US3477682A - Ingot mold with hot top and refractory lining for inducing progressive axial solidification - Google Patents

Description

N V- 1. 1969 K. M. SHUPE INGOT MOLD WITH HOT TOP AND REFRACTORY LININ FOR INDUCING PROGRESSIVE AXIAL SOLIDIFICATIO Filed May 17, 1965 F IG.4

INVENTOR KAY MSHUPE av 97 ATTORNEY United States Patent 3,477,682 IN GOT MOLD WITH HOT TOP AND REFRACTORY LINING FOR INDUCING PROGRESSIVE AXIAL SOLIDIFICATION Kay M. Shupe, Fredonia, N.Y., assignor t0 Allegheny Ludlnm Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania Filed May 17, 1965, Ser. No. 456,434 Int. Cl. B22d 7/10; B22c 1/00 U.S. Cl. 249-106 Claims ABSTRACT OF THE DISCLOSURE Apparatus is described for reducing the tendency to form secondary pipe in ingots. It includes a refractory lining to an ingot mold with the use of a hot top for inducing progressive axial solidification from the bottom to the top of the mold cavity.

This invention relates to apparatus for use in the casting of molten metal, and in particular to the effective composition of an ingot mold which is suitable for use in the production of ingots having a reduced tendency to exhibit secondary piping.

Considerable prior art is available in which it is taught that the manner of ingot solidification affects the quality of the solids produced from the ingot. Such variables as porosity, alloy segregation, dendrite size and direction of growth, grain size, and the amount of hot top end loss due to shrinkage are highly influenced by ingot mold design. This problem becomes more acute where the relative temperature difference between the solidus and liquidus lines of the metal being teemed is quite large. Some of the significant factors affecting ingot mold design include the relationship between the inside-outside dimensions of the mold, the method of hot topping the ingot, variations in design, and material in the stool or base plate where an open bottom mold is used, temperature of the metal being teemed into the ingot mold, a general configuration of the ingot mold such as big-end-up and big-end-down, and whether the mold is rectangular, round, fluted or square in cross section.

An object of the present invention is to provide an eifective composition for an ingot mold which will reduce the tendency for ingots to exhibit secondary piping.

A more specific object of this invention is to control the heat flow through the walls of an ingot mold to provide for progressive axial solidification to take place from the bottom to the top of the mold cavity.

Other objects of this invention become apparent when read in conjunction with the following description and the drawings in which:

FIG. 1 is a schematic illustration demonstrating the cooling rates of metal in an ingot mold wherein the ingot produced therefrom displays secondary piping;

FIG. 2 is a schematic illustration of an ingot mold which demonstrates the manner in which progressive axial solidification takes place from the bottom to the top;

FIG. 3 is a schematic illustration of a portion of an ingot mold which is utilized in one embodiment of the present invention;

FIG. 4 is a schematic illustration of another embodiment of the present invention similar to FIG. 3; and

FIG. 5 is a schematic illustration of a portion of a bigend-up ingot mold which illustrates another embodiment of the present invention.

Some grades of steel shrink much more during solidification than others. These grades are plagued by the problem of secondary piping which is caused by a discontinuous axial solidification of the metal. As a result thereof, bridging results during solidification, which the result 3,477,682 Patented Nov. 11, 1969 that when the molten metal has completely bridged over a liquid portion contained within the mold, normal solidification shrinkage results in the creation of porosity or piping.

Reference is directed to FIG. 1 which diagrammatically illustrates this problem. An ingot mold is shown generally at 10 which may be generally designated a bigend-up ingot mold and is formed of side walls 12 and a base 14, the side walls 12 substantially uniformly tapering upwardly and which are characterized by having the narrowest cross-sectional area at 16 near the top of said side walls 12. A hot top 18 is provided in order to retain a molten supply of metal near the top of the ingot. This molten supply of metal acts as a reservoir for feeding molten metal into the ingot mold as the ingot shrinks during solidification. The arrows 20 represent the freezing rate at any given instant. Molten metal in the area designated x within the ingot mold cavity is trapped by the bridging as at 24 so that when the liquid metal designated x solidifies and shrinks, porosity will result.

Ideally, it is desirable, in order toprevent secondary piping, to control the fiow of heat to provide for progressive axial solidification for the prevention of bridging. Referring now to FIG. 2 which diagrammatically illustrates this phenomenon, reference again is directed to the ingot mold 30 which is formed of upwardly extending side walls 32 and a base 34. A hot top 36 is provided near the upper extremity of the side walls 312 to serve as a rservoir of molten metal. The molten metal 38 contained within the mold 30 ideally possesses a controlled heat flow so that the arrows 40 represent the freezing rate at any given instant. Since there will be no bridging as at 24 in FIG. 1 during the freezing of the molten metal, progressive axial solidification will take place from the bottom to the top, thereby resulting in the production of sound, homogeneous ingots.

As stated hereinbefore, the apparatus of the present invention is useful in the casting of molten metal, and specifically is directed to providing an effective composition of the ingot mold so as to control the flow of heat therefrom to provide for the progressive axial solidification of molten metal from the bottom to the top. Reference is now directed to the embodiment of FIG. 3 which illustrates, in part, one embodiment of the apparatus for so controlling the flow of heat. In FIG. 3 the ingot mold is partially shown as at 50 and comprises substantially upwardly extending side walls 52 in which the interior wall 54 tapers outwardly from the center line. The ingot mold 50 may be provided with an integral bottom (not shown) and the side walls substantially taper uniformly .upwardly so that the narrowest horizontal portion or cross-sectional area of the ingot mold walls occurs near the upper extremity thereof. In the embodiment shown in FIG. 3, the interior walls 54 are provided with a stepped portion 56 which occurs a predetermined distance below the upper extremity of the side wall 52. The stepped portion 56 of the interior side walls 54 functions to provide a seat upon which a sheet metal liner 58 is disposed to rest. The sheet metal liner 58 is characterized by upwardly extending walls 60 which are inwardly inclined from the slope of the stepped portion of the interior walls 54. The sheet metal liner 58 may terminate in the frustum of a pyramid as at 62, or in any other suitable shape so long as the same extends a predetermined distance above the top level or upper extremity of the side wall 52. A retaining ring 64 is disposed in seating engagement on top of the ingot mold walls 52 and thus provides a somewhat annular type gap or opening 66 into which a refractory composition 68 is placed, said refractory composition 68 usually extending from the stepped portion of the interior wall 54 and upwardly to substantially the upper extremity of the retaining ring 64, the portion of the refractory compound 68 which extends above the upper extremity of the upwardly extending side walls 52 functioning as a hot top. It has been found that the sheet metal liner may be made of any metallic composition which will not unduly change any of the ingot analysis desired in the final product, and the refractory composition 68 which is disposed within the space 66 between the retaining ring 64 and the sheet metal liner 58 most conveniently takes the form of sand. It will be appreciated that since the refractory composition 68 is disposed between the ingot mold wall and the metal being cast in the ingot mold cavity, the effective composition of the ingot mold is thereby changed so that the upper portion thereof will have a much slower or controlled heat flow than that of the bottom portion. In this respect, the ingot mold design can be varied so that the stepped portion of the upwardly extending side walls can occur at any predetermined point below the upper extremity of the side walls, depending upon the composition of the steel of the metal being cast. In addition to providing for a substantially large effective cross section of the refractory compound in the space 66 between the liner 58 and the retaining ring 64, additional means can also be employed for maintaining the hot top portion of the ingot mold in a molten condition, said means including the use of exothermic compounds which, through chemical reaction, generate heat for maintaining the metal in the hot top portion molten. Success is also obtained with the application of gas or electric hot tops which provide for the application of an external source of energy to supply the heat necessary to maintain the metal in the hot top molten until the balance of the ingot has solidified progressively axially from the bottom of the ingot to the top thereof.

Reference is now directed to FIG. 4 which illustrates another embodiment of the presentinvention which is similar to that of FIG. 3. In FIG. 4, an ingot mold is shown generally at 70 which comprises upwardly extending side walls 72, which are joined at the bottom by a base (not shown), said upwardly extending side walls 72 having internal surface 74 which defines a mold cavity shown generally at 76. The upwardly extending internal surfaces 74 are provided with a stepped portion 78 at a predetermined distance below the upper extremity of the ingot mold 70. The upwardly extending side walls 72 substantially taper so that at the upper extremity thereof, the horizontal cross-sectional area is at a minimum. As illustrated in FIG. 4, it is preferred that the ingot mold 70 be of the big-end-up type in which the internal surfaces 74 are substantially outwardly inclined from a vertical axis through the ingot mold cavity 76. A castable refractory compound 80 or a refractory brick is disposed on the stepped portion 78 adjacent internal surfaces 74 and extends from the stepped portion 78 to the upper extremity of said upwardly extending side walls 72. The castable refractory material 80, for example, is of the type sold under the trade name of Alfrax No. 57 by the Carborundum Corporation and has a nominal composition of about 94.5% A1 about 1% SiO and about 4% CaO, which can be formed in place and thereafter cured through the application of heat. Where bricks are employed in this embodiment, they can be cemented into place with refractory cement. It has been found that brick sold under the trade name of Dando ladle brick by the H. K. Porter Company having a nominal composition of 70% SiO and 30% A1 0 is satisfactory for this purpose. As in the illustration of FIG. 2, a standard hot top can be employed together with a gas or electrical hot top or the application of exothermic compounds to the hot top can be employed in order to provide a reservoir for molten metal to be fed into the mold cavity 76 as the metal solidifies progressively axially upward from the bottom to the top of the mold.

As a further embodiment of the apparatus of the present invention, reference is directed to FIG. 5 which demonstrates another means for controlling the flow of heat from an ingot mold. In FIG. 5, an ingot mold, preferably of the big-end-up type, is represented generally at 90, and which comprises upwardly extending side walls 92, having an interior surface 94, which are connected to any suitable base (not shown) said side walls 92 uniformly tapering upwardly so that the slope of the interior walls 94 forming the mold cavity 96 are substantially outwardly extending from a vertical axis through the center of the mold cavity 96. A refractory lining 98 is interposed adjacent the interior mold walls 94 and extends a predetermined distance downwardly from the top of the ingot mold to the desired depth within the mold cavity. The refractory lining 98 may consist of a plurality of layers of asbestos, for example, each layer of which may have a successively shorter length in order to provide a substantially tapering refractory lining which is characterized by having its greatest horizontal crosssectional area adjacent the upper extremity of the ingot mold 90. Thus, by varying the number of layers and progressively decreasing the depth that said refractory lining layers extend from the upper extremity of the ingot mold wall downwardly, a refractory lining is provided which will permit the greatest heat flow near the bottom of the mold, which heat flow will diminish as the level in the mold increases. Thus the over-all effect of the refractory lining is to retard the solidification near the upper end of the mold and provide for the progressive solidification transversely inwardly from the ingot mold walls and upwardly from the bottom of the ingot mold to the hot top portion. Moreover, in the embodiment of FIG. 5, standard hot top procedures can be used which may include the application of an exothermic mix or the provision for gas or electric hot topping facilities.

In practice, an ingot mold having a configuration similar to the embodiment illustrated in FIG. 3 was employed in teeming a heat of steel having a nominal composition of AISI type H-13 tool steel. The ingot mold 50 was provided with a sheet metal liner 58 disposed in seating engagement on the stepped portion 56 of the interior surfaces 54 of the side walls 52. A sheet iron retaining ring 64 was thereafter placed in seating engagement on top of the upwardly extending side walls 52, and a white sand was packed into the opening 66 between the sheet metal liner 58 and the retaining ring 64. Upon solidification, the ingot was removed, and after heat treatment, was cogged on a forging press to produce a 24" square billet. Upon cooling, it was determined that the ingot produced 25,250# out of a possible 26,900# of Class A sonic material. Further castings of ingots having the same nominal composition of A181 type H-13 tool steel resulted in 17,000# of material which, at the 24" square billet size, was classified as Class A sonic. The difference between the embodiment of FIG. 3 and the embodiment of FIG. 4 in the reported ingot weight resulted from a difference in the type of hot topping in that the hot top utilized in the embodiment of FIG. 4 was a refractory hot top which sat within the confines of the interior surfaces of the ingot mold thereby greatly reducing the volume of metal which was cast into the ingot mold.

The apparatus of the present invention is effective for substantially completely eliminating that characteristic known as secondary piping, which is one of the difficulties that has plagued the production of tool steel in large ingot sizes. Utilization of the apparatus is simple and straight-forward, and the ingot mold is reusable in the same manner as a conventionally designed ingot mold. By using any of the embodiments set forth hereinbefore, success has resulted in the production of ingots which are characterized by a reduced tendency to exhibit secondary piping.

I claim:

1. Apparatus for use in the casting of molten metal which is characterized by the production of ingots having a reduced tendency to exhibit S T'QQBdary piping, comprising; an ingot mold having an interior wall defining a mold cavity, a hot top disposed in seating engagement on the ingot mold, a permanently fixed refractory lining disposed within said mold and extending downwardly from the top of the mold into the mold cavity a predetermined distance below said hot top a sufiicient distance to preclude entrapment of molten metal within the solidified portion of said ingot, said refractory lining having a cross section progressively larger upwardly from its downward extent reaching a maximum cross section in the mold cavity at the engagement of the hot top and the ingot mold, whereby the progression of solidification of the cast metal within the mold is controlled by the length and thickness of the refractory.

2. Apparatus for use in the casting of a molten metal which is characterized by the production of ingots having a reduced tendency to exhibit secondary piping, comprising an ingot mold having stepped interior walls defining a mold cavity, said mold cavity having its greatest crosssectional area at its upper extremity, a hot top disposed in seating engagement on the ingot mold, an upwardly extending permanently fixed sheet metal lining disposed in seating engagement on the stepped portion of the mold cavity, said sheet metal liner being inclined inwardly from the interior walls of the mold, and a refractory compound, substantially non-reactive with the molten metal, disposed between the sheet metal liner and the interior mold walls with the maximum cross section of the refractory compound being disposed adjacent the hop top, said stepped wall, sheet metal lining and refractory lining extending into said mold cavity a sufficient distance to preclude entrapment of molten metal within the solidified portion of said ingot and said liner and refractory having a combined cross section progressively larger upwardly from the seating engagement on the ingot mold Within the mold cavity and reaching a maximum cross section in the mold cavity at the engagement of the hot top and the mold, whereby the progression of solidification of the cast metal within the mold is controlled by the length and thickness of the refractory.

3. Apparatus for use in the casting of molten metal which is characterized by the production of ingots having a reduced tendency to exhibit secondary piping, comprising; an ingot mold having stepped interior walls defining a mold cavity, said mold cavity having its greatest crosssectional area at its upper extremity, a hot top disposed in seating engagement on the ingot mold, and a refractory lining, substantially non-reactive with the molten metal fixedly disposed within said mold cavity in the stepped portion of the interior walls, said stepped portion and refractory lining extending into said mold cavity a sufficient distance to preclude entrapment of molten metal within the solidified portion of said ingot and said refractory lining having a cross-section progressively larger upwardly from its seating engagement on the stepped portion of the interior walls and reaching a maximum cross-section in the mold cavity at the engagement of the hot top of the ingot terior walls having a stepped portion disposed a predetermined distance below the top thereof and said mold cavity having its greatest horizontal cross-sectional area at its upper extremity, a hot top disposed in seating engagement on the ingot mold, an upwardly extending sheet metal lining fixedly disposed in seating engagement on said stepped portion of the ingot mold cavity, said sheet metal liner being inclined inwardly from the slope of the interior walls of the mold, and a refractory sand, substantially non-reactive with the molten metal, disposed between the sheet metal liner and the interior walls of the mold, said stepped portion, sheet metal lining and refractory sand extending into said mold cavity a sufficient distance to preclude entrapment of molten metal within the solidified portion of said ingot and said refractory sand having a horizontal cross-section progressively larger upwardly from its engagement with the stepped portion and reaching a maximum horizontal crosssection in the mold cavity at the engagement of the hot top and the ingot mold, whereby the progression of solidification of cast metal within the mold is controlled by the length and thickness of the refractory.

5. Apparatus for use in the casting of molten metal which is characterized by the production of ingots having a reduced tendency to exhibit secondary piping, comprising; a big-end-up ingot mold having outwardly extending interior walls defining a mold cavity, said mold cavity having its greatest cross-sectional area at its upper extremity, a hot top disposed in seating engagement on the ingot mold, and a refractory lining, substantially non-reactive with the molten metal, fixedly disposed within the mold cavity adjacent the interior walls, said refractory lining extending into said mold cavity a sulficient distance to preclude entrapment of molten metal within the solidified portion of said ingot and said refractory lining being inclined upwardly from the slope of the interior Walls and extending downwardly a predetermined distance below the hot top, said refractory lining having a cross-section progressively larger upwardly from its downward extent reaching a maximum horizontal cross-section in the mold cavity at the engagement of the hot top and the ingot mold, whereby the progression of solidification of the cast metal within the mold is controlled by the length and thickness of the refractory.

References Cited UNITED STATES PATENTS 139,798 6/1873 Lobdell 249-198 2,567,525 9/1951 Morris 249-199 1,634,999 7/1927 Krause 249-112 3,012,296 12/ 196 1 Wiesner .249-112 3,072,981 1/1963 Davidson 249-201 3,166,807 1/1965 Daley 249-201 FOREIGN PATENTS 386,860 l/ 1933 Great Britain.

522,086 6/1940 Great Britain.

J. SPENCER OVERHOLSER, Primary Examiner ROBERT D. BALDWIN, Assistant Examiner US. Cl. X.R. 249-174

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