwise be caused by evaporation loss.
Dimensional change tsPring back) after sintering is - -shown in Figure 4 by the relationship between the density and compression rate of the green compact. Figure 5 shows the rate -of loss in weight of zinc during sintering, and Figure 6 shows the physical strength of thie resulting sintered body. The rela-tionship between the density and porosity of the sintered com-pact is shown in Figure 7. As shown by Figures 4 to 7, a gold-colored sintered compact can be obtained which has high physical strength and dimensional accuracy and~which is beautifully lust-rous on its surface.
When a brass powder (40% Zn - 60~ Cu) which has not been -treated with alkali metal is compacted and sintered in the same way as above, thermal expansion takes place at around 550 C. Its rate is 2 to 4% in the diametral direction and 5 to 8% in total :~:
` ` t -27-lOS~732 length. Even if the temperature exceeds 700 C, no densification of the sintered compact takes place with growth of the necks and zinc is lost by evaporation. Also, no shrinkage of the sinter-ed compact is caused at 800 C. This sintered compact is weak in mechanical strength, its tensile strength being less than 10 kg/cm . The loss of zinc by evaporation exceeds 8~.
Although the present invention has been described with respect to a powder consisting of a copper-based alloy having a high zinc content (35 to 45~), it is of course possible to obtain the sintering powder directly from brass. Even when using con-ventional brass (20% Zn or 30% Zn), the loss of zinc by evapora-tion is only about ~ to 5%, and the density of the sintered com-pact is about 7.0 g/cm at its highest.
The properties of the brass sintered compacts manufactur-ed according to the above described process are as shown in Figures 3 to 7. It will thus be appreciated that the above process is an economical brass working method as compared with -the conventional forging-machining processes. The sintered compacts can be highly densified by warm forging to provide pressure-proof parts. Also, when an alkali metal is added to the base powder other metals such, for example, as Fe or Ni may also be added in a suitable amount to produce a friction material. `
Thus, the above process provides not only powders for obtaining the zinc-rich brass sintered parts but also inexpensive matrices for use in powder metallurgy.
i `
.
~' ' .
Claims (19)
1. A mixture for use in producing a sintered compact comprising at least one metal in powder form, the particles com-prised in said powder having a coating containing a metal select-ed from the group consisting of alkali metals and alkaline earth metals.
2. A mixture according to claim 1 wherein said powdered metal has an atomic number not less than 26 nor greater than 30.
3. A mixture as claimed in claim 2 in which said metal having an atomic number not less than 26 nor greater than 30 is an alloy of copper and zinc.
4. A mixutre as claimed in claim 3 in which said zinc constitutes at least 35% of said alloy.
5. A mixture as claimed in claim 1 in which said powder has been annealed.
6. A mixture according to claim 1 wherein said coat-ing is a compound containing a metal selected from the group consisting of alkali and alkaline earth metals.
7. A mixture according to claim 6 wherein said compound is selected from the group consisting of carbonates, oxalates, acetates, halides and silicofluorides of said metals.
8. A mixture according to claim 2 wherein the sintering metal is selected from the group consisting of iron, iron alloys, copper, copper alloys, nickel and nickel alloys.
9. A mixture according to claim 1, 2 or 6 wherein the metal powder has a particle size of less than 50 mesh.
10. A mixture according to claim 6 in which said sin-tering metal consists essentially of copper and zinc and contains at least 35% zinc, and said compound is added in an amount such that the metal in said compound constitutes about 0.1% by weight of total metal.
11. A mixture according to claim 1 in which said at least one sintering metal includes a metal which normally sublimes at the sintering temperature used, and a sufficient quantity of an alkali metal or alkaline earth metal is added to inhibit such sublimation.
12. A sintered compact produced by sintering the mix-ture claimed in claim 1 said compact including at least one metal selected from the group consisting of alkali metals and alkaline earth metals.
13. A sintered compact according to claim 12 further including a metal having an atomic number not less than 26 nor greater than 30.
14. A sintered compact according to claim 12 or 13 wherein said metal selected from the group consisting of alkali metals and alkaline earth metals constitutes at most 1% by weight of said mixture.
15. A sintered compact according to claim 13 wherein said metal having an atomic number not less than 26 nor greater than 30 is an alloy of copper and zinc.
16. A method of producing a sintered product comprising the steps of adding to a metal powder a compound containing a metal selected from the group consisting of alkali metals and alkaline earth metals heating said powder and said compound to a temperature higher than the decomposition temperature of said compound, and compacting and sintering said powder and compound to produce a sintered compact.
17. A method according to claim 16 including the step of forging said sintered compact.
18. The method claimed in claim 16 which comprises the further step of compacting and rolling said sintered mixture.
19. The method of making the sintered compact as defined in claim 12 which comprises the steps of:
adding to the initial metal powder consisting princi-pally of copper and zinc at least one compound containing an additive metal selected from the group consisting of alkali metals and alkaline earth metals, and thereby producing a mixture consisting essentially of said at least one compound, copper and zinc, heating said mixture to a temperature higher than the decomposition temperature of said compound, and then compacting and sintering said mixture, said at least one compound being of a type which decom-poses into at least one gas which has no corrosive effect on said initial metal powder, together with at least one substance selec-ted from the group consisting of said additive metals and their oxides which substance forms a coating on said initial metal pow-der during said annealing step which inhibits subsequent volata-lization of said zinc during said sintering step.
adding to the initial metal powder consisting princi-pally of copper and zinc at least one compound containing an additive metal selected from the group consisting of alkali metals and alkaline earth metals, and thereby producing a mixture consisting essentially of said at least one compound, copper and zinc, heating said mixture to a temperature higher than the decomposition temperature of said compound, and then compacting and sintering said mixture, said at least one compound being of a type which decom-poses into at least one gas which has no corrosive effect on said initial metal powder, together with at least one substance selec-ted from the group consisting of said additive metals and their oxides which substance forms a coating on said initial metal pow-der during said annealing step which inhibits subsequent volata-lization of said zinc during said sintering step.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP82273A JPS522390B2 (en) | 1972-12-26 | 1972-12-26 | |
| JP6541074A JPS5524485B2 (en) | 1974-06-08 | 1974-06-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1055732A true CA1055732A (en) | 1979-06-05 |
Family
ID=26333912
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA216,397A Expired CA1055732A (en) | 1972-12-26 | 1974-12-18 | Sintered blanks for rolling and forging and method of producing same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1055732A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115044793A (en) * | 2022-06-16 | 2022-09-13 | 江苏精研科技股份有限公司 | Manufacturing method for preparing two-phase high-entropy alloy by adopting powder injection molding |
-
1974
- 1974-12-18 CA CA216,397A patent/CA1055732A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115044793A (en) * | 2022-06-16 | 2022-09-13 | 江苏精研科技股份有限公司 | Manufacturing method for preparing two-phase high-entropy alloy by adopting powder injection molding |
| CN115044793B (en) * | 2022-06-16 | 2023-09-08 | 江苏精研科技股份有限公司 | Manufacturing method for preparing two-phase high-entropy alloy by powder injection molding |
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