US2472071A - Mold assembly for producing cast metal slabs - Google Patents

Description

E. GATHMANN MOLD ASSEMBLY FOR PRODUCING CAST METAL SLABS Filed Au 6, 1945 2 Sheets-Sheet 1 INVENTOR.

fi/W/L GATHMA xwv N N A M H T A G E mom) ASSEMBLY FOR rnonucme CAST METAL smas Filed Aug. 6, 1945 2 Sheets-Sheet 2 mmvrok. a GATHMA nw Patented 1...... 1, 1949' MOLD ASSEMBLY FOR, PRODUCING CAST METAL SLABS Emil Gathmann, Baltimore, Md., assignor to Gathmann Research Incorporated, Catonsville, Md., a corporation or Maryland Application August t, 1945, Serial No. 609,066

Reference is made to my copending application Serial No. 614,377 filed September 4, 1945, which is a continuation-in-part of the present application 609,066.

This invention relates to easily shatterable cast metal slabs, and methods of and molds for producing such slabs or other cast articles. More particularly, the invention relates to the casting of easily shatterable blocks or slabs of alloys containing, for example, chromium, or vanadium.

Heretoiore it has been the practice to cast slabs of special alloying compositionsand to then break the slabs into small chunks, pieces, or fragments of three to four inch maximum section. These pieces or fragments are then further crushed to somewhat smaller size and used as alloying additions to baths or heats of molten steel. Previously such slabs or blocks have been cast'in bigend-up molds in which the mold proper and hot top casing or slag pocket have been formed integrally. There has been considerable difficulty in breaking up such slabs, especially those of low carbon chrome alloys, because the crystals formed on solidification of the metal in big-end-up molds are, to a considerable extent, of an interlaced structure. This interlacing of the crystalline structure makes for strength and causes great difficulty in the breaking up of the slab, both in the initial breaking and in the subsequent crushing operation.

I have found that the line of fracture formed under an impact upon such a slab runs parallel with the direction of the crystalline growth, and. that it is much easier to break the slab into the approximate sizes required when the largest possible number of crystals or lines of crystalline growth run in the same general direction and when interlacing of the crystals is absent or at a minimum.

An object of the invention is to provide an easily shatterable cast metal slab in which there is a minimum of interlacing of the crystals and in which the crystals or lines or growth of the crystals substantially all extend in the same general direction, substantially perpendicularly to the two larger area faces of the slab.

Another object of the invention is to provide a method of producing a cast metal slab having the structure and characteristics pointed out above.

A i'urther 'object of the invention is to provide an improved mold or mold assembly in which to cast such a slab.

A still further object of the invention is to provide an improved big-end-down mold in which the lower edges of the matrix side walls are 2 Claims. (01. 22-139) 2 rounded so as to deter damaging of the mold walls by the heat and cutting action of the molten metal poured into the mold.

Other objects of the invention will become apparent from a reading of the following description, the appended claims, and the accompanying drawings, in which:

Figure 1 is a central vertical sectional view of a. mold assembly embodying the invention in one form, this figure being drawn on twice the scale of Figures 2 to 8, inclusive;

Figure 2 is a top plan view of a mold bottom or stool;

Figure 3 is a section on the line 3-3 of Figure 2; 1

Figure 4 is a top plan view of a mold proper or matrix side wall annulus;

Figure 5 is a section on the line 5-5 of Figure 4;

Figure 6 is a top plan view of Figure 7 is a section on the line of Figure 6; and I Figure 8 is a perspectiveview of an ingot or slab cast in the mold assembly shown in Figure 1.

I- have found that the crystalline formation of ingot metal is more purely dendritic and progresses more rapidly from the bottom upwardly in a big-end-down mold of the class referred to than in any other kind of mold, as there is 'constant and close contact between ingot and mold bottom or stool and no air gap to interfere with the extraction of the heat from the bottom oi the ingot. At the same time, a considerable air space is formed between the sides of the ingot and the vertical walls of the mold, due to the shrinkage of the ingot metal and the cross sectional contraction of the ingot. As the ingot contracts it draws away from the mold. This drawing away is most rapid when the walls of the big-end-down mold are highly tapered.

Crystallization occurs at substantially right angles to the perimeter of the mold chamber and to the mold bottom. Assuming that the mold is made of cast iron and is circular in cross section (the preferred contour for forming easily shatterable slab ingots) and that the stool bottom closure is very massive or heat absorptive, the crystal growth will be much more rapid from the bottom upwardly than it will be in the directions corresponding inversely to the radius of the circular walls defining the sides of the mold chamber. In fact, the freezing and crystallization irom'the side walls will be relatively shallow, due not alone to the loss of contact between ingot and mold but due also to the interference of the crystals that a hot top casing; I

have their nuclei at the face of the mold stool. By thus directing the formation of the crystals, 90% to 95% or even more of the usual sized alloy slab ingot will be formed of dendrites that are not interlocked or interlaced with others. As a consequence, the block or slab can be readily broken into the desired fragments.

The usual method of casting slabs or ingots of this kind is to lip pour from the ladle soon after the metal has been taken from the electric furnace. There is a very large quantity of slag; in fact, the slag is several times the volume of the metal but, having a lower specific gravity than the metal, it rises to the upper surface of the ingot. Fortunately the slag solidifies at a much lower temperature than the chromium or other alloy metal, so that it acts as a hot blanket for the top of the ingot and prevents its oxidation and rapid cooling at the top surface.

If the mold and hot top are not an integral unit, as has been the more usual practice, the metal hot top casing is fitted to the mold proper to hold the slag. Often a portion of the slag is permitted to run off into a container adjacent to the mold.

It is not the object of the present improvement to produce a sound, that is, a strong ingot. As previously stated, an object is to produce a slab or block ingot, preferably not over 4 inches to inches thick, which can be readily broken into relatively small fragments. These fragments are in turn crushed to sizes suitable for use in the art of alloying steels.

Figure 1 shows a preferred mold assembly embodying the invention and adapted to be used in performing the method and producing the slab in accordance with the invention. The assembly includes a mold bottom or stool A, a mold proper B mounted on the stool A, and a hot top casing C supported on top of the mold proper B. Also illustrated in Figure 1 is a slab or ingot S cast in the mold assembly. For the purposes of simplicity and clearness of the illustration of the essential features of the invention, the body of slag normally surmounting the slab S is not shown.

The stool A, shown in detail in Figures 2 and 3, includes a substantially circular body I formed with handling and clamping ears 2 and a pad 3 on the upper surface of the stool body. The purpose of the pad will be explained later.

The mold proper B shown in Figures 4 and 5 comprises continuous side or matrix walls 4 formed with handling or clamping ears 5 and with lugs 6 adapted to position the hot top casing C in the manner shown in Figure 1. The matrix.

walls in reality comprise a single circular wall but since the mold matrix or chamber is surrounded on all sides, the walls of the mold proper B are referred -to in the plurality. Furthermore, the invention may be embodied in molds in which the horizontal cross section is other than circular. For example, it may be embodied in square or polyhedral matrix molds. A round or circular mold is preferred because, having no corners, interlacing of the crystals as referred to above is avoided or maintained at a minimum.

The hot top casing C is indicated as being of metal, as are the stool A and the mold proper B. In the form shown, it comprises an annulus I provided with handling hooks or loops 8. The annulus I is formed with a spout orrun-oif pipe 9 through which slag may overflow.

In assembling the mold preparatory to pouring a slab or ingot, the mold proper B is centered 4 with respect to the stool A so as to leave a space indicated at l0 between the lower inner portions of the matrix side walls and the periphery of the stool pad 3. In accordance with a further feature of the invention the lower inner faces of 4 operating economy without deleteriously affecting the slab or ingot cast in the mold.

In practicing the method in accordance with the present invention the molten metal is top poured into the mold assembly until the molten metal reaches a level preferably somewhat below the top of the mold proper B. Usually slabs of this kind are poured from the lip of the ladle and a large quantity of slag flows into the mold assembly. The slag will float on the top and if 'an excess of slag is introduced into the mold the surplus slag will flow off through the overflow spout 9.

The shapes and the weight proportions or the heat absorptive capacities of the stool A and mold proper B are of importance in achieving the improved results described above. In the form shown, the inner matrix walls of the mold proper B have a taper of about 4 inches per foot. The minimum taper for obtaining good results is 1 to 2 inches per foot. This high degree of taper is important in assuring that during contraction of the slab it will draw away from the matrix side walls to form the dead air space between the periphery of the slab and the inner matrix walls. With such taper there is no likelihood of the slabs hanging up in the mold proper B by contact with its inner matrix walls. Consequently, the slab will rest firmly upon the mold bottom or stool A and the bottom face of the slab will be chilled effectively. In this way the lines of den- .dritio crystalline growth are caused to extend straight up or perpendicularly through the slab from the bottom face to the top face thereof. These vertical lines of crystalline formation are indicated at I2 in Figure 1. It is only at the extreme marginal part of the slab that some slight horizontal dendritic crystallization is present, as indicated at 13 in Figure 1.

A further important factor in providing the desired crystalline formation is the application to the bottom face of the slab of a chilling or heat extracting influence considerably greater than that applied to the edge of the slab. The weightor heat absorptive capacityof the mold bottom or stool A should preferably be not less than two. to three times that of the metal confining portion of the matrix walls. In the form shown in Figure 1 the weight of the stool A is about five times as great as the weight of the matrix walls up to the level of the slab S. Although these relative weights and the shapes, described above are considered the best for a mold of the size shown,

it will be apparent that the relative weights and shapes may be varied to some extent in the production of smaller or larger slabs or slabs of different cross sections and different types of metal. As an indication of the'size of the mold and slab illustrated by way of example, the minimum matrix cross section is about 52 inches and the ma mum matrix cross section is about 55 inches. The drawings are substantially to scale and other dimensions can be determined by comparison. The dimensions shown are the preferred dimensions of the particular mold shown, but are not to be considered in a limiting sense.

It will be seen that the pad 3 projects, as it were, up into the slab S so as to provide a peripheral rim on the bottom of the slab. The rim and the pad 3 thus interlock with each other and cooperate to maintain the slab centered so that, when it contracts, theperiphery of the slab will pull away from the matrix walls evenly and provide a uniform dead air space between the slab and the matrix walls.

The disc-like slab shown in Figures 1 and 8 has the desired crystalline structure described above and therefore is easily shatterable. The lines of growth of the dendritic crystals extend in substantially straight lines perpendicularly through the slab between the two larger (upper and lower) faces thereof except at the extreme margin of the slab.

Preferred embodiments and a preferred manner of practicing the invention have been described in some detail but it will be understood that various changes may be made in the described constructions and procedure without departing from the invention as defined in the claims.

I claim:

1. In a mold assembly for casting an easily shatterable metal slab, a mold proper the matrix walls of which are highly tapered; a supporting stool having a high heat absorptive capacity as compared to that of said matrix walls; and a substantially flat pad on said stool of less height than said matrix walls extending up into the matrix and having its margin spaced inwardly from the lower portions of the matrix walls to provide a space for forming a narrow marginal rim cast integrally with the slab, whereby said pad and said rim will maintain the slab centered with respect to the matrix walls to provide for the formation of a substantially uniform dead air space between the slab edges and the matrix walls when the slab contracts on cooling, the ratio of the mold matrix horizontal dimension to the mold matrix height being much greater than two-to-one so that a casting formed in said matrix will be in the form of a thin slab.

2. In a mold assembly for casting an easily shatterable metal slab, a mold proper the matrix walls of which are highly tapered; a supporting stool having a high heat absorptive capacity as compared to that of said matrix walls; and a substantially fiat pad on said stool of less height than said matrix walls extending up into the matrix and having its margin spaced inwardly from the lower portions of the matrix walls to provide a space for forming a narrow marginal rim cast integrally with the slab, whereby said pad and said rim will maintain the slab centered with respect to the matrix walls to provide for the formation of a substantially uniform dead air space between the slab edges and the matrix walls when the .slab contracts on cooling, the

heat absorptive capacity of the stool being great-' er than that of the metal confining part of the mold proper, the ratio of the mold matrix horizontal dimension to the mold matrix height being much greater than two-to-one so that a casting formed in said matrix will be in the form of a thin slab.

EMIL GATHMANN.

REFERENCES CITED The following references are of record in the file of thispatent:

UNITED STATES PATENTS Number 'Name Date 97,017 Johnston Nov. 16, 1869 1,019,244 Gathmann Mar. 5, 1912 1,327,987 Coates Jan. 13, 1920 1,419,454 Gathmann June 13, 1922 1,493,602 Coates May 13, 1924 1,531,388 Girdler Mar. 31, 1925 1,810,041 Gathmann June 16, 1931 1,892,569 Gathmann Dec. 27, 1932 1,961,399 Shook June 5, 1934 2,054,597 Gathmann Sept. 15, 1936 2,088,696 Gathmann Aug. 3, 1937 2,282,462 Dormin May 12, 1942 2,282,463 Dormin May 12, 1942 2,324,786 Lindermuth July 20, 1943 FOREIGN PATEN'IS Number Country Date 278,032 Great Britain Sept. 29, .1927 383,941 Germany Oct. 20, 1923

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