US2018762A - Method and mold for eliminating ingot surface defects - Google Patents

Description

Oct. 29, 1935.

E. J. KAUFFMAN METHOD AND MOLD FOR ELIMINATING INGOT SURFACE DEFECTS Filed April 18, 1932 0 04 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000000000000000000 0 0 0 00 00000 000 0 0 0 0 0 0 0 0 w 0 00n0N0M0 0 0 0 0 0 0 0 0 0% 0 0 0 0 0000 0000 00000.

00 000000000000000000000000000 000000000000000000000000000 000000000000000000000000000 0000000000000000000000000000000000000000000000 0 0000000000000000000000000000000000 00000000000000 w0n0w0n0w0N00N0VN0 %%0 0 0$$$$$$$V$W-WWM0 0 %0 0 0 0 0 0 0 0 0 0 Patented Oct; 29, 1935 PATENT OFFICE METHOD AND MOLD FOR ELHVIINATING INGOT SURFACE DEFECTS Edmund J. Kaufiman, Girard, Ohio, assignor to Valley Mould and Iron Corporation, Hubbard, Ohio, a corporation of New York Application April 18, 1932, Serial No. 605,965

13 Claims.

The present invention relates to metallurgy and more especially to a method and apparatus for preventing surface defects in ingots.

Steel ingots are usually cast in cast iron molds. The molten steel poured into the cast iron mold solidifies or freezes because of the heat being dissipated from the molten steel to and through the mold until the temperature has dropped below the freezing point of the steel. The contact of the molten steel with the relatively cold matrix walls of the mold quickly produces a thin frozen layer known in the art as skin. This skin, while thin and hot, has less tensile strength than when colder and thicker, and, therefore, tends to crack and break when under moderate stress. The skin when first formed is in direct contact with the mold walls, butas the steel freezes; it contracts and the outside frozen skin tendsto pull away from the mold walls and leave an air space surrounding the ingot. When the skin pulls away from the side wall of the mold, the dissipation of heat from the mold is retarded since the air gap between the matrix wall and the mold skin acts as an insulator and differential cooling results. This difierential cooling results in severe stresses and resultant strains being set up in the skin.

During the critical period after the skin has formed, the skin over the middle third zone lengthwise of the ingot is the hottest part of the ingot and, therefore, is the last portion of the ingot to shrink away from the mold wall. This hottest part of the ingot occurs in substantially the vertical middle part of the ingot and extends a length equal substantially to one-third of the height of the ingot. Also this portion of the ingot has the thinnest skin because it is the hottest zone; the weight of molten metal forming the interior of the ingot presses this skin outwardly and tends to stretch the same. This part of the surface of the ingot is thus frequently bound to the side walls of the mold and as the lower portion of the ingot cools, the shrinkage continues and the vertical shrinkage forces tend to lift the bottom of the ingot from the mold. This imposes very severe stresses on the thin skin adjacent the lower part of the hot zone. As the action continues, it frequently happens that the skin breaks just below the middle hot zone and the molten steel from the interior of the ingot runs through the crack thus formed and comes into contact with the cold mold wall, forming what is known as a bleed-out scab or button between the mold and the ingot. This button wedges the lower middle portion of the ingot tightly to the mold wall and since the ingot is anchored at this point, the continued cooling causes secondary skin cracking which becomes serious. As soon as air strikes the hot metal surfaces produced by the cracks, these surfaces are oxidized and each crack means an oxidized .crevice in the surface of the ingot. These oxidized crevices will not weld in subsequent treatment of the ingot. The cracks, therefore, introduce serious flaws in any article of manufacture fabricated from such an ingot. It is customary in the art to carefully inspect each ingot and chip out all of the cracks so that clean metal is exposed so that upon reheating and working the metal, these surfaces may tend to weld together, but this does not always happen. Where tar is used as a mold wash, as is the present tendency in the art, these cracking conditions are somewhat aggravated, sinceportions of the ingot tend to slip as soon as pressure is relieved while the hot middle zone tends to wedge tighter. It is the localized tension and drag on the mold skin which causes the difficulties above outlined.

Another difliculty is encountered due to circumferential shrinking which in a rectangular mold tends to produce longitudinal cracks in the ingot adjacent the corners of the mold because the corners of the ingot tend to cool faster than the side walls thereof, and the same condition which has been explained relative to the longitudinal stresses, which produce horizontal cracks, operate at the corners to produce circumferential stresses that result in longitudinal cracks. This condition also occurs on the crests of corrugations in corrugated molds. After a crack once starts, it may extend for a substantial distance. Furthermore, cracks frequently intersect, thereby produc-, ing deeper and more serious defects. The part of the ingot which tends to crack is under the maximum localized stress due to the concentration in one place of the total shrinkage over a large area which stretches the mold skin at this place beyond its elastic limit. After a crack once starts, that portion of the skin having broken, the resistance to stress has diminished and the crack becomes deeper and wider as the ingot continues to cool.

The present invention overcomes the above difliculties by preventing concentrated stresses and by equalizing the stresses over a large surface of the ingot subjected to stress so that small unit areas of the mold skin are held against movement, thereby permitting these small unit areas to absorb localized stresses by the stretch- .ing of the mold skin. Where the stresses due to the longitudinal shrinkage of several inches in a long ingot are concentrated at one point in the ingot, as was the prior art practice, cracks were certain to appear; whereas if these stresses are distributed throughout the entire length of the critical zone of the ingot, the stretching action for each unit area is very small, and is entirely within the elastic limit of the skin of the ingot at that particular small area and the cracks are prevented. Consequently, in accordance with the present invention, since the stresses are distributed throughout a large area of the surface of the ingot, the skin is not fractured and the difficulties are avoided.

The present invention contemplates a method and a mold whereby the thin skin of the ingot during initial freezing is subjected to uniformly distributed stresses rather than highly concentrated ones, thereby avoiding the resultant cracks and other surface defects such as bleed-out scabs" and the like. i

The present invention may be carried out in different ways and by different means but preferably comprises an ingot mold which is circumferentially thermally balanced by having relatively thick side walls as compared to the corner walls and wherein the surface of the mold is roughened over the critical area to such an extent as to anchor the initial skin to the mold wall. As the skin contracts, the anchorage causes the thin skin to stretch locally, thereby distributing the contracting forces while the skin is hot and elastic, so these stresses do not become critical. One means for accomplishing this purpose is to provide a plurality of small interlocking members between the mold and the ingot. This may be accomplished by roughening the matrix Gil mold wall, as for example, by providing small ribs or protuberances on the matrix wall of the mold. thereby resulting in indentations in the ingot skin, or by providing small pockets, recesses, or small grooves completely covering the matrix wall surface over critical zones, thereby providing small ribs or projections on the surface of the ingot in these zones. Projections on the ingot are preferred because they freeze quickly and thus hold the skin anchored while the skin is thin and thereby cause the skin to stretch locally. As the ingot cools down, it contracts a substantial amount so as to entirely withdraw these small interlocking portions from the mold wall so that the roughness provided on the matrix surface does not in any way interfere with stripping the ingot from the mold.

Realizing that the present invention may be embodied in structures other than those specifically illustrated herewith, it is to be understood that the disclosure herewith is illustrative and is not to be considered in the limiting sense.

Fig. 1 illustrates a vertical section through an ingot mold in accordance with the present invention which section is taken on line li of Fig. 2.

Fig. 2 is a plan view of the top of the mold shown in Fig. 1.

Fig. 3 illustrates a form of beads and grooves comprising interlocking members between the side wall of an ingot mold and an ingot.

Fig. 4 illustrates a frusto-conical form of interlocking members between the side wall of an ingot mold and an ingot.

Fig. 5 illustrates a wave form of interlocking members between an ingot mold and an ingot.

Fig. 6 indicates the preferred arrangement of intersecting grooves forming interlocking means between an ingot and a mold wherein preferably the grooves are arranged diagonally to the vertical axis of the mold.

Fig. 7 illustrates the portion .of a mold or ingot side wall provided with a plurality of pits 5 or recesses of frusto-conical formation to form interlocking means between the mold and the ingot.

The present invention may be carried out in an ingot mold of any well known contour, in 10 view of the fact that the present invention has to do entirely with the prevention of surface defects.

Figs. 1 and 2 illustrate a well known form of ingot mold having relatively thin corner walls I and thickened side walls 2. In order to locally stretch the initial skin formed on the ingot, roughened surfaces 4 are formed on the matrix walls of the mold. The matrix surface may be roughened by intersecting grooves, projections, etc., of uniform depth; however, even better re-- suits may be obtained by making the roughening deeper in the bottom zones than in the middle or top zones.

- Fig. 3 illustrates grooves 6 in the side wall. 2 2,5 of the mold which results in beads I in the side wall of the ingot 8.

Fig. 4 illustrates a trough-like groove 9 in the side wall 2 of the mold which results in wedgeshaped projections or ribs H) of the ingot 8. ,0

Fig. 5 illustrates waves II on the wall 2 of the mold which produces valleys I2 on the side of the ingot 8.

Fig. 6 illustrates the preferred arrangement of interlocking means between the mold and the R ingot comprising grooves and beads in that these members run diagonal to the vertical axis illustrated by the arrow A of the mold.

Fig. '7 illustrates a matrix surface provided with recesses 84 of the frusto-conical type and adapted to produce corresponding interlocking members upon the ingot.

It is to be understood that the interlocking members may be reversed, that is, the moldwall may either carry a bead or a groove. If a bead i is provided in the mold, then a groove is formed in the ingot. If a groove is provided in the-mold, then a bead is formed on the ingot. The same interchange applies to other forms of interlocking members. Preferably, the interlocking mem bers are provided with inclined side walls such as illustrated in Figs. 4 and 5 so that during the final cooling of the ingot and the final shrinkage accompanying the same, the contacting surfaces between the interlocking members will slide 01' separate one from the other on the diagonal lines, such as the lines it and it in Fig. 4. This obviates any undue stress being imposed on either the ingot or the mold in the final shrinkage stages after the ingot has substantially solidified. During the early stages of freezing and especially immediately after the mold skin is formed, the interlocking members between the matrix wall and the ingot anchor the skin to the mold so that as the initial skin cools, it is locally stretched and this stretching effect being distributed over substantially a large area of the ingot does not accumulate at any one point, and, therefore, the

local stretching being well within the elasticity of the skin, the skin does not tend to break. The 9- depth of the interlocking roughened surfaces are proportioned relative to the shrinkage of the ingot so that as theingot continues to cool, it shrinks away from the mold walls and the interlocking members are completely disengaged so that there 7 is no difficulty in stripping the ingot from the mold.

The effect of the roughness on the matrix surface of the mold is to sub-divide this surface into small unit areas wherein the shrinkage forces are localized Within the said small unit areas and movement of the initial mold skin is prevented relatively to the said matrix surface thereby obviatingthe starting of surface cracks.

By means of the present method and mold, surface defects in ingots heretofore common in the art have. been completely eliminated, thereby producing better ingots at a decidedly more economical cost of production.

What I claim is:-

1. An ingot mold for steel ingots comprising a cast iron body having the surface of the matrix walls provided with a plurality of projections and adjacent recesses adapted to interlock with the initial skin of an ingot to prevent relative movement between said skin and said matrix walls during initial solidification of the ingot, said projections and recesses being deepest in the lower portion of the mold.

2. The method of preventing surface defects in steel ingots comprising interlocking the initial skin of an ingot over small critical areas of the ingot to the matrix wall of the mold.

3. The method of preventing surface cracks in steel ingots comprisinglocalizing the shrinkage of the initial skin of the ingot to a plurality of small subdivisions of a large area of the surface of the ingot during teeming of the ingot.

4. The method of preventing surface cracks in metallic ingots comprising sub-dividing'a large area of the ingot surface into small unit areas and initially holding the boundaries of the small unit areas against movement to cause shrinkage forces in the skin of the ingot produced by cooling to be localized within the boundaries of each unit area.

5. The method of preventing surface cracks in a metallic ingot comprising interlocking the boundaries of small unit areas of the initial skin over a major portion of the surface of the ingot with the matrix wall of the ingot mold in which the ingot is cast to cause initial shrinkage forces within said unit areas to be substantially limited to said small areas.

6. The method of preventing the formation of cracks in the initialskin of a steel ingot during casting thereof which comprises pouring the ingot in an ingot mold and causing an initial skin to form adjacent the matrix walls of the mold, securing said skin, as it forms, at the boundaries of a plurality of closely spaced areas in fixed position, temporarily holding the skin thus secured against substantial sliding movement with respect to the matrix walls of the mold during the initial freezing stage and until the skin has grown to a self-sustaining, non-cracking thickness, releasing the thickened skin from the points of securement to permit the skin to slide relative to the matrix surface of the mold for removal of the solidified ingot from the mold.

7. The method of preventing the formation of cracks in the initial skin of a steel ingot during casting in a chill mold, which comprises pouring the ingot in a chill mold and causing an initial skin to form on the ingot, interlocking said skin, as it forms, to the mold matrix wall at closely spaced areas over a substantial portion of the surface of the ingot and thereby holding the skin against movement during initial solidification of the ingot and until the skin has grown to a self-sustaining, non-craking thickness, and releasing the thickened skin from said mold matrix wall to permit the skin to move along the surface of the mold for the final shrinkage of the ingot in the mold.

8. An ingot mold for steel ingots having the major portion of the matrix wall divided into small areas presenting a rough surface adapted to interlock the initial skin of an ingot to the matrix walls at the boundary of each small area over the roughened surface to compel the initial skin of the ingot to stretch locally within the boundary of each small area and thereby obviate the cracking of the skin of the ingot during initial freezing.

9. An ingot mold for steel ingots having the major portion of the matrix wall divided into a plurality of small adjacent areas bounded by means adapted to interlock the initial skin of an ingot during initial freezing to the boundaries of said areas to localize shrinkage forces within the said boundaries of each small area and thereby obviate cracking of the skin of the ingot during initial freezing.

10. An ingot mold for steel ingots comprising a cast iron body having the major portion of the surface of the matrix walls thereof provided with a plurality of closely spaced securing elements adapted to temporarily secure the initial skin of an ingot thereto to cause local stretching within small, adjacent areas of the skin of the ingot thereby obviating the concentration of shrinkage forces in said skin, said elements being disengaged from said skin upon final shrinkage of the ingot, whereby the same may be stripped from the mold.

11. An ingot mold for steel ingots comprising a cast iron body having the major portion of the surface of the matrix wall thereof provided with small area projections and surrounding recesses adapted to engage complemental recesses and projections formed in the initial skin of an ingot cast in the said mold, to form interlocks between the skin of the ingot and matrix wall and prevent accumulative movement of said skin along said matrix wall during the initial solidification of the ingot, said projections and recesses being of a size and shape such as to be disengaged upon final shrinkage of the ingot to permit the same to be stripped from the mold.

12. An ingot mold for steel ingots comprising a body having the majorportion surface of the matrix walls thereof provided with a plurality of shallow recesses adapted to produce complemental projections on the initial skin of an ingot cast in said mold and being so spaced over.

the surface of the matrix of the mold as to prevent concentration of shrinkage forces in said skin of the ingot such as would create cracks in said skin.

13. An ingot mold for steel ingots comprising a body having the major portion of the surface of the matrix wall thereof provided with a plurality of intersecting grooves adapted to produce complemental projections on the initial skin of an ingot cast in said mold, said grooves being so distributed over the matrix surface of the mold as to prevent concentration of shrinkage forces in said skin such as would create cracks in said skin, said grooves being of a dimension such as to permit the complemental projections on the ingot to be withdrawn therefrom upon final solidification of the ingot, whereby the latter may be stripped from the mold;

EDMUND J. KAUFFMAN.

Images