CA1200655A - Method of stabilizing silicate bonded sands - Google Patents
Method of stabilizing silicate bonded sandsInfo
- Publication number
- CA1200655A CA1200655A CA000433361A CA433361A CA1200655A CA 1200655 A CA1200655 A CA 1200655A CA 000433361 A CA000433361 A CA 000433361A CA 433361 A CA433361 A CA 433361A CA 1200655 A CA1200655 A CA 1200655A
- Authority
- CA
- Canada
- Prior art keywords
- silicate
- sand
- aqueous solution
- sodium silicate
- lithium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Mold Materials And Core Materials (AREA)
Abstract
ABSTRACT
A method is disclosed for stabilizing silicate bonded sand particles against humidity degradation. The method comprises mixing sand particles with an aqueous solution containing a lithium modified sodium silicate of the formula XSiO2.M2O (where X is a number between 2.5 and 3.4 and where M is Na/Li in a ratio of 5:1 to 20:1), and precipitating silica glass from the mixture to form a rigidized body of sand particles bonded by the glass, preferably by use of thermal energy or microwave energy dehydration. The solution may have a solid content of 33-44% by weight of the solution.
A method is disclosed for stabilizing silicate bonded sand particles against humidity degradation. The method comprises mixing sand particles with an aqueous solution containing a lithium modified sodium silicate of the formula XSiO2.M2O (where X is a number between 2.5 and 3.4 and where M is Na/Li in a ratio of 5:1 to 20:1), and precipitating silica glass from the mixture to form a rigidized body of sand particles bonded by the glass, preferably by use of thermal energy or microwave energy dehydration. The solution may have a solid content of 33-44% by weight of the solution.
Description
;5~i ~ 1 --METHOD OF ST~ILIZING SILICATE BONDED SANDS
BACRGRO~ND OF THE INVENTION
Silcate bonded foundry sands are ~idely known.
They have been used extensively in making molds and cores for the casting of steel~ iron, aluminum, and brass. S~ch ~oundry sand mixtures comprise a major proportion of suit-able ~efractory sand, an alkali metal silicate binder and ~omet.imes a small amount of other materials such as clay and finely divided coal or other organic matter to improve certain properties of the foundry sand. The silicate bond i~ obtained by precipitating a silica gel from the alkali ~etal silicate by either (1) the addition o an organic ester or an acid producing gas, such as carbon dioxidei -to chemically activate the formation of the gel, or (2) 15 by dehydrating the alkali metal silicate, to form a glass, ~uch as by evaporation~ pulling a vacuum, or a heating reaction brought about by use o microwave energy or conductive heat, such as from a hot-box or core drying oven.
~20 Sllicate is usually added in the form of a solu-tion to enable the binder material to regularly and uniformly coa-t the grains of sand, forming a network o~
i~terengaged silicate films. When the gel is precipitated by dehydration, water is removed from the silicate solution reverting the binder to a water soluble glass which is . rigid. The new form or shap~ of the glass, whieh it has assumed as a result of coating the sand grains, envelopes ~he sand grains and acts as a bridge tying the sand particles together mechanically.
The efect is similar, but not as strong, when chemicals are used to activate the formation of the gel, ~uch as by use of A C2 gas, the gas being used to cure the sllicate solution which coats the sand grains. The 2 ~hemically reacts with water to change the acid content of the solution resulting in the precipitation of silica gel :~'~3~}~
or a silicate with much lower sodium content and a sodium carbonate. Againt droplets of gel ~or sili~ate and car-bonate~ remain as intecconnections or films on the sand grains which, when stiffened by sufficient time, promote an enveloping network that binds the sand grains of the mixture.
Whether the sand mass is prepared by either the chemical activation method or the dehydration method, upon exposure to a humid environment, the tensile strength will ~rop to 10 psi or lower and the mass of sand particles will completely disintegrate. The hygroscopic nature of water glass is substantial. The ability to pick up moisture during storage must be reduced or eliminated if silicate mvlding processes are to become viable commercial methods.
The invention is a method of stabilizing silicate bonded sand particles against humidity degradation. Large ~cale production foundries must store prepared molds or cores for ready use, which storage may be for several days.
High humidity conditions in such foundries can cause the bond strength of such sand masses to deteriorate signifi-cantly during such storage. To obtain a stabilized high bond strength for short or long term storage, the present i~vention has discovered that the problem can be obviated by (a) mixing the sand particles with an aqueous solution containing a lithium modified sodium silicate of the formula XSiO2.M20 (where X is a number between 2.5 and 3.4 and where M is Na/Li in a ratio 5:1 to 20:1); and (b) precipitating silica glass from said mixture to form a 3~ rigidized body of sand particles bonded by said glass.
PreEerably, the aqueous solution of step ~a) is prepared by dissolving LiOH.E~20 in a commercial aqueous solution of sodium silicate. The resulting solution should preerably have a solid content constituting 33-44% by _ 3 _ welght of the solu~ion. The term "solid content" is de~
fined as the material that will not vaporize when heated above 105C at one atmosphere pressure. Preferably, the lithlum should be used in an amount providing a Na/Li ratio of 8.5:1 to 15:1, and advantageously the lithium ~hould be present in an amount of 2 grams per kilogram (g/kg) of aqueous solution.
It is advantageous if the alkaline metal silicate solution uses sodium silicate wi th the mole rcttio of silica to soda being in the range of 2.5-3.8:1, and optimally about 2.6-3.3:1.
It is preferable if the sand employed has an aYerage particle size of 30-90 AFS, said particle standard being defined in 1'he Foundry Sand Handbook, published by The American Foundryman's Society, 7th Edition (1963).
Although not requisite for the stahilization processl the sand may contain acid demanding components up to an acid demand value ~ADV) of 40 and up to 1% AFS clay as defined by The American Foundryman's Society. Thus the sand for 20 this process need not be purified~ The mixture may also include small amounts (5~ oe less by weight~ of other materials such as organic resins or cereals introduced for shakeout and other physical properties.
In carrying out step ~b), it is preferable iE
precipitation is carried out by use of heat to dehydra~e the mixture. The mixture and the aqueous alkaline metal silicate solution is heated to a temperature in excess of 100C, advantageously 105~115C. Higher temperatures may be used but no particulae benefit is obtained and energy costs are increased. Dehydration modes may include use of conductive heat ~y use of a core box, microwave energy, convective oven, or a vacuum.
DETAILED DESCRIPTION
A preferred mode for ca~cying out the inventive method is as follows: (a) sand particles are mixed with an aqueous solution containing a lithium modiied sodium silicate, and (b) precipitating silica glass ~rom the mixture to form a rigidized body of sand particles bonded by the glass.
Mixing Sand partioles are mixed with an aqueous solution of lithium modified sodium silicate~ The sand may be mixed with water prior to the aqueous solution of lithium modi-fied sodium silicate. The quantity of such water addition is dete~mined by the specific sand and silicate formulation used as well as the final strength required. The sodium silicate to be modified is employed substantially in a pure form and is commercially available as a colloidal suspen-sion. It is normally prepared by heating SiO2 in ~he presence of sodium oxide, Na2O~ or other equivalent salt to produce a glass. The glass is then dissolved in water to provide the colloidal suspension. These commercial aqueous sodium silicates are colloidal suspensions and are marketed based on the solid content of the specific suspension and on the weight ratio of silica, SiO2, and soda, Na2O, used in their formulation.
The sodium silicate is modifie~ by mixing l.iOH.H2O
into the sodium silicate colloidal suspension. Within a period of 3-12 hours the colloid will absorb the LiOH.~20 and shift the silicate ratio downward, forming a silicate of the formula XSiO2.M20 (where X is a number be~ween 2.5 and 3.4 and M is Na/Li in a ratio controlled to be in the range of 5-20:1. Such controlled ratio is achieved by knowing the ratio, solid content, and amount of sodium silicate to start with and adding known quantities of lithium hydroxide followed by mixing to dissolution. When the sodium/lithium ratio is allowed to decrease below 4:1, the resulting silicate will precipitate resulting in a i5 gummy mass that cannot be mixed efficiently with sand. If the sodium/lithium ratio is allowed ~o exceed ~0:1, hu~id-ity sensitivity will return to the sand mass equivalent to the unmodified silicate usage. The most preferred range or the sodium/lithium ratio is 8.5:1 to 15:1, because in this range the following properties will be optimally ~ncreased: tensile st~ength, humidi~y resistance, and ease of s~akeout.
It is desirable i the alkaline metal silicate employed has a mole ratio of silica/soda in the range of
BACRGRO~ND OF THE INVENTION
Silcate bonded foundry sands are ~idely known.
They have been used extensively in making molds and cores for the casting of steel~ iron, aluminum, and brass. S~ch ~oundry sand mixtures comprise a major proportion of suit-able ~efractory sand, an alkali metal silicate binder and ~omet.imes a small amount of other materials such as clay and finely divided coal or other organic matter to improve certain properties of the foundry sand. The silicate bond i~ obtained by precipitating a silica gel from the alkali ~etal silicate by either (1) the addition o an organic ester or an acid producing gas, such as carbon dioxidei -to chemically activate the formation of the gel, or (2) 15 by dehydrating the alkali metal silicate, to form a glass, ~uch as by evaporation~ pulling a vacuum, or a heating reaction brought about by use o microwave energy or conductive heat, such as from a hot-box or core drying oven.
~20 Sllicate is usually added in the form of a solu-tion to enable the binder material to regularly and uniformly coa-t the grains of sand, forming a network o~
i~terengaged silicate films. When the gel is precipitated by dehydration, water is removed from the silicate solution reverting the binder to a water soluble glass which is . rigid. The new form or shap~ of the glass, whieh it has assumed as a result of coating the sand grains, envelopes ~he sand grains and acts as a bridge tying the sand particles together mechanically.
The efect is similar, but not as strong, when chemicals are used to activate the formation of the gel, ~uch as by use of A C2 gas, the gas being used to cure the sllicate solution which coats the sand grains. The 2 ~hemically reacts with water to change the acid content of the solution resulting in the precipitation of silica gel :~'~3~}~
or a silicate with much lower sodium content and a sodium carbonate. Againt droplets of gel ~or sili~ate and car-bonate~ remain as intecconnections or films on the sand grains which, when stiffened by sufficient time, promote an enveloping network that binds the sand grains of the mixture.
Whether the sand mass is prepared by either the chemical activation method or the dehydration method, upon exposure to a humid environment, the tensile strength will ~rop to 10 psi or lower and the mass of sand particles will completely disintegrate. The hygroscopic nature of water glass is substantial. The ability to pick up moisture during storage must be reduced or eliminated if silicate mvlding processes are to become viable commercial methods.
The invention is a method of stabilizing silicate bonded sand particles against humidity degradation. Large ~cale production foundries must store prepared molds or cores for ready use, which storage may be for several days.
High humidity conditions in such foundries can cause the bond strength of such sand masses to deteriorate signifi-cantly during such storage. To obtain a stabilized high bond strength for short or long term storage, the present i~vention has discovered that the problem can be obviated by (a) mixing the sand particles with an aqueous solution containing a lithium modified sodium silicate of the formula XSiO2.M20 (where X is a number between 2.5 and 3.4 and where M is Na/Li in a ratio 5:1 to 20:1); and (b) precipitating silica glass from said mixture to form a 3~ rigidized body of sand particles bonded by said glass.
PreEerably, the aqueous solution of step ~a) is prepared by dissolving LiOH.E~20 in a commercial aqueous solution of sodium silicate. The resulting solution should preerably have a solid content constituting 33-44% by _ 3 _ welght of the solu~ion. The term "solid content" is de~
fined as the material that will not vaporize when heated above 105C at one atmosphere pressure. Preferably, the lithlum should be used in an amount providing a Na/Li ratio of 8.5:1 to 15:1, and advantageously the lithium ~hould be present in an amount of 2 grams per kilogram (g/kg) of aqueous solution.
It is advantageous if the alkaline metal silicate solution uses sodium silicate wi th the mole rcttio of silica to soda being in the range of 2.5-3.8:1, and optimally about 2.6-3.3:1.
It is preferable if the sand employed has an aYerage particle size of 30-90 AFS, said particle standard being defined in 1'he Foundry Sand Handbook, published by The American Foundryman's Society, 7th Edition (1963).
Although not requisite for the stahilization processl the sand may contain acid demanding components up to an acid demand value ~ADV) of 40 and up to 1% AFS clay as defined by The American Foundryman's Society. Thus the sand for 20 this process need not be purified~ The mixture may also include small amounts (5~ oe less by weight~ of other materials such as organic resins or cereals introduced for shakeout and other physical properties.
In carrying out step ~b), it is preferable iE
precipitation is carried out by use of heat to dehydra~e the mixture. The mixture and the aqueous alkaline metal silicate solution is heated to a temperature in excess of 100C, advantageously 105~115C. Higher temperatures may be used but no particulae benefit is obtained and energy costs are increased. Dehydration modes may include use of conductive heat ~y use of a core box, microwave energy, convective oven, or a vacuum.
DETAILED DESCRIPTION
A preferred mode for ca~cying out the inventive method is as follows: (a) sand particles are mixed with an aqueous solution containing a lithium modiied sodium silicate, and (b) precipitating silica glass ~rom the mixture to form a rigidized body of sand particles bonded by the glass.
Mixing Sand partioles are mixed with an aqueous solution of lithium modified sodium silicate~ The sand may be mixed with water prior to the aqueous solution of lithium modi-fied sodium silicate. The quantity of such water addition is dete~mined by the specific sand and silicate formulation used as well as the final strength required. The sodium silicate to be modified is employed substantially in a pure form and is commercially available as a colloidal suspen-sion. It is normally prepared by heating SiO2 in ~he presence of sodium oxide, Na2O~ or other equivalent salt to produce a glass. The glass is then dissolved in water to provide the colloidal suspension. These commercial aqueous sodium silicates are colloidal suspensions and are marketed based on the solid content of the specific suspension and on the weight ratio of silica, SiO2, and soda, Na2O, used in their formulation.
The sodium silicate is modifie~ by mixing l.iOH.H2O
into the sodium silicate colloidal suspension. Within a period of 3-12 hours the colloid will absorb the LiOH.~20 and shift the silicate ratio downward, forming a silicate of the formula XSiO2.M20 (where X is a number be~ween 2.5 and 3.4 and M is Na/Li in a ratio controlled to be in the range of 5-20:1. Such controlled ratio is achieved by knowing the ratio, solid content, and amount of sodium silicate to start with and adding known quantities of lithium hydroxide followed by mixing to dissolution. When the sodium/lithium ratio is allowed to decrease below 4:1, the resulting silicate will precipitate resulting in a i5 gummy mass that cannot be mixed efficiently with sand. If the sodium/lithium ratio is allowed ~o exceed ~0:1, hu~id-ity sensitivity will return to the sand mass equivalent to the unmodified silicate usage. The most preferred range or the sodium/lithium ratio is 8.5:1 to 15:1, because in this range the following properties will be optimally ~ncreased: tensile st~ength, humidi~y resistance, and ease of s~akeout.
It is desirable i the alkaline metal silicate employed has a mole ratio of silica/soda in the range of
2.S-3~8:1, and optimally about 2.6-3.3:1. The sand should have an average particle size of 30-90 AFSq The sand formulation may include small amounts (5% or less by weight) of other materials, such as coal, organic resins or cereals, introducéd for shakeout and other physical pro-perties. The aqueous solution should be added to the sand in a preferable amount of .75-5.0% by weight of the sand.
Lower mole ratio of silicate solutions, lower than 2. 5 SiO2.M20, tend to increase the alkali metal, which ~o promotes water pickup in the final bonded sand mass and contributes excessive amounts of alkali residue that must be removed before the sand can be reusedO Although a higher mole ratio alkali metal to silicate solution may be employed, being in- excess of 4.0, it is disadvantageous because such silicates form discontinuous Eilms on sand and thin-necked junctions when the glass is precipitatedO
The wleight percent of the sillcate solution employed is defined as including the weight of the soda and silica in the formulation as well as the weight of the bound water. The bound water, after dehydration, will be present as h~droxyl ions and protons. It is possible within the operable limits of this method to use weight percent alkaline metal silicate solutions above 4%, but such amounts add considerably to the C06t of the method without a proportionate justi~ication for it in terms of increased usefulness of the product~ The stcength of the :lZ(.~
~and mass accordingly increases wlth increasing amounts of silicate. However, the shakeout characteristic of the sand mass is significantly ceduced. There is a production of rock particles within the sand as a result of the m~tal heating which prohibits the sand from being easily removed if the weight percent of the silicate is excessive. The optimum weight percent of silicate has be~n found to be in the range of 1-1.5~ of the weight of the sand mass.
The particular sand employed for the method need not be of any special kind. However, the average particle size should preferably in a range of 30-90 ~FS. The method and silicate ~aterials we describe are tolerant of impuri-tie~ in the sand such as clay, acid demanding minerals, and moisture conten~.
Mixing can be appropriately carried out in a mulling device or other equivalent mixer for a period of time until the liquid solution substantially uniformly coats each of the sand grains. Some mulling devices subject the sand/silicate mixture to turbulen~ conditions which create air drafts that dry the mixture prematurely.
Should this be the case, water can be added to the sand system to insure more efficient mixing~ The mold mixture is then preferably and carefully tucked into a molding device for either ~orming a casting mold or a core, which body is then treated in the remainder of the process.
Precipitation The silica glass is then precipitated from the mixture to form a rigidized body of sand particles bonded by the glass. It is desirable to employ dehydration for the precipitation of the silicate glass. Such dehydra-tion might employ microwave energy, thermal energy in a hot core box or core oven, or the dehydration might be accom-plished by application of a vacuum to the sand mass.
The microwave heating or curing works when an electromagnetic wave of microwave dimension is pcopagated in a heating dielectric material, its energy being con-verted to heat. Water is the major dielect~ic material in this method that is heated by microwave energy; the dielectric is more accurately a modified sodium silicate/
water solution. The water molecules consist of hydrogen and oxygen atoms arranged so that each molecule is elec-trically neutral. Because of this arrangement, the elec-trical charges within the molecule have a dipole moment and are said to be polar. Different molecules have different degrees of polarity. A microwave field exerts a twisting force on the polar molecule that attempts to align the molecule within the field. When the direction of the field is reversed, the molecule attempts to reverse its orienta-tion. However, in doing so, frictional forces created by the molecules r~bbing toge~her have to be overcome. Energy is thereby dissipated as heat. ~riction generates heat and the dielectric becomes hot. Electrical energy ~hat should be stored in the dielectric material is in part lost as heat, often called dielectric lossiness The modified sodium silicate/water solution is particularly dielectrically active or 105sy in this regard and heats up quickly when exposed to a microwave fieldO
The frequency of this microwave radiation is typically about 2450 megahertz. However, the level of energy employed should be that which is necessary to raise the temperature of the sand body to at least 100C, preferably above 105-115~C. The amount of microwave energy employed may be regulated in a ratio of about .71 kilowatt for each 100 grams of sand mixture.
Hot-box core curing is the most common method of foundry sand core production in the casting industry. The hot-box process works by conduction of heat energy ~hrough the sand body from the outside surfaces of the hot metal pattern. The amount of energy necessary to dehydeate a silicate bonded sand body depends on the configuration of the sand body. It is desirable to employ metal core boxes s~
heated to the range of 150-300C and optimally about 200-~30C for this dehydration process. The sand body should remain in the hot~box for a time sufficient to dehydrate the outer 1/4 inch; that time depends on the configuration of the core and the moisture content of the silicate. It is preferable to blow heated air through the sand body to ~peed the dehydration process. The temperature of such heated air is preferably 105-200C and optimally 110-175C.
The watee glass (the silicate formed as a result of the dehydration) is not sticky or adhesive. It carries out a bonding function by forming a film about each of the sand grains, incorporating the surface of ~he sand grains, and which ilms are interconnected at necked portions to adjacent films. The glass, which is rigid, forms an inter-connected structure enveloping the sand grains, such net-work forms a very strong intersupporting mechanismO It is typical to obtain strength levels of at least 450 psi (3.1 MPa) when employing alkali me~al silicate in amoun~s of at least 2~ by weight of the sand mixture. Typically, dehy-drated sand/silicate strengths can range from 100-600 psi.
The use of the above described method is particu-larly advantageous because it is much more economical than any other method of curing silicate bonded sands; it i5 odorless, and it provides exceptionally fine stablized sand mixtures a~ainst humidity degradation. The convenience by which this method can be used in a factory environment is exceptional.
Examples 1. A stock solution of lithium hydroxide modified sodium silicate was prepared by mixing 4.13 grams of LiOH.H2O with 317 grams of commercial sodium silicate~ the latter having a 3.22:1 ratio of sodium silicate and a 43.5 ~olids content. The lithium hydroxide dissolved readily with stirringO A sand mixture was prepared by mixing 1200 grams of sand with 6~93 grams of water and then adding 34.72 grams of the silicate stock solution to the damp )(}~s~
~and. Test samples were prepared and dehydrated using a Redford Hot-~ox Core alower. The tensile strength of the samples with modified sodium ~ilicate was measured to be 212 psi. Other test samples were prepared uslng ~he same sand formulation but uslny a microwave cure; such samples had equivalent or comparable strength.
Other test samples were prepared using the same silicate solid content and by ~he same procedure bwt without lithium in their formulation; such samples had 290 psi tensile strength, or 140% o the li~hium containing samples. Each of the dehydrated or cured samples was subjected to a humidity test which involved placing the samples in a humid environment for an extended period of time and then measuring humidity resistance in terms of the tensile strength of the specimens. The te-t chamber con-tained 97% relative humidity, and the samples were exposed and subsequently tested for periods of 12 hours, 24 hours, 48 hours, up to five days, respectivelyO After 12 hours of humidity treatment, the lithium modified samples exhibited
Lower mole ratio of silicate solutions, lower than 2. 5 SiO2.M20, tend to increase the alkali metal, which ~o promotes water pickup in the final bonded sand mass and contributes excessive amounts of alkali residue that must be removed before the sand can be reusedO Although a higher mole ratio alkali metal to silicate solution may be employed, being in- excess of 4.0, it is disadvantageous because such silicates form discontinuous Eilms on sand and thin-necked junctions when the glass is precipitatedO
The wleight percent of the sillcate solution employed is defined as including the weight of the soda and silica in the formulation as well as the weight of the bound water. The bound water, after dehydration, will be present as h~droxyl ions and protons. It is possible within the operable limits of this method to use weight percent alkaline metal silicate solutions above 4%, but such amounts add considerably to the C06t of the method without a proportionate justi~ication for it in terms of increased usefulness of the product~ The stcength of the :lZ(.~
~and mass accordingly increases wlth increasing amounts of silicate. However, the shakeout characteristic of the sand mass is significantly ceduced. There is a production of rock particles within the sand as a result of the m~tal heating which prohibits the sand from being easily removed if the weight percent of the silicate is excessive. The optimum weight percent of silicate has be~n found to be in the range of 1-1.5~ of the weight of the sand mass.
The particular sand employed for the method need not be of any special kind. However, the average particle size should preferably in a range of 30-90 ~FS. The method and silicate ~aterials we describe are tolerant of impuri-tie~ in the sand such as clay, acid demanding minerals, and moisture conten~.
Mixing can be appropriately carried out in a mulling device or other equivalent mixer for a period of time until the liquid solution substantially uniformly coats each of the sand grains. Some mulling devices subject the sand/silicate mixture to turbulen~ conditions which create air drafts that dry the mixture prematurely.
Should this be the case, water can be added to the sand system to insure more efficient mixing~ The mold mixture is then preferably and carefully tucked into a molding device for either ~orming a casting mold or a core, which body is then treated in the remainder of the process.
Precipitation The silica glass is then precipitated from the mixture to form a rigidized body of sand particles bonded by the glass. It is desirable to employ dehydration for the precipitation of the silicate glass. Such dehydra-tion might employ microwave energy, thermal energy in a hot core box or core oven, or the dehydration might be accom-plished by application of a vacuum to the sand mass.
The microwave heating or curing works when an electromagnetic wave of microwave dimension is pcopagated in a heating dielectric material, its energy being con-verted to heat. Water is the major dielect~ic material in this method that is heated by microwave energy; the dielectric is more accurately a modified sodium silicate/
water solution. The water molecules consist of hydrogen and oxygen atoms arranged so that each molecule is elec-trically neutral. Because of this arrangement, the elec-trical charges within the molecule have a dipole moment and are said to be polar. Different molecules have different degrees of polarity. A microwave field exerts a twisting force on the polar molecule that attempts to align the molecule within the field. When the direction of the field is reversed, the molecule attempts to reverse its orienta-tion. However, in doing so, frictional forces created by the molecules r~bbing toge~her have to be overcome. Energy is thereby dissipated as heat. ~riction generates heat and the dielectric becomes hot. Electrical energy ~hat should be stored in the dielectric material is in part lost as heat, often called dielectric lossiness The modified sodium silicate/water solution is particularly dielectrically active or 105sy in this regard and heats up quickly when exposed to a microwave fieldO
The frequency of this microwave radiation is typically about 2450 megahertz. However, the level of energy employed should be that which is necessary to raise the temperature of the sand body to at least 100C, preferably above 105-115~C. The amount of microwave energy employed may be regulated in a ratio of about .71 kilowatt for each 100 grams of sand mixture.
Hot-box core curing is the most common method of foundry sand core production in the casting industry. The hot-box process works by conduction of heat energy ~hrough the sand body from the outside surfaces of the hot metal pattern. The amount of energy necessary to dehydeate a silicate bonded sand body depends on the configuration of the sand body. It is desirable to employ metal core boxes s~
heated to the range of 150-300C and optimally about 200-~30C for this dehydration process. The sand body should remain in the hot~box for a time sufficient to dehydrate the outer 1/4 inch; that time depends on the configuration of the core and the moisture content of the silicate. It is preferable to blow heated air through the sand body to ~peed the dehydration process. The temperature of such heated air is preferably 105-200C and optimally 110-175C.
The watee glass (the silicate formed as a result of the dehydration) is not sticky or adhesive. It carries out a bonding function by forming a film about each of the sand grains, incorporating the surface of ~he sand grains, and which ilms are interconnected at necked portions to adjacent films. The glass, which is rigid, forms an inter-connected structure enveloping the sand grains, such net-work forms a very strong intersupporting mechanismO It is typical to obtain strength levels of at least 450 psi (3.1 MPa) when employing alkali me~al silicate in amoun~s of at least 2~ by weight of the sand mixture. Typically, dehy-drated sand/silicate strengths can range from 100-600 psi.
The use of the above described method is particu-larly advantageous because it is much more economical than any other method of curing silicate bonded sands; it i5 odorless, and it provides exceptionally fine stablized sand mixtures a~ainst humidity degradation. The convenience by which this method can be used in a factory environment is exceptional.
Examples 1. A stock solution of lithium hydroxide modified sodium silicate was prepared by mixing 4.13 grams of LiOH.H2O with 317 grams of commercial sodium silicate~ the latter having a 3.22:1 ratio of sodium silicate and a 43.5 ~olids content. The lithium hydroxide dissolved readily with stirringO A sand mixture was prepared by mixing 1200 grams of sand with 6~93 grams of water and then adding 34.72 grams of the silicate stock solution to the damp )(}~s~
~and. Test samples were prepared and dehydrated using a Redford Hot-~ox Core alower. The tensile strength of the samples with modified sodium ~ilicate was measured to be 212 psi. Other test samples were prepared uslng ~he same sand formulation but uslny a microwave cure; such samples had equivalent or comparable strength.
Other test samples were prepared using the same silicate solid content and by ~he same procedure bwt without lithium in their formulation; such samples had 290 psi tensile strength, or 140% o the li~hium containing samples. Each of the dehydrated or cured samples was subjected to a humidity test which involved placing the samples in a humid environment for an extended period of time and then measuring humidity resistance in terms of the tensile strength of the specimens. The te-t chamber con-tained 97% relative humidity, and the samples were exposed and subsequently tested for periods of 12 hours, 24 hours, 48 hours, up to five days, respectivelyO After 12 hours of humidity treatment, the lithium modified samples exhibited
3.8 times stronger stren~th levels than samples bound with unmodified sodium silicate. After 48 hours of treatment, the samples bound with lithium modified silicates had still intact, 70 psi tensile strength, while the non~
lithium modified samples could not support their own weight. Hence~ hium modiication allows the sodium silicate bound sand to be used in conditions of high humidity where unmodified sodium silicate failsO Curves showing the strength re~ained by dehydrated silicate bonded test samples are shown in Figure 1 2. A stock solution of li~hium modified sodium silicate was prepared by mixing 4.56 grams of LiOH.H2O with 1~0.56 grams of co~nercial sodium silicate, the latter having a silicate ratio of 3.22:1 and 43.2% solids content.
The lithium hydroxide required about four hours of con-,35 tinuous stirring to dissolve. The resulting silicate i55i 10 - ' formulation was 2.8 SiO2:M2O with Na:Li=5 and 42O5%
silicate solids content.
Test samples were prepared by mixing 1200 grams of Wedron 5010 sand, 12.00 grams of water, and 28.23 grams of 2.8 SiO2:M2O solution. This sand mixture is characterized as having 1% BOS silicate solids. Test samples were pre-pared using a LRedford Hot-Box Core Blower and were found to have 255 psi tensile strength. Samples were transferred to a 97% relative humidity chamber and were found to have 210 psi tensile strength after one day humidity exposure, 125 tensile strength after two days, and 39 psi tensile strength after three days.
3. A stock solution of lithium modified sodium silicate was prepared by mixing 11.67 grams LiOH.H2O with 291.75 grams of commercial sodium silicate, the latter having a 3.22:1 silicate ratio and 43.2~ solid content.
The dissolution of the LiOH.H2O required 24 hours of stir-ring. The formulation of this silicate was 2~5 SiO~:M2O
with Na:Li=3 and 46.4% solid content.
lithium modified samples could not support their own weight. Hence~ hium modiication allows the sodium silicate bound sand to be used in conditions of high humidity where unmodified sodium silicate failsO Curves showing the strength re~ained by dehydrated silicate bonded test samples are shown in Figure 1 2. A stock solution of li~hium modified sodium silicate was prepared by mixing 4.56 grams of LiOH.H2O with 1~0.56 grams of co~nercial sodium silicate, the latter having a silicate ratio of 3.22:1 and 43.2% solids content.
The lithium hydroxide required about four hours of con-,35 tinuous stirring to dissolve. The resulting silicate i55i 10 - ' formulation was 2.8 SiO2:M2O with Na:Li=5 and 42O5%
silicate solids content.
Test samples were prepared by mixing 1200 grams of Wedron 5010 sand, 12.00 grams of water, and 28.23 grams of 2.8 SiO2:M2O solution. This sand mixture is characterized as having 1% BOS silicate solids. Test samples were pre-pared using a LRedford Hot-Box Core Blower and were found to have 255 psi tensile strength. Samples were transferred to a 97% relative humidity chamber and were found to have 210 psi tensile strength after one day humidity exposure, 125 tensile strength after two days, and 39 psi tensile strength after three days.
3. A stock solution of lithium modified sodium silicate was prepared by mixing 11.67 grams LiOH.H2O with 291.75 grams of commercial sodium silicate, the latter having a 3.22:1 silicate ratio and 43.2~ solid content.
The dissolution of the LiOH.H2O required 24 hours of stir-ring. The formulation of this silicate was 2~5 SiO~:M2O
with Na:Li=3 and 46.4% solid content.
4. The preparation of silicate with the for-mulation 2.0 SiO2:M2O was attempted by mixing 4.60 grams LiOH~H2O with 57.15 grams of commercial sodium silicate~
The lithium hydroxide had not dissolved after one week of stirring.
The lithium hydroxide had not dissolved after one week of stirring.
Claims (13)
1. A method of stabilizing silicate bonded sand particles against humidity degradation, comprising:
(a) mixing sand particles with an aqueous solu-tion containing a lithium modified sodium silicate of the formula XSiO2:M2O (where X is a number between 2.5 and 3.8 and where M is Na/Li in a ratio of 5:1 to 20:1); and (b) precipitating silica glass from said mixture to form a rigidized body of sand particles bonded by said glass.
(a) mixing sand particles with an aqueous solu-tion containing a lithium modified sodium silicate of the formula XSiO2:M2O (where X is a number between 2.5 and 3.8 and where M is Na/Li in a ratio of 5:1 to 20:1); and (b) precipitating silica glass from said mixture to form a rigidized body of sand particles bonded by said glass.
2. The method as in claim 1, in which said aqueous solution is prepared by dissolving LiOH.H2O into an aqueous solution of sodium silicate.
3. The method as in claim 1, in which the solid content of said aqueous solution is 33-44% by weight.
4. The method as in claim 1, in which M is sodium and lithium in a ratio of 8.5:1 to 15:1.
5. The method as in claim 2, in which said lithium is present in said solution in an amount of about 2 grams per kilogram of aqueous solution.
6. The method as in claim 1, in which said solute for said aqueous solution consists essentially of said lithium modified sodium silicate with less than 5% other materials.
7. The method as in claim 1, in which said preci-pitation is carried out by the use of microwave energy to dehydrate said mixture at a temperature of at least 100°C.
8. The method as in claim 1, in which said pre-cipitation of step (b) is carried out by use of a reactive gas.
9. The method as in claim 1, in which said pre-cipitation of step (b) is carried out using a heated core box .
10. The method as in claim 1, in which said pre-cipitation of step (b) is carried out using a convection oven.
11. The method as in claim 1, in which said precipitation is carried out by use of a vacuum.
12. The method as in claim 2, in which the sodium silicate employed as an element of the solute has a mole ratio of silica to soda in the range of 2.5-3.8:1.
13. The method as in claim 12, in which the mole ratio of silica to soda is in the range of 2.6-3.3:1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41392782A | 1982-09-01 | 1982-09-01 | |
| US413,927 | 1982-09-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1200655A true CA1200655A (en) | 1986-02-18 |
Family
ID=23639233
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000433361A Expired CA1200655A (en) | 1982-09-01 | 1983-07-27 | Method of stabilizing silicate bonded sands |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1200655A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7984750B2 (en) * | 2008-11-14 | 2011-07-26 | GM Global Technology Operations LLC | Binder degradation of sand cores |
| CN102317005A (en) * | 2008-12-18 | 2012-01-11 | 滕内多拉内马克有限公司 | Method and composition of binder for manufacturing sand molds and/or cores for foundries |
| EP2570028A1 (en) * | 2011-09-15 | 2013-03-20 | Gebrüder Dorfner GmbH & Co. Kaolin- und Kristallquarzsand-Werke KG | Free-flowing composite particle for inhibiting plant growth and use of same |
| DE102013106276A1 (en) * | 2013-06-17 | 2014-12-18 | Ask Chemicals Gmbh | Lithium-containing molding material mixtures based on an inorganic binder for the production of molds and cores for metal casting |
-
1983
- 1983-07-27 CA CA000433361A patent/CA1200655A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7984750B2 (en) * | 2008-11-14 | 2011-07-26 | GM Global Technology Operations LLC | Binder degradation of sand cores |
| CN102317005A (en) * | 2008-12-18 | 2012-01-11 | 滕内多拉内马克有限公司 | Method and composition of binder for manufacturing sand molds and/or cores for foundries |
| CN102317005B (en) * | 2008-12-18 | 2014-07-23 | 滕内多拉内马克有限公司 | Method and composition of binder for manufacturing sand molds and/or cores for foundries |
| EP2570028A1 (en) * | 2011-09-15 | 2013-03-20 | Gebrüder Dorfner GmbH & Co. Kaolin- und Kristallquarzsand-Werke KG | Free-flowing composite particle for inhibiting plant growth and use of same |
| DE102013106276A1 (en) * | 2013-06-17 | 2014-12-18 | Ask Chemicals Gmbh | Lithium-containing molding material mixtures based on an inorganic binder for the production of molds and cores for metal casting |
| US9968989B2 (en) | 2013-06-17 | 2018-05-15 | Ask Chemicals Gmbh | Lithium-containing molding material mixture based on an inorganic binder for producing molds and cores for metal casting |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| RU2699133C2 (en) | Mixture of lithium-containing molding material based on inorganic binder to obtain molds and rods for casting metal | |
| DE102012020510B4 (en) | Forming substance mixtures based on inorganic binders and process for producing molds and cores for metal casting | |
| CA1120204A (en) | Method of making foundry molds and adhesively bonded composites | |
| Owusu | Physical-chemistry study of sodium silicate as a foundry sand binder | |
| JPS58151356A (en) | Hydraulic cement composition | |
| US2992930A (en) | Low density refractory oxide | |
| CA1319490C (en) | Method for the preparation of moulds and cores used in the casting of metals | |
| SK5722002A3 (en) | Binding agent system, core sand mixture and a method for producing the same | |
| CA2152494A1 (en) | Improvements in or relating to water dispersible moulds | |
| WO2014059969A2 (en) | Mould material mixtures on the basis of inorganic binders, and method for producing moulds and cores for metal casting | |
| US4347890A (en) | Method for binding particulate materials | |
| US4412863A (en) | Inorganic cement compositions having controlled thermal expansion coefficients | |
| EP0005371B1 (en) | Process for preparing olivine foundry sand and mould compositions containing olivine foundry sand | |
| US2914413A (en) | Cement composition and method of preparation | |
| US3718491A (en) | Process for silicate-perlite structures | |
| CA1200655A (en) | Method of stabilizing silicate bonded sands | |
| US4056399A (en) | Acid and heat resistant mortars for cellular glass bodies | |
| JPS5952026A (en) | Vibration dampening foundation for installing machine | |
| PL191425B1 (en) | Ceramic product based on lithium aluminium silicate | |
| US4396431A (en) | Process for preparing olivine sand cores and molds | |
| US4522651A (en) | Foundry mold and core composition | |
| CA1191016A (en) | Bond stabilization of silicate bonded sands | |
| US4422496A (en) | Process for preparing olivine sand cores and molds | |
| US4390370A (en) | Metal silico-phosphate binders and foundry shapes produced therefrom | |
| US4445565A (en) | Process for preparing cores and molds |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |