US3023113A - Foundry sand composition - Google Patents

Description

3,023,113 FOUNDRY SAND COMPOSITIQN Thomas E. Barlow, Mel-teary, 11L, assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Filed Dec. 22, 1958, Ser. No. 781,868

' Claims. (Cl. e38.8)

This invention relates to foundry sand compositions for use in casting molten metal and to a method of preparing these compositions. More particularly, this invention relates to molding sand compositions containing a carbonaceous material comprised of a high melting point asphaltic pitch and lignite.

Present and past foundry compositions used in the casting of molten metal have generally been comprised of a sand, a clay, water, and a carbonaceous material such as sea coal. In some instances a low melting point asphaltic pitch, or a mixture of bituminous coal and a low melting point asphaltic pitch has been employed as the carbonaceous component of the foundry sand composition. However, these compositions have a relatively low green strength. Furthermore, the low melting point asphaltic pitch is rendered non-water dispersible at the temperatures attained during the molding operation, and renders other solid components water repellent. For this reason the water repellent solids cannot be reused in additional molding sand compositions, since they would then impair the green strength thereof.

A similar foundry sand composition is disclosed by Burgess P. Wallace in US. Patent No. 2,686,727, issued August 17, 1954. Wallace admixes wood flour with a dilute aqueous emulsion of asphalt and finely divided bituminous coal having a particle size of less than 10 microns. The bituminous coal does not readily absorb the aqueous emulsion, and hence the pro-portion of aqueous emulsion in the mixture is limited to the relatively small proportion that can be absorbed by the wood flour. Furthermore, employing finely divided bituminous coal in this process, creates dusting and handling problems.

Other foundry sand compositions are comprised of a sand, a clay, a resin coated silica, and water (as described in US. Patent No. 2,444,413). While these compositions have been very useful, their green strength has not been high, and it is not possible to control the hot strength of these compositions over a predetermined temperature range. Also many of the present foundry compositions display a tendency to stick to and fuse onto the poured castings, resulting in imperfect surface detail, high cleaning costs, and appreciable defects in the surface finish thereof with accompanying high percentage of rejections, attended by rising production costs. Thus, a need exists for a foundry sand composition having good hot strength, good flowability, good green strength, and containing a carbonaceous component which remains water wettable and water dispersible upon drying.

A primary object of this invention is to prepare an improved foundry sand composition.

A further object of this invention is to provide a foundry sand composition with improved green strength.

Another object of this invention is to provide a foundry sand composition with good flowability.

Still another object of this invention is to provide a foundry sand composition with good hot strength and in which the hot strength can be controlled over a desired temperature range.

A further object of this invention is to provide a foundry sand composition that has an improved peel of sand from the casting.

Yet another object of the invention is to provide a novel additive for foundry sand compositions.

"ice

These and other objects will be apparent from the following detailed description of the invention.

The present invention, in one aspect, is a novel composition comprised of a mixture of lignite and an aqueous emulsion of a high melting point asphaltic pitch, which imparts superior strength and handling properties to foundry sand compositions when used as an additive thereto.

In another aspect, the invention comprises a method for the preparation of such compositions.

The method of this invention comprises suspending in water a finely divided high melting point asphaltic pitch to form an emulsion, admixing this emulsion with lignite to form a carbonaceous additive for foundry sand compositions, and further admixing the carbonaceous additive with a sand, a clay, and water. This carbonaceous additive material is essential and critical to the obtaining of the improved and unique features of the foundry sand compositions of this invention.

Foundry sand, when mixed with the clay and carbonaceous additive material and suitably compacted or molded by methods familiar to those skilled in the art, displays admirable resistance to penetration by molten metal, and at the same time effectively resists substantially all tendency towards fusing onto or sticking of the sand to the poured casting. The carbonaceous additive material contributes toward this result by insuring a predominantly reducing atmosphere at, and shortly after, the time of pouring the molten metal into the mold. The compositions possess improved green strength, while retaining permeability, so that all gases and vapors flashed at the time of pouring are quickly vented without danger either to the mold or to the casting.

Each of the elements of the foundry composition will now be described in detail. Typical foundry sands are composed mainly of silica and may be sharp (contain little or no naturally occurring clay), or naturally bonded (contain moderate or substantial amounts of naturally occurring clay). Other types of sands, such as zircon sand, alumina sand, carbon sand, and the like may be used in preparing the foundry compositions of this invention. The particle size of the sand commonly used for preparing the foundry compositions disclosed herein is intermediate in size between particles classed as silt and particles classed as gravel.

Clays suitable for the practice of this invention include southern bentonite, western bentonite, and fire clay. Clays are used in mixtures of foundry molding sands to bond the grains of sand together. Each type of clay contributes specific properties to the molding sands. Western bentonite produces high dry strength and high hot strength up to about 1500 F. Southern bentonite produces high green strength and high flowability. Fire clays produce relatively low green strength, in comparison to an equal Weight of Western or southern bentonite, but fire clay is more durable than bentonite, i.e., fire clay retains its bonding power after repeated use of the foundry sand composition containing it. Sands bonded with sufficient fire clay have the highest hot strengths at 2000 F. Changes in the properties of the molding sand can, therefore, be accomplished by using different clays or blends of two or more clays.

The carbonaceous material is comprised of a mixture of lignite and an aqueous emulsion of a high melting point asphaltic pitch. Any aqueous emulsion of a high melting point asphaltic pitch which remains substantially water wettable and water dispersible at temperatures attained during the molding operation can be employed as a component of the carbonaceous additive material. The term high melting point asphaltic pitch as used throughout the description and claims refers to any asphaltic pitch having a melting point above about F. The term emulsion, rather than suspension or slurry, is used throughout the description and claims to describe the mixture of water and asphaltic pitch, because the asphaltic pitch is in colloidal form when admixed with the water, having a particle size smaller than about 3 microns, and such a mixture is appropriately designated as an emulsion. Such emulsions of high melting point asphalts, when admixed with lignite, sand, and clay to form a molding sand composition and then used as a mold for molten metal. will readily reemulsify when contacted with water. In contrast to this, aqueous emulsions of low softening point asphalts, when treated in the same manner, do not reemulsify because they are converted to a form that is not water dispersible during the casting operation. In the latter case, the dried low softening point asphalts adhere to the surface of the other solid components in the foundry sand composition, rendering these solids water repellent, thus substantially inhibiting further binding and preventing re-use of the foundry sand composition. A further advantage of aqueous emulsions of high melting point asphalts over emulsions of low melting point asphalts is that when the former emulsion is admixed with lignite and the resulting mixture is used as a component of the foundry sand composition, a slurry of water, clay, sand and carbonaceous additive having a high solids content and a low viscosity can be prepared, thereby substantially reducing the amount of water required to obtain the desired consistency or flowability and improving the green strength of the molding sand composition. A preferred commercially available form of the aqueous emulsion of a high melting point asphaltic pitch is designated CB-190, a product of Continental Bitumens, Inc. The physical properties of CB-l90 are as follows: The softening point range of the asphaltic pitch component is from 190 to 205 F. The asphaltic pitch component is very hard and has a penetration number of at 77 F., 100 grams, and 5 seconds. This aqueous emulsion generally contains about 58.5% asphaltic solids and about 41.5% water, but the solid content may be around 55 to 60% by weight. There are presently no other standards by which this product can be measured, because it does not fall into the category of standard road grade or industrial emulsified asphalts This particular high melting point asphaltic pitch-water emulsion has the advantage of being water Wettable and water dispersible in used molding sands. Other asphaltic or petroleum base materials tend to waterproof the molding sands.

Any coal which meets the specifications for the class designated as Class IV, Lignitic, is ASTM Designation D388-38, Classification of Coals by Rank, can satisfactorily be employed as the lignitic component of the carbonaceous additive material. If desired, peat can also be employed as the lignitic component. Any coals falling within the aforesaid classes are designated as lignite or lignitic throughout the description and claims. The particle size of the lignite is preferably between about 50 and about 150 mesh, but may be finer or coarser if desired.

Because of the porous nature of the lignite employed in the instant invention, a relatively large proportion of the aqueous emulsion can be absorbed by the lignite, thereby permitting the use of concentrated emulsions of asphalt. Furthermore, it has been discovered that relatively coarse lignite can be effectively employed, i.e., particles in the size range around -50 +150 mesh, thereby eliminating the dusting and handling properties encountered when colloidal bituminous coal is employed, as in the prior art.

Lignite and the aqueous emulsion of high melting point asphaltic pitch are preferably premixed before admixing with the sand and clay, but they may be added separately to the sand and clay if desired. However, if lignite and the aqueous emulsion are added separately, a lower green strength and a higher demand for water are encountered. The emulsion and lignite are admixed in a weight ratio between about 0.5 and about 8 parts of emulsion per part of lignite, and preferably in a ratio between about 1:1 and about 2.5:1. Accordingly in the preferred embodiment employing CB-190, the weight ratio of asphaltic pitch solids to lignite is in the range of about 0.3:1 to about 4.7:1 and desirably from about 0.621 to about 1.46:1. If the weight ratio of emulsion to lignite is less than about 0.511, the resulting foundry sand composition has a low green strength, and requires a large amount of water. If the ratio is in excess of about 8:1, the foundry sand composition has an excessive hot strength which leads to defects in the castings. The mixture of lignite and emulsion, having a weight ratio in the range between about 0.5 :l and about 8:1, varies in consistency from a damp solid to a thick slurry or paste. This mixture which constitutes the carbonaceous additive material, is intimately admixed with the foundry sand, and clay in a suitable mechanical mixer such as a plug mill or sigma mixer. The resulting mixture is then shaped into the desired mold for receiving molten metal.

Some variation in the preparative procedure is, of course, possible. To illustrate, the clay may be mixed with the carbonaceous additive material before it is admixed with the sand. Also, the carbonaceous additive material may be admixed with the sand before the clay is intermixed.

Foundry sand compositions of this invention, having improved properties of green strength, hot strength, fiowability, and peel of mold from the casting are realized when the following components are present in the indicated weight proportions:

A mixture comprised of lignite and an aqueous emulsion of a high melting point asphultic pitch.

The proportion of clay added to the mixture varies with the type of clay employed. For example, when western or southern bentonite is employed as the clay component, the preferred proportion is between about 2 and about 7% by weight. However, when fire clay is employed, the preferred proportion is between about 9 and about 15% by weight.

Various modifications of the novel composition and method of this invention can be employed without departing from the spirit of the invention. For example, a minor portion, up to about 35% by weight, of the lignitic component of the carbonaceous additive material can be replaced with carbonaceous substances such as wood flour, coke breeze, or mixtures thereof. When the carbonaceous substance is employed to replace a portion of the lignite, the emulsion to lignite and pitch solids to lignite ratios discussed earlier are calculated as emulsion or pitch solids to lignite and carbonaceous substance.

The following examples, which were prepared in accordance with the general procedure set forth above, are intended to illustrate more specifically the foundry compositions of this invention. Juniata type sand, having an American Foundrymens Society fineness number of about was employed in each example. Weathered lignite obtained from the Kincaid mine, Minot, North Dakota, having a particle size in the range between about 50 and mesh, was employed in Examples 1 to 4.

In the examples, the green, dry and hot compressive strengths were determined in accordance with the procedures set forth in Foundry Core Practice, Harry W. Dietert, American Foundrymens Society, Chicago, Illinois. 1952.

The impact strength of the mixtures was determined in accordance with the procedures set forth in Foundry Sand Handbook, American Foundrymens Society, Chicago, Illinois, 1952.

For ease of consideration of the examples, data obtained therefrom are presented in tabular form. All parts and percentages are by Weight unless otherwise 3. The method of preparing an improved foundry sand composition which comprises admixing an aqueous emulsion of asphaltic pitch having a melting point above about 150 F. with lignite in a weight ratio of between 5 about 0.5 and about 8 parts of emulsion per part of specified. lignite to provide a weight ratio of asphaltic pitch solids TABLE I Types and proportions of components in foundry sand compositions Clay carbonaceous material Sand pro- Water Ex portion, prp..

percent Propor- Proporpercent Type tion, 1 Type tion, 1

percent percent 1 925 Southern bentonite. 5.0 1 part OB-1109: 1 part lignite 2. 3. 5 2 92. 5 Western bent0uite 5.0 1 part CB-190: 1 part lignite 2. 5 3.6 92. 5 0 5.0 4 parts (DB-190: 3 parts lignite: 1 part soft wood flour 2. 5 3.6 4 90 2 {Fire clay .1 4. 5 5 parts CB-190: 2 parts lignite 2.8 3. 4

Western bentonite 2.5 5 89. 0 Fire clay 9.0 Sea co 2.0 3. 9

1 Percent of total, dry basis.

TABLE II to lignite in the range between about 0.321 to about 4.7:1, Properties of foundry sand Composition and admixing the resulting mixture of emuls1on and 11gn.te with foundry sand and clay to produce a foundry Com ressi e Smn th Si sandcomposition, said mixture of emulsion and lignite p v g Impact, 30 being added in a proportion equivalent to between about Ex Hot f i g g 0.5 and about by weight of the foundry sand com- Green Dry (high) position. I

1 OUOQF 1 500%. 2 OOOQF 4. The method of preparing an improved foundry sand composition which comprises admixing an aqueous 1&6 103 78 148 173 32 35 emuls1on of asphaltic pitch having a melting point above 16,0 177 146 314 233 30 about 150 F. with lignite and a carbonaceous substance 2$ 3% selected from the group consisting of wood flour, coke 1113 76 77 117 s 15 breeze and mixtures thereof, the proportion of said carbonaceous substance in said mixture being up to about In the above tables, Examples 1, 2, and 4 are illustrative of the improved foundry composition of this invention, wherein the carbonaceous material is comprised of a mixture of lignite and an aqueous emulsion of a high melting point asphaltic pitch (CB-190). Example 3 is further illustrative of the improved foundry sand compositions of this invention wherein soft wood flour replaced of lignite in the mixture of lignite and aqueous emulsion of a high melting point asphalt (CB-190). Example 5 is presented for purposes of comparison to show that when the mixture of lignite and aqueous emulsion is replaced with sea coal, the green strength, dry strength and hot strength of the resulting foundry sand composition is reduced substantially.

Having now thus fully described the invention, what is desired to be secured by Letters Patent is set forth in the appended claims.

1. A novel foundry sand composition comprised of a mixture of between about 65 and about 96% by weight of sand, between about 1 and about 20% by weight of clay, between about 2.5 and about 5% by weight of water, and between about 0.5 and about 4% by weight of a carbonaceous material consisting essentially of lignite, an aqueous emulsion of asphaltic pitch having a melting point above about 150 F. and a carbonaceous substance selected from the group consisting of wood flour, coke breeze and mixtures thereof, the proportion of said carbonaceous substance in said mixture being up to about by Weight of the lignite, the weight ratio of said aqueous emulsion to said lignite and said carbonaceous substance being between about 1:1 and about 2.5 :1 and the weight ratio of asphaltic pitch solids to lignite and carbonaceous substance being between about 0.6:1 and about 1.46:1.

2. The novel foundry composition of claim 1 wherein said carbonaecous substance is wood flour.

35% by weight of the lignite, the weight ratio of said aqueous emulsion to said lignite and carbonaceous substance being between about 0.5:1 and about 8:1 and the weight ratio of asphaltic pitch solids to lignite and carbonaceous substance being in the range of between about 03:1 and about 4.7:1, admixing the resulting mixture with clay and foundry sand to produce a foundry sand composition, the proportion of clay being equivalent to between about 1 and about 20% by weight of the foundry sand composition, the proportion of sand being equivalent to between about 65 and about 96% by weight of the foundry sand composition, and the proportion of the mixture of aqueous emulsion, lignite and carbonaceous substance being between about 0.5 and about 10% by weight of the foundry sand composition.

5. A novel foundry sand composition comprising a mixture of sand, clay, water, and from about 0.5 to about References Cited ,in the file of this patent UNITED STATES PATENTS Wallace June 26, 1951 Wallace Aug. 17, 1954 OTHER REFERENCES Condensed Chemical Dictionary, pub. 1950 by Reinhold, New York, N.Y., page 397.

Claims (1)

1. A NOVEL FOUNDRY SAND COMPOSITION COMPRISED OF A MIXTURE OF BETWEEN ABOUT 65 AND ABOUT 96% BY WEIGHT OF SAND, BETWEEN ABOUT 1 AND ABOUT 20% BY WEIGHT OF CLAY, BETWEEN ABOUT 2.5 AND ABOUT 5% BY WEIGHT OF WATER, AND BETWEEN ABOUT 0.5 AND ABOUT 4% BY WEIGHT OF A CARBONACEOUS MATERIAL CONSISTING ESSENTIALLY OF LIGNITE, AN AQUEOUS EMULSION OF ASPHALTIC PITCH HAVING A MELTING POINT ABOVE ABOUT 150*F. AND A CARBONACEOUS SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF WOOD FLOUR, COKE BREEZE AND MIXTURES THEREOF, THE PROPORTION OF SAID CARBONACEOUS SUBSTANCE IN SAID MIXTURE BEING UP TO ABOUT 35% BY WEIGHT OF THE LIGNITE, THE WEIGHT RATIO OF SAID AQUEOUS EMULSION TO SAID LIGNITE AND SAID CARBONACEOUS SUBSTANCE BEING BETWEEN ABOUT 1:1 AND ABOUT 2.5:1 AND THE WEIGHT RATIO OF ASPHALTIC PITCH SOLIDS TO LIGNITE AND CARBONACEOUS SUBSTANCE BEING BETWEEN ABOUT 0.6:1 AND ABOUT 1.46:1.