US2913788A

US2913788A - Method of casting ingots

Info

Publication number: US2913788A
Application number: US355880A
Authority: US
Inventors: Kramig Anna Louise
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-05-18
Filing date: 1953-05-18
Publication date: 1959-11-24
Anticipated expiration: 1976-11-24

Description

,9 8 METHODLQF CASTING lNGoTs Robert a. Kramig, Jr., cineinn ti,".ohieg'fitmiagmuise Kramlg, executrix and trustee of the estate of said Robert E. Kramig, Jr., deceasetl No Drawing. Application May 18, 1953- t Serial No. 355,880 i v 3 Claims. (c1. 21-200 This invention relates to the casting of ingots. of steel, iron and other metals. The invention isa'ddressed particularly to the problem of pre'venting'theadherenceof an ingot casting to the stool up'ontwhich the ingotmold is mounted, and to prevent deterioration of the stool by the molten metal during'casting. f I

In the fabrication of sheets and shapes' of steel, it is conventional procedure to first produce aniir'igot from the molten and refined metal. For this purpose a'tubular tapered ingot mold is placed vertically'uponla large heavy plate or so-called stool which is made'o'f cast iron,

the-upper surface of the plate forming the bottom closure of the mold cavity. Molten metal at a temperature of approximately 3400 F; is poured into the cavity from a ladle and is allowedjtdcool andsolidify within the cavity. Subsequently theingotmold and the contained casting is lifted from the plate and removed to another place where the mold is, separated from the casting. An empty. ingot iriold is later placed upon the plate for the production of: another ingot.' The ingots produced in this manner vary,fidepehding upon mold comes into direct engagement withthe surface of the stool, at the velocity which it attains in falling from a height of seven feet or more, causes the surface metal of the stool to become melted and dislodged. For this reason, a crater is produced in the stool surface, the

size of the crater becoming progressively larger following each pouring operation. For this reason, itis requisite that the stools be replaced from time to time, which, in view of their substantial. size, involves considerable expense. p 7

Under ideal conditions, the relatively low temperature of the stool at the start of a pouring operation is sufficient to prevent actual adhesion of the cast ingot to the stool surface. However, it frequently occurs that the molten metal actually integrates itself with the metal of the stool, as though the two became welded together.

In this event, it is impossible to lift the ingot from the stool and it then becomes necessary to,separate, the stool from the ingot by whatever means may bexrequired; usually, the entire assembly is removed to ayard where the stool can be pounded upon with a heavy weight in order to break theweldments where theingot and stool areseized together. Such. operations are obviously costly and interfere withorderly. production.

In order to facilitate the parting of theiingot casting from the stool after solidification of the casting, it has been conventional procedure in' some steel plants to 2 a throw a layer of calcium carbide over the'stool surface. To. some extent, this procedure reduces the frequency with which so-called stickers occur. However, the heavy stream of molten metal which falls against the 'stool surface flushes away the light powder'layer-with the result that this"expedient, though helpful, has by no means either cured the problem of preventinga'dherence of the casting to'the stool or the problem 'of preventing cratering of the stool surface by the molten metal. Other expedients have also been proposed, 'such as recessing the stool surface at the area thereof which normally receives the falling stream of metal and of placing a block of carbon in the recess so as to enable carbon to insulate the metal of the stool against the deteriorating effects of the molten metal stream. In this practice, however, it is found thatthe molten steel dissolves or absorbs carbon from the target block and, therefore, the steel first poured into the mold is different metallurgically from the metal in the balance of the ingot.

It has also been proposed to use a wound coil of strap steel as the target at the bottom of the mold against which the falling stream can be directed. In this arrangement, it is intended that the steel of the target be melted by the molten steel of the casting and thereby absorbed within it, meanwhile chilling the adjacent molten steel sufficiently to prevent seizure or sticking. However, targets of this type introduce metallurgical variations into the steel ingot and are not reliable in the performance of their intended function. I

Various heat insulating compositions which might be sufiiciently refractory to withstand the high temperature at which the steel is poured are undesirable because they interfere with the intended conductance of heat from the casting to the steel. i

This invention is based upon the paradoxical determination that. a resin-laminated asbestos plate placed over the stool'face at the bottom of an ingot mold is capable of protecting the stool face against cratering by the molten metal, is capable of preventing so-called stickers or adhesion of the metal of the ingot casting to the stool, and is also capable of providing the desired conductance of heat from the casting to the stool plate so that cooling of the casting at a normal rate' may be achieved.

The practice of this invention, therefore, contemplates the disposition of a densely compacted layer of bonded asbestos fibers within the mold, either over the entire bottom area thereof or at that area thereof against which the stream of molten metal is directed at the start of the pouring operation. The bonding agent, if resinous,

as is preferred, carbonizes under the intense heat to which it is subjected, but the carbon with which the molten steel comes into contact in this manner does not change the metallurgical composition of the steel in appreciable degree, either because the carbon is not adequate in amount orbecause it is retained by the asbestos fibers to such a degree that substantial dissolution thereof within the steel does not occur.

' A plate of this type may be called a smirch plate, suffering destruction as an incident to the pouring of the molten metal into the mold cavity but coincidentally protecting the stool against'cratering and adhesion of the casting thereto while also providing the desired heat conductance to the stool. The cost of such a plate is low in comparison with the costs that are involved in stool replacement or in separating a seized casting from a stool, and is also low in comparison with the cost of the various expedients which heretofore have been proposed but found to be only partially elfective.

Asbestos is-nominally considered a good heat insulator; this is confirmed by its extensive usage on boilers,

pipes and elsewhere where heat transmission is to be prevented. Actually, however, it is found that densely compacted asbestos fibersbonded into intimate contact by a synthetic resin has high heat conductance properties. The-asbestosfibers themselves are of refractory nature, but the resin in the bond is rapidly decomposed into elemental carbon at temperatures of the type in question. Even though this decomposition of the bond occurs with- .in the'mold, the residual asbestos fibers still provide the conductanceof heat from the casting to the stool metal, withthe result that the desired rate of cooling is attained.

An important characteristic of the smirch plates of the present invention is that they are capable of retaining their physical integrality throughout the initial period when first subjected to the impact of the falling stream of molten steel. As soon as steel is poured into the mold to a depth of two or three inches, this liquid layer protects the smirch plate against the attrition of the falling stream, and what happens thereafter to the smirch plate is of no consequence.

A typical smirch plate of the present invention is fabricated conveniently from asbestos paper which is coated with synthetic resin of, for example, the phenol formaldehyde type, then laminated with similar layers until an assembly of suitable thickness is built up, after which the assembly is placed in a press where it is cured under a pressure of several hundred pounds per square inch or more, to thermally set the resin. During curing, the pressure whichis exerted upon the laminate assembly causes migration of the resin and coincident compaction of the asbestos fibers one to another, and the resin also becomes thermally set.

A smirch plate produced in this manner may be from M: of an inch in thickness to A of an inch or more, depending upon the relative size of the ingot mold with which it is to be used.

Various synthetic resins may be used as the bonding medium for the asbestos fibers of the smirch plate, the phenol formaldehyde resins generally being the cheapest to use and, therefore, preferred. Resin content may constitute from approximately to by Weight of the finished plate. If the resin content is much below 15 the bonding of the fibers is not usually sufficient to provide the physical integrality which is requisite to enable the plate to withstand destruction during the initial pouring of the ingot, whereas a resin content above approximately 30% merely increases cost without providing commensurate advantage, and, in fact, is undesirable to the extent that the excess merely. introduces an additionalquantity of carbon at the end of the ingot, which might be undesirable metallurgically.

Phenol formaldehyde resin conveniently may be employed in the form of an aqueous dispersion of approximately 80% resin content applied either by coating or immersion or in other suitable manner to the asbestos. Resin in particle or granular form or in other than aqueous medium also may be used. It is to be noted, however, that. whatever vehicle .is employed for the purpose of distributing the resin upon the asbestos be removed before useof the final product, either by predrying before curing or by vapor liberation during curing. The presence of moisture or solvents in the finished product will, of course, cause violent vapor liberation of the smirch plate during use with resultant rupture of the plant laminations or fibers.

Commercial grades of asbestos paper constitute a convenient source of asbestos fibers; a six pound commercial asbestos paper, for example, has been found to be satisfactory. To make a smirch plateapproximately A of an inch in thickness, approximately twenty layers of asbestos paper, each coated with synthetic resin may be used, with curing under a pressure ofapproximately 250 pounds persquare inch, at a temperature of about 325 F. for a period of twenty to thirty minutes or more.

"Unit pressure which is maintained upon. the plate'during the curing of the resin will, of course, govern the degree of compaction "of the fibers, the greater the pressure the more dense and the less thick the resulting sheet will be.v

Under a curing pressure of approximately 250 pounds per square inch, with a resin content of 20%, a smirch plate approximately of an inch thick is produced which displays remarkable heat resistance. Such a plate, for example, iscapable of surviving direct heat of an oxyacetylene torch for a period of sixty-five seconds before penetration of th; torch flame through the sheet. A similar plate only A; of an inch thick resists penetration by the flame for a period of approximately twenty seconds. Inasmuch as the pouring cf molten metal into an ingot mold is usually completed in a period of from approximately thirty to sixty seconds, this test thus provides a simple means of determining the suitability of a plate of gii'en composition or thickness for the purpose. The flame of an oxy-acetylene torch is generally accepted to 'be 6800 F., which, of course, is approximately twice the temperature at which steel usually is poured.

The invention also contemplates smirch plates in which a layer of calciumcarbide is embraced within or upon the outer laminations or lamination at one or both sides of the plate, whereby the calcium carbide layer effectively constitutes an interface between the stool and the ingot metal. To provide such a smirch plate, calcium carbide of powdery consistency may be sprinkled between the outermost laminations at one or both sides of the sheet during their assembly and prior to curing so as to become firmly bound between the sheets during curing under heat and pressure. In similar manner, a layer of calcium'carbide may be provided as the outermost face at one or both sides of the plate by placing powdered calcium carbide upon the plate prior to curing in the press. The resinous binder which is present at the outermost sheet layer holds the calcium carbide in place after curing, or, if desired, a thin sheet of paper may be laid over the outermost layerto protect the carbide powder against dislodgment prior to use. In place of calcium carbide powder, refractory fillers or parting compositions commonly used in foundry practice may be employed.

Having described my invention, I claim:

1. The method of casting a metal ingot, which method comprises placing a plate having a thickness of from approximately to A of an inch and made of resinbonded asbestos fibers arranged in densely compacted relationship on the surface of a stool, superimposing an ingot mold upon the stool in position to embrace the plate over an area which is normally engageable by a stream of molten metal poured into the mold and then pouring molten metal into the mold so that it falls upon the plate, whereby the plate prevents cratering of the stool and adhesion of the ingot metal thereto.

2. The method of casting an ingot, which method comprises placing a plate of densely compacted asbestos fibers bonded together by phenolic resin upon the upper surface of a stool, said plate having a thickness of from approximately A; to A of an inch, superimposing an ingot mold upon the stool in a position to embrace the said plate over an area which is normally engageable by a stream of molten metal poured into the mold, then pouring molten metal into the mold so that it falls upon the said plate,-'whereby the plate protects the stool against cratering" and adhesion of the ingot metal thereto.

3. The method of casting a metal ingot, which method comprises placing a plate made of resin-bonded asbestos fibers-arranged in densely compacted relationship on the surface of -a stool, superimposing an ingot mold upon the stool in po'sitionto embrace the plate over'an area which is normally engageable by a stream of molten metal pouredi'nto the mold and then pouring molten 'metallinto the-mold so that it falls upon the plate,

whereby the plate-prevents cratering of the stool and adhesion of the ingotmet al thereto.

v (R fer t m s' n f llow g page) References Cited in the file of this patent UNITED STATES PATENTS Parks Nov. 13, 1900 Mains Aug. 23, 1938 5 Hanley July 15, 1941 Anderson July 20, 1948

Claims

1. THE METHOD OF CASTING A METAL INGOT, WHICH METHOD COMPRISES PLACING A PLATE HAVING A THICKNESS OF FROM APPROXIMATELY 1/8 TO 1/4 OF AN INCH AND MADE OF RESINBONDED ASBESTOS FIBERS ARRANGED IN DENSELY COMPACTED RELATIONSHIP ON THE SURFACE OF A STOOL, SUPERIMPOSING AN INGOT MOLD UPON THE STOOL IN POSITION TO EMBRACE THE PLATE OVER AN AREA WHICH IS NORMALLY ENGAGEABLE BY A STREAM OF MOLTEN METAL POURED INTO THE MOLD AND THEN POURING MOLTEN METAL INTO THE MOLD SO THAT IT FALLS UPON THE PLATE, WHEREBY THE PLATE PREVENTS CRATERING OF THE STOOL AND ADHESION OF THE INGOT METAL THERETO.