US3219465A - Foundry mold coating - Google Patents

Description

United States Patent 3,219,465 FOUNDRY MOLD COATING Phillip F. Herkimer, Royal Oak, Neil M. Lottridge, In, Warren, and Douglas G. McCullough, Rochester, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Filed May 26, 1961, Ser. No. 112,755

7 Claims. (Cl. 106-3823) This invention relates to a Coating composition, which when applied to foundry sand mold and core surfaces, functions as an effective anti-veining coating to appreciably improve the surface finish of castings produced by the use of such a mold or core. In addition, the fluidity of molten casting metals, such as gray cast iron, malleable iron, spheroidal graphite cast iron, aluminum alloys and magnesium alloys, poured into contact with the coated mold or core is significantly increased. More specifically, the invention pertains to a foundry mold or core wash containing finely divided mica, corn cereal and wood flour suspended in a liquid carrier.

In the past it was frequently impossible to successfully cast some thin sections of the aforementioned metals except by superheating the casting metal, preheating the mold and/or substantially increasing the metallostatic pressure. Obviously it is desirable to eliminate these procedures. A principal object of the present invention, therefore, is to provide a coating for foundry sand molds and cores which materially increases the fluidity of molten casting metals contacting such molds and cores without employing superheat, preheated molds or undersirably high metallostatic pressures. As a consequence, sound castings of very thin section can be formed by conventional procedures. The term fluidity, as used herein, refers to that property of molten casting metal in contact with a mold which allows the metal to flow into the mold and fill it before solidification obstructs further flow of the metal.

The above and other objects of this invention are attained with a foundry mold and core coating comprising a slurry of mica or vermiculite powder, powdered corn cereal, wood flour and a liquid vehicle, such as methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, a chlorinated hydrocarbon, commercial mineral spirits or water. Small amounts of a suspension agent, a binder, a low-foaming, nonionic wetting agent and an antifermentation agent also may be beneficially included in the slurry. The coating composition thus provided is relatively inexpensive and can be readily applied to the mold surfaces by conventional means, such as spraying, dipping or brushing.

It will be understood that the term mold, as hereinafte'r generally employed, means a casting form which includes both molds and cores, this invention not being limited to the former. Likewise, the word sand" is used in its generic sense and is not restricted to silica particles.

This mica powder should constitute about 70% to 95% by weight of the solids content of the coating composition, while the amount of corn cereal to be used may vary from approximately 2% to of the weight of the solids. In general, the wood flour content can range between about 1% and 12%. The preferred solids composition includes approximately 75% to 90% by weight of mica powder, 4% to 14% by weight of corn cereal and 3% to 8% by weight of wood flour. For most applications the particle sizes of these powdered constituents should be between 80 and 325 mesh, although finer powders may be used.

The presence of the corn cereal permits the slurry to be handled more conveniently than the mold coatings ice heretobefore proposed for the same purpose. This is possible because of the lower liquid-to-solids ratio permissible with the new coating composition and the resultant faster drying time. The suspension is easier to apply to molds and cores, particularly by dipping, and its superior consistency reduces the amount of coating material lost due to dripping. Also, a smaller amount of wetting agent can be employed, and the wet-ting agent may be eliminated entirely for some applications. In addition, the presence of corn cereal permits a reduction in wood floor content with a consequent decrease in the amount of mold gas generated during pouring of the molten casting metal. As a result, the castings are sounder and less porous.

The coating slurry preferably is applied to green sand molds by a spraying procedure, and when this is done it is advantageous to mix the above-described powdered constituents with a volatile organic liquid, such as commercial methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, a chlorinated hydrocarbon or naphthol spirits. A slurry of this type also can be used to spray baked sand molds and cores, or water may be employed as a less expensive carrier if the molds and cores are subsequently reheated to dry the coating. Of course, in the case of baked sand cores, it is convenient to apply a water slurry by a dipping operation. When alcohol is used as the liquid carrier, any excess alcohol can be readily burned off.

In order to obtain a proper dispersion of the coating composition on the mold surfaces when a water suspension is used in a dipping operation, it is desirable to include a wetting agent. A low-foaming, nonionic wetting agent is preferred. Examples of such'a wetting agent are those available under the trade names Ir-62 Pluronic and L-64 Pluronic. Likewise the adherence of the coating to the mold may be further improved for some applications by adding a thickener or binder to the slurry. Methyl cellulose has proved to be a satisfactory water thickener, but other short-chained alkyl celluloses, such as ethyl cellulose, butyl cellulose and propyl cellulose, may be employed. Ceron N-4S also has proved to be an excellent suspension agent and binder. This water-soluble derivative of wheat starch is a nonionic, etherified polymeric carbohydrate. A water thickener of this type appreciably improves the dipping character istics of the slurry and increases the hardness and durability of the dried coating.

The amount of liquid carrier used should be sufficient to provide a slurry which can be readily applied to the mold. If it is desired to dip the mold, the ratio of the liquid carrier to the solids content of the coating composition may vary between approximately 4 to 1 and 10 to 1. On the other hand, this ratio may be as low as 2 to 1 for spray coatings. Thus it will be seen that the amount of liquid in the slurry may constitute about 65% to 91% of the total weight of the slurry, but a coating having a water content of approximately to is generally preferred.

When a wetting agent is used in the mixture, the addition of 0.5 gram to 2 grams of this material to 500 milliliters of slurry has proved to be adequate. In fact, as little as about 0.1% by weight of wetting agent improves the coating composition, and as much as 1% wetting agent Sometimes may be used to advantage. Dipping characteristics and slurry suspension are further improved when the composition contains Ceron N-4S in an amount equal to about 1% to 5% by Weight of the solids in the composition. Approximately 2 to 3 grams of this material added to 500 milliliters of the slurry has proved to be particularly effective. When methyl 3 cellulose is used it preferably constitutes approximately 0.2% to 1% by weight of the solids in the slurry.

In addition to the above-described constituents, urea formaldehyde or other soluble resins may be included agitated. In general, it is desirable to maintain the pH of the water between 5 and 7 because some of the solid constituents appear to disperse somewhat better in water which is slightly acidic. If urea formaldehyde is to be in the slurry, particularly if a wetting agent is to be 5 included in the coating, it is the last constituent added to used, to further increase the hardness and durability the slurry. The coating composition should be stirred of the dried coating. A relatively small amount of for several minutes and not used for at least four hours. other binder materials also may be added to the slurry N y it is pp to the Casting-defining surfaces of to improve the adhesion of the coating to the sand mold t ld at r m mperatureif the binder is soluble in the liquid carrier. Among 10 The following table lists specific examples of coating these binding agents are thermoplastic resins such as compositions prepared in accordance with the present inpolyvinyl chloride, vinylidene chloride, polyvinyl alcohol vention:

Example Example Example Example Example I II I IV V Water 100 gaL. 40 gal 500ml 800 m1. Isopropyl alcohol 300 m Mica powder (-160 mesh) 100111... 58.5 lb... 85 gm. Corn cereal 11lb. 3.411)--.. 10 gm. Wood flour (-80 mesh) 5.6 lb 3.4 lb 5gm. Wetting agent 300 grn 401111.-.. 1 lgrn. Ceron N-4S thickener 41b"... 1.67 lb.-. 4 gm. Calcined clay CuSO4-5H2O 0.241b. 60gm 02gm Phenol-formaldehyde resin and polyvinyl acetate, and thermosetting resins such as Each of the above coating compositions had excellent phenolformaldehyde and melamine formaldehyde. Of dipping characteristics, dried in a reasonable period of course, Various other binders besides the polymeric vinyl time and was hard and durable upon drying. In addiand phenolic resins can be employed, For example, tion, the coatings substantially reduced Chill in thin seclinseed oil and certain clays, such as bentonite cla tions and materially aided in the cleanup of the castings. are u eful as bi d tim t Furthermore, use of these coatings as compared with When a coating composition having mineral spirits or currently commercially used green Sand mold p y and al h l as th carrier i t b applied b Spraying, core washes significantly decreased metal penetration into tain thermoplastic, lignin-type resinous materials derived e meld and/01: Ceres, thereby improving the Surface from wood and containing both methoxyl and hydroxyl finlsh 0f the ngs in h ir a aSt eonditlon. groups have proved to be useful as additional binders if W ry Sand test molds were coated with the aboveincluded in the slurry in small amounts. Such materials described Shlffies, the fluidity of y Cast iron, malleable may be obtained from a variety of wood products, includiron and spheroidal g p Cast iron Poured at normal i d t waste li f h paper i d d casting temperatures into these molds was increased more chips, etc., by physical and/or chemical treatment. Illusthan 100% as comp With Similar meldsWhieh W r trative of one type of thermoplastic resinous material is uneoated- T i y 0f the molten m te-1 1n themolds a substantially gasoline-insoluble resinous material obwas deteflhlhed y means of a double SPITel fluldlty test tained by extracting a resinous wood with a coal tar e in Which One pir l i a ed With the mold wash hydrocarbon, removing the hydrocarbon by evaporation, Whlle the other remains uncoated, both being fed y leaving a residue comprising a mixture of wood rosin h Same Pellflhg basin and down P e- The relative and thermoplastic resinous material, and extracting the dlstahces the metel f l in Spiral IS a e Of rosin with a petroleum hydrocarbon, leaving a thermothe Improvement 1h h y- This e e de$1gI1 1I1d plastic resinous material. Such a product is available the Procedure for using it are described In Transa tlons under the trade name Vinsol. of the American Foundrymens Society, volume 67.

Of course, more than one binder may be used in the Pages 496 to coating composition, but the total binder content in ad- Tests have been conducted on Castings of y iron, dition to the corn cereal normally should not constitute malleable iron, spheroidal g p Cast iron and umimore than about 5% of the weight of the solids in the hum alleys Which Were f m d in molds coated in acti t i l, E 05% b Weight f th ddicordance with this invention. As a result of these tests, tional binder in the coating causes it to adhere more it Was found that these metals Could he Successfully east strongly to the mold. in thin sections by using the above-described mold wash A water Slurry t i i d fl com cereal and that the resultant castings all had exceptionally high and/ or Ceron N-4S will ferment after a relatively short ultimate tensile hg d nesstime, thereby reducing the bonding action of the Ceron p thlek seetlons of gray iron cast N 4S a d th com l, H we h fo d it d in green sand mold portions coated with this mold wash sirable to include a small amount of an antifermentation were compared with g y Specimens of th ame agent to retard the growth of bacteria. Copper sulfate, composition f heh thlek se lons cast in the potassium chromate, sodium chromate, sodium hypersame molds without a The f I1 th chlorate, urea formaldehyde and paraformaldehyde all h thlek Seetlons had pp y hlghef llltlmate have proved to be useful for this purpose. Shelf life e g an ardness than the cast iron in the A6- of an aqueous slurry has been increased from approxih th lek Seetlohs- {\tteInPtS to Cast -ln hl k seemately 3 days to more than 2 we k because f th titlons without first coatlng the surfaces of the mold cavities b t i l ti f h an ddi i were unsuccessful because the molten metal would not The above-described coating slurry may be prepared P p y feed i fill t e narrow mold cavities. in the following manner: The dry materials, such as the The gray cast lI'OIl WhlCh did feed lnto these /8-111Ch mica, com cereal d d flour, are preferably fi t cavities of uncoated molds was chilled, and hence these blended to powder form. Next, the wetting agent is Peftlehs 0f the Castlhgs were hard, brlttle d unmaadded to the desired amount of water, assuming an chinable. Green sand molds, each having two cavities aqueous slurry is to be used; and the blended solids are o r inches Wide and 18 inches l g, With ns 43' introduced slowly into the slurry while the latter is being inch and -inch deep, were used 1n these tests.

It was further noted that the microstructure of the /sinch thick sections of gray iron castings poured into the coated mold portions was slightly more refined than the microstructure of gray iron specimens cast into the A inch thick uncoated portions of the same mold. No primary carbide was evident in either section.

Additional tests under production conditions also showed that use of the new mold coating improved the surface finish of the castings and decreased the incidence of veining, thus greatly reducing the amount of labor necessary in cleaning operations. Moreover, the coating prevented misruns and cold shuts. As a consequence, leakers were eliminated, and the scrap rate due to such defects was lowered from approximately 9% to less than 1%. Furthermore, the mold coating described herein has a relatively short drying time and a wide drying temperature range. It may be dried at a temperature up to approximately 500 F. without blistering and coatings on port cores for gasoline engine cylinder head castings were dried in only about five minutes at 500 F. This coating composition also has good dipping characteristics and is uniform in thickness both before and after drying, as Well as being relatively inexpensive to use.

While our invention has been described by means of certain specific examples, it is to be understood that its scope is not to be limited thereby except as defined by the following claims.

We claim:

1. A slurry for coating casting-defining surfaces of foundry sand molds, said slurry being formed from a dry blend consisting essentially of about 70% to 95% by weight of mica powder, about 2% to 20% by weight of corn cereal and about 1% to 12% by weight of wood flour to which has been added a liquid carrier in an amount sufficient to constitute about 65% to 91% of the total weight of said slurry.

2. A coating slurry for application to casting-defining surfaces of a foundry mold, said slurry consisting essentially of a liquid carrier and a dry blend, said dry blend consisting essentially of about 75% to 90% by weight of mica powder, about 4% to 14% by weight of corn cereal and about 3% to 8% by weight of wood fiour, said liquid carrier being selected from the group consisting of methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, mineral spirits, naphthol spirits and water in proportions such that said dry blend constitutes approximately 15% to 25% of the total weight of said slurry.

3. A coating slurry for application to casting-defining surfaces of a foundry mold, said slurry consisting essentially of about 65% to 91% by weight of water and about 9% to 35% by weight of a dry blend, said dry blend consisting essentially of about 70% to 95% by weight of mica powder, about 2% to 20% by weight of corn cereal, about 1% to 12% by weight of wood flour and about 1% t by weight of a nonionic, etherified polymeric carbohydrate, the particle sizes of said mica powder, corn cereal and wood flour not exceeding approximately 80 mesh, said slurry containing about 0.1% to 1% by weight of Wetting agent.

4. A coating composition for application to castingdefining surfaces of a foundry sand mold, said composition consisting essentially of a suspension of a powder in water, said powder consisting essentially of, by weight, about 75% to 90% mica, 4% to 14% corn cereal and 3% to 8% wood fiour, said suspension containing a polymeric organic binder in an amount not in excess of about 10% of the weight of said powder.

5. A foundry mold for use in producing a metal casting having at least one thin section, said mold being formed of foundry sand and having casting-defining surfaces provided with a thin coating consisting essentially of about to 95% by weight of mica, 2% to 20% by weight of corn cereal and 1% to 12% by Weight of wood flour.

6. A foundry mold for use in producing a metal casting having at least one thin section, said mold being formed of foundry sand and having casting-defining surfaces provided with a thin coating formed by applying to said surfaces a slurry consisting essentially of a liquid carrier and a dry blend, said dry blend consisting essentially of about 70% to 95% by weight of mica powder, about 2% to 20% by weight of corn cereal, about 1% to 12% by weight of wood flour and about 1% to 5% by weight of polymeric carbohydrate and a small amount of an antifermentation agent, the amount of liquid carrier being sufficient to constitute about 65% to 91% of the total weight of the slurry.

7. A foundry mold for use in producing a metal casting having at least one thin section, said mold being formed of foundry sand and having casting-defining sur faces provided with a thin coating formed by applying to said surfaces a slurry consisting essentially of a dry blend suspended in a liquid carrier, said dry blend consisting essentially of about to by weight, of mica powder, about 4% to 14%, by weight, of corn cereal, about 3% to 8%, by weight, of wood flour, the amount of liquid carrier in said slurry being sufiicient to constitute about 65% to 91% of the total weight of said slurry, said liquid carrier being selected from the group consisting of methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, mineral spirits, naphthol spirits and water.

References Cited by the Examiner UNITED STATES PATENTS 1,858,083 5/1932 Goldsmith 10638.24 2,735,814 2/1956 Hodson et al 10638.24 2,798,817 7/1957 Lund 10638.23 3,115,414 12/1963 Lottridge et a1. 10638.23

OTHER REFERENCES Websters New International Dictionary, 2nd Edition, G. and L. Merriam Company, Springfield, Massachusetts, 1959, (page 725).

ALEXANDER H. BRODMERKEL, Primary Examiner.

JOHN R. SPECK, LESLIE H. GASTON, Examiners.

Claims (1)

1. A SLURRY FOR COATING CASTING-DEFINING SURFACES OF FOUNDRY SAND MOLDS, SAID SLURRY BEING FORMED FROOM A DRY BLEND CONSISTING ESSENTIALLY OF ABOUT 70% TO 95% BY WEIGHT OF MICA POWER, ABOUT 2% TO 20% BY WEIGHT OF CORN CEREAL AND ABOUT 1% TO 12% BY WEIGHT OF WOOD FLOUR TO WHICH HAS BEEN ADDED A LIQUID CARRIER IN AN AMOUNT SUFFICIENT TO CONSTITUTE ABOUT 65% TO 91% OF THE TOTAL WEIGHT OF SAID SLURRY.