US2686727A - Additive composition for sand molds and method of making same - Google Patents

Description

Patented Aug. 17, 1954 UNITED STATES A'IENT OFFICE ADDITIVE COMPOSITION FOR SAND MOLDS AND METHOD OF MAKING SAME No Drawing. Application December 20, 1952, Serial No. 327,153

6 Claims. 1

This invention relates to the casting of metals, more especially ferrous metals, bronze and high melting-point metal alloys and has for its principal objects the provision of an additive composition for admixture with loose molding sand for use in making green sand molds that have excellent facing characteristics and a minimum factor of expansion, whereby smooth patterntrue castings can be produced that are essentially free from burnt-on sand grains and rat tails, or such other defects as cracks, buckles and the like that commonly result from excessive sand expansion and which castings can be readily stripped from adhering sand without resort to prolonged and expansive mechanical finishing operations. Other objects of the invention are the provision of a molding composition having an optimum degree of flowability, gas-permeability and afiinity for tempering water and which composition does not tend to cumulatively waterproof the sand heap from which supplies are drawn for the production of subsequent molds. Further objects of the invention are hereinafter set forth.

In my co-pending application, Serial No. 173,245, filed July 11, 1950, now Patent 2,622,963 issued December 23, 1952, there is disclosed an additive composition for admixture with naturally or synthetically bonded loose molding sand. Such compound is prepared by combining wood flour or like cellulosic flours with colloidal solid bitumen particles in such a manner that the flour employed remains absorptive of water and yet contains within its pores the bitumen in such a finely divided form that it does; not objectionably waterproof the cellulosic flour or molding sand admixed therewith. Such impregnated material acts not only as an ideal facing because of the heavy hydrocarbon vapors given oif by the bitumen present during a casting operation, which results in clean castings being obtainable when employing such material, but also acts to substantially inhibit and prevent expansion in sand molds formed therewith, due principally to the fact that the flour and the bitumen carried thereby burn away leaving practically no ash when molten metal comes in contact therewith, thus affording voids into which the hot sand particles can freely expand.

As set forth in said Patent 2,622,963 such additive composition is preferably prepared as follows:

1,000 lbs. of wood flour of any good commercial grade is introduced into a mulling machine of the usual type wherein two heavy wheels revolve over a pan. Between 25 and 100 lbs. of a Water-soluble starch derivative, such for example as dextrine either in a dry pulverulent state or dissolved in 50% of its weight of water, are then distributed in small increments over the wood flour and then, in turn, over this mixture is distributed, also in small increments, 1,000 lbs. of a water dispersion of colloidal discrete, solid bitumen, either native or pyrobitumen artifically produced, such dispersion containing about to 50% of such bitumen. Upon the introduction of the bitumen dispersion into the wood hour, the mulling Wheels are immediately started and then a very peculiar action occurs, viz., the bitumen dispersion starts to break under the dehydrolizing action of the wood flour and this action tends to remove the water from the dispersion. The bitumen used should be hard, i. e. neither sticky nor tacky. In fact, the penetration number of the bitumen so used should range from 10 down to zero at 77 F., grams, 5 seconds and preferably a bitumen having a penetration number of zero is selected. This is extremely important, as the bitumen, if it has any tack or any stickiness at all, will cause the particles of the wood flour to ball up to such an extent that the bitumen cannot be effectively distributed over the individual wood flourparticles and driven into the pores thereof.

Under the action of the muller and upon the removal of the water, by absorption, into the pores of the wood flour, the very fine colloidal particles of bitumen in the dispersion will be gradually dispersed and both absorbed and ad sorbed on and into the particles of wood flour, thereby resulting in an extremely even distribution of the bitumen in the mass of wood flour to the extent that the total mass will. contain 30%, approximately, of bitumen solids. The

, bitumen does not, however, afiect the water-ab sorbing capability of the wood flour; in fact, the retention of such property is essential to the proper distribution of the colloidal. bitumen throughout the wood flour mass. When molding sand is incorporated, as hereafter specified with such a mixture, the wood flour will still retain to an optimum degree its ability to absorb moisture from such molding sand.

The colloidal particles of the bitumen. employed by me in said prior additive composition, are so minute that even when melted by the heat of the metal they will be so quickly destroyed by such heat that they will have no opportunity to waterproof either the wood flour or the sand that has been admixed therewith. Moreover, the

Wood flour and bitumen on and in proximity to the inner surfaces of the mold are both destroyed on contact with molten metal, thereby leaving practically no ash, and consequently the sand grains upon expansion by heat will afforded voids to move into or, in other words, the s ace left when the wood flour and bitumen m is burned is converted to gas space into which the sand can expand. Somewhat further back in the mold, where the heat has'not been sufiicient to destroy the wood flour and bitumen, the heat of the sand may still be sufilcient to melt the bitumen but the particles thereof will be of minute dimensions that they will be readily absorbed by the wood flour without rendering it completely waterproof and, once absorbed by the wood flour particles, the bitumen is no long free to envelop and waterproof any gra. in proximity thereto.

While the foregoing additive composition and the molding composition prepared therewith represent an important contribution to the art of metal-=casting, nevertheless in practice it has been found that the same possess certain limita tions which it is the object of my present invention, hereinafter set forth in detail, to elimihate or overcome. For example, as a result of an intensive study, I have ascertained that when making such additive the amount of emulsified asphalt solids that can be introduced in the form of a spray into the wood flour, is, due to the high water absorption characteristics of such emulsion, limited to about 30% by weight of such wood flour, as the water content of the mix in creases in direct proportion to the amount of solid asphalt employed and if the latter exceeds about 30% so much water is carried into the mix that if the finished product is packed in paper bags not only do the same tend to separate at the seams but the additive composition tends to solidify during shipment and also the ship ping weight of the composition is unduly large.

I have also discovered as a result of the large scale commercial manufacture of such additive composition that if a colloidal dispersion of a phalt solids is sprayed through a nozzle or otherwise distributed in small increments over wood flour, only a very small portion of the colloidal asphalt solids penetrate into the capillary in terstices of the flour and the major portion of theasphalt adheres as a coating on the flour particles; This constitutes a rather serious disadvantage and further limits'the amount of asphalt solids that can be incorporated in the additive compound because even asphalt with a penetration as low as zero at 77 F., has a tendency to coalesce when subjected to pressure and consequently the coated particles, due to this tendency of the asphalt, will first coalesce into larger ones, then into still larger ones and so on until there is a clumping of the particles in the container in which they are packed and also agglomerates of coalesced asphalt particles are obtained that are larger than is desirable, with the result that there will be a tendency for the V spent particles of a mold prepared with said molding composition, containing the aforesaid additive compound, to become slightly waterproofed and of thereby having their usefulness for makin new molds impaired.

My investigations have led to the discovery that if a relatively weak or dilute dispersion of colloidal asphalt is sprayed or, otherwise added in small increments to wood flour it is possible to accomplish a much better penetration of the f asphalt particles into the capillary tubes or interstices of the wood flour than were a strong dispersion employed, with the result that much fewer colloidal solid particles of asphalt remain as a coating on the wood flour particles and hence there is far less coalescence of the externally deposited colloidal asphalt particles, with the consequence that no excessively large agglomerates or lumps thereof are deposited on the wood flour particles. However, the employment of such a dilute dispersion results in a reduction of the colloidal asphalt content of the mix which would be undesirable were it not for the fact that colloidal bituminous coal is employed to counteract this deficiency'of carbonaceous substances on the surfaces of the wood flour par ticles. Due to such dilution of the dispersion of colloidal asphalt particles, as compared with that employed in my aforesaid additive disclosed in my said prior application, a better penetration of the dispersion into the flour particles results and the water therefore is absorbed more rapidly into the capillary interstices of the flour carrying with it the colloidal asphalt particles. As a result of such supplementing of the asphalt content of the mix by colloidal bituminous coal it is possible to increase the volatile hydrocarbon content of the mix well beyond that obtainable when employing only an asphalt dispersion such as described in my prior application.

Among the other advantages of supplementing an asphalt dispersion with colloidal coal, which desirably is of a fineness of about ten microns or less whereby they tend to readily coat and adhere to the wood flour particles, is the reduction accomplished in the water content of the additive compound, namely from about 20% in my aforesaid additive compound disclosed'in my prior application to some 8%, a figure at which the moisture content of wood flour 'is about constant. This insures that the additive compound can be shipped in a dry, not a damp, state to users thereof, which condition is impossible'to attain when sufficient asphalt dispersion such as described in my prior application is employed to impart a 25% to 30% asphalt content to the additive composition." 7 Anotherivery fortuitous and quite unexpected development is the fact that, when bituminous coal is ground to a high degree of fineness, there is definite tendency for the coal to become somewhat greasy on its surface. This is due to the fact that bituminous coal is holding within its structure certain resins which impart there to a somewhat greasy or oily'feel; words, bituminous coal is a fatty coal and when broken down to the degree of subdivision of a colloidal nature, this fattiness has a tendency to become apparent on the surface of the particles, probably due to the pressure developed when the mill grinds these particles so finely. In any event, irrespective of the correctness of the foregoing explanation, the colloidal particles of coal are extremely waxy on their surface and they tend to stick to any other surface with which they come in contact. This property is made very good use of in this invention, as the coal particles, when admixed with the slightly dampened, cellulosic or wood flour particles, tend to stick to these particles even if admixed in a dry form, and this is a very important point in con nection with this invention, as, if the coal par ticles were not in themselves adherent or made adherentin some way, they would completely separate from the wood flour. This would be In other mass, if such should be done.

extremely disadvantageous, both from the standpoint of shipping and also from the standpoint of safety in the foundry as the above mix, if used without the coal adhering to the wood flour particles, would be so extremely dusty that it would be impossible to handle the same conveniently and would even constitute an explosion hazard. Furthermore, the mere fact that the coal exhibits this waxy quality and tends to adhere to any surface will cause it to tightly adhere to the wood flour particles and hence there will be no tendency whatsoever for the materials to segregate or even to dust. This is true even after all water has been driven out of the In other words, once the coal has come in contact with the wood flour particles, it loses its tendency to separate therefrom,

In carrying out the invention it is desirable to proceed as follows:

1,000 lbs. of a commercial grade of cellulosic flour, such as wood flour for example, is introduced into a mulling machine of the usual type wherein two heavy wheels revolve over a pan. Thereupon 500 lbs. of colloidal dispersion composed of 200 lbs. of water and approximately 300 lbs. of the above specified discrete bitumen, desirably asphalt which is of a particle size of less than about five microns in average diameter, is sprayed or otherwise distributed in small increments onto the flour while the same is being constantly agitated in the muller. .After the dispersion has been intimately incorporated in the flour, 1,000 lbs. of bituminous coal, of an average diameter of about ten microns or less and desirably in the millimicron range, say less than about one micron in average diameter, are thoroughly incorporated into the treated flour particles. Such final mix will have a total weight of 2,500 lbs. and contain approximately 24% of volatile hydrocarbons and but about 8% of water. This mix may be incorporated with molding sand, whether the same be naturally or synthetically bonded, either at the foundry or at the source of production of the sand and desirably the amount of such additive admixed with the sand should range between one-tenth to 5%, by weight of the sand.

.When a sand mold, prepared from a molding composition consisting of my improved additive admixed with molding sand, is employed for casting metal, there is little tendency for the heavy hydrocarbon ingredients therein to melt or envelop and consequently waterproof either the sand particles or the wood flour in the composition. On the other hand, had the additive employed been prepared by merely grinding the solid bitumen to a fine powder, approximating the fineness of wood flour, some 300 mesh, and then mechanically mixing the same while in a dry state with the wood flour, such bitumen would, due to its relative coarseness and also because of the fact that it would have a relatively low melting point, as do all bitumens, readily melt at the temperature prevailing in the mold and freely run around the particles of wood flour and molding sand, thereby rendering the same waterproof with the result that the spent sand heap would becomeunusable.

The term wood flour as employed herein is intended to include ordinary wood flour as. well as flour made from corn cobs, bagasse and like vegetable substances.

The term bitumen as employed herein is intended to include native and pyrogenous asphalts 6: and pitches, gilsonite and like substances capable of substitution therefor in my improved additive composition, whether the substances be native or artifiical.

The amount of cellulosic flour employed should desirably range from about two to ten times that of the bitumen solids in the dispersion that is admixed therewith.

Preferably I employ a residual asphalt having the following characteristics:

1. Penetration number, after distillation at 77 F., grams, 5 seconds, 0 to 5.

2. Solubility of asphalt solids in carbon disulphide, 95%.

3. Flash point COC (Cleveland Open Cup) 525 F., plus or minus.

4. Specific gravity 1.0 at 77 F.

5. Softening point by ring-ball method, 170 to 210 F. 1

6. A particle size of less thanabout two microns in average diameter.

I am well aware that it has been proposed to prepare an additive preparation for molding sand by dissolving petroleum asphalt in fuel oil and then admixing hard maple flour therewith. Such preparation is greasy and the amount of asphalt that can be employed therein is limited by the amount of fuel oil that carries the same. This is in turn limited by the ability of the hard wood flour to hold the fuel oil, sponge-like, to prevent it from separating out and staining the packages, usually paper bags, containing the same. This maple flour-fuel oil additive preparation also is objectionable in that its use necessitates the introduction of fuel oil into molding sand mixes which in turn cause molding difficulties. I specifically disclaim any such additive product from the scope of the appended claims.

The advantages realized from the employment of both a bitumen and bituminous coal in my improved additive composition will be appreciated when it is taken into consideration that the coal ingredient has a maximum volatile hydrocarbon content of but about 36% as compared with about 80% in the case of asphalt and like bitumens. Furthermore, the volatile hydrocarbons of bitumens have a much lower boiling point than those of bituminous coal and con sequently their facing values are substantially greater during a casting operation. Moreover, due to the dusting tendency of bituminous coal and the consequent difiiculties encountered in handling the same, it is not feasible to employ an amount of such coal in the additive composition that is in excess of by weight, of the cellulosic flour in the mix and even such a large amount would, if no bitumen were employed, impart a volatile hydrocarbon content to the mix of but about 18% exclusive of the volatile hydrocarbon content imparted to the additive composition by the bitumen.

The amount of water employed in the mix should be at least suflicient to moisten the coal and thereby minimize the dusting thereof to admit of the adequate handling of the latter and also suflicient to support the bitumen in suspension in the dispersion, such amount being at least 5% of the mix, by weight. On the other hand, the maximum amount of water employed should not, for the reasons set forth herein, exceed about 15% of the additive composition. Based on the weight of the cellulosic flour, the amount of water in the dispersion should range between about 12 and 37 95. 1

The amount of bitumen solids incorporated in the additive com 'oosition should range between about and 40%, by" weight, of the flour and the amount of bituminous coal, on the other hand, should be at least about'25% and 'not more than 115%, by weight of the flour.

Various changes in the ingredients and the proportions thereof, as well as in the method of thereof, of solid, non-tacky colloidal particles of a bitumen of an average particle size of less than about five microns in diameter and said flour also containing from' about'25% to 110%,

by weight of the flour, of colloidal bituminous coal of a particle size of less than ten microns average diameter, said product having an affinity for water at least sufficient to admit of its being tempered therewith when preparing sand molds in which the additive is a component part. I J

The method of making a product suitable for use as an'addit ive for loose molding sand, which consists in mulling together a 'cellulosic hour with an aqueous dispersion containing.

'rom about 10% to 30% of water and from about a 10% to 35%, by weight of the fiouiy'oi a hard,

non-tacky colloidal bitumen of a particle size of less than about five microns in average diameter and after so incorporating the bitumen in the cellulosic flour mulling into the mix from to 110%, by weight of the cellulosic flour,

or" bituminous coal of a particle size of less than about ten microns in average diameter.

3. The method of making a product suitable for use as an additive for loose molding sand, which consists in mulling together a cellulosic flour with an aqueous dispersion containing from about 10% to of water and from about 10% to by weight of the flour, of a hard, nontacky colloidal bitumen of a particle size of less than about two microns in average diameter and after so incorporating the bitumen in the cellulosic flour mulling into the mix from 25% to 110%, by weight of the cellulosic flour, of bituminous coal of a particle size of less than about one micron in average diameter.

i. A loose powdered product for use as an additive for loose molding sand, consisting essentially of discrete particles of a cellulosic flour containing from about 25 to 40% by weight thereof of solid, non-tacky colloidal particles of a bitumen of an average particle sizeof less than about five microns in diameter and said flour also containing from about to by weight of the flour, of colloidal bituminous coal and from 5% to 15% of water, said product have ing an afiinity for water at least suficient to i 6. A powdered product as claimed in claim 4 which has a bitumen content of at least 28%,

by weight, of the cellulosic flour and a water content "of not exceeding 10%, by weight of the product.

Beferences Cited'in the file of this patent UNITED STATES PATENTS V Number Name Date 2,558,402 Wallace June 26, 1951 2,622,963

Wallace Dec. 23, 19 5 2

Claims (1)

1. A LOOSE POWDERED PRODUCT FOR USE AS AN ADDITIVE FOR LOOSE MOLDING SAND, CONSISTING ESSENTIALLY OF DISCRETE PARTICLES OF A CELLULOSIC FLOUR CONTAINING FROM ABOUT 10% TO 40%, BY WEIGHT THEREOF, OF SOLID, NON-TACKY COLLOIDAL PARTICLES OF A BITUMEN OF AN AVERAGE PARTICLE SIZE OF LESS THAN ABOUT FIVE MICRONS IN DIAMETER AND SAID FLOUR ALSO CONTAINING FROM ABOUT 25% TO 110%, BY WEIGHT OF THE FLOUR, OF COLLOIDAL BITUMINOUS COAL OF A PARTICLE SIZE OF LESS THAN TEN MICRONS IN AVERAGE DIAMETER, SAID PRODUCT HAVING AN AFFINITY FOR WATER AT LEAST SUFFICIENT TO ADMIT OF ITS BEING TEMPERED THEREWITH WHEN PREPARING SAND MOLDS IN WHICH THE ADDITIVE IS A COMPONENT PART.