Claims
- 1. In a continuous casting apparatus wherein molten metal flows through a die progressively and is solidified in the die and withdrawn from the die, a die and cooling assembly comprising
- a tubular die having an external tapered surface which is uniformly tapered radially inwardly in the direction of movement of metal to the die,
- a cooling sleeve having an internal surface adapted to be complementary to the external surface of the die and in substantial intimate surface contact with the external surface of said die,
- an annular cooling shell surrounding said cooling sleeve and having portions thereof spaced from said sleeve to define a cooling chamber,
- the cooling sleeve being made of a material having a greater coefficient of expansion than the coefficient of expansion of the material of said tubular die,
- at least one inlet to said chamber,
- at least one outlet from said chamber,
- said tubular die having an internal surface which is uniformly tapered radially inward in the direction of movement of metal to the die such that as the molten metal flows progressively through the die and is solidified and contracts, substantially intimate contact is maintained between the internal surface of the tubular die and the solidified metal so that improved heat transfer is achieved,
- the tapered external surface of said tubular die having greater external diameters at ambient temperature before assembly and at operating temperature after assembly than the corresponding tapered internal surface of the cooling sleeve at ambient temperature before assembly and at operating temperature after assembly such that when said cooling sleeve is heated to a temperature above the operating temperatures of the die and cooling sleeve, telescoped over the tubular die, and permitted to cool and be shrunk fit on said tubular die, the tubular die is in compression at both ambient and operating temperatures and when the die and cooling sleeve is utilized at operating temperatures, the tubular die remains in compression and intimate contact is maintained between the cooling sleeve and the tubular die at the operating temperatures,
- the diameter of the cooling sleeve being determined by the factor of the coefficient of expansion of the sleeve and the temperature of the sleeve at the operating temperatures so that upon expansion, the internal surface of the cooling sleeve will maintain contact with the external surface of the die,
- a mandrel associated with said tubular die for forming tubular products, said mandrel including an internal chamber to which said coolant is directed, said mandrel including openings in the end thereof for directing said coolant from said chamber toward the interior surface of the product being formed;
- said mandrel including a tapered external surface extending from the freezing zone such that substantial intimate contact is maintained by the tapered surface with the internal surface of the tubular product being formed.
- 2. The continuous casting apparatus set forth in claim 1 wherein the taper of the internal surface of the tubular die is determined by the factors of coefficient of expansion of the die, diameter of the die, coefficient of expansion and contraction of the metal being continuously cast, and the temperatures to which the die is subjected in use such that the inward taper of the internal surface will be substantially that corresponding to the shrinkage of the molten metal as it solidifies and contracts in moving from the inlet to the outlet.
- 3. In a continuous casting apparatus wherein molten metal flows through a die progressively and is solidified in the die and withdrawn from the die, a die and cooling assembly comprising
- a tubular die having an external tapered surface which is uniformly tapered radially inwardly in the direction of movement of metal to the die,
- a cooling sleeve having an internal surface adapted to be complementary to the external surface of the die and in substantial intimate surface contact with the external surface of said die,
- an annular cooling shell surrounding said cooling sleeve and having portions thereof spaced from said sleeve to define a cooling chamber,
- the cooling sleeve being made of a material having a greater coefficient of expansion than the coefficient of expansion of the material of said tubular die,
- at least one inlet to said chamber,
- at least one outlet from said chamber,
- said tubular die having an internal surface which is uniformly tapered radially inward in the direction of movement of metal to the die such that as the molten metal flows progressively through the die and is solidified and contracts, substantially intimate contact is maintained between the internal surface of the tubular die and the solidified metal so that improved heat transfer is achieved,
- the tapered external surface of said tubular die having greater external diameters at ambient temperature before assembly and at operating temperature after assembly than the corresponding tapered internal surface of the cooling sleeve at ambient temperature before assembly and at operating temperature after assembly such that when said cooling sleeve is heated to a temperature above the operating temperatures of the die and cooling sleeve, telescoped over the tubular die, and permitted to cool and be shrunk fit on said tubular die, the tubular die is in compression at both ambient and operating temperatures and when the die and cooling sleeve is utilized at operating temperatures, the tubular die remains in compression and intimate contact is maintained between the cooling sleeve and the tubular die at the operating temperatures,
- the diameter of the cooling sleeve being determined by the factor of the coefficient of expansion of the sleeve and the temperature of the sleeve at the operating temperatures so that upon expansion, the internal surface of the cooling sleeve will maintain contact with the external surface of the die,
- a mandrel associated with said tubular die for forming tubular products,
- said mandrel including a tapered external surface extending from the freezing zone such that substantial intimate contact is maintained by the tapered surface with the internal surface of the tubular product being formed.
- 4. In a continuous casting apparatus wherein molten metal flows through a die progressively and is solidified in the die and withdrawn from the die, a die and cooling assembly comprising
- a tubular die having an external tapered surface which is uniformly tapered radially inwardly in the direction of movement of metal to the die,
- a cooling sleeve having an internal surface adapted to be complementary to the external surface of the die and in substantial intimate surface contact with the external surface of said die,
- an annular cooling shell surrounding said cooling sleeve and having portions thereof spaced from said sleeve to define a cooling chamber,
- the cooling sleeve being made of a material having a greater coefficient of expansion than the coefficient of expansion of the material of said tubular die,
- at least one inlet to said chamber,
- at least one outlet from said chamber,
- said tubular die having an internal surface which is uniformly tapered radially inward in the direction of movement of metal to the die such that as the molten metal flows progressively through the die and is solidified and contracts, substantially intimate contact is maintained between the internal surface of the tubular die and the solidified metal so that improved heat transfer is achieved,
- a mandrel associated with said tubular die for forming tubular products,
- said mandrel including a tapered external surface extending from the freezing zone such that substantial intimate contact is maintained by the tapered surface with the internal surface of the tubular product being formed.
BACKGROUND AND SUMMARY OF THE INVENTION
This application is a continuation of application Ser. No. 687,503, filed Jan. 4, 1985, which is, in turn, a continuation of application Ser. No. 466,619 filed Feb. 15, 1983, now both abandoned.
This invention relates to continuous casting.
In continuous casting of metals such as brass and the like, it is common to permit molten metal to flow from a crucible through a die which is surrounded by a cooling apparatus so that the molten metal progressively solidifies and is withdrawn by suitable apparatus. A major consideration in the efficiency of such a device is the ability to remove heat from the product being formed.
More specifically, as the molten metal moves through the outlet of the die, the cooling sleeve absorbs heat from the metal through the die, thereby reducing the temperature of the metal. The metal begins to solidify at the inside surface of the die in what is known as a freezing zone.
Conventionally, the dies are made of fine grade graphite which will with stand the temperature of the molten metal to a high degree of 4000.degree. F. For example, copper melts at about 1941.degree. F. and has a liquidus state at 1981.degree. F.
The metal is initially cooled at a greater extent on the exterior surface of the product being formed and progressively cooled radially inwardly until it solidifies. The cooling occurs as the metal is moved from the inlet to the outlet of the die. As the metal solidifies, the outside diameter moves toward the center of the product being cast and away from the inside diameter of the forming die. As the product being formed moves towards the exit of the die and away from the freezing zone, it no longer has an intimate contact with the die and is only cooling by radiation.
If the speed of movement of the product through the die is slow, the freezing zone will be at a higher level inside the forming die resulting in slow production and increased friction between the inside diameter of the product and the mandrel in case of tubular products. Also, in many cases where the product being formed is not symmetrical in cross section so that the cooling is not uniform, the product will deform away from the casting center line of the forming die increasing the chances of damage to the die wall at the exit area. It is thus necessary that the product move out of the freezing zone in a short period of time and away from the mandrel forming section in order to secure uniform wall thickness without forming stress cracks or changes in the molecular structure on the outside diameter of the products being cast.
In order to provide intimate contact between the die and the cooling sleeve, it is common to provide a taper on the external surface of the die and a complementary taper on the internal surface of the cooling sleeve. In one method of assembly, the die and cooling sleeve are forced together axially. In another method of assembly, the die is revolved as it is assembled to the cooling sleeve in an effort to obtain more intimate contact between the die and the sleeve.
Another problem in continuous casting relates to the thickness of the graphite die or mold. For each nominal outside diameter of product being cast there is an inside calculated diameter of a cooling sleeve and the thickness of the graphite mold must be sufficient to accommodate the hydrostatic pressures and the friction type pressure between the formed products and the inside surface of the die without at the same time reducing the thermal conductivity of the die. Thus, appropriate thickness of the wall of a small diameter die (e.g. 2.00 inch) may be 1/4 of an inch. The wall thickness of the graphite die will be increased according to the outside diameter of the products being formed to compensate for the hydrostatic pressure. On the other hand, the strength of a graphite die decreases as the temperature rises up to 2000.degree. F. so it is common to compensate for the loss of strength by increasing the thickness of the graphite mold. However, the thermal conductivity of the graphite die is much less than that of the cooling sleeve. Thus, although increasing the thickness of the graphite will increase the strength of the die, it will decrease the thermal conductivity of the die walls.
Where the product being formed is tubular further problems exist because the interior surface will not be cooled at the same rate as the exterior.
Where the tubular product has a thick wall, the inside surface of the product is usually very inconsistent in diameter and surface finish. Because of the inability to cool the outer and inner wall surfaces properly and the longer period for withdrawing the product from the die due to the large mass of metal, the metal is in a very molten stage when leaving the straight portion of the mandrel and the low melting metal constituents such as lead, tin and zinc are not solidified and migrate to the outside surface. At this stage the product cools very slowly from the outside to the inside and by the time the product leaves the end of the mandrel, the low melting constituents are still in a molten stage and migrate and solidify on the inside diameter of the product with very large irregularities. Often, the remaining molten metal extrudes through partially solidified metal resulting in interruption of the casting. The disadvantage of not cooling both surfaces with the same rate reduces the rate of production and results in defective tubular products. Thus, it would be very advantageous to form the products with a similar rate of cooling at the internal diameter and external diameter.
Accordingly, among the objectives of the present invention are to provide a continuous casting apparatus and method of making the apparatus which improves the transfer of heat from the metal being cast thereby increasing the quality and production rates and wherein when forming heavy walled tubular products the cooling of the outside surface and the inside surface is similar thereby obviating the problems inherent in making such products.
In accordance with the invention, the tubular die has an internal surface which is uniformly tapered radially inward in the direction of movement of metal to the die such that as the molten metal flows progressively through the die and is solidified and contracts, substantially intimate contact is maintained between the internal surface of the tubular die and the solidified metal so that improved heat transfer is achieved. In addition, the tubular die has a tapered external surface with greater external diameters before assembly than the internal diameters of the mating tapered surface of the cooling sleeve before assembly and the cooling sleeve is shrunk fit on the tubular die such that the tubular die is in compression at ambient temperature and the strength of the die is increased and such that as the cooling sleeve temperature increases in usage, causing expansion thereof intimate contact is maintained between the cooling sleeve and the die. Where a heavy walled tubular product is being formed, a cooled mandrel is provided to facilitate the cooling of the internal surface of the tubular product being formed. The mandrel preferably includes a tapered lower end constructed and arranged to maintain intimate contact with the internal surface of the tubular product being formed.
Non-Patent Literature Citations (1)
| Entry |
| Perry, Robt. H. et al., Eds., Chemical Engineers' Handbook, 5th Ed. (McGraw-Hill, 1973), pp. 3-99 and 3-100. |
Continuations (2)
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Number |
Date |
Country |
| Parent |
687503 |
Jan 1985 |
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| Parent |
466619 |
Feb 1983 |
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Patent Grant
4901783
