US2867871A - Hot-top for ingot mold - Google Patents

Description

United States Patent HOT-TOP FOR INGOT MOLD Application July 10, 1956, Serial No. 596,910 7 Claims. (Cl. 22-147) Pittsburgh, Pa., assignor to Columbus, Ohio, a cor- This invention relates to the casting of metal ingot-s and the like in ingot molds having hot-tops for preventing pipe and other imperfections. More particularly this invention relates to permanent hot-tops which are lined with an exothermicallyreacting material capable of producing and retaining sufficient heat to assure high yields of sound castings.

Following the completion of refining operations in the process of manufacturing steel, the molten steel is teemed into a cast iron mold where the steel is allowed to solidify into ingots. As the metal cools in the mold, imperfections such as pipe are formed in its interior by shrinkage and entrapped gases. For example, when a fully killed steel is teemed into either a big end-up or a big end-down mold, a deep cone-shaped cavity, known as pipe, forms in the upper end of the ingot as a result of shrinkage of the metal during cooling.

The formation of pipe due to metal shrinkage in steel ingots has been found to be preventable by the application of a hot-top to the mold for retaining and feeding molten metal to the shrinking ingot. The refractory material from which such a hot-top is generally constructed or with which it is lined absorbs heat from the metal less rapidly than the cast iron walls of the mold so that the top of the ingot remains molten until after the remainder of the ingot has solidified. An overlying pool of liquid steel is thus furnished which feeds metal down into the ingot to overcome the shrinkage due to solidification of the metal.

One form of hot-top used in the above manner is made in the form of an outer cast iron shell having a refractory lining in its interior to reduce the heat loss. Only the refractory requires replacement from time to time while the hot-top casting can be reused many times. The placement of cast iron hot-tops on the ingots creates a substantial problem of hanging ingots, however. When the hot-top casting is placed on the cast iron mold, molten metal tends to run out through the joint or interface formed between them. This runout chills as part of the ingot skin to form fins which, in flange-like fashion, hold the ingot securely in place in the mold. As a consequence, when the ingot cools and shrinks within the mold, it is held hanging off of the mold bottom. Tremendous stresses are set up in the ingot skin because of the weight of hanging metal and defects, known in the industry as hanger cracks, are formed in the ingot. Various devices have been employed in the past to seal the joint between the hot-top and the mold. In most instances these devices have been expensive, cumbersome to use, and susceptible to damage by the shrinking metal. For example, a refractory lining or hot-top has been made to extend downwardly into the mold and act as a sealing agent for preventing the molten steel being' teemed into the mold from reaching the crack between the mold and the hot-top. In another attempt to correct this difficulty, the portion of the refractory hot-top extending into the mold was formed with a wiper blade to prevent molten 2,867,871 Patented Jan. 13, 1959 metal from reaching the crack between the mold and hottop.

Attempts have been made in the foundry industry to increase the effectiveness of the hot-top and thereby reduce the amount of metal needed to feed an ingot. These attempts have generally followed along the line of increasing the temperature and heat transfer characteristics of the hot-top. In this regard, the use of hot-tops lined with an exothermically reacting or heat-producing material has achieved wide acceptance in foundry practice. One such material is shown in U. S. Patent 2,591,105. This patent describes heat producing mixtures containing aluminum and one or more oxidizing agents along with a controlled amount of a fluoride. Such mixtures are described as being useful in the casting of molten metal, and more particularly, this patent points out that sand casting risers which are lined with sleeves composed of this heat-producing material instead of a refractory will provide much higher casting yields and substantial improvements in the quality of the casting itself.

It is, therefore, one object of the present invention to improve the construction of a permanent hot-top and mold for preventing the runout of metal between the hottop and the mold, while at the same time making the most efiicient use of the mold volume without increasing the mold depth to accommodate a projection of the hottop or using wiper strips or other mechanical devices to prevent such runout.

It is another object of the present invention to improve the feeding efiiciency of permanent hot-tops and to reduce the volume of the feeder head required for a particular size of ingot mold.

It is a further object of the present invention to improve the construction and simplify the use of permanent hottops having linings formed of exothermically reacting materials for increasing both the heating and insulating characteristics of the hot-top.

It is still a further object of the present invention to produce an improved ingot by eliminating the laminar layers of metal heretofore formed when permanent hottops having liners of exothermically reacting materials are used on the ingot molds.

Other objects and advantageous features will become apparent as the following description proceeds, taken in connection with the accompanying drawing in which:

Figure l is a plan view of a hot-top constructed according to present invention.

Fig. 2 is a sectional elevation view of a hot-top and ingot mold taken substantially in plane of line 22 of Fig. 1.

Fig. 3 is a fragmentary sectional elevation view similar to Fig. 2 and showing a mold and hot-top illustrative of the present invention having teemed therein a charge of molten metal.

Fig. 4 is a fragmentary sectional elevation view similar to Fig. 3 and showing the ingot metal at a later time after it has cooled.

While the invention is susceptible of various modifica tions and alternative constructions, a certain preferred embodiment has been shown in the drawing and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed but, on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the sp rit and scope of the invention as expressed in the appended claims.

Referring more particularly to the drawings, there is shown in Figs. 1-4 a cast iron ingot mold 10, of the big end-up type, having a mold cavity 11 opening into an upper surface 12. The bottom (not shown) of the mold can either be integral with the side walls 15 or be formed as a stool on which the mold sits. A hot-top, shown 3. generally as 18, is placed on the top of the mold and comprises a. permanent casting 19 formed with a feeder head cavity 20 extending therethrough and lined with a sleeve or liner 21 made up of 'sand or the like containing an exothermically reacting material.

The hot-top casting 19 preferably formed of cast iron, comprises a riser portion 24 terminating in a base 25 approximately the shape of the upper end of the mold 10 on which it is to be used. A pair of lifting hooks 26 or the like are formed on the outer surface of the riser 24 for engagement by a hoist or other lifting device. The

riser 24 is formed with a substantially cylindrical shaped cavity 20 and is provided with a pair of opposed recesses 28 adjacent its upper end.

Fitted within the hot-top casting cavity 20 is a complementary sleeve or liner 21 formed of moldable exothermically reacting material and shaped to correspond to the casting cavity 20. The liner 21 is supported within the casting by a pair of lugs or projections 29 integrally formed thereon which seat in the recesses 28 on the casting 19. In this manner, the liner can be easily replaced each time the hot-top 18 is used and no mechanical connections or attachments are necessary to support the liner.

One exothermically reacting or heat producing mixture useful in accordance herewith is sold under the trademark Feedex and has a preferred composition lying within the ranges set forth below:

Percent Aluminum in divided form such as a mixture of powder and sawings 30-50 Sodium nitrate or barium nitrate -10 Manganese dioxide or iron dioxide or a mixture Reference is made to U. S. Patent No. 2,591,105 for a more detailed description of the above composition. Details as to methods of forming shapes from the granular material as well asto the variations in the composition which are dependent on the type of metal being cast are set forth in such patent.

An ingot is cast by placing a permanent hot-top casting fitted with a lining of exothermically reacting material, as described above, on a mold and teeming molten steel into the mold through the hot-top. Pouring is continued until the mold and the hot-top is full (Fig. 3). As the molten steel rises into the hot-top and into contact with the heat producing lining, the heat of the metal initiates the reaction of the exothermically reacting materials making up the liner. A substantial amount of heat is produced by this reaction and this heat keeps the metal in the hot-top in the molten state. A reservoir or feeder head 31 of molten metal is thus kept available for feeding the ingot as it solidifies and shrinks.

In accordance with the-present invention, provision vis made for preventing runout of molten metal in the crack 32 between the mold and the hot-top 18 which results in the formation of hanger cracks in the solidified ingot. This is accomplished by projecting the bottom surface 33 of the hot-top casting 19 inwardly from the mold walls to overhang the mold cavity 11- opening into the top of the ingot mold 10. The overhang is desirably formed by having the bottom opening of the feeder head cavity in the hot-top casting smaller than the corresponding opening of the mold cavity 11.

For most efficiently preventing runout, it has been found that the hot-top casting should extend over the.

mold cavity an equal amount from side wall 15 of the ingot mold and that the extent of this overhang should be at least about /2 inch. The molten steel, when poured intothe mold, contacts this overhanging hot-top surface 33 and is locally chilled to form a protective skin 35 which prevents runout in the crack 32 between the hot top casting 19 and mold 10. By preventing this runout, hanger fins cannot form and the formation of undesirable hanger cracks is avoided.

In addition to projecting the hot-top casting 19 over the mold cavity 11 where it acts as a chill, the contacting surfaces 12, 33 of the mold and the hot-top are desirably machined smooth and flat. These fiat surfaces afford a tight fit between the mold and hot-top to effectively prevent runout before the molten metal has chilled and a protective skin has formed.

In order to prevent the chilling action of the hot-top casting from causing the ingot metal to freeze over beneath the feeder head before the ingot has solidified, the exothermically reacting liner 21 is located within the hottop casting 19 with its lower surface 36 in substantially the same plane as the interface or crack 32 between the hot-top casting and the mold. In this manner the heat given off by the liner keeps molten the cast metal near the center of the ingot mold and effectively localizes the chill effect of the hot-top casting overhang. As a result a metal skin is prevented from forming over the upper surface of the ingot before the feeding action is complete.

As the molten ingot metal solidifies, the ingot 38 shrinks and pulls away from the top of the mold as shown in Fig. 4. The peripheral portions of the ingot solidify first and, when molten metal comes in contact with these relatively cooler solid portions, laminar layers of metal are formed which cause difliculties when rolling and working the ingot. Therefore, provision is made for preventing the flow of molten metal 31 from the hot-top over the solidified top portion of the ingot 38. To this end the heat producing liner 21 is spaced from the permanent hot-top casting to provide an annular space 39 between them. This space is maintained by dimensioning the projections 29 relative to the recesses 28 in the casting 19 such that the minimum clearance is obtained even when the lug contacts the recess wall or any other suitable spacing means can be provided to maintain the desired spacing. When molten steel is teemed into the ingot mold, it rises into this annular space 39 between the liner 21 and the casting 19 and is chilled by contact with the metal casting to form an annular collar or dam 40 on the upper end of the ingot. As the ingot 38 solidifies and shrinks and the top of the ingot falls below the upper surface of the mold and away from the hot-top, the dam 40 serves to confine the molten metal 31 from the hottop to the central area of the mold.

It has been found that the thickness of the annular space 39 between the heat-producing liner 21 and the permanent hot-top casting 19 is an important factor in producing sound castings and should be at least 5 and preferably in the range of M to Vs" for the most desirable results. When this thickness is in the range of A to A", the chill effect of the permanent casting is sufficient to freeze the annular collar or dam 40 and overcome the heatin effects of the heat producing liner 21. Furthermore, as this dam of metal 40 drops out of the annular space 39 between the liner 21 and the casting 19 as the ingot 38 shrinks, the air space remaining serves as an insulation and effectively reduces heat losses from the linear to the casting.

If the clearance between the liner and the permanent tive and metal in the annular space will stay molten longer.

In the latter situation the metal penetrates to the top of the sleeve and too high a dam is formed. As a result, a permanent layer of thin metal sticks to the ingot after the ingot has solidified and rolling mill difliculties are encountered.

In the design of hot-tops for ingot molds according to the present invention, it has been found that the volume of the hot-top and heat-producing lining need seldom exceed 8% of the mold capacity to produce soundingots, and volumes as low as 4% of the mold capacity can be successfully used with most grades of metal. For most eflicient feeding, it has been found that the heat-producing lining or sleeve should have an average inner diameter to height ratio rates of l to l (D:H==1:l) and that the range of ratios for efiicient feeding is from 2:1 to 1:2. The thickness of the heat producing lining will depend on the amount of heat necessary to keep the metal in the feeder head molten for the desired length of time.

It has been found also that an exothermically reacting material substantially identical to that employed in making the sleeves but without the binder or other materials required in sleeve manufacture, will even further reduce the amount of feeder metal required in ingot molding. By topping the molten metal with the additional exothennically reacting material, loss of heat to the air is reduced to a minimum. Thus, in accordance with the preferred method of employing heat-producing liners of exothermically reacting material in hot-tops, a relatively thin layer of a hot-topping compound containing the same essential ingredients as the sleeve, i. e. aluminum, an oxidizing agent such as iron oxide or manganese oxide, and an alkali fluoride, should be placed on the molten metal as soon as it has risen to the top of the riser. This hot-topping compound, when placed on the molten metal in the hot-top in a layer of from about one-quarter to three quarters inches in depth and preferably about onehalf inch in depth, adds more heat to the metal in the feeder head, and acts as an effective insulation to prevent heat loss from exposed metal in the hot-top.

By improving the construction of hot-tops in accordance with the invention herein described and claimed, the feeding efiiciency of metal to an ingot is substantially improved inasmuch as the molten metal so fed is confined to the central area of the ingot. This results in substantial savings in cost over more conventional methods because less exothermically reacting material, a relatively expensive item, is needed. Furthermore, the improved construction described herein is extremely successful in preventing runout between the hot-top and the mold in a manner heretofore believed to be impractical. The elimination of runout and its attendant consequence of hanger cracks in the ingot has been accomplished too, in a simple and inexpensive way, and the need for elaborate devices and pouring methods to prevent such runout is avoided. In addition, substantial savings in cost result from the use of a permanent hot-top casting in which only the heat-producing lining need be changed for reuse.

I claim as my invention:

1. In combination, an ingot mold and an improved hot-top, said mold comprising a metallic body portion having a mold cavity therein opening into the upper surface thereof, said hot-top comprising a metallic body portion having an inner wall defining a cavity extending therethrough and opening into a lower surface of said hot-top, said hot-top cavity being lined throughout its length with a liner formed of a moldable exothermically reacting material, said hot-top cavity opening being smaller than said mold cavity opening to the extent that when said but top opening is complementary to said mold opening said hot top surface extends at least /2 inch over said mold opening around the entire periphery thereof, said liner being spaced from the inner wall of said hot-top to form an annular space between said liner and the wall opening adjacent the lower surface of said hot-top, said space extending completely to the bottom of said hot top and having a thickness in the range of M inch to inch.

2. In a hot-top for use on an ingot mold defining a mold cavity, the combination of a cast metal member having an inner wall defining a cavity therein, said hot-top cavity being smaller than the ingot mold cavity when the hot top is placed on the ingot mold so that said member overhangs the mold cavity, with a liner of moldable exothermically reacting material arranged within said hot top cavity and spaced from the wall thereofto define an annular space extending to the bottom of the hot top and opening into the mold cavity, said space being at least about inch.

3. In a hot-top for use on an ingot mold defining a mold cavity, the combination of a cast metal member having an inner wall defining a cavity therein, said hot top cavity being smaller than the ingot mold cavity so that said member overhangs the mold cavity when the hot top is placed on the ingot mold, with a liner of moldable exothermically reacting material arranged within said hot top cavity and spaced from the wall thereof to define an annular space extending to the bottom of the hot top and opening into the mold cavity, said space being in the range of A inch to M; inch, and said liner extending the length of said hot top cavity.

4. In combination, an ingot mold defining a mold cavity, a cast metal hot-top member having an inner wall defining a cavity therein, said cavity being smaller than the ingot mold cavity so that said member overhangs the mold cavity, and a liner of moldable exothermically reacting material arranged within said hot-top cavity and spaced from the wall thereof to define an annular space extending to the bottom of the hot top and opening into the mold cavity, said space being in the range of 5 inch to 4; inch.

5. In a hot-top for use on an ingot mold having a mold cavity opening into an upper hot-top supporting surface, the combination comprising, a metallic body having a feeder-head cavity extending therethrough and opening into a lower surface of said body, said feeder-head cavity opening being smaller than the mold cavity opening to the extent that when said feeder-head opening is complementary to the mold opening said hot-top surface extends at least /2 inch over the mold opening around the entire periphery thereof, and a liner of moldable exothermically reacting material arranged within said feederhead cavity and having its lower end adjacent to said lower end adjacent said lower surface, said liner being spaced from said cavity walls to the extent of 5 inch to inch for defining an annular space extending to the bottom of the hot top and opening adjacent said lower surface.

6. A method of forming a sound ingot comprising teeming molten metal into an ingot mold having a hot-top on its upper surface defining a cavity for containing molten feeder metal, chilling a portion of said metal in the vicinity of the joint between said hot-top and said mold to prevent runout and the formation of hanger fins, forming a thin annular metal dam on said ingot adjacent to said chilled portion and between said chilled portion and the hot top cavity, and adding heat to the metal in the hot-top cavity to keep the metal therein molten for feeding the center of the ingot as it cools and shrinks, said darn preventing the molten metal fed to the ingot by the hot-top from solidifying in layers on top of said chilled portion as the ingot shrinks in the mold.

7. In a metallic ingot mold, the combination with a mold body having walls defining a mold cavity and a hot top positioned on said mold body and a bottom and an inner wall, said inner wall defining a cavity of smaller horizontal cross section than the mold cavity and extending through the-hot top and opening into the mold cavity, said bottom extending over the mold cavity from the mold walls, of a liner of moldable exothermically reacting material arranged within said hot top cavity and spaced from thewall thereof to define an annular space extending to said horizontal surface and opening into the mold cavity, said space being at least about 5 inch.

(References on following page) References Cited in the file of this patent' UNITED STATES PATENTS Kenney Dec. 5, 1916 Hitt et a1. July 11, 1922 Rowe Sept. 2, 1924 Howard Jan. 13, 1925 Gathmann Dec. 10, 1929 8 Haws Mar. 15, 1932 Dumas June 13, 1933 Charman Dec. 11, 1945 Udy Sept. 2, 1947 Strauss Apr. 1, 1952 FOREIGN PATENTS France July 13, 1954

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