US2786771A - Core wash - Google Patents

Description

2,786,771 Patented Mar. 26, 1 957.

CORE WASH Ernest L. Waterhouse, Vassar, and Lawrence L. Zinsmeister, Saginaw, Mich., assignors to Eaton Manufacturing Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application July 7, 1952, Serial No. 297,575

13 Claims. (Cl. MIG-38.28)

The present invention relates to a core Wash. More particularly this invention concerns improved core Wash compositions especially suitable for coating sand cores for use in gray iron or alloy steel casting in permanent molds.

In foundry practice, sand cores are customarily employed in conjunction with sand molds when it is desired to cast articles having cavities therein. The mold walls are permeable to gases, and any gases generated during the casting operation are automatically vented through the sand mold wall. In the casting of gray iron articles using permanent cast iron molds in conjunction with dry sand cores, difiiculty has been experienced for a long time in the elimination of burn-on or surface roughness in the surface of the castingin contact with the core. Gases which are generated during the casting operation apparently tend to penetrate the sand core and to carry the molten metal into the surface so that a rough surface is obtained on the casting.

It is, therefore, the principal object of the present invention to provide a coating composition for sand cores or a core wash composition which eliminates burn-on on sand cores used in conjunction with permanent molds.

Another object of the invention is to provide an improved core wash which provides uniform coverage of the cores and a core coating free from tears and water breaks.

A further object is to provide an improved core wash which is highly refractory and capable of withstanding extremely high pouring temperatures and producing exceptionally smooth finish on the surface of the casting" adjacent to the core.

A still further object is to provide a method for treating sand cores with the core wash of this invention, and in general to provide both a core'wash composition for treating sand cores which is easy of manufacture, utilizes commercial materials which are available and non-toxic, and a method which is simple, rapid and inexpensive.

Other objects and advantageous features of the invention will be specifically pointed out or will become appar cut when the present disclosure is considered in its entirety.

In general the improved core wash compositions of this invention comprise as essential ingredients, calcium oxide, magnesium oxide, water, graphite and an alkali metal carbonate. The graphite is preferably in the form of flakes and the calcium and magnesium oxides are preferably present in excess of the amount required to react with all of the alkali carbonate which is present. If desired, for special applications, small quantities of talc and a resinous or gum binder may also be added and small proportions of carbon in forms other than flake graphite may be used.

The relative proportions of the essential ingredients which may be employed for the purposcs ofithis inven-.

tion are given in Formula I.

FORMULA I Concentration, percent Calcium oxide 21.0-30.0 Magnesium oxide 2.6- 4.0 Flake graphite 46.5-65.0 Carbonate (as alkali metal carbonate) 1.0 5.0

Water to make The quantities of essential ingredients together with some other ingredients which are not essential but which are beneficial for particular applications are shown in Formula II.

1.4- 1.6 Water to make 100%. t

The presence of the binder in Formula H tends to increase the adherence to the core surface and to facilitate the build-up of relatively thick coatings on the core surface where desired. Talc and finely ground carbon of the amorphous type such as lampbiack, tend to supplement and fill in the interstices of the layered flake graphite and to increase resistance to penetration of the core surface by the molten metal.

The calcium oxide and magnesium oxide are believed to function jointly as an adhesive and penetrant for securely attaching the minute, smooth leaf-like particles of graphite to the surface of the core and as a refractory filler to supplement the graphite coating and to fill any uncoated areas so as to present a uniformly covered core surface. While calcium and magnesium oxides are preferred, the oxides of other metals may be used to replace 'calcium or magnesium, such as cadmium or zinc, insubstantially equivalent amounts. Some alkaline earth metal carbonate is thought to be formed from the reaction of the alkali metal carbonate and the alkaline earth metal oxide and this carbonate lends hardness to the coating.

The alkali metal carbonate may conveniently be added in any of the various hydrated forms such as soda ash or sodium carbonate decahydrate, potassium dior trihydrate or ammonium carbonate mono hydrate, etc. Soda ash is preferred for commercial use because of its availability and cheapness.

In the presence of an auxiliary binder such as a natural gum or mixture of natural gums in powdered form, it is unnecessary that the carbonate be present. A gum mixture of gum tragacanth and gum arabic in the preparation of Formula II, for example, forms a satisfactory wash composition in the absence of any carbonate and yet provides substantially similar hardness and increased adhesiveness'of the coating. As the proportion of gum binder is increased, the tendency for the formation of tears or runs is increased until at quantities above about 2.5%, the uniformity of coverage is below standard and undesirable. In the absence of carbonate, the proportion of gum is preferably maintained between about. 2.2% and 2.5%, but in the presence of carbonate, the proportion may decrease down to a lower limit of about 0.8%. The effect of gum on the adhesiveness of the coating is not sufficiently pronounced at quantities below about 0.8% to make its use desirable, and such smaller quantitiesare n r s en s W using casein a an ili ry binder, a carbonate should be used concurrently inasmuch-as. the degree of enhancement of coating adhesion is-somewhatlessthan is obtained with gumbinders. Pro: portions of casein above about 1% confer little improve ment and are not recommended for use.

The presence of quantities of carbonate in excess of that shown in Formulas I and II causes the formation of water breaks or unevenness of coating in which certain areas are practically devoid of coating whereas proportions below about 1% are of little benefit in increasing coating hardness.

The compositions of this invention may be applied in dilute aqueous form to the surface of dry sand cores by dipping, spraying or brushing, as desired. The sand cores which may be improved by such treatment include sand cores fabricated in accordance with conventional foundry practice using core oil or resin bonded sand cores made by the shell molding process. No disadvantage in use or in compatibility has been observed be tween the ingredients of the compositions of this invention and the fully polymerized resinous constituents of the sand cores manufactured by the shell mold process.

The compositions of this invention may be formulated and applied to sand cores in a variety of specific ways. The following procedure of compounding and treating the surface of sand cores is given by way of illustration. The various ingredients of the below given Example I, being in finely ground condition are uniformly admixed in a tumbler, rotary mixer, muller mixer or the like.

Onehundred pounds of the mixture are added to about 12 gallons of water in a rotary mixing drum. The mixture is preferably added slowly after the mixer is started and thorough mixing is obtained in about one-fourth to one-half hour producing a relatively viscous concentrate. The concentrate is then diluted to the desired consistency by the addition of water during rapid agitation with a suitable agitator such as a propeller type mixer. The most desirable consistency will vary with the depth of coating desired, the shape of the core, the size of the casting being made, the temperature of pouring, etc. and may be readily determined by a few simple experiments under operating conditions. In any event, a satisfactory consistency will normally be found between 20 B. and 60 B. and for best results a consistency between about 36 B. and 46 B. is recommended. The thicker aqueous mixtures are suitable for brush application while the thinner mixtures may be used in spraying. the aqueous mixture is continuously agitated, the sand core is dipped, sprayed or brushed with the aqueous mixture and the mixture dried on the core preferably at an; elevated temperature such as 500 F. to 1000'F. for-about three to ten minutes, asrequired. Thesand core is coated with a uniform film having a thickness on the order of about 0.002 to 0.010 thick which is free of cracks and blisters. The use of such cores in the casting of gray iron articles in permanent molds at temperatures of about 2700 F. to 2800 F. produces a surface on the casting adjacent to the core which is smooth and "free from bubbles or pock marks. The cores peel cleanly from the castingand are easily disintegrated.

The-compositions of this invention are sufficiently heat resistant to withstand metal pouring temperatures ashigh as about 3500 F. without any disruption of the coating from the inflow of molten metal. Such compositions are extremely useful in the casting of alloy steels, but, of

'course, because of the carbon content of the compositions, their use'shoul-d be restricted-to high earbonalloy steels.

While 1 Especially goodcastings having smooth surface finish adjacent the v.cnrahave. been .cflatainedv f om the use of sand cores, the surface of which was treated with the formulations of Examples II and III.

Flake graphite in rrr:--r.-.-9v..-vr..-r---r "-7 Example II] Percent Calcium oxide c, 25.0 Flake graphite 64.8 Magnesium xid r-r-fr-rrrrr- -r--?r: Soda ash 5.2

Casein 0.8

All percentagesused in the foregoing examples and in the appended claims are percentages by weight.

at s cl i e is;

1. YA composition for treating sand cores consisting essentially of 21% to 30% calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5% to 65% flake graphite, carbonate, as alkali metal carbonate, in an amount of 1% to 5.0% and the balance Water.

2. A composition .for treating sand cores consisting essentially of' 21% to 30% calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5% to 65% flake graphite, 8.3% to 10.9% tale, 2% to 2.5% natural gum binder, 1.4% to 1.6% amorphous carbon, and the balance Water.

3. A composition for treating sand cores consisting essentially of 21% to 30% calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5% to 65.0% flake graphite, 8.3% to 10.9% talc, .8% to 2.5% natural gum binder, 1.0 to 5.0% .carbonateas alkali metal carbonate, 1.4% to 1.6% amorphouscarbon, and the balance Water.

4. A composition for treating sand cores for use in conjunctionwith permanent molds which comprises an aqueous mixture consisting essentially of 21% to 30% calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5% to 65% graphite, carbonate as alkali metal carbonate in an amount of 1% to 5.0% and the balance water, said aqueous mixture having a specific gravity in the range of -36? B..t o 46 B.

5. A composition for treating sand cores for use in conjunction with permanent molds which consists essentially of 26.3% calcium oxide, 2.6% magnesium oxide, 56.0% flake-graphite, 9.7% talc and 5.4% soda ash.

6A;scrap .i:t a for eat n and o s or use in conjunction with permanent molds which consists essentially of 22.1% calcium oxide, 4.4% magnesium oxide, 59.1% flake-graphite, 10.4% talc, 1.5% lampblack and 2.5% natural gum binder.

7. Acornposition for treating sand cores for use in coniunct on. ith srmarsntmqld ish ns ent a o ZS-0% salrium e is s. 64.8% flake a h e. m

nesium oxide, 5.2% soda ash and 0.8% casein.

8, The methodof coating a sand core which comprises the steps-of contacting the surface of a sand core with an aqueous mixture consisting essentially of 21% to 30.0%

calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5% ,to 65% flake-graphite, carbonate, as alkali metal carboasts. n. aaa uoumof t an t balance ater.-

' 9. The method of coating a sand core which comprises the steps of contacting the surface of a sand core with an 10. The method of coating a sand core which comprises the steps of contacting the surface of the core with an aqueous mixture consisting essentially of 21% to 30% calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5% to 65% flake graphite, 8.3% to 10.9% tale, .8% to 2.5% natural gum binder, 1.0% to 5% carbonate as alkali metal carbonate, 14% to 1.6% amorphous carbon and the balance Water.

11. The method of coating a sand core which comprises the steps of contacting the surface of the core with an aqueous mixture consisting essentially of 21% to 30% calcium oxide, 2.6% to 4.0% magnesium oxide, 46.5 to 65% flake graphite, carbonate as alkali metal carbonate in an amount of 1% to 5.0% and the balance water, said aqueous mixture having a specific gravity in the range of 36 B. to 46 B.

12. A sand core having on the surface thereof a dried continuous refractory coating consisting of calcium oxide, magnesium oxide, flake graphite and calcium carbonate, said coating resulting from the application of and the drying on the surface of a sand core the composition of claim 1.

13. A sand core having on the surface thereof a dried continuous refractory coating consisting of calcium oxide, magnesium oxide, flake graphite, calcium carbonate and talc, said coating resulting from the application of and the drying on the surface of a sand core the composition of claim 2.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Dona, Manual of Mineralogy, copyright 1912, page 186.

Claims (1)

1. A COMPOSITION FOR TREATING SAND CORES CONSISTING ESSENTIALLY OF 21% TO 30% CALCIUM OXIDE, 2.6% TO 4.0% MAGNESIUM OXIDE, 46.5% TO 65% FLAKE GRAPHITE, CARBONATE, AS ALKALI METAL CARBONATE, IN AN AMOUNT OF 1% TO 5.0% AND THE BALANCE WATER.