US2510220A - Foundry composition and method - Google Patents

Description

Patented June 6, 1950 FOUNDRY COMPOSITION AND METHOD Kenneth Ray Grube, Columbus, Ohio, assignor,

by mesne assignments, to Eastern Clay Products, Inc., Indiana, Pa., a corporation of Maryland No Drawing. Application April 7, 1948, Serial No. 19,631

6 Claims. (Cl. 22-188) My application is a companion of my application Serial No. 768,941 of August 15, 1947, now Patent 2,491,006 of December 13, 1949 entitled Method of conditioning foundry sand, and the present invention relates to foundry sands and molding compositions, and more particularly concerns the production of sands displaying good facing qualities, and of compositions for imparting the required good facing properties to the sands. As well, it concerns the method of producing the same.

An object of my invention is to provide facing I sands and mold compositions wherein nearly all tendency of burning on of the sand particles or the hinder, or both, to the poured metal is effectively suppressed; which sands and molding compositions are produced, in simple, ready and effective manner, and with thoroughly reliable, predictable and reproducible results, all with a minimum of investment of both time, equipment and labor.

Another object is to provide a sand or mold composition of the general type described wherein the sand will fiow readily and can be molded and tamped into close conformity with the details of the pattern, which possesses a high degree of green strength together with requisite controllable and predictable developed or dry strength, and which requires but a small additive of binder to ensure requisite qualities of moldability.

Another object is to provide a method of treating foundry sands wherein the added binder, while imparting its desired high binding qualities to the mold composition to which it is admixed,

at the same time is effectively precluded from burning onto the poured metal and, as well, from fluxing the sand so that the latter can burn onto the poured'casting.

A further object is to provide a molding composition and a method of producing the same, wherein the controlled low developed or dry strength will permit thorough breakdown of the mold composition following opening of the flask, so that the used sand can be screened and the screened product rehabilitated and readied for reuse by the admixture thereto of but a small quantity of my new treating composition.

All the foregoing, together with many additional highly desirable advantages and objects, attend upon the practice of my invention, part of which will be obvious and part of which v.ill be pointed out hereinafter in greater detail during the course of the following description.

As conductive to a more thorough understanding of my invention, it may be noted at this time that the art of casting metals extends far back into history. It has long been realized that for many reasons sand molds are highly suited for the pouring of casting metals. This is in part attributable to the highly refractory nature of silica sands, and the relatively impervious qualities which they display to the high temperatures of the poured metal.

A striking disadvantage is inherent in these sands, however, in that there is little, if any, quality of either cohesion of the grains of the sand amongst themselves or adherence thereof to the walls of the flask. A certain amount of cohesion is necessary between the particles of sand before they can display the qualities of moldability requisite in closely conforming to and retaining the contours of the pattern. At the same time, the sand must be reasonably free from tendency towards adherence to the surface of the pattern. Such freedom from adherence can be achieved in several manners, well recognized in the art, and not forming part of this invention.

Much eflort and research has been directed over the years to the problem of imparting the required satisfactory qualities of moldability to the sand. The admixture to the sand of binders has in large measure been decided upon. Reliance upon the bonding qualities of suitable binders has come more and more to the fore as the principal mode of resolving this problem. The binders are added directly to the sands. In recent years the workers in the art have been directing their eiforts towards the montmorillonites, particularly southern bentonite, with its non-swelling colloidal qualities, and western bentonite, with its swelling colloidal characteristics and its characteristic of imparting high dry strength.

Now, while this admixture of a binder is undesirable, diluting as it does, the good qualities of the sand, it constitutes a compromise which is necessary in order to permit efiective use of the molding sand. lllustratively, it may be noted that the binder represents a source of decreased porosity. Its fine particles sifting into the interstices between the particles of sand, particularly upon colloidal swelling when wetted down, form a sort of solid solution or emulsion which tends to block the venting of gases evolved when the metal is poured into the mold. Blow holes sometimes result. Moreover, the clay serves as a flux, lowering the melting point of the sand and causing burning on of sand or clay or both, onto the poured metal when this latter is poured under 3 the high temperature conditions which are necessary to liquefy certain metals or alloys, illustratively, iron and steel.

Thus, much effort has been directed towards reducing the tendency of the binder and sand.

towards burning onto the face of the poured casting. In this connection it has been suggested to mix with the sand and binder some pitch or sea coal, or other hydrocarbon, the tendency of which is to form a reducing atmosphere in the region of the poured casting, thereby prevent ing the oxidizing of the surface of the. metal. Possibly, the vaporized hydrocarbon serves as a physical insulation between the metal and the silicous and argillaceous materials. Various disadvantages attend upon the described practice, however, primarily because of the elements of increased expense, duration of processing and the tendency towards diminished porosity.

It has been suggested by a recent investigator that the tendency towards burning on can be prevented in large measure by physically separating the bonding material from the particles of sand by some combustible, carbonaceous material. The theoryadvanced is that while upon pouring the metal undergoing casting, the temperature of this latter will fuse the bonding clay, nevertheless, the simultaneous combustion of the carbonaceous material lying between the bond ing material and the same will temporarily insulate these two, and will prevent the clay from fiuxing the sand. By the time that the curtain of carbonaceous material is entirely consumed, the poured metal will have passed into a solid phase, and it will be impossible for the clayfiuxed sand to burn on. Thus, in the prior art sand and carbonaceous material are mixed together, so that the sand is coated with the carbonaceous material, whereupon bentonite or other bonding clay of high degree of fineness is added. The carbonaceous material which coats the sand physically separates the sand and the bentonite, while the bentonite retains its desirable bonding qualities.

As distinguished from the prior art, my experiments disclosed that novel action of the bentonite, entirely different from what had hitherto been conceived to be its role in foundry compositions, could be availed of by directly mixing the hydrocarbon which produces the reducing atmosphere during pouring with the binder, either just prior to or at the time that the sand is mixed therewith. In short,'by so doing, the hydrocarbon apparently efiectively encapsulates the binder, and prevents it from fluxing the sand. Since a much smaller quantity of binder is employed than sand, a much lesser quantity of hydrocarbon is required than where attempt is made to encapsulate the particles of said. At the same time effective physical separation between the sand and binder is achieved. Even when the added ingredients are introduced into the mix at one time, then upon proper heating in the manner hereinafter discussed subsequent microscopic study demonstrated that the bentonite was thoroughly encapsulated.

An important object of my invention, therefore, is to avoid in substantial measure the several disadvantages and defects which confronted the art as the same heretofore existed; to provide a new mode of utilizing the bonding element thereof, wherein the particles of binder are thoroughly coated with a suitable non-thermal setting carbonaceous material and substantially insulated from the foundry sand, which foundry composition involves the use of but limited quantities of specialized materials, is easily and rapidly produced in certain and predictable manner, which displays high green strength and only moderate developed or dry strength, and which possesses a high degree of porosity; and, as well, to provide a method of producing foundry compositions of the general type just described and possessing the general qualities just hereinbefore recited.

Keeping in mind that western bentonite is ordinarily employed in order that advantage might be taken of its well-known colloidal swelling qualities upon ,the presence of added water, giving increased dry or developed strength, it will appear that with the bentonite apparently losing its separate identity under microscopic study due to the encapsulation of the particles in the pitch or hydrocarbon, it would thereupon lose its swelling properties when water is added to mix of which it constitutes an ingredient. My studies have disclosed, however, that such is not the case; but that, on the contrary, due to some physical phenomenon as yet not fully understood by me, the normal swelling qualities of the bentonite are nevertheless displayed upon the addition of water, despite such encapsulation. In brief, I achieve upon the practice of my new mode of procedure, highly satisfactory results not heretofore appreciated nor believed to be possible. Such new process is attended by the use of a radically diminished mulling time-a phenomenon of great practical advantage in foundry practice coupled with a simplification of the manipulative steps, the use of simplified and inexpensive equipment, and a demand for labor of but moderate skill.

During the course of my investigations, and under microscopic study of sands coated with that plastic carbon or hydrocarbon known under the trade name of Vanadiset, concerning the use of which more will be said at a later point herein, and bonded with bentonite, and thereafter reacted with a solvent applied to the coating to enhance the chemical bonding action thereof, I discovered that upon shaking the sand out of the flask, sifting and preparing the same for reuse, the bentonite completely disappeared from the slide plate of the microscope as observed through the viewing aperture of the latter. At the same time, the bonding action of the bentonite persisted, substantially unabated. It was upon a consideration of the practical significance of this phenomenon that my present invention is predicated.

In research predicated upon my observations, therefore, I prepared a mechanical mix of a suitable non-thermal setting hydrocarbon, preferably a resin, and in the particular instance undergoing illustration, that known as Vanadiset, together with western bentonite.

Vanadiset is a non-thermal setting petroleum pitch which is substantially free of products that are volatile below about 550 F. It is black in the mass, fractures conchoidally and gives a brown streak on porcelain. The specific gravity at 77 F. is about 1.12 and the molecular weight about 3200. It softens at F. to 340 F. and is soluble in carbon disulphide, benzene and other aromatic solvents. Vanadiset essentially consists of asphaltenes 20% to 70%, asphaltic resins 5% to 15%, and oily constituents 26% to 51%, with carbenes not over about 1%. Chemical analysis reveals that it contains about 21% to 64% unsaturated hydrocarbons, with the fixed carbon content amounting to about 36% to 18% and the hydrogen content about 9% or less. The ash content is less than 15% of which vanadium is the principal constituent.- (See, United States Patent 2,409,437 and the Bulletin of October 1,

1947, of the Wilson Carbon Company, Inc., 60

East 42d Street, New York 17, New York.)

In making my mix I used substantially equal parts of each material, Vanadiset" and western bentonite. These were mixed for a relatively short time until an intimate admixture was obtained. No further treatment of this mix was involved at that stage in the process. I admixed the mechanical mixture thus obtained with unbonded sand, preferably comprising subangular particles; and thereupon heated the resulting product to a temperature of approximately 500 F. and mulled the same intimately for a short period oftime.

Examination of the resulting product disclosed that there was produced a sand which was coated with a smooth layer, which layer was comprised of a mixture of bentonite and petroleum resin. Microscopic study disclosed that no particles of bentonite were visible. This justified acceptance of the theory that the bentonite was insulated by a coating of pitch from contact with water.

As has been suggested hereinbefore, it would appear that by consequence, the addition of water would not be attended by swelling of the bentonite or increase of either its bonding action or of the dry strength of the sand attendant upon its use. Quite on the contrary, however, I have found that, upon activating the hydrocarbon by the addition of a liquid containing the three ingredients, Vanadiset," an aromatic solvent for the pitch, and additional water, the coating comprising a mixture of bentonite and petroleum pitch exhibited the qualities of a high degree of bonding action, a high green strength, and requisite developed or dry strength. Perhaps the addition of the aromatic solvent momentarily sweeps aside the hydrocarbon capsule and exposes the otherwise encapsulated bentonite to the action of the added water. I do not, however, desire to be bound by such explanation. Regardless of the exact reason why, my experiments amply bear out the conclusion that high bonding action and requisite green and dry strength are achieved, and that castings produced from molds formed of such sands display finish details as good or better than those produced from molds formed of coated sand mixed with bentonite and water to which was added a liquid-containing solvent and resin, that is to say, sands evolved in general according to the practice exemplified in the prior practice referred to.

The overlying advantage of my new procedure as contrasted with the known prior techniques, is the great saving in time and in the requirement of but a minimum of labor, and this relatively unskilled. Provided that the new procedure approximates the known techniques in satisfactory results, it is apparent that my new procedure not only involves the recognition of a new principles of operation, but incorporates many practical advantages.

In the practice according to my new technique, the bentonite is apparently protected from contact with water because of the pitch coating. Nevertheless, a highly satisfactory bonding action takes place between the bentonite and the sand, particularly upon the addition of the activating liquid.

Moreover, it is to be noted that while in the mulling or mixing of the bentonite-petroleum mixture with the sand, the bentonite was raised to a temperature at which its advantageous properties would normally be destroyed, nevertheless its bonding qualities apparently are in no wise impaired, while the thorough physical separation of the bentonite from the sand is ensured and the time of the process diminished. Moreover, although the Vanadiset and the bentonite are thoroughly intermixed, causing a. thick, impure layer of resin about the particles of sand, rather than a thin, pure protective coating such as is employed in the prior processes, yet my observations have been uniformly to the effect that the subsequent chemical activation of the treated sand by the addition of a petroleum base remains substantially unchanged, when viewed from a commercial standpoint.

.Despite the presence of the thick, impure layer of resin, rather than a thin, pure coating thereof. I have observed that the surface of the casting produced in molds formed of my new treated sand are better than usual. This indicates that no fusion to the surface of the cast metal occurs, even when iron and steels are employed, involving high pouring temperatures, either of the silica sand or of the bentonite. Apparently, therefore, it appears that my new procedure provides protection of the bentonite fromthe usual action of heat thereon, while at the same time it does not interfere with the bonding action thereof. As stated hereinbefore, however, I am unable to explain the exact nature of the bonding action of the bentonite in the practice according to my invention. I observe no wedge action of the bentonite; that is, no substantial tendency for the bentonite to concentrate at the angles formed between two sand grains. Neither is there a continuous layer of either bentonite or bentonite and water.

Hereinbefore, I have referred to the use of Vanadiset. It is, of course, possible to employ in the stead thereof any suitable non-thermal setting hydrocarbon. This carbonaceous material resists burning on or sticking of the sand or clay to the poured metal by insuring that a predominantly reducing atmosphere exists at and shortly after the time of pouring the casting from the molten metal. It should persist sufficiently long to permit the poured metal to solidify. Moreover, such materials should impart no substantial impairment to the flow and lay of the molten metal. It should offer little impairment to the green strength of the sand and should provide no appreciable increase in the dry or developed strength thereof. Porosity should remain substantially unimpaired, so that all gases and vapors flashed during the pouring operation may be quickly vented to the exterior without appreciable likelihood of damage either to the mold or to the casting. To satisfy the foregoing requirements, I find that the resin may be any suitable heavy hydrocarbon residue which is non-thermal setting in nature.

I desire that the hydrocarbon be non-thermal setting, so that the sand may be shaken out of the flask, and after the addition of a small amount of additional binder and carbonaceous material, be subjected toreuse in the preparation of additional molds. Typical of suitable petroleum products may be listed asphalts, asphaltites, hydrocarbons, carbonaceous materials, and the like. Vanadiset," which is a high-carbon, low-hydrogen, hydrocarbon produced from Venezuela crude oil, I find particularly satisfactory for my purpose. Its high carbon content, together with low hydrogen especially suits it for resisting scaling of the casting and burning on of the sandor clay.

The practice of my invention results inappreciable reduction of the mulling or mixing time when the sand is being used for the first time. As compared to an ordinary seven-minute mulling time, my new technique saves more than five minutes, or more than '70 Important time savings of this type are vital to successful foundry practice. Greater uniformity of the product is obtained since the bentonite and resin particles according to one practice of my invention are distributed before being worked into the sand. Minimum quantities of clay and hydrocarbon are therefore employed with resultant advantages in diminished working time, diminished labor costs, decreased costs of materials, increased porosity, diminished efiect on green and developed strength and increased ease of shaking out of the flask ,following pouring. The initial mulling cycle is simplified, since the only additive need be water, or water together with a suitable solvent.

Foundry compositions produced according to the practice of my invention display appreciable green strength with required moderate retained strength. Their ready flow and tamping qualities permit them to take sharp impressions, while the cohesion between the particles of the composition contribute towards resistance of marginal crumbling of the pattern. The carbonaceous coating resists the penertation of the molten metal into the body of the mold. Improved casting appearance results, due in part perhaps to the reducing atmosphere towards which this material contributes, in the region of and at the time of pouring the molten metal. Burning on and sticking of the sand and clay particles to the surface of the casting is prevented. I am able to produce cleaner and sharper castings, free from surface scale and other defects, so that but a minimum of subsequent grinding and pickling is required to condition them for use.

In connection with the foregoing, a further advantage from a manufacturing standpoint attends upon the practice of my invention. This concerns the brittleness of the hydrocarbon coating under conditions of rapid cooling. Should the pitch, asphalt, or petroleum hydrocarbon be first mixed with the sand and then heated, giving a smooth coating of the sand particles, nevertheless it is observed that when this material is rapidly mulled, in an attempt to increase unit production, particles of the coating will fiake oil. This is most undesirable, resulting in sticking of the sand particles to the casting, and in the production of a casting with rough surface detail. Should, however, the mixture of bentonite, together with resin or hydrocarbon, be used in the same process accordingto the practice of my invention, high production is made possible with minimized likelihood of spalling and in the substantial absence of defective castings or rejects. Perhaps in my new technique the bentonite serves as a cushion.

Further refinement attendant upon the practice of my invention is the increased cleanliness and control of the coating which for the first time is made possible. In this connection, it is to be noted'that ground and crushed petroleum resins such as Vanadiset are quite dusty. A definite, yet uncontrollable loss occurs when a mixture of resin and sand is placed in a dryer or heater. Not only is this undesirable, due both to the unpleasant natute of the dust particles, the hazard created thereby and the loss of material, but as well, there is possibility oi' the production of a non-uniform product. When, however, a hentonite-resin mixture is added to the sand, particularly in the presence of a small quantity of water, the dust loss is rendered inappreciable and a more uniform product results, possessing superior qualities.

In accordance with the practice of my invention, the quantity of added clay and carbonaceous material is insuflicient to affect detrimentally the porosity of the mold or to bring about increase of the dry strength 01' the latter. Since the same mixture or similar mixture of bentonite and resin'may be used to maintain the sand during the course of its use and reuse in the foundry, it is to be observed that the used foundry composition is susceptible of ready recovery and reuse with but little loss of material. Such reconditioning can be achieved with but minimum additives of carbonaceous ingredients and minimum reworking. Accordingly, a substantial quantity of petroleum and bentonite coating remaining on the sand, it follows that upon the admixture of but a small additional quantity of resin-bentonite mixture thereto, the used and screened sands are thoroughly conditioned for reuse. Thus, I admix about to three per cent by weight of the 50-50 bentonite-Vanadiset mix to the used sand, intimately admixing the same therewith and thereby conditioning it for reuse.

It is to be noted that since the heavy petroleum residue which I employ is non-thermal setting in nature, it does not case-harden in operation. Hence, the sand particles retain their desirable properties upon reuse.

The method is extremely rapid, and treated sands are prepared readily and in'simple manner with but minimum requirement of time and use of materials, and with the use of labor of but moderate skill. The admixture of the coating material with the sand is carried out in simple manner, while reclaiming and reconditioning is readily accomplished. All these and many other highly practical and advantageous results attend upon the practice of my invention.

While in accordance with the practice of my invention, as illustratively described above, the bond clay and resin are first mixed together in dry state, heated at 500 F. and then intimately mixed with silica sand by mulling. I find that satisfactory results are had by heating and mulling concurrently. This I achieve by dumping hot sand into the muller and accomplishing the mixing with the mixed binder before the temperature of the whole drops below about 350 F. Excellent results also are achieved where the muller itself is heated, as by a special heating chamber built around the shell of the muller, and the sand consequently heated by contact with the hot shell during the mulling operation.

Also, I find that certain benefits are achieved by mixing the bonding mix of clay and resin with silica sand in a rotary dryer. The combination of time and temperature in the dryer (sufficient to heat the composition to 500 F. or more) is such as to give a reasonably satisfactory coating of the sand particles. Although the results had are not as good as those achieved in accordance with the preferredembodiment of my invention, the manner of treatment is not as expensive either. For many classes of work, therefore, the alternative method is entirely adequate.

It is apparent from the foregoing that many modes of realization of my inventive concept will readily suggest themselves to those skilled in the art, once the present procedure is disclosed. Similarly, it will be apparent that many modifications of the present embodiment will likewise suggest themselves, all falling within the scope of my invention. Accordingly, I intend the foregoing disclosure simply as illustrative, and not by way of limitation.

I claim as my invention:

1. The method of producing treated foundry sands, comprising intimately and mechanically admixing about equal parts by weight of dry powdered western bentonite and dry powdered Vanadiset and heating the mixture and simultaneously mixing with silica sand particles at such temperature that the composition is maintained at approximately 500 F. for a suflicient time to encapsulate the bentonite particles in Vanadiset and to 'form a fused coating of the encapsulated bentonite on the particles of sand.

2. The method of producing treated foundry sands, comprising intimately and mechanically admixing about equal parts by weight of dry powdered western bentonite and dry powdered Vanadiset at a temperature of about 500 F. and mulling the mixture together with hot silica sand at temperatures of approximately 500 F. for the whole composition for a period slightly less than two minutes.

3. The method of producing activated foundry sands, comprising intimately and mechanically admixing approximately equal parts by weight of dry powdered western bentonite and dry powdered Vanadiset and mulling the same with silica sand particles at elevated temperatures such that the composition is maintained at a temperature of 500 F., and thereafter activating the mix thus obtained through the addition of a liquid containing an aromatic solvent and water.

' crete sand particles with the encapsulated ben- 4. Treated foundry sand consisting essentially of discrete-silica sand particles, with a thermally fused coating thereon initially consisting of powdered western bentonite and powdered Vanadiset admixed in about equal parts by weight, the bentonite being thoroughly encapsulated in the Vanadiset, and the mixture of bentonite and Vanadiset forming the thermally fused coating on the particles of sand.

5. Activated foundry sand consisting essentially of discrete silica sand particles having a thermally fused coating thereon consisting of a mechanical mixture of about equal parts by weight of powdered western bentonite and powdered Vanadiset and wetted by liquid contain ing an aromatic solvent, water and additional Vanadiset.

6. The method of reconditioning a foundry sand system, comprising mechanically mixing dry powdered western bentonite and dry powdered Vanadiset at a temperature of about 500 F. and mixing the same with used silica sand particles at such temperature and for such period of time to encapsulate bentonite in Vanadiset and to achieve a desired fused coating of distonite and Vanadiset. KENNETH RAY GRUBE.

REFERENCES CITED Z The following references are of record lin the file of this patent:

UNITED STATES PATENTS Number Name Date 2,159,952 Jones May 23, 1939 2,162,059 Chedic June 13, 1939 2,256,832 King Sept. 23, 1941 2,409,437 La Cross Oct. 15, 1946 2,432,702 Wallace Dec. 16, 1947 2,444,413 Weston July 6, 1948

Claims (2)

1. 3. THE METHOD OF PRODUCING ACTIVATED FOUNDRY SANDS, COMPRISING INTIMATELY AND MECHANICALLY ADMIXING APPROXIMATELY EQUAL PARTS BY WEIGHT OF DRY POWDERED WESTERN BENTONITE AND DRY POWDERED VANADISET AND MULLING THE SAME WITH SILICA SAND PARTICLES AT ELEVATED TEMPERATURES SUCH THAT THE COMPOSITION IS MAINTAINED AT A TEMPERATURE OF 500*F., AND THEREAFTER ACTIVATING THE MIX THUS OBTAINED THROUGH THE ADDITION OF A LIQUID CONTAINING AN AROMATIC SOLVENT AND WATER.
2. 4. TREATED FOUNDRY SAND CONSISTING ESSENTIALLY OF DISCRETE-SILICA SAND PARTICLES, WITH A THERMALLY FUSED COATING THEREON INITIALLY CONSISTING OF POWDERED WESTERN BENTONITE AND POWDERED VANADISET ADMIXED IN ABOUT EQUAL PARTS BY WEIGHT, THE BENTONITE BEING THOROUGHLY ENCAPSULATED IN THE VANADISET, AND THE MIXTURE OF BENTONITE AND VANADISET FORMING THE THERMALLY FUSED COATING ON THE PARTICLES OF SAND.