CA1143507A - Method of making foundry molds and adhesively bonded composites - Google Patents

Abstract

A B S T R A C T
The present invention concerns the use of an aqueous solution of n silicate as a binder, particularly for hardening foundry molds and cores without the use of acid or other re-agents to convert the silicate into a silica gel. According to the present invention, the silicate binder is not reacted but instead is rapidly dried, preferably enough within the space of 5 seconds to 10 minutes to reduce the initial water content of the aqueous silicate solution by at least 25%. In the preferred embodiments, this is achieved by forcing air through opposed porous sides of the mold box and the green sand contained therein.
The present invention is also applicable to other composite forms such as the manufacture of plywood, particle board, birquettes, and the like.

Description

~ ~ ~350~

This application relates generally to the manufacture of molds and cores for t~e casting o~ metals.
Metals such as light alloys, aluminum, bronze, gray irons and steels are frequently cast with the aid of casting forms such as cores and molds made of particles of a foundry sand bound together with a suitable binder. One type of binder which has been extensively used in the foundry industry is an aqueous solution of a soluble silicate such as sodium silicate, i.e., water glass.
Aqueous solutions of alkaline silicates are generally known to have adhesive properties, see, for example, Houwink et al. "Adhesion and Adhesives", Elsevier Publishing Co. 1965;
Volume I, chapter 8; Vail "Soluble Silicates" Reinhold Publishing Co. 1952. Adhesion must be developed, however, by slow drying below the boiling point of water to avoid destruction of the ad-hesive film. (Vail supra, Vol. II; page 411). Because of the need for relatively 510w drying, other means of rapid hardening the sodium silicate are required. To provide the rapid hardening re-quired in practical foundry operation, it has become known to use an acidic gas such as carbon dioxide or hydrochloric acid which rapidly converts the sili~ate into silica gel with a liberation of water and an alkaline carbonate. After an initial set has been obtained, the mold may then be baked to prepare it for use.
The carbon dioxide-hardened, silicate-bound foundry 6and, however, has generally been recogni~ed to lack adequate ~trength particularly under the conditions of high production - volume such as encountered in the automotive industry. Accor-dingly, for the past twenty years foundry sand users have sought alternatives to the use of silicate as a binder for foundry sands.
These alternatives have resided largely in the use of a variety - of synthetic resins which are cured to provide the desired set to the mold.

~143507 One such technique ~hich has been sug~ested is a so-called hot box procedure in ~hich a li~uid resinous composition, typically of the phenol or ~uran type, is mixed with the foundry sand and packed into a mold ~ox. Alternately, others have sug~
gested using dry powdered resinous compositions blended with the - sand. In any ev~nt, the resinous composi~ions are heated to fuse the resin, sometimes using a liquid or gaseous material to facil-itate hardening of the mold. Heat curing, however, presents handling difficulties, since the ~orker must take precautions to avoid ~eing burned by the hot heated cured mold. Moreover, during casting, the hot metal causes decomposition of the resin binder. This can result in the release of noxious gases that must be disposed of and in some cases, require special safety pre-cautions to avoid exposure of the workers involved. Not infre-quently, the resinous systems also present fire hazards.
Powdered resins have other disadvantages as well. The powder resin, since it has a substantially different density from the foundry sand, tends to segregate during mixing and handling which results in an uneven distribution of binder and an im-2Q properly bond mold. Further, the powdered resins separates ordusts out during handling and mixing, and the resin dust resul-ting creates an additional air pollution hazard.
Still another procedure which has been proposed for binding foundry sands is described in U.S. Patent 3,409,579, which concerns a binder composition containiny a phenolic resin which combines with a polyiKx~anate to cross link without heating.
The procedure of this patent avoids the necessity of the hot box curing. ~owever, curing in this case requires the use of a ter-tiary amine which has liquid triethylamine which presents serious difficulties in handling from the safety standpoint.

The use of furan resin bonded sands which are hardened with sulfur dioxide have a~so been proposed. Here also there ~1~3507 are obvious drawbacks associated with use and disposition o~ a noxious gas used to harden the ~and.
Summary of ~he Inven*ion I ha~e now discovered a new method for preparing rapidly hardened silicate bound sands in which only a relatively low amDunt of silic ~ is required -- usually less than 3% by weight of the sand. In accordance with thP present invention a green foun-dry sand is prepared using an aqueous silicate binder and packed into a mold box containing the pattern to be duplicated using com-mercial techniques such as blowing, etc. Optionally, (and pre-ferably) adjuvants which are more fully described below are used to impro~e the setting and shake-out propertieS of the mold. The sand is cured by rapidly removing water from it sufficiently to cause the sand to set. Typically, such rapid setting is achieved by removing 30~ or more of the water in less than 10 minutes; in preferred practice, less than one to two minutes. The present in~ention provides a method by which silicate-bonded sands will yield instant tensile strength substantially in excess of the instant tensile strength obtainable with the corresponding sands hardened by carbon dioxide gassing.
The present invention~ in one aspect, resides in a method for manufacturing foundry molds or cores comprising (a) forming a green foundry sand around a pattern in a box having at least two air permeable faces, said sand comprising from 94 to 99.9~ of a refractory foundry sand and having 0.1% to 6% by weight of an aqueous solution containing a soluble silicate as a binder, said silicate containing an alkali metal, ammonium, an ammonium complex, or mixtures thereof as a cation and a sili-cate as the anion, the anion to cation mole ratio being between 1:1 and 4:1, said fioluble silicate further containing ~rom 47 to 70% water. and ~43507 (b) applying 8 diferenti~1 pxe5sure ~et~een fiaid air permeable fac~s suficient to force air therebet~een at a rate ~ufficient in less than two minutes to remove at lea6t 30% of the water contained in said a~ueous solution ~nd to barden the same to ~n instant tensile strength in excess o~ that obtainable from hardening said green sand by carbon dioxide gassing.
The invention, in another ~spect, resides in a method for forming a desired shape from a particulate material selected from ~and, charcoal, uood, ores, refractory oxides, fiberglass, vermiculite, diatomaceous earth and asbestos, comprising (a) molding a green mixture of said particulate mater-ial and an aqueous solution of a soluble silicate as a binder into said desired shape, said green mixture containing from 6 to 100 parts by weight of aid aqueous solution for each 100 parts by weight of said particulate material, the amount of said aqueous solution being sufficient to form a porous, plastic mass when combined with said particulate material, said soluble silicate containing an alkali metal, ammonium, an ammoniumf complex, or mixtures thereof as a cation, and a silicate as the anion, the anion to cation mole ratio being between 1:1 and 4:1, said soluble silicate further containing ~rom 47 to 70~ water;
(b) said green mixture being molded in a box having an air premeable face with an open area of at least 1.5%; and (c) subjecting said molded shape to a force drying period of not more than about two minutes, during which at least 30% of the water in said aqueous solution is evaporated and said molded ~hape is hardened to a tensile ~trength of at least 20 pounds per ~quare in~h.

: L1435i07 These aspects of the invention are also disclosed, and are claimed, in Canadian Patent Application No. 330,753, filed June 28, 1979, of which the present application is a divisional.
The procedure of the present invention is quite surpris-ing since the only example known to me. previously of using air dried silicate binders in foundry practice i5 in the construction of investment molds fiuch as described for example in U. S. patent

2,945,273 to HerzmRrk et nl. In inYestment casting usually two - Sa -~l1435~7 or three layers of a sand-~ter ~la~ muxture ~r~ applied t~ a wax pattern and hardened by exposure to an acidic gas such as carbon dioxide or hydrochloric acid. Additional layers of the sand-water glass mix are then applied and hardened ~y a current of warm air. In this instance, air hardening of the investment mold iS 810w, requiring as much as 30 to 40 minutes under the influence of the warm air stream to harden each layer, and is limited to drying of relatiYely thin films. So far as I am aware, drying three dimensional permeable objects bonded by soluble silicates, in the manner of the present invention has not heretofore been ~uggested.
Detailed Description of the Invention As indicated generally above, the present invention in-vol~es combining foundry sands, silicate binders and, optionally, adjuvants, which are cured in a novel manner to produce molds and cores having high initial strength and scratch resistance. In more detail, the materials used in the invention are the following:
Foundry sands The present invention is applicable generally to the conventional foundry sands available in the art. Many such sands are known. Those denoted as subangular are industrially used, as well as those containing a higher percentage of spherical or rounded particles. Lake sand, Wedron sand, and Ottawa sands are all especially desirable. Also usable are refractory material such as zircon sands, olivine sands, carbon, refractory oxides and other refractory particulate substances. It is preferred that the sand not contain significant portions of impurities such as organic matter, silt, clays or other colloidal matter, lime and the like. Some impurities are especially undesirable as they tend to react with or to absorb the silicate binder, or interfere with its coating capacity and binding strength.

~143507 Foundr~ sands are pre~erablx dr~ and ~ree ~lowin~.
Their size may be varied according to the particular usage and may range from coarse (from 50 to 70 mesh~ to fine (as 150 mesh) and even as fine as 250 mesh. However, because the present inven-tion depends on rapid ~ithdra~al of ~ater from the silicate binder in the interior of the mold, it is preferable to avoid fine mesh sands unless they are necessary to the surface finish of the cast article. Relatively coarse sands, for example, having an average mesh size of 50-70, permit passage of drying air through the mold and cores more easily than do fine sands, such as sands having an average particle size of 120 mesh which generally doubles the drying time at a fixed pressure drop.
-Silicate Binder The simplest silicate binders for purposes of the pre-sent invention are exemplified by water glass, i.e., sodium sili-cate containing silica, sodium oxide and water in varying propor-tions. It is, of course, well known that there are a variety of alkali metal silicates, and all of these may be used in substitu-tion for sodium silicate. Such other common alkali metal sili-cates are potassium silicate and lithium silicate. Also usableare "ammoniated" sîlicates, that is, alkali metal silicates to which G onium hydroxide has been added. These generally, and preferably, have a high ratio of silica to soda (or alkali metal oxide~ such as 2.2 or higher. Also quaternary ammonium silicates can be used in combination with the alkali metal silicates. Such quaternary ammonium silicates are described, for example, in U. S.
patents 3,239,521, 3,345,194 and 3,372,038.
Silicate binders generally have silica to metallic ox-ides mole ratios o~ 1:1 to 4:1, and preferably from 2.2:1 to

3.2:1. These proportions correspond generally to metasilicates, disilicates, trisilicates or higher silicates. Such silicates in solution are characterized by increasing amounts of branched rings ~35V~7 and complex structures charactexized as "pol~silicate anions", and it is believed that it is the ~ranched ring and complex structures which give rise to the ~ind~ng properties of aqueous silicates.
The silicate binder also contains water to form a syrup-like aqueous composition having colloidal or gel-like film-forming eharacteristics. In commercially practicable silicates, there is generally from 47 to 70~ water, the soluble silicate solution having a viscosity ranging from 100 up to 50,Q00-70,000, depen-ding upon the amount of water and the composition of the silicate.
I have had best results in using, as the soluble silicates, sodium silica~e "N", sodium silicate "R", sodium silicate "RU" and sodium silicate "D" of the Philadelphia Quartz Company. The grade "N"
soluble silicate contains silica to sodium oxide in a 3.22 weight ratio, the syrup containing 37.2% sodium silicate solids, having a density of ~1.0Be and a viscosity of 180cp. Grade "K" has a SiO2:Na2O ratio of 2.~8 and contains 42.7~ solids. Grade "RU"
has a silicate to sodium oxide weight ratio of 2.40, a solids content of 47%, a density of 52.0Be and a viscosity of 2100 cp.
Grade "D" has a SiO2:Na2O ratio of 2.0 and contains 44.1~ solids.
Sodium oxide when present in a soluble silicate binder tends to reduce the melting point of the foundry sand. This im-parts adverse shake-out properties, and is more severe with more alkaline water glasses, notwithstanding that the more alkaline silicates produce better tensile properties in the mold. At the same time, however, while a soluble silicate containing a high ratio of silicate to soda such as 3.6, for example, affords fa-vorable ~hake-out characteristics, it tends to produce relatively weak binding. Accordingly, there is a desire notwithstanding the adverse effect of soda to use a soluble silicate of the highest practical alkalinity -- lowest practical ratio of silicate to soda.

In part, this difficulty can be mitigated by replacing some of the sodium oxide of water glass by other alkali metal ~35~7 oxides such as potassium. Such other alkali metals have a lesser tendency than does sodium to flux the foundry sand and lower its fusion point, but they add to the expense of the binder.
It is preferred, and an important discovery in its own ri~ht in accordance with the present invention, to add ammonia or a quaternary ammonium compound to the sodium silicate for the purpose of increasing its alkalinity ~ithout introduction of ad-verse quantities of ~odium oxide. In this aspec~ of the inven-tion it is preferred, therefore, to use a sodium silicate con-taining a silica to sodium ratio of 2.2 or higher (but preferablynot Aigher than 3.2) to which ammonia is added up to an amount which increases the effective alkalinity of the mixture to the equivalent of a sodium silicate having silica to metal oxide ratio of 1.8 to 2.2. This is calculated by treating 1 mole of ammonia as the equivalent of 1 mole of sodium hydroxide. This aspect of the invention is particularly surprising because it had been thought heretofore that addition of ammonia to sodium silicate tended to convert the sodium silicate to an insoluble gel. I have found that, upon addition of ammonia, if a mixture is stirred vig-orously for at least 30 minutes if gellation occurs, and is allowedto age for several hours (or preferably a day or more) at room temperature, the homogeneity of the ammoniated sodium silicate re-appears and the mixture indeed becomes less viscous than the ori-ginal sodium silicate.
The ammoniated silicate provides a binder with excep-tiona~l tensile properties. Moreover, because the ammonia is vola-tile under the influence of sand drying and heat of casting, the ammonia evaporates leaving behind a mold of excellent shake-out properties and because the introduction of soda is limited, the foundry sand retains its reuseability for a greater period of time.
Adjuvants Another method which I ~an use for reducing the tendency 1~435~7 of the ~ilicate binder to ~orm glass-like sub~tances durin~ cast-lng is to include in it adjuvants ~ich improve the shake-out characteristics of the silicate binder. In general such binders, under the influence of heat during casting will decompose in a manner that disrupts $he strength of the film or binding action of the silicate. ~or example, additives carbonize upon exposure to temperatures of the casting metal, and may evolve small amounts of gases at such temperatures. This facilitates shake-out of the mold and cores from the finished casting. According to this invention, preferred adjuvants are film forming materials which will also enh~nce the drying and strength properties of the silicate binder, so that the same or even improved strength is obtained with re~
duced amount of silicate.
The additives are preferably miscible with the silicate binder or dispersible therein, and have no detrimental effect on it. It has been found that a small amount of gas formed in the sand of the mold and core contributes to good casting. However, excessively gassy adjuvants should be avoided since large amounts of gas will cause porous cas~ings, and adversely affect the cast surfaces and dimensional integrity of the casting. Additives rich in nitrogen, for example, are not preferred for this reason.
A great number of additives have been used in silicate binders. These are:
1. Alumina, borax, and various inorganic clays, such as kaolin, bentonite, iron oxide, silica flour, and graphite.
2. Resinous or polymeric film forming compositions ex-emplified by phenol-formaldehyde resins, urea-formaldehyde resins, ureaphenol-formaldehyde resins, urea-furfural resins, bituminous resins, 'osin, shellac, sytrene-butadiene latexes, and polyvinyl acetate.
3. Sugars such as sucrose, dextrose, and glucose, in-cluding forms of commercial glucose produced by hydrolysis of ~L~4350~

carbohydrates, fructose, lactose, m~ose, levulose and maltose and blends thereo~. Also ~uitable are substances such as corn syrup containing one or more of the foregoing, as well as poly-saccharides when used in combination with urea resins. The reduc-ing sugar reaction with the formaldehyde to provide a binder en-hances the binding properties of the silicate used as a primary binder.

4. Special additives more fully described below which I
have discovered for use with silicate binders in accordance with the present invention provide exceptional results and are preferred.

5. Various mixtures of the foregoing materials can also be used if desired.
The preferred adjuvants are generally those of the second through fourth class described above~ The additives of the first category -- i.e. various inorganic substances~ have the disadvan-- tage that they tend to add fines to the sand, and because of thist their use must be limited so as not to reduce permeability and in-crease resistance to air flow of the green sand. These charac-teristics interfere with the desired rapid drying of the silicate binder in accordance with the present invention.
Adjuvants of groups 2 through 4, when used, are desir-able because they permit blending of a binder composition con-taining reduced amounts of ~ilicate. Thus, for example, a sand may be formed using 3%-5% binder of which possibly one-half may constitute the adjuvant, the remaining major portion being a sili-cate binder. Thus, the effective silicate content of the binder is reduced so that upon reuse of the foundry sand after the cas~-ing- has been completed, the accumulation of low melting alkali metal oxides is reduced.
One class of adjuvant useful in the present invention are those described in my British Patent 1,309,606. Such adju-vants are a condensation product of a ~yrupy mixture composed of li~3507 44-77~ reducing sugar, 5-22~ urea~ A~19% ~ormaldehxde~ and 9-18%
water. The mixture is reacted at a pH of 5~16 for 15-120 minutes at 110-118C. For application in the present process these may be modified by reducing the amount of urea and formaldehyde.
As indicated, however, preferred adjuvants are those which`have been specially formulated for use with foundry sands bound by a soluble silicate in accordance with the present inven-tion. These preferred adjuvants are formed from ~i) a reducing sugar such as glucose, pure syrup or other reducing sugars such as mentioned above; (ii~ a lower dibasic carboxylic acid or acid anhydride such as maleic acid, maleic anhydride, succinic acid, succinic anhydride, glutaric acid or anhydride, citric acid, tar-tariC acid, etc. and; tiii~ a stabilizer to pre~ent carameliza-tion of the reducing sugar that the process and temperatures re-quired, I have found that boric acid is generally suitable as a stabilizer. In general, the lower dibasic carboxylic acid should contain from 3 to 6 carbon atoms, be miscible with the reducing sugar at the processing temperature, and may contain hydroxy groups. Optionally there may also be included polyhydric alcohols containing 2 to 8 carbon atoms and 2 to 6 hydroxy groups, which alcohols ~unction as a plasticizer. Typical such alcohols are ethylene glycol, propylene glycol, glycerine, pentaerythritol and sorbitol.
The foregoing ingredients are blended together to form a mixture containins (on a dry weight basis) from 1 to 12~ of the dibasic carboxylic acid anhydride and preferably from 1 to 3%;
from 1/2 to ~ of the stabilizer (such as boric acid), and pre-ferably from 1/2 to 1%; and from 0 to 6% of the optional poly-hydric alcohol preferably from 0 to 4%. The balance of the com-position is made up of the reducing sugar. The reducing sugarmay be either as a dry powder or as an aqueous syrup containing up to 20% water. The foregoing proportions are based on the weight of the dry ingr~dientæ.

11435V'7 The mixture is heated to remove an~ water contained in the reducing ~ugar as well as t~e ~ater condensation~ Heating generally is for a period of 30 to 90 minutes at a temperature of 110 to 150C. The heating step should preferably not be carried on as long as to cause caramelization or thermodegregation of the adjuvant. After heating to remove water, while the reac-tion mixture is still hot, an aqueous alkali is then added, such as an alkali metal hydroxide (NaOH, XOH, etc.~ or ammonia. The amount of alkali and water added at this stage should be suffi-cie~t to provide from 10 to 25~ water in the final produc~, and from about 1/2 to 2% alkali. The amount of alkali added should be sufficient to neutralize unreacted carboxylic acids and to aid in the dilution process. After cooling, the finished product is a syrupy fluid.
The present invention, in a further aspect, resides in a composition of matter for use in binding a particulate composition prepared by (a) combining (i) a reducing sugar, (ii) a lower dibasic carboxylic acid or acid anhydride, and (iii) a stabilizer effective to prevent caramelization of the sugar during reaction, said dibasic carboxylic acid or acid anhydride being, on a dry weight basis, from 1 to 12% by weight of said mixture, and said stabilizer being on a dry weight basis, from 1/2 to 2% by weight of said mixture, the balance thereof being made up of said reducing sugar;
(b) heating said mixture to remove water therefrom;
and (c) thereafter adding an alkali and water to provide a final product containing from 10% to 25% water and from about 1/2% to 2% of said alkali.

11~3507 Formulation The sand, silicate bindex and toptionally) adjuvants, are mixed in standard mixers or mullers. It is desirable to accomplish the mixing at rapid speeds to minimize costs and in-crease output for higher production foundry sands. Thorough mix-ing in about 1-2 minutes is a desirable and readily attainable standard.
Generally, the silicate binder composition i8 provided in an amount sufficient to yield a green sand containing fromO.1%

to 6% silicate. However, in preferred foundry practice, the green sand will contain 0.5% to 3% by weight of silicate binder or more preferably 1-3% by weight. The lowest binder content consistent with the requisite strength is desirable because too high a binder content destroys the porosity of the foundry sand. Reduced poros-ity restricts the gas flow required to set the sand, as well as gas flow through the mold when contacted by hot metal.
The adjuvant is used in proportions generally sufficient to promote breakup of the binder under the influence of the heat - 13a -~1~350~

of the molten metal. The adjuvant preferably has film-f~rming and plasticizing characteristics ~hich aid the strength of the silicate binder prior to the casting, and, upon casting, decom-poses to break up the film of silicate binding material thereby pro~iding improved shake-out characteristics to the mold. The adjuvant is used in proportions generally sufficient to promote the breakup of the bînder under the influence of heat of the molten metal during casting. Depending on the adjuvant selected, the desired portion of adjuvant may range from 25% to as much as 200~ adjuvant based on the weight of the silicate binder, prefer-ably from 5Q% to 150% adjuvant. As indicated above, an advantage of using an adjuvant is that it decreases the amount of silicate required for binding in a particular sand composition, thereby reducing the accumulation of alkali metal oxides when the sand is reused. For this reason, therefore, it may be preferred to in-crease the amount of ad~uvant relative to the amount of silicate consistent with the requirements of good casting performance.
Dehydration and ~ardening -In accordance with the present invention, it has been found that green sands prepared with an aqueous soluble silicate binder should be rapidly hardened, in the space of a few minutes or seconds by forced evaporation of water from the silicate binder.
It has been found, surprisingly, that if the green sand is force-dried to remove water rapidly, vastly improved results are obtained. Rapid water removal can be accomplished by elec-tronic heating, for example, by microwave heating, which generates heat, volumetrically within the mass of the mold and core. In this embodiment, the green sand is packed in a mold box, using a pattern, of wood, plastic or other non-conductiye materials, which are porous and thereby permit the escape of water ~apor as it is evaporated from the sodium silicate. When electronic heating is used, obviously metal must be excluded from the mold ~3S0~7 box as ~ell as the general vicinit~ D~ the mold box area and therefore from the standpoint of practical foundry practice has certain disadvantages. Electronic heating is ~est applied on 6ilicate bonded cores which have been taken out of the mold box ~na which retain their shape prior to hardening by virtue of the cohesiveness and the green strength of the sand.
Preferred practice, therefore, is to construct a mold ~ox having two or more air permeable sides adapted to permit air to be forced or drawn through the body of the mold and core by application of air pressure or vacuum. A simple mold box is il-lustrated in Figures 1 and 2 in which Figure l is a plan view of ~he mold box showing, by broken-away sections, the air permeable faces and mold cavity; and Figur`e 2 is a side view through line 2-2 of Figure 1.
In the simple embodiment illustrated in Figures 1 and 2 of this application~ the top 1 and bottom 2 of the mold box are provided with perforated faces. Typically, perforations are spaced on 1/10 in. to 1/4 in. centers, the perforations being sufficient in size to provide at least 1.5 to 10% open area. Pre-2a ferably 3 1/2% or greater open area is provided. Greater openarea can be added, but does not materially improve results~
Slots providing equivalent ventilation of the mold faces 1 and 2 may also be used. Better results are obtained if the perforations are more closely spaced. Alternately, the faces 1 and 2 of the mold may be of air permeable substances such as sintered metal, sintered glass, open-cell plastic foams, or wire screen of various composite materials. For best results, the mold box is designed so that the area of the opposing ventilation faces relative to the Yolume of the core and mold to ~e hardened is as large as practical. This will ordinarily result if the ventilated faces of the mold box are positioned so that air is ~orced or drawn across the thinnest section of the mold.

11~*3507 According to this invention, the core and mold can ~e fully or partially hardened before removal. Silicate binders rapidly reach their potential strength in the practice of this invention with adequate air ventilation in less than 40 ~econds.
Ventilation of the mold and core for a shorter period of time, for example, 10 seconds, will result in a core which has been hardened in the vicinity of the face ~here air enters, but may still be soft or plastic on the exit face of the mold. Such molds and cores, ho~ever, continue to harden after removal from the mold box and rapidly reach their ultimate strength character-istics.
While the present invention can be practiced using air at ambient temperatures, more rapid curing is obtained when using air at temperatures of 100 to 230F., or such other temperature as is suitable provided that the mold is not heated during harden-inq by the warm air to a point which creates a handling problem when removing the hardened mold from the mold box.
For most purposes, in the practice of the present inven-tion, it will be sufficient to provide for an air flow rate in the range of lQ0 CFM to about 1500 CFM. The flow rate of air required is dependent to some extent on the amount of sand to be cured and the thickness of the mold which the drying air must traverse. Air may be supplied either by a ~uitable blower and compressor provid-ing air at su~ficient pressure, bearing in mind the permeability of the mold and the mold faces which the air must traverse to pro-vide the desired hardening. Ordinarily, 5 to 30 lbs. pressure will be quite adequate. Under some conditions it may be desirable to employ higher pressure; however in such cases, of course, the mold box must have sufficient mechanical strength to withstand 3Q the pressure drop across it during hardening r Alternately, air may be drawn through the mold box by applying ~uction to one face.

1~3507 The air is orced throu~h the mold box containin~ a green sana for a period of 5 seconds to several minutes, during which time the mold and core will achieve an initial set suffi~
cient to permit handling and to evaporate 25~ or more of the water originally present in the binder. The water content of the sili-cate binder should usually be decreased so that the "dried" binder is at least 54~ solids. Accordingly, the more dilute silicates may require a more extensive drying to set than the more concen-trated silicates. Preferably drying is sufficient to evaporate 50~-70~ of the water content of the binder, while the preferred drying time is less than one or two minutes. Surprisingly, when the mold and core parts are set aside, they will then continue to gain in tensile strength.
By way of illustration, for example, in one series of tests a foundry sand bound with RU grade sodium silicate, has an initial water content of 13 moles of water for each mold of sodium silicate. If sufficient water was removed to reduce the water content of the silicate in the green sand to 9.5 moles per mole of sodium silicate, an initial set strength of 20 psi was obtained.
When drying was continued to decrease the water content of the sodium silicate to 7 moles, the initial set strength was 45-60 pounds. Further drying decreasing the water content to 4 moles increased the set stren~th to over 100 psi. The experiment was discontinued when the water content of the sodium silicate had been reduced to 2.3 moles, at which point a set strength of 150 pounds per square inch had been obtained.
When working in a comparable series with grade N sodium silicate, more water was present, and less strength was obtained.
~rade N sodium silicate initially contained 23 moles of water per 3~ mole of sodium silicate. I was able to dry a green sand using grade N sodium silicate as a binder to the point where the sili-cate contained only 7 moles of water, at which point the set ~1~3507 strength of the mold ~as 78 p~unds pex s~uare inch. Dif~iculty was experienced, however, in ~urther reducing the water contellt of the grade N sodium silicate.
The present invention has applications in areas other than construction of foundry molds. One application o~ it, for example, is in the manufacture of pl~wood. Laminates of wood may be adhered, for example, with silicates in accordance with the present invention. In this case, a layer of a silicate binding agent is cast or otherwise applied to the surface of the wood laminates to be adhered, and then they are pressed and, electron-ically heated, for example, by microwave heating, to rapidly ex-tract the water. Rapid extraction of water from the adhesive layer is accelerated when wood is bound using the present invention because of the wicking or absorbing characteristics of the wood, which tends to extract water from the silicate.
It has been found, in this connection, that silicates tend to be brittle. For this reason, bond stabilization of the silicates can be provided, thereby reducing brittleness. Such stabilization is obtained by addition of one or more of the adju-vants described above.
The present invention is also applicable in the manufac-ture of composites of various shapes, such as charcoal briquettes, particle board, ore briquettes, and the like. The proce~ure in manufacturing such briquettes is generally the same as that followed in the manufacture of foundry molds. In such cases, it may be de-sirable to increase the amount of silicate binder generally to a range of 6-100 parts by weight for each 100 parts by weight of the particulate material to be bound into a composite. The green mixture should be o~ a putty-like consistency and retain sufficient porosity that water vapor within the interstices of the desired shape can escape during the rapid drying ctep described above.
In the case of such evaporation, the drying time may be extended for up to ~ive to ten minutes.

~1~35~'~

The selection of ~ilicate binders follows the same general principles, bearing in mind that particularly in the case of ores that some ores may be reactive with the 601uble ~ilicates, and in such cases the silicate mus~ be ~elected so that it will retain its binding capacity in the presence of the ~re to be briquetted.

.... ... .
EXa~ple_l One kilo of a foundry sand from Martin-Marietta Company identified as Portage-60 having an average particle size of about 60 mesh, was combined with 20.4 grams of Type RU soluble silicate, Philadelphia Quartz Company, and 13.6 grams of an adjuvant pre-pared in accordance with Exam~le 5 of British patent No. 1,309,606.
Type RU is a sodium silicate having a silica to sodium oxide ratio of 2.4 and containing 47% solids. The green sand was packed into ample molds in the shape of standard A.~.S. tensile test speci-mens. The top and bottom of the mold box were "Plexiglas "* per-forated with 90 holes having an open space of about 5~ of the face of the sample.
Hot air at 2209F. was ~ucked through the mold at a rate of about 100 CFM by the aid of a vacuum pump at the bottom face of the mold box such as shown in Figure 1 for a period of time between 10 and 60 ~econds. The samples were tested immedi-ately for water loss and their instant tensile strength loss.

* Trademark for poly (methyl methacrylate) resin in ~heet form; it has exceptional transparency.

The ~ollowing result~ were obtained:
Instantaneous Tensile Strength ~si Water Loss Percentage*
10 seconds 30 psi O.43 gms. 304 n 32 0 ~ 56 39 . 4 %
~I 58 n 0 ~ 70 ~ 49 ~ 2P6 n 88 n 0 ~90 n 63 a 128 ~ 00 n 709~
o 50 ~ 174 n 1~ 09 77 ~ 7%
n (no break)**1.19 n ~3. 9%

- * The percentaqe of water loss is based on the total amount of water initially present in the green 6and.
** Tensile strength over 400 psi - l9a -~35(~7 Improved results were obtained when the perforated "Plexiglas "**~ faces of the mold box were replaced by a wire screen.
~xample 2 1-1/2 kilograms of New Jersey silica 50 (New Jersey Silica Company, average particle size 50) was combined with 24~2 gms. of a soluble silicate prepared by evaporating 12 gms. of water from 2Q0 gms. of Type RV soluble silicate (Philadelphia Quartz Companyl and adding 2 gms. sodium hydroxide thereto. In addition, 17.6 gms. of adjuvant P-13 were blended into the green sand.
P-13 adjuvant was prepared by combining 400 gms. of glucose (9% water), 6.6 gms. of maleic anhydride and 2.66 gms.
of boric acid, the mixture was heated to 122-131C. for one hour during which 22.6 gms. of water was lost. While still hot, 40 cc.
of 10~ sodium hydroxide and 34 cc. of water were added. The mix-ture, when cooled to room temperature, was tacky and capable of d~ying in air.
The green ~and was packed into a mold for tensile bar samples and hardened by drying air therethrough at 220~., as described in Example 1, for 10 to 45 seconds. The following re-sults were obtained:

Instantaneous Tensile Water Loss, Drying TimeStrength psi grams 10 seconds 24 psi 0.4 gms.
" 40 " 0.55 "
n 46 0-57 9~ 58 n O .64 n n 10 4 ~ 0.86 "

Example 3 1.0 kilograms of Wedron sand ~Wedron Silica Company:
120 average particle size) was comhined with Type N soluble silicate (Philadelphia Quartz Company). Type N soluble silicate ***Trademark ~143S~7 has a 8ilica to sodium oxide ratio cf 3.22 and contains 374 solids. The green 6and in this example contains a 4.43~ of the silicate binder.
The green sand was packed into tensile bars and hardened using air which had been heated to 220F. ac described in Example 1. The fo~lowing results were o~tained:

Instantaneous Tensile Water Content, moles Drying Time Strength psi Water/Mole N*

20 seconds 12 psi 17.6 30 n 30 n 15 .
45 ~ 36 ~ 12.8 55 n 40 n 11.8 -78 6~7 *The amount of drying in this example is reported as the amount of water remaining in the 6ilicate binder expressed as a molar ratio of water to silicate solids. For Type N silicate the initial ratio is 23 Fxample 4 The effect of varying the porosity of the top and bottom faces of the mold was investigated. Standard tensilè bars were prepared in molds in which the porosity of the top and bottom faces were increased by increasing the number of perforations drilled. For purposes of this test, a green sand was used pre-pared from one kilogram of 26 average particle size Portage sand (as in Example 1) combined with 34.6 gms. of Type RU soluble 8ili-cate. The samples were packed into standard tensile bars and hardened with 220F. air for 40 seconds as in Example 1. The following results were obtained:

Instantaneous Percentage No. of ~olesTensile Strength psi Water Loss 14 0 16.3%
34 20 25.6%
96 160 59.9%
190 312 64.8%
In the foregoing table, the hole ~ize used in each ~ase was the same. When 190 holes had been drilled in the top and bottom faces, th~ open area within the 6ample area was 10%.

35(~7 Example 5 The effect o Varying drying conditions were further studied in the ~ollowing series of experiment~:
One kilogr~m of Portage sand average particle &ize 60, 20.4 grams Type R~ sod;um silicate and 13.6 grams of P-14 adju-vant were com~ined to make a green sand. The green sand was cured in standard tensile bar moles using 220F. air as in Example 1.
The P-14 adjuvant used in this ex2mple was prepared by combining 400 grams of glucose (9% water), 6.6 grams citric acid and 2.66 grams of ~oric acid. The reaction was carried out as described in Example 2.
(A~ In a first test, the sample was treated in the normal manner, the top and bottom plates containing 190 holes having 10~ open area. During 50 seconds curing time, the sample lost one gram of water and achieved a tensile strength of 220 psi.
(B~ The test A was repeated using, however, room tem-perature air rather than 220F~ air. In 60 seconds only 0.62 grams were lost, and the tensile strength achieved was only 80 psi.
(C) Test B was repeated using the same vacuum pump, but replacing the top plate of the mold with a plate ha~ing no per-forations at all. In this test the water los~ was further redu~-ed, to 0.53 gram~ and the tensile strength achieved in 60 seconds ~as only 60 psi.
Example 6 An ammoniated silicate for use in accordance with the present invention was prepared as follows:
38 grams of Type N 601uble silicate (silica to sodium oxide ratio 2.33, 37% solids) were combined with 3.8 grams of concentrated ammonium hydroxide (28% ammonia). The mixture was shaken intensely for a minute or two. At this point a slight amount of gel appeared. The mixture was then allowed to set il~3S~)7 overnight. The following da~ the gel had disappeared and a homo-genous solution resulted ~ich was more fluid than the original Type N ~oluble silicate.
Example 7 41 grams of a sodium, ammonium silicate prepared as in Example 6 were combined with 1 kg. Portage sand of average par-ticle size 60. The mixture was packed into stan~ b~ile test molds and hardened in 220F. aîr a~ described in Example 1. The follow-ing results were obtained:

Instantaneous Water Loss Drying TimeTensile Strength psi Grams Percent 20 seconds 24 0.89 34.4 n 60 1. 30 50 . 3 n 93 1.69 65.5 " 125 1. 97 76 . 3 " 190 2.12 82.1 ~ 16~ 2.23 86.4 For comparison purposes, a similar sample was made using Type N soluble silicate as a binder without any ammonia having been added thereto. When these samples were tested for - strength, the following results were obtained:

Instantaneous Drying TimeTensile Strength psi 20 seconds 18 " 40 n 64 ~5 ~ 88 n 88 n 116 Example 8 Following generally the procedures of Examples 6 and 7 ~
an ammoniated silicate was prepared from Type RV soluble silicate to which ammonia had been added to provide an ammoniated silicate containing 2% ammonia. 20 grams of the ammoniated sodium silicate were combined with 1 kg. of Portage sand. The mixture was packed into standard tensile test molds and dried in 220F~ air as des-cribed in Example 1. For comparison purposes, corresponding sam-ples were made for a mixture of 1 kilogram of Portage sand with 1~350~7 22 grams of Type RU soluble silicate~ The follo~in~ results were obtained:
Drying Time Instantaneous Tensile ~tren~th ps Type RU plus 2% ammonia pe RU
10 seconds 26 18 " 52 32 " 80 48 " 98 62 " 98 84 n 160 B4 Example 9 Portage sand (average particle size 60) was used to make a green foundry sand of the following composition:
1~5~ Type RU soluble silicate 0.68~ of an adjuvant prepared in accordance with Example 5 of British Patent 1,309,606 0.1~ borax 0.24% of a styrene butadiene resin latex, known as "Dylex 553"***, from the Arco Chemical Company The green sand contained 1.093% water. It was packed into standard tensile bar molds and hardened in 220F. air in accordance with Example 1. The following results were obtained:
Instantaneous Tensile Strength psi _ Water Loss Instan- After After Drying Timetaneous 1 hr.** 24 hrs.** Grams Percent*
-10 seconds 20 - - 0.36 33%
n 28 - - 0.46 42%
n 52 80 - 0.60 54.9%
n _ 100 124 n 78 - - 0~83 75.9~
n 88 - - 0.89 8i,4%

*Expressed as percent of total water present **Tensile strength of these samples were also measured after the samples had been allowed to age for the indicated period of time at ambient conditions which at the time of the test were 30 70F. relative humidity 64%.

~**Trademark Green sands suita~le ~or use in the present invention can be prepared of the following compositions generally in accor-dance with the procedures of Examples 1 and 2:
A L C D
_ _ .
Sand 1.5 kg. 1.5 kg. 1.5 kg.1.5 kg.
Silicate ~inder 28.2 gms. 28.2 gms. 28.2 gms. 28.2 gms.
Sucrose 15 gms.
Glucose 16 gms.
10 Corn Syrup 17 gms.
Urea furfural resins 15 gms.
Example 11 - 1.5 kilograms of foundry sand from the New Jersey Silica Company having an average particle size of 50 were com-bined with 40.3 grams of a binder prepared by blending the following:
28 grams of a soluble silicate prepared as described in Example 2.
14 grams of a quaternary ammonium silicate prepared in 20 accordance with V. S. patent 3,239,521 obtained from the Philadelphia Quartz Company and identified as "Q-220"*.
20 grams of an adjuvant prepared in accordance with Example 5 of British Patent 1,309,606.
The green sand was packed into standard tensile bar molds and hardened by forcing cold air through it at a flow rate ; of 30 to 40 cu. ft. per minutes. The following results were ob-tained:
Drying TimeTensile Strength, psiWater Loss, gms.
1 min. 12 0.4 1' 30" 30 0~57 2' 52 approx. 0.6 *Trademark ~35~7 Since the standard tensile ~est ~ar contains about 100 grams of material ~AFS Mold and Core Test Handbook, Section 11), the ventilation rates in this example correspond to flow rates through the sample of at least about 30 cubic feet per minute per 100 grams of sand~
Example 12 In accordance with the present invention, the amount of silicate in the binder may be varied, particularly where adju-~ants were used. In some cases, the adjuvant was P-13 (see Example 2). In other cases the adjuvants of Example 5 of British Patent No. 1,309,606. The following sample~ were prepared gen-erally following the procedure of Example 1 (percentages being expressed as weight percent of the green sand):
A B C D E F

Soluble Silicate Binder 2.14% 1.88% 1.61% 0.813% 0.546% 0 Adjuvant 0.84% 1.0% 1.17~ 1.67~ 1.8% 2.4%

Tensile Strength134 145 104 78 72 64*
at 45 seconds psi psi psi psi psi psi *After 30 minutes the strength had risen to 96 psi.
Example 13 A series of ammoniated sodium silicates were prepared by adding ammonium hydroxide (28%) to various sodium silicate solutions. Immediately following addition of the ammonium hy-droxide, the mixture was vigorously stirred by hand for 30 to 40 minutes and then allowed to age at least 3 to 4 hrs. (In some samples aging was overnight). The amount added was sufficient, in each sample to increase the alkalinity to the equivalent of a 2.1 ratio silicate.

Tensile test bars were then prepared using sand contain-ing about 1 1/2% silicate binder (dry olid basis). For compari~
son purposes, a similar series of samples were prepared from the sodium silicates employed in these tests before ammonia had been - ~6 ~

3~ 7 added. The following results were obtained:

SodiumSoda/Silica Sample Drying Tensile Strength Silicate Ratio Time Initial Ammoniated Type Sodium Sodium Silicate Silicate . _ Type ~U 2.4 45 sec. 84 160 Type R 2.88 120 1I 110 178 Type N 3.2 45 " 64 93 Type S-35 3.75 9O n 22 28 Example 14 .
Plywood was prepared in accordance with the present invention by bonding 1/8" laminates of wood, in one case with soluble silicate Type RU (identified below as sample A) and in the second case, soluble silicate Type N (identified below as sample B). Additional samples were prepared in which 10 parts of Type RU soluble silicate or Type N soluble silicate were re-s~ectlvely combined with 5 parts of the adjuvant described in Example 5 of British Patent No. 1,309,606. These samples are respectively identified as samples C and D below. Still further examples of plywood were prepared in accordance with the present invention using an adhesive prepared from 10 parts Type RU or 10 parts of Type N soluble silicate respectively combined with 5 parts of the adjuvant of Example 5 of the British Patent No.
- 1,309,606 and 1.5 parts of a styrene butadiene resin.

Each of the samples thus prepared was heated in a home microwave oven for 25 seconds to harden the silicate. The oven operated at a frequency of 2450 megacycles and was rated at 1500 watts. In parallel with the heating of samples, a small watch glass having 1.5 grams of the binder was heated to provide a measure of water lost from the binder caused by the microwave heating.
After each test the wa~ch glass was reweighed to deter-mine water 10SB. After 24 hrs. each of ~he samples was sawed ~35~7 into strips of approximatel~ 1 in. ~idth ~ox further testin~.
Additionally, the loss of water from the hinder was estimated.
The following results were obtained:
Sample- A - The weight loss determination showed that sample A
had lost sufficient water that the soluble silicates remaining were 60% solids (Type RU silica initially contains 47% solids). Sample A could not be cut into test samples because the laminates shattered under the ~ibration of the saw.
-Sample B - The water loss measurement showed that the soluble silicate remaining in sample B after heating contained 514 water (Type N soluble silic~te contains 37.6~
solids). Sample B could not be cut into test pieces because the silicate bond shattered under the saw vibration.
Sample C - Water loss measurements showed that the solids content of the silicate binder plus adjuvant increased from 53% to 89%. No splitting occurred when the sample was cut into test pieces. The test sample delaminated after immersion in water for 24 hrs.
Sample D - Water loss measurements showed that the solids content of the soluble silicate -- binder mixture increased during drying from 50% to 76%. No splitting occurred when the sample was cut into pieces. After immersion in water for 10 days, the sample had not delaminated.
Sample E - Water loss measurements showed that the solids content of the soluble silicate --adjuvant mixture increased from 57% to 89%. No splitting occurred when the sample was cut under test pieces. Samples immersed in water showed delamination after two days.

-S&mple F - Water loss measurements showed that the solid content of the binder-adjuvant mixturQ increased from 60% to ~35V7 80~. No splitting occurred upon cutting into test pieces. Test pieces did not show delamination e~en after water immersion for 10 days.
Example 15 50 grams of wood shavings with fines removed were com-bined with 30 grams of ammoniated Type N soluble silicate pre-pared in accordance with Example 6. In addition, 12 grams of an adjuvant prepared in accordance with Example 5 of British Patent No. 1,309,606 were included in the binder system. The mixture had a putty-like consistency, but was porous. Samples were packed into standard tensile test specimens and air dried by drawing air across the sample under vacuum at 230F. for 3 minutes.
The specimens could be sawn within 2 hrs., or could be sanded or otherwise worked~
Additional samples were tested for flammability. It was found that the sample was non-flammable and did not lose its strength under flaming conditions.
The materials produced are porous and could be valuable ~or their thermal and sound insulating properties, as well as for their mechanical properties. Such adhesively bonded composites can be useful in making molds for the present invention because of their porosity.
It will be recognized that similar component particle compositions can be made from fiberglass, vermiculite, diatomac-eouS earth, asbestos and the like in accordance with the fore-going example.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition of matter for use in binding a particulate composition prepared by (a) combining (i) a reducing sugar, (ii) a lower dibasic carboxylic acid or acid anhydride, and (iii) a stabilizer effective to prevent caramelization of the sugar during reaction, said dibasic carboxylic acid or acid anhydride being, on a dry weight basis, from 1 to 12% by weight of said mixture, and said stabilizer being on a dry weight basis, from 1/2 to 2% by weight of said mixture, the balance thereof being made up of said reducing sugar;
(b) heating said mixture to remove water therefrom;
and (c) thereafter adding an alkali and water to provide a final product containing from 10% to 25% water and from about 1/2% to 2% of said alkali.

2. A composition according to claim 1 wherein said stabilizer (iii) is boric acid.

3. A composition according to claim 1 or claim 2 wherein said alkali is an alkali metal hydroxide or ammonium hydroxide.