US3121269A

US3121269A - Mold wash

Info

Publication number: US3121269A
Application number: US71446A
Authority: US
Inventors: Jr Paul J Neff
Original assignee: Amsted Industries Inc
Current assignee: Amsted Industries Inc
Priority date: 1960-11-25
Filing date: 1960-11-25
Publication date: 1964-02-18
Anticipated expiration: 1981-02-18

Description

United States Patent 3,121,269 MGM) WASH Paul J. Nefi, .in, Lansing, Ill, assiguor to Amsted industries Incorporated, tlhieago, Ill, a corporation of New Jersey No Drawing. Filed Nov. 25, 196%, Ser. No. 71,446 ll Claim. (Cl. 22--2l6.5)

This invention relates to shell molding and particularly to the elimination of surface defects in low carbon, low alloy steel castings produced in conventional shell molds.

Shell molds, as well known in the art, are generally formed of a mixture of zircon or silica sand and a thermosetting phenolic resin either in powder form or in a solvent. If desirable, dust suppressants may be used and in some instances a release agent may be incorporated into the mixture to prevent the shell from adhering to the pattern which is heated during the forming of the shell to set the resin.

Although such molds ordinarily produce commercially acceptable iron castings and stainless steel castings, it is well known that low carbon, low alloy steel castings, such as those formed, for example, of grade B steel, are subject to various sunface defects when formed in such molds. The so called characteristic surface defects of such castings, such as blow holes, porosity, pock marking and the like, are generally completely eliminated by the utilization of a mold Wash comprising certain metal oxides as disclosed and claimed in US. Letters Patent 2,847,741. It has been found, however, that the metal oxide washes, while effective to eliminate characteristic shell mold defects, were not completely effective to eliminate other types of defects. For example, when structures were cast having configurations which tended to form localized hot spots due to unequal sectional thicknesses, or to the merging of metal sections, the metal surface at the localized areas contained a roughness comprising globular protuberances or What are commonly called positive type surface defects.

Accordingly, the primary object of the present invention is the elimination of surface defects from low carbon, low alloy steel casting formed in shell molds, particularly those surface defects which are of the positive type.

According to the invention, it is theorized that the roughness, or positive type defects, are caused by a recarburization efiect in localized areas after the formation of a metal skin. Such carburization lower the melting point of the metal. As a consequence, the metal which had solidified and formed the skin remelts and then bleeds or drips because the bulk of the metal is cooling, contracting, and pulling away from the mold.

According to the present invention, when a highly oxidizing wash is applied to the surface of the shell mold, the carburizing and consequent remelting of the metal apparently do not occur and the positive type surface defects together with the typical shell mold defects are elfectively eliminated. In view of the fact that the mold wash is generally applied to a warm mold, which may be at a temperature of approximately 200 B, it is preferable that the agent utilized for a wash does not decompose or liberate oxygen at a temperature of less than 250 F. Of course, if an unheated mold is to be coated, the decomposition or oxygen liberating temperature may be as low as slightly above room temperature. It is essential 3,l2l,2 Patented Feb. 18, 1954 that the decomposition temperature of the wash, either alone or in the presence of a catalyst, is less than the melting point of the metal to be poured and, preferably, the decomposition temperature should be less than about 1500" F. in order that the oxygen will be liberated quickly enough to accomplish its intended purpose.

The oxidizing agent, in order to be applied to a shell mold surface in sufiicient quantities to be effective, must be rather highly soluble in Water or in other solvents, such as for example, alcohol. It is prefer-able also that oxidizing agent should be non-toxic upon decomposition and for practicability should be commercially available at a reasonable cost.

The following table sets forth various chemical agents which were coated on shell molds in which were poured low carbon, 10W alloy steel castings. The table also sets forth the decomposition temperature, the solubility and the effectiveness of each agent in eliminating positive type surface defects.

The above table indicates clearly that the effectiveness of the agent utilized for a wash lies in the release of oxygen at the time of casting which influences the mold atmosphere in such a manner, apparently by converting the carburizing carbon monoxide to non-carburizing carbon dioxide, that carburization and remelting of the cast metal cannot occur. For example, agent number 8, namely, sodium borate, might be expected to be as effective as agent number 3, sodium nitrate. However, it will be noted that sodium borate is only slightly soluble as compared to sodium nitrate and, for this reason, it is impossible to apply a suflic-ient amount of sodium borate to the mold surface to provide an effective quantity of oxygen. Similarly, it might :be expected that agent No. 7, potassium perchlorate, would be more effective than agent No. 6, potassium chlorate, due to the fact that the former has a greater amount of oxygen available for a given weight of the agents. Once again, however, the potassium perchlorate, having extremely low solubility, was less effective. The potassium chlorate, having a higher solubility rating, was fairly effective but still was less effective than the first five agents listed, all of which were much more soluble. It will be noted also that agents 10 and ll, namely manganese dioxide and titanium dioxide, which were effective in eliminating characteristic defects, are practically insoluble and also ineffective to eliminate positive type defects.

The oxygen releasing agents are effective for the designated purpose when used alone in a suitable solvent. iowever, it may be desirable that other substances also be used either to add coloring or opaqueness to the coating solution or to eliminate side eifects which at times may be undesirable. For example, fluxing, or lowering of the fusion point of the sand in the shellmold, may occur. This may be prevented by the utilization in the wash of a suitable ceramic material, such as titanium dioxide, iron oxide, manganese dioxide or the like.

Several typical Washes are set forth below, by Way of example only, to illustrate the various combinations of additives which may be utilized with the oxygen releasing agents and also to illustrate the Wide range in strength of solution which is effective.

Wash No. 1

KClO "grams" 10 E cc 150 MnO grams 100 Cellulose gum gram .75 Wash No. 2:

LiNO grams 52 H O ml 100 Alcohol ml 50 Wash No. 3:

LiClOn; g-rams 10 Ti0 do 10 E 0 ml 100 Wash No. 4:

KCIO gran1s 1-0 TiO do 50 H O ml 150 Wash No. 5:

LiClO grams 1O H O ml 100 Wash No. 6:

LiClO4 grams 60 E 0 ml 100 Wash No. 7:

LiClO grams 60 MnO do 100 H2O In1 Wash No. 8:

NaNO grams 60 E 0 do 100 Wash No. 9:

LiClO "grams" 45 E 0 cc 100 Wash No. 10:

LiClO grams 45 TiO do 30 E 0 cc 100 Wash No. 11:

LiClO grams 45 M1102 do 30 "E0 do 30 H O cc 100 Wash No. 12:

LiClO "grams" 30 Ti0 do M110 do 20 H2O CC Wash No. 13:

Mg(ClO grams 50 H O cc Wash No. 14:

LiClO grams 36 Ti0 do 24 Fe O do 24 E 0 cc 100 Wash No. 15:

Mg(ClO grams 25 H O cc 100 The agents which were selected and utilized in the formulations set forth in the above table are those which release oxygen on heating or in the presence of a catalyst, which are inexpensive, and which are readily available commercially. With regard to the use of a catalyst it will be noted that wash No. 1 was slightly more effective than Wash N0. 4. The reason for this is that the manganese dioxide in Wash No. 1 acts as a catalyst to release oxygen from the perchlorate, whereas the titanium dioxide utilized in Wash No. 4 does not. It should also be noted that wash No. 6, which contains lithium perchlorate to the limit of its solubility, was slightly more effective than wash No. 5, thereby showing the desirability of having the largest amount out oxygen available in order to effectively prevent clarburization.

The Wash may be applied to the casting surface of the mold cavity by brushing, but preferably, in order to obtain a uniform coating, the wash should be sprayed onto the mold. The controlling factor for the quantities of solid materials which are suspended in the solution is the viscosity of the wash, which must be such that the wash can be sprayed with conventional spraying equipment.

It has been found that the Wash soaks into the mold to such an extent that it is difiicult to apply too heavy a coating. The actual amount of Wash which is utilized is not critical, and the wash may be sprayed until it begins to run on the mold surface. The wash should not be so thickly applied that undue cooling of the shell occurs because it is desirable that the wash should dry and the mold he usable several seconds after application of the Wash.

The sequence of steps in preparing the mold Wash also is not critical. However, it is preferred that the oxidizing agent first be dissolved while agitating the solvent. The solids are then added While continuing to agitate the solvent. If desired, an emulsifying agent may 'be utilized to hold the solids in suspension.

1 claim:

A method of producing low carbon, low alloy steel castings consisting essentially of: making a shell mold having sand particles bonded together with a thermosetting resin, then coating the mold cavity with a solution of a metallic compound selected from the group consisting of nitrates, chlorates and perchlorates, and having a solubility rating of at least about 7 grams per milliliters of cold Water, and then filling the mold with molten metal.

Budd May 10, 1870 Meves et al Aug. 19, 1958