US3216078A - Process for casting steel and compositions of matter for use therein - Google Patents

Description

United States Patent 3,216,078 PROCESS FOR CASTING STEEL AND COMPOSI- TIONS 0F MATTER FOR USE THEREIN Arthur H. Zrimsek and George J. Vingas, Arlington Heights, Ill., assignors to Magnet Cove Barium Corporation, Houston, Tex.

No Drawing. Filed Aug. 30, 1962, Ser. No. 220,532

6 Claims. (Cl. 22-215) This invention relates to the art of making steel castings. It is particularly directed to processes and compositions of matter useful to improve the surface appearance and smoothness of cast steel objects and for reducing ceroxide defects in the surface of such objects.

It is customary to prepare foundry sands for use in casting steel from clean silica sand by intimately mixing minor proportions of a binder with the base sand. The binder may be an inorganic material, such as a hydratable clay, together with suflicient water to hydrate the clay to a desired extent. Alternatively, the binder may be an organic material or mixture of organic materials, such as cereal, flour, sugar, starch, organic resins, such as the polyelectrolyte compounds described in U. S. Patent No. 2,817,128, co-polymers of acrylic acid and polyacrylonitriles, or other polymeric resinous materials. Also classified las binders are certain thermo-setting organic materials, such as linseed oil, fish oils, urea resins, and furan resins.

The usual function of a binder is to hold the sand grains together, and in the case of molding sands, to give the required green strength to a mold made from the sand composition. Under circumstances where sand is used to make a core, the binder serves primarily to form a rigid bond on heating or oxidizing to allow handling of the core. In both instances the workability of the sand composition may also be a factor. Choice of binders is usually made with these factors in view combined with the economic factor to get the required characteristics of the sand as cheaply as possible. The term binder is used in this specification and claims to mean any one of or mixture of the materials described above.

Steel castings are subject to certain defects not usually encountered in the casting of gray or white iron, aluminum and other metals. Ceroxide defects, for example, are a minor problem in the casting of the irons but a major cause of defects in steel castings. These defects are extremely common so that in some cases up to 40 percent of the castings made by usual foundry practice may have ceroxide defects of greater or lesser extent.

Ceroxide defects are shallow depressions in the surface of a casting and are almost invariably found on the cope side. These defects occur more frequently in small, thin castings made in green sand molds than in large, bulky castings made in well dried molds. These defects are called snotters, scum, dirt, slag, macro-inclusions, etc.; but the term ceroxide defect is becoming standard nomenclature.

The material causing the ceroxide defect apparently results from a reaction between atmospheric oxygen and de-oxidizers introduced into the steel prior to pouring. This reaction product tends to float upon molten steel as a scum, and is carried into the cavity when the steel is poured. Even careful skimming of molten steel does not eliminate the ceroxide scum as it continues to form during exposure of the steel to air in the pouring operation, in sprues, gates, and in other parts of the mold.

The higher incidence of ceroxide defects in small castings with thin sections is believed due to the fact that the small, thin castings have to be poured at higher temperatures to avoid mis-runs, and high temperature differentials at the faces of the molds result in precipitation 3,216,078 Patented Nov. 9, 1965 "ice of more of the ceroxide than occurs when larger castings with thicker sections are poured. The latter require longer to solidify, and heat the molding sand to high temperatures. Thus, larger castings remain molten and permit the ceroxide material to float out of the metal and to penetrate into the relatively super-heated mold wall rather than to accumulate in the surface of the steel casting where they are trapped and immobilized by solidification of a thin layer, or skin, of solid steel.

If not too extensive, cavities resulting from ceroxide defects may be filled up by welding, or they may be removed by machining. However, breakage of high speed machine tools frequently occurs when castings showing this defect are machined; and at any rate, either machining or welding to remove these defects is expensive so that, when the cavities are extensive, it is frequently cheaper to discard the casting and send it back for remelting.

A second difficulty encountered in producing steel castings in sand molds is the removal of sand from the cast surface. It is not unusual for steel castings, when shaken from the mold, to have a large portion of their surface covered with a layer of adhering sand. The sand is held tightly to the casting by a glassy flux formed during the casting operation. Removal of the sand layer from the casting surface by means of blasting or grinding is required to bring the casting to a saleable condition.

It is an object of this invention to provide a foundry process for casting steel wherein ceroxide defects are greatly reduced or substantially eliminated.

It is another object to provide such process and compositions of matter for use therein wherein ceroxide forming at an interface between the steel and mold is absorbed into the sand mold.

Another object is to provide such process wherein a thin layer of glassy material normally formed upon the face of a sand mold in contact with molten steel is reacted with a material selected from the group consisting of chlorine, bromine, iodine, and mixtures thereof; and the properties of the glassy layer are greatly changed to the extent that upon shake-out, adherence of sand to the cast surface is substantially reduced or eliminated.

Another object is to provide an improved mold for receiving molten steel.

Another object is to provide an improved binder material for incorporation with a silica sand to produce a foundry sand composition.

Another object is to provide an improved wash for application to the surface of a cavity in a mold for receiving molten steel.

Another object is to provide an improved dusting powder for application to the surfaces of such cavities.

Other objects, advantages and features of this invention will be apparent to one skilled in the art upon a consideration of the Written specification and claims.

This invention is based upon the discovery that, when steel is poured into a mold and an atmosphere rich in a material selected from the group consisting of chlorine, bromine, iodine, and mixtures thereof is maintained in the mold adjacent to a cavity receiving the molten steel, a thin, molten layer of glassy or slag-like material normally forming on the surface of the mold defining the cavity has changed properties. Thi thin, molten layer normally hardens to a glass which is transparent and has a color ranging from light amber to rose; but in the pres ence of an atmosphere rich in one or more of these halogens, the color becomes much darker, usually black, and this layer is opaque. The important change i that this layer no longer has a tendency to wet steel at the interface but icks up ceroxide, which has also been affected by the halogen-rich atmosphere, from the surface of the steel and transmits the ceroxide into the sand mold where it solidifies.

The course of this reaction is unknown but its existence is proven by the change in color and appearance of the glassy layer and the fact that ceroxide inclusions normally occurring in the surface of the steel casting are greatly reduced or substantially eliminated, while the ceroxide masses have been found in the sand of the mold adjacent to the glassy layer. It seems possible that a decrease in the viscosity of the ceroxide occurs together with increased wetting or solvent power of the glassy layer for ceroxide and decreased ability of this layer to wet the surface of the steel. However, we do not wish to be bound by any theory or mechanism of reaction since we have not been able to determine exactly what occurs other than by inspection of steel objects cast and investigation of the sand and glassy layer in the vicinity of the surface of the mold after solidification.

Based upon this discovery, we have provided a process which includes generating an atmosphere rich in a material selected from the group consisting of chlorine, bromine, iodine, and mixtures thereof in the mold adjacent to a face of the mold defining the cavity concomitantly with pouring steel into the cavity and maintaining the halogen-rich atmosphere in the mold adjacent to the cavity during at least a latter part of the pouring step and for a time thereafter suflicient to improve the surface appearance and smoothness of the resulting casting and to decrease ceroxide defects. A small amount of corresponding hydrogen halide, i.e., HCl, HBr or HI, also will be present since there is always some water vapor present and at the temperatures normally present in the mold there will be some interaction between the water vapor' and halogen with formation of hydrogen halide.

It is preferred that the halogen-rich atmosphere be generated by thermally decomposing an organic halide containing from about to 90 percent of halogen adjacent to the surface of the mold defining the cavity. The organic halides used decompose at temperatures near their boiling points, and at temperatures normally present in the mold adjacent to the cavity during the step of pouring the steel.

Organic chlorides, bromides and iodides which are incompletely decomposed at normal mold temperatures are not efficient in preventing ceroxide defects. Many such compounds, as for example chlorinated parafiin Waxes which may contain up to 70 percent chlorine, partially decompose at mold temperatures to form a black, tarry residue containing a large part of the original chlorine content of the wax.

Organic compounds containing less than 20 percent of chlorine, bromine or iodine also may present problems due to excess carbon in this location, and the low ratio of halogens evolved to carbon residue makes Such compounds undesirable.

The stable, highly volatile, organic halides, such as carbon tetrachloride, chloroform, ethylenedichloride, etc. usually do not eleminate ceroxide defects nor do the volatile, stable hydrogen halides HCl, HBr or HI. Volatile materials of this type apparently vaporize as the mold warms up and pass back from the cavity through voids between sand grains in the mold with little, if any, decomposition so that an atmosphere rich in halogen is not generated or present at the surfaces of the mold defining the cavity when stable, volatile halides are used. The organic and inorganic fluorides also fail to show appreciable effect in elimination of ceroxide defects, and this was found to be true without regard to their volatility and stability.

Among the many inorganic halogen salts tested none Were particularly effective in reducing the incidence of ceroxide defects. However, the thermally unstable chlorine, bromine, or iodine inorganic salts do produce the glassy surface which 't fi characteristic of non-wetability for steel resulting in sand-free cast surfaces, and thus result in improved surface appearance and smoothness of the steel objects cast. It seems probable that the metallic ion combined with halogen in such salts increases the quantity of ceroxide formed and also prevents fluidization of the ceroxide, thereby preventing its transfer into the sand.

The unstable organic compounds are preferred because they not only reduce ceroxide and improve the casting surface but also are more compatible with normal foundry sand formulations. While workability and physical properties of foundry mixtures are greatly affected by the inorganic halogen salts, changes caused by addition of the organic compounds is not perceptible. The shortcomings of the inorganic salts do not however preclude the successful use of the unstable metallic salts as dusts or Washes to improve smoothness and appearance of cast steel surfaces.

We prefer to generate the halogen-rich atmosphere by blending a suitable halogen-containing compound with the sand mixture when the mold is prepared, or introducing the halogen compound blended in a wash or dusting powder applied to the surfaces of' a mold cavity which is to receive molten steel. Then When the steel is poured, the compound is decomposed at the high temperatures resulting in the mold, thus generating a halogen-rich atmosphere in the vicinity of surfaces of the mold defining the cavity.

Preferred organic compounds are materials selected from the group consisting of hexachlorocyclohexane, hexachlorobenzene, tetrachlor'obenzene, trichlorobenzene, hexabromobenzene and mixtures thereof. If desired, a mixture of chlorinated camphenes having a chlorine content in the range from 67 to. 69. percent by'weight, 1-2-4-5-6-7- 8 8 octachloro-2-3-3a-4-7-7a-tetrahydro-4-7-methano indene, usually sold under the trademark Chlordane," a terpene polychlorinate having a chlorine content of about 66 percent by weight sold under the trademark Strobane, 1 (or 3a) 4-5-6-7-8-8-heptachloro-3a-4-7-7a-tetrahydro- 4-7-methanoindene, usually sold under the trademark Heptachlor, a mixture of chlorinated camphenes having a chlorine content in the range from 67 to 69 percent by weight, sold under the trademark Toxaphene, tetrachloro-p-xylene, heXachloro-p-xylene, hexachlorobutadiene, or dichlorodiphenyltrichloroethane, sold under the trademark DDT may be used. However, as stated above, any of the organic compounds which are decomposed at temperatures near their boiling points and which are thermally unstable at temperatures normally occurring in the mold adjacent to the cavity during pouring of steel may be used for the elimination of ceroxide defects.

When large, heavy castings are to be prepared and ceroxide defects are not serious, it is possible to use many of the inorganic halides for increasing surface smoothness only. Among these materials are cup'rous bromide,"potassium iodate, potassium iodide, ferrous chloride, bismuth trichloride and many other thermally unstable inorganic chlorine, bromine and iodine salts. However, the inorganic halides cannot be used when it is desired both to improve the smoothness and surface appearance of the casting and to eliminate ceroxide defects therein. All inorganic salts tested were ineffective for the elimination of ceroxide defects.

Typical formulations of molding and core sands including thermally unstable, halogen-rich compounds containing 20 to percent of chlorine, bromine or iodine may be formulated as follows:

parts sand 3 to 15 parts clay (bentonite or fireclay) .5 to 2 parts cereal or .02 to 2 parts acrylate resin 2.5 to 5.5 parts water to 5 P s halogenh compoun 100 parts sand 3 to 15 parts clay 2 to 5.5 parts water to 3 parts wood dust 0 to 2 parts sugar or sulfide liquor or wood sugar 0 to 2 parts natural or synthetic resin or rosin .1 to parts halogen-rich compound 3. 100 parts sand 0 to 3 parts cereal 0 to 3 parts core oil, resins or rosins 0 to 5 parts iron oxide 0 to 3 parts clay 2 to 5 parts water 0 to 30 parts silica flour .l to 5 parts halogen-rich compound 4. 100 parts sand 0 to 5 parts phenolic resin 0 to 5 parts furan resin .1 to 5 parts halogen-rich compound Thus, addition of from 0.1 to 5.0 percent of an organic compound which contains from 20 to 90 percent of a material selected from the group consisting of chlorine, bromine or iodine and which is thermally unstable at temperatures near its boiling point to molding sands of all commonly used types is feasible. Similar quantities of thermally unstable inorganic salts of chlorine, bromine and iodine may be used when only improvement in surface smoothness, or peel, is required.

We have found that the presence of 0.1 to 5.0 percent of the unstable halogen compounds in the sand adjacent to the surfaces defining the cavity is sufiicient that a halogen-rich atmosphere is generated during the pouring of steel and to provide a required quantity to decompose slowly enough that the halogen-rich atmosphere is maintained for a time sutficient to improve the surface appearance and smoothness of the steel casting and to eliminate ceroxide defects.

The time the halogen-rich atmosphere should be maintained cannot be stated definitely as it is variable with the size and shape of the object cast and corresponds substantially to the time required for a film or skin of solidified steel to form on the surface of the cast object. Until this surface layer solidifies there is a possibility of further formation of ceroxide or movement of preformed ceroxide into the surface layer where it can react with the halogen, and the possibility of further reaction and movement is eliminated when a skin of solid steel forms on the surface of the casting.

While the use of the unstable halogen compounds in molding sand is a practical one, we prefer to use the halogen-containing material in a wash or dusting powder applied to the surface of the cavity.

It is customary in the casting of steel to increase the smoothness of the sand mold surfaces which define the cavity into which steel is poured by spraying a liquid wash on the cavity surfaces or dusting such surfaces with powder.

A great many proprietary washes are on the market and these usually include a finely divided material selected from the group consisting of silica, zircon, magnesia, alumina, Alundum, molochite, olivine, calcined fireclay, berylia, dolomite, and chromite in proportions up to 60 percent. Talc may be used in quantities up to 40 percent in some formulations while other materials, such as iron oxide, clays, sugars, sulfite liquor wastes, synthetic resins, rosin, core oil, defoaming agents, CMC, alginates, acrylates, preservatives, such as sodium benzoate, and cereals, may be used in smaller amounts together with a suitable liquid to dissolve or suspend the other components of the wash and this liquid is usually either water or an alcohol of low molecular weight although acetone or other ke- 6 tones of low molecular weight are sometimes used. Dusting powders have essentially the same composition as the washes but do not include the liquid solvent or suspending agent.

The term wash is used in this application to mean a suspension or solution of one or more of the above ingredients in a liquid for spraying upon the surfaces of a sand mold defining a cavity suitable for receiving molten steel, and the term dusting powder is used to mean an apparently dry powder contaning one or more of the solid ingredients set forth above and suitable for application to such mold surfaces.

We prefer to incorporate our unstable halogen-rich material in a wash or dusting powder used for smoothing the surface of a mold. Used in this manner a lesser quantity may be employed than when it is mixed with the entire sand composition of the mold and still the required halogen-rich atmosphere is generated and maintained for the requisite length of time.

When thin or small castings are to be made and ceroxide defects are expected to be severe, we have found that only the thermally unstable organic compounds containing 20 to percent of a material selected from the group consisting of chlorine, bromine and iodine and de-' composing at temperatures near their boiling points should be used and among these compounds the chlorides are preferred because of their cheapness and ready availability. One preferred material available on the market is a by-product material separated from the gamma type of hexachlorocyclohexane in the preparation of insecticides. This material is in the form of a cake which contains principally the alpha and beta forms of hexachlorocyclohexane. The cake itself is easily disintegrated and blended with any of the materials mentioned above as suitable for use in a wash or dusting powder. This material is preferred because of its low price, ready availability, effectiveness, and the ease with which it can be blended in the desired compositions.

Another preferred method of introducing the thermally unstable halogen compounds into the mold adjacent to mold surfaces defining a cavity is to blend the halogen compounds in a binder which is later incorporated in the sand composition. Since core and mold sand compositions are commonly prepared by adding the sand and the various materials which are to be used as a binder, such as clay, starch, cereal, or resinous materials separately into a muller and mulling the entire mixture until uniform dispersion is attained, we prefer to mix the unstable halogen compounds with only one of the binder materials which is to be used. For example, a preferred type of mixture may contain starch, a resinous material such as a co-polymer of acrylic acid and polyacrylamide used as a substitute for or to supplement starch or cereal with the thermally unstable organic compound containing from 20 to 90 percent of the material selected from the group consisting of chlorine, bromine and iodine and decomposing at temperatures near its boiling point. This method of introducing the thermally unstable halogen compound into the mixture is preferred because it requires less mix ing to get good dispersion than would be required if all the binder materials including clay were to be mixed with the halogen compound prior to mixing with the sand. However, any of the binder materials or any mixture thereof included in the term binder as defined above may be mixed with the halogen compound if preferred and the binder later mixed with the sand.

Thus, it will be seen that the unstable compounds containing 20 to 90 percent halogen may be directly admixed with the core sand, or with the sand composition used for making a core or mold, may be pre-mixed with one or more of the binder materials which is to be used in a molding or core sand composition, or may be introduced upon the surface of a cavity in the mold in a wash or dusting powder; but when used in the sand composition, or in a binder dispersed throughout the sand composition,

somewhat larger quantities of the halogen compound will be required than when applied to the surface of the mold defining the cavity.

The quantities to be used will be in the range from 0.1 to 5.0 percent of the total quantity of sand composition used in the core or mold. When applied to the surfaces of the mold defining the cavity in the form of a wash or dusting powder or-similarly applied upon the outside of a core, the quantities required will be in the lower part of this range; while if the halogen compound is dispersed throughout the sand mixture of the core or mold, quantities in the upper part of this range may be necessary, although the quantity required will vary also with the percentage of halogen contained in the unstable compound as will be obvious to those skilled in the art.

The following examples give typical results in improving peel, or surface smoothness, and decreasing ceroxide defects in steel castings by decomposing unstable compounds containing from 20 to 90 percent of a material selected from the group consisting of chlorine, bromine and iodine, said materials decomposing at temperatures near their boiling points and normally occurring in sand molds adjacent to the faces thereof defining a cavity into which molten steel is poured.

EXAMPLE I Chemical Surface Appearance Rough surface. No i]r)nprovement.

o. Very rough surface.

Sulphur Excellent peel, shiny surface.

Copper bromide- Potassium iodate.

Aluminum fluoride No improvement.

Potassium fluorobor Very small improvement in peel. Chrome metal- No effect.

Nickel metal-.. Do.

Teflon (polytetr oethylene) Sllght improvement In peel. Magnesium metal No effect.

Regular rework sand Better than new sand.

It was noted that all halogen compounds which were admixed with the molding sand composition resulted in good peel with the exception of aluminum fluoride and potassium fluoroborate and Teflon. The lack of effect in improving peel shown by the aluminum fluoride and the potassium fluoroborate was strongly distinguished from the effect shown by the unstable compounds containing chlorine, bromine and iodine. The very slight results in improving peel shown by Teflon is believed to be due to the fact that the Teflon did not decompose thoroughly at the temperatures normally present in the mold adjacent to the molten steel.

EXAMPLE ]1 Molds were prepared from the sand composition described in Example I and had cavities therein suitable to receive two-inch plugs of steel. The chemicals listed below were added to other portions of the same sand mixture and similar molds were prepared from the various resulting mixtures. In one case the cereal was omitted from the sand mixture using only clay as a binder. After pouring the two-inch plugs, the plugs were allowed to cool and were shaken out from the sand molds and their surfaces were inspected. The following results were noted:

Chemical Surface Appearance Better than with clay only, rough surface with sand adhering. Shing surface, good peel.

Regular sand Potassium iodate Copper bromide 0. Clay only, cereal om Rough surface, bad peel.

EXAMPLE III Molding sands havingthe compositions shown in the table below were prepared, and molds having a cavity to receive a plate eight and'one-half inches in diameter and one inch thick were prepared from each sand composition. Molten steel was poured into the cavities and allowed to cool, and the resulting plates were shaken out of the molds. The following results were observed:

Chemical Surface Appearance Ceroxide defects large, good peel.

Do. Ceroxide defects small, good peel.

Good peel, large ceroxide defects.

In each test where an unstable inorganic iodide was used, ceroxide defects were present although good peel was obtained. Addition of hexachlorobenzene or hexachlorocyclohexane resulted in both good peel and substantial elimination of ceroxide defects.

EXAMPLE IV Molds having the composition shown in the tables below were prepared for casting plates as in Example HI and both iron and steel castings were poured. After shakeout, the following results were observed:

Table 1 IRON CAS'IIN GS Chemical Surface Appearance 7.45% bentonite, 4.75% seacoal Excellent peel. 7.45% bentonite Sand sticks badl,

7.45% bentonite, 1% hexachlorobenzene 7.45% bentonite, 1% copper bromide 7.45% bentonite, 1% potassium iodate Do. Bad peel, sandstielM Table 2 STEEL CASTINGS Chemical Surface Appearance 4.75% bentonite, .5% potassium iodate fect, good peel. 4.75% bentonite, 25% potassium iodate Do. 4.75% bentonite, 1% cereal, sprayed with potas- Do.

siurn iodate 60% solution. 4.75% bentonite, 1% copper bromide Do. 4.75% bentonite, 2% carbontetrachloride Large ceroxide defeet, medium peel. 4.75% bentonite, .5% hexachlorobenzene, and No ceroxide defect,

10 grams hexachlorobenzene in runner. good peel. 4.75% bentonite. 25% hexachlorobenzene, and Do.

10 grams hexachlorobenzene in runner.

Large ceroxide de- The difference in effect of adding thermally unstable halogen compound to molds for casting iron and steel is clearly illustrated by these tables.

EXAMPLE V Molds, as in Examples III and IV, were prepared from sands having the compositions shown in the following 9 table.

The thermally unstable chlorine and iodine compounds were introduced as shown in the table.

Chemical Surface Appearance 4.75% bentonite, 1% cereal 7.45% bentonite, 25% hexachlorobenzene, grams hexachlorobenzene in runner.

10% bentonite, 25% hexachlorobenzene, 10 grams hexachlorobenzene in runner.

4.75% bentonite, sprayed with ferrous chloride-alcohol.

4.75% bentonite 7 .45% bentonite, 1% bismuth chlo- 7.45% bentonite, 1% sodium chloride, and 10 grams sodium chloride in mold.

7.45% bcntonite, 1% potassium iodate.

10 grams hexachlorobenzene in gate or runner, none in casting cavity.

10 grams hexachlorobenzene dusted onto cope surface. 10 grams bismuth chloride in mold Large ceroxide defect, very rough surface with much adhering sand.

No ceroxide defect, sprinkhng of eroded sand on cope.

Very small ceroxide defect. smoother surface than the one above.

Large ceroxide defect area, uneven oxide crust, producing rough surface.

Do. Excellent peel, big ceroxide defect.

No ceroxide defect.

Excellent peel, no ceroxide defect.

Rough surface, large ceroxide defeet in cope.

Excellent peel, scab in drag and ceroxide defect in cope.

Excellent peel, large ceroxide defeet in cope, rounded edges due to slow pour.

Rough casting, peel fair, considerable shallow ceroxide defect.

Good peel, rough drag, medium ceroxide defect.

Very rough dull finish, only very slight ceroxide defect. Fair finish, good peel, but very 10 grams sodium chloride in mold large ceroxide defect.

The results showed that the introduction of hexachlorobenzene in the runner to the mold does not give good results. This was believed to be due to decomposition of the halide outside the mold. Introducing the hexachlorobenzene into the sand mixture, spraying upon the surfaces, or apply it as a dry powder dusted upon the surface of the mold gave good results. A large series of castings were made to test the reproducibility of results shown in the table above. The results obtained by use of hexachlorobenzene as compared to results from casting without this material were easily reproducible.

EXAMPLE VI A large number of tests, similar to those described in Examples III to V above, were made using other thermally unstable organic compounds containing chlorine and bromine. Hexabromocyclohexane gave results comparable to those obtained from heXachlorocycloheXane. Chlorinated parafin waves containing up to 70 percent chlorine were tested and found less effective than hexachlorocyclohexane for preventing ceroxide defects, but gave good peel, and resulted in a black tarry residue containing a large part of the original chlorine content of the wax. Trichlorobenzene, tetrachlorobenzene and a mixture of chlorinate camphenes containing about 67 percent chlorine and sold under the trade name Toxaphene gave good results in preventing both adherence of sand to the surfaces of steel castings produced and substantial elimination of ceroxide defects in the castings.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the process.

It will be understood that certain features and subcombinations are of utility and may be employed with- I out reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

The invention having been described, what is claimed 1. In a process for casting steel wherein molten steel is poured into a mold constructed principally of sand and a binder and having a cavity therein adapted to receive molten steel, ceroxide normally collects in a surface layer of the steel, a thin layer of molten glassy material having a tendency to wet and adhere to the surface of the molten steel normally forms upon a face of the mold defining the cavity, and the poured molten steel is cooled and solidified in the cavity, that improvement which comprises thermally decomposing a sufficient quantity of an organic material containing from 20 to percent of an element selected from the group consisting of chlorine, bromine and iodine and which decomposes substantially completely with release of said element in gaseous condition at a temperature near the boiling point of said organic material and normally present in the mold during the step of pouring steel thereinto to generate an atmosphere rich in said element in the mold adjacent the cavity; maintaining said element in gaseous condition in the mold adjacent to said cavity until a thin layer of solidified steel forms upon the surface of the molten steel, reacting said element in gaseous condition with said molten glassy layer on the face of the mold until said glassy layer no longer tends to wet and adhere to the surface of the steel and transmitting ceroxide from the surface of the steel through said molten glassy layer into the mold adjacent said cavity.

2. The process of claim 1 wherein the organic material is a material selected from the group consisting of benzene hexachloride, hexachlorocyclohexane and mixtures thereof.

3. The process of claim 1 wherein the organic material is hexachlorocyclohexane.

4. The process of claim 1 wherein prior to the step of pouring molten steel the organic material is admixed in a wash and the wash is sprayed upon surfaces of the mold defining the cavity in quantity to provide the organic material in the range from 0.1 to 5.0 weight percent of the sand composition.

5. The process of claim 1 wherein the organic material is admixed with a dusting powder and the dusting powder is applied to surfaces of the mold defining the cavity in quantity to provide the organic material in the range from 0.1 to 5.0 of the Weight of the sand composition prior to the step of pouring molten steel.

6. The process of claim 1 wherein the organic material is intimately mixed with a binder prior to mixing sand and binder to form the mold and the quantity of said organic material is in the range from 0.1 to 5 .0 weight percent of sand composition.

References Cited by the Examiner UNITED STATES PATENTS 2,080,159 5/37 Archer 22215 XR 2,394,522 2/46 Pace 1175.2 2,425,978 8/47 Anderson et al. 1175.2 3,019,497 2/ 62 Horton et al 22196 3,075,847 1/63 Henry et al. 106-3822 MARCUS U. LYONS, Primary Examiner.

MICHAEL V. BRINDISI, Examiner.

Claims (1)

1. IN A PROCESS FOR CASTING STEEL WHEREIN MOLTEN STEEL IS POURED INTO A MOLD CONSTRUCTED PRINCIPALLY OF SAND AND A BINDER AND HAVING A CAVITY THEREINADAPTED TO RECEIVE MOLTEN STEEL, CEROXIDE NORMALLY COLLECTS IN A SURFACE LAYER OF THE STEEL, A THIN LAYER OF MOLTEN GLASSY MATERIAL HAVING A TENDENCY TO WET AND ADHERE TO THE SURFACE OF THE MOLTEN STEEL NORMALLY FORMS UPON A FACE OF THE MOLD DEFINING THE CAVITY, AND THE POURED MOLTEN STEEL IS COOLED AND SOLIDIFIED IN THE CAVITY, THAT IMPROVEMENT WHICH COMPRISES THERMALLY DECOMPOSING A SUFFICIENT QUANTITY OF AN ORGANIC MATERIAL CONTAINING FROM 20 TO 90 PERCENT OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF CHLORINE, BROMINE AND IODINE AND WHICH DECOMPOSES SUBSTANTIALLY COMPLETELY WITH RELEASE OF SAID ELEMENT IN GASEOUS CONDITION AT A TEMPERATURE NEAR THE BOILING POINT OF SAID ORGANIC MATERIAL AND NORMALLY PRESENT IN THE MOLD DURING THE STEP OF POURING STEEL THEREINTO TO GENERATE AN ATMOSPHERE RICH IN SAID ELEMENT IN THE MOLD ADJACENT THE CAVITYU; MAINTAINING SAID ELEMENT IN GASEOUS CONDITION IN THE MOLD ADJACENT TO SAID CAVITY UNTIL A THIN LAYER OF SOLIDIFIED STEEL FORMS UPON THE SURFACE OF THE MOLTEN STEEL, REACTING SAID ELEMENT IN GASEOUS CONDITION WITH SAID MOLTEN GLASSY LAYER ON THE FACE OF THE MOLD UNTIL SAID GLASSY LAYER NO LONGER TENDS TO WET AND ADHERE TO THE SURFACE OF THE STEEL AND TRANSMITTING CEROXIDE FROM THE SURFACE OF THE STEEL THROUGH SAID MOLTEN GLASSY LAYER INTO THE MOLD ADJACENT SAID CAVITY.