US2770022A - Method of continuously casting molten metal - Google Patents

Description

Nov. 13, 1956 J. B. BRENNAN METHOD OF CONTINUOUSLY CASTING MOLTEN METAL Filed Dec. 8, 1952 nite States Patent METHOD OF CONTINUOUSLY CASTING MOLTEN METAL Joseph 13. Brennan, Cleveland, Ohio 7 Application December 8, 1952, Serial No. 324,795

6 Claims. (Cl. 22-200.1)

The present invention relates generally as indicated to a method of casting metal wire, strip, tubing, and the like continuously from a supply of molten metal. The present application is a continuation-in-part of my application Serial No. 121,517, filed October 15, 1949, now abandoned.

A primary object of the present invention is to provide a method of casting by which accurate, smooth-surfaced castings are continuously produced without the problem of sticking of the metal in the die passage as is encountered in methods wherein the castings are solidified during the course of their travel through die passages and without the problem of distortion of the castings as is encountered in methods wherein the castings are discharged from the die passages in molten condition.

Broadly stated, in the present method molten metal is discharged from a supply crucible through a die passage having the desired cross-section shape of the wire, strip, tubing, and the like which is to be cast, the molten metal in flowing through such die passage being thereby hot formed or shaped, then sli htly cooled so that the metal assumes a self-sustaining plastic state (intermediate the solid and molten conditions thereof) and during such cooling the skin of the casting is heated to molecularly mobile or slippery condition so that the casting does not stick against the walls of the die passage. The selfsustaining but slippery-skinned casting upon emergence from the die passage, is then cooled to solidify the same to the final desired shape.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

in said annexed drawing,

Fig. 1 is a cross-section view centrally and vertically through one form of apparatus for practicing the present method;

Fig. 2 is a similar central and vertical cross-section view of a modification wherein a wall portion of the die passage is defined by a rotary wheel which moves in unison with the casting; and

Fig. 3 is a fragmentary cross-section view taken substantially along the line 33, Fig. 2.

As shown in Fig. 1, there is provided a graphite crucible 1 containing molten metal 2 supplied thereinto as from the feed tilt crucible 3 so as to maintain a constant head of molten metal in said crucible during the casting operation. A high frequency induction coil 4 surrounding the crucible 1 maintains the molten metal 2 at a constant temperature and in molten condition.

A pressure dome 5 as of dense heat resisting material such as asbestos, quartz, ceramic material, or metal together with a base 6 surrounds the crucibles 1 and 3. Said pressure dome 5 when made of conductive material will be large enough so as to be outside of the influence of the high frequency field of the coil 4; and, of course, said dome 5 and plate 6 may be artificially cooled if desired by water coils or the like (not shown herein).

Helium gas, for example, may be fed at constant pressure through the pipe 7 into the pressure dome 5 to assist in the discharge of the molten metal 2 through a die 8. A sight glass 9 may be provided on the pressure dome 5 to enable observation of the crucibles 1 and 3.

Adjacent the discharge end of said die 8 and preferably spaced from such die end are a pair of" temperature controlled rolls 10 for the purpose of; chilling the metal as it emerges from said die 8; and, if desired, coolant spray pipes 11 may additionally be provided for this purpose.

Surrounding the discharge end of said die 8 is another high frequency coil 12 which coil is water cooled and in sliding contact around the discharge end portion of said die.

In one specific apparatus for casting metal strip 1" wide and /8" thick, according to the present method gas pressure at 10 p. s. i. was maintained within the pressure dome 5, said gas entering the dome through the pipe 7 and the molten metal 2 in said crucible 1 was maintained at a constant head of 12 from the upper end of the die passage 14 to the upper surface of the molten metal pool. The die 8 extended downwardly approxi mately 10 from the bottom of the base 6 and the water cooled high frequency coil 12 was approximately 4 long and disposed in contact around the lower end portion of the die 8 as best shown in Fig. 1.

-With this apparatus SAE copper-base alloy No. 79.1 was cast at the rate of about six inches per minutes. Said SAE alloy No. 791 has the following composition:

Percent Sn 3.5-4.5 Pb 3.5-4 5 Zn 1.5-40 Fe 0.1 Other elements 0.2 Cu Remainder This metal, at a temperature of 2350 F, was poured into the crucible ft and maintained therein at a temperature of approximately 2200 F. by means of the high frequency induction coil 4. As said metal fiowed downwardly through the die 8 under the influence of the head and gas pressure aforesaid, the temperature thereof was approximately 1860 to 1900 F. and during the course of its travel downwardly the same was cooled to a selfsustaining plastic state intermediate the solid and molten conditions thereof. Thus, the metal was hot formed; and, in order to eliminate sticking of the so-formed metal in the die passage 14, the high frequency induction coil 12 operating at 540 kilocycles and in contact around the die 8 was operative to maintain a slippery skin on the self-sustaining plastic casting. Of course, this skin was immediately solidified by the contact of the casting between the temperature controlled rolls l0 and further by the coolant sprays 11. As the metal flowed through the portion of the die surrounded by the high frequency coil 12, the outer surface was at a temperature slightly over 2000 F. for a depth of approximately .010".

The die 8 of approximately A3" wall thickness is preferably made of a non-conductive material such as fused zirconium oxide, for example, and so far as I have been able to ascertain, the die 8 being of non-metallic refractory material effected cooling of the metal partly by radiation and partly by the effect of the cooling water circulated through the high frequency coil 12. The high frequency field of coil 12 apparently affects the surface of the metal with the high frequency eddy currents so as to keep the skin of the casting to approximately .010" depth in the molecularly mobile or semi-fluid state so that the same does not stick in the die. In any event, whatever the scientific explanation may be, the watercooled high frequency coil 12 amounts to a surface heating unit which keeps the temperature of the die 8 lower that the melting point of the metal which is being cast due to its contact with the die and the circulation of coolant therethrough and which heats the surface of the metal as it emerges so that the metal slides through the die passage 14 without sticking thereto. Moreover, as the casting issues from said die 8 while not being in a fully solidified condition, is in a soft but self-sustaining plastic condition intermediate the solid and molten conditions. That such is the case is evident from the fact that the casting continuously issues from the die without changing its shape while yet the exterior skin thereof is in substantially molten condition to eliminate sticking in the die. Higher frequencies may also be employed in coil 12 even up to 1520 megacyclcs.

The metal casting at the zone 15 is externally soft and plastic after emerging from said die 8 until the same is chilled by the rolls 10 and/ or by the coolant sprays 11; and after this treatment the casting 16 is solid. The casting 16 at zone is frail and weak and if the metal is copper, for example, the same is at least red hot when discharged from the die 8 and this condition of the metal is plastic as I mean it. The strip 16 may be supported after leaving said die 8 by the rolls 10 until the skin is solidified. The strip 16 retains its shape'that is, the shape to which it was hot formed during the course of its travel through the die passage 14, and the only change in shape is that due to shrinkage by cooling. Of course, the casting 16 as it emerges from die 8 may be rolled or otherwise worked to a different size or shape.

As aforesaid, with the relatively low head of 12' and a relatively low gas pressure of approximately 10 pounds p. s. i., the casting 16 will emerge from die 8 at a velocity of about six (6) inches per minute but, obviously, the velocity of the casting 16 will be considerably higher such as 100 to 1000 feet per minute when higher pressures (head or gas) are employed. In any event, the velocity of discharge of the casting 16 must be correlated with the cooling means such as the rolls 10 and/or the sprays 11 so that the shape of the exteriorly plastic casting does not substantially change in the distance from the exterior end of the die 8 until entering the cooling zone as defined by said rolls 10 and/or the sprays 11. This distance may vary from a fraction of an inch to a few inches depending upon the temperature of the casting 16, its rate of discharge, and its degree of plasticity.

In any case, the metal casting 16 at least is exteriorly plastic when it emerges from die 3 and the entire cross section thereof may be plastic, but although in soft condition, it must be shape-retaining for at least a short distance after emerging from said die. The exterior of the casting 16 does not stick in said die 8 because its molecularly mobile surface is non-adherent to the wall of the die passage 14. The length of die 8 is such that the metal flowing therethrough will cool to the extent of being shape-retaining while yet relatively soft and plastic. Because of the high frequency coil 12, disposed as illustrated herein, the exterior surface of the casting 16 is maintained in a soft, plastic or molten condition so as to avoid sticking while the remaining section of the casting is shape-retaining. 7

Obviously, the shape of the casting 16 may be changed and may be tubular or half tubular or round or other shape. The tubular or round (or half tubular) die shapes have an advantage in that they make it easier to maintain the skin of the casting in plastic condition because the high frequency coils 12 are similarly of tubular of cylindrical shape and the resulting fields are more efiicient in surface heating.

The rolls 10 are used primarily for contact cooling; and therefore, may be very thin and light and arranged to be propelled by the surface friction with the casting 16 and preferably the rolls 10 to not appreciably change the shape of the casting 16.

As previously mentioned, the solidification zone is spaced from the discharge end of die 8 and at least the exterior of the casting 16 is molecularly mobile as the casting emerges from die 8. The shape of the casting 16 although in plastic condition is retained during the passage of the same from die 8 to the solidification zone as defined by the bight of the rolls 10 and/or by the cooling sprays 11.

The apparatus shown in Figs. 2 and 3 is generally the same as that illustrated in Fig. 1; and, therefore, like reference numerals have been used to denote similar parts. In the construction shown in Figs. 2 and 3, the die 20 has a passage 21 in communication with the molten metal 2 in crucible 1 and with a die passage 22 as defined by said die 20 and the periphery of a rotary wheel 23. Said die 20 is further provided with a dam 24 which insures the flow of the metal in a counterclockwise direction through the die passage 22, which passage in this case is defined by a peripheral groove 25 formed in said wheel and the inner arcuate surface 26 of said die '20. As best shown in Fig. 3, a water cooled high frequency coil 27 is disposed part way around the exit end portion of the die passage 22; and, as evident, said induction coil 27 is designed to operate in the same manner as the high frequency coil 12 as illustrated in Fig. 1. Therefore, repetition is not deemed necessary. The groove 25 may have a fiat strip of metal such as steel therein if it is desired to laminate cast a second metal thereover. In such case, the face of said strip must be heated to bonding temperature by the high frequency coil or other means.

The wheel 23 is supported for rotation as in a support 28 and said wheel may be power driven or not, as desired. In any event, the die passage surface as defined the groove 25 around said wheel preferably moves in unison with the metal as the same is hot formed or shaped in the die passage 22. Of course, the coil 27 again serves to render the exterior surface of the casting 29 in exteriorly mobile condition to eliminate any sticking thereof against the stationary portion of the die passage formed in said die 20.

Here again, as in Fig. 1, the casting 29 may be solidified in a solidification zone as defined, for example, by suitable rolls 10 and/or by coolant sprays 11.

With further reference to lamination casting it has been i found that the present method is well suited for the production of steel back bronze strip for the making of bearings, the steelfstrip forming one wall of the die passage against which molten bronze is cast as previously explained. The same conditions of operation will prevail, i. e. the surface of the bronze component will be rendered slippery and the steel component will be surface heated to bonding temperature.

What I do according to this invention is to. continuously cast metal of a constant cross section directly down from a pool of molten metal in a heated chamber crucible or container assisted by the head of molten metal therein and partially cool the descendingstring of metal to shape retaining condition due to cooling action of a surrounding die for a space and time for the string of cast metal to be definitely hot shaped to the die; and after so hot shaped to the die, the string of metal passes through a high frequency coil, preferably radio frequency, at least partially surrounding the string of cast metal so as to surface actuate and make slippery the exterior skin of the cast string of metal adjacent and nearest to the high frequency coil by skin heating effect.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method of continuously casting molten metal which comprises the steps of cooling successive longitudinal portions of a laterally confined, longitudinally flowing stream of molten metal of substantially uniform crosssection size and shape to a self-sustaining state, and heating the surface of successive longitudinal portions of the self-sustaining, laterally confined stream to melt at least a substantial portion thereof to provide a slippery skin thereon facilitating continued longitudinal, laterally confined fiow of said stream.

2. The method of continuously casting molten metal which comprises the steps of cooling successive longitudinal portions of a laterally confined, longitudinally flowing stream of molten metal of substantially uniform crosssection size and shape to a self-sustaining state, heating the surface of successive longitudinal portions of the selfsustaining, laterally confined stream to melt at least a substantial portion thereof to provide a slippery skin thereon facilitating continued longitudinal, laterally confined fiow of said stream, and cooling the slipperyskinned, self-sustaining stream to form a solid continuous casting of such uniform cross-section size and shape.

3. The method of continuously casting molten metal which comprises extracting heat laterally from successive longitudinal portions of a laterally confined, longitudinally flowing stream of molten metal of substantially uniform cross-section size and shape to form a continuous hot-formed casting, and skin-heating to melt at least a substantial portion thereof successive longitudinal portions of an exterior surface portion of such hot-formed casting while laterally confined to provide a slippery skin thereon facilitating continued longitudinal, laterally confined flow of such self-sustaining casting.

4. The method of continuously casting molten metal which comprises extracting heat from successive longitudinal portions of a laterally confined, longitudinally fiowing stream of molten metal of substantially uniform cross-section size and shape to form a continuous hot- 6 formed casting, and skin-heating to melt at least a substantial portion thereof and trowelling successive longitudinal portions of an exterior surface portion of such hotformed casting while laterally confined.

5. The method of continuously casting molten metal which comprises extracting heat gradually from successive longitudinal portions of a laterally confined, longitudinally flowing stream of molten metal of substantially uniform cross-section size and shape to form a continuous hot-formed casting in self-sustaining state which has a soft exterior surface, and thereafter skin-heating to melt at least a substantial portion thereof and trowelling successive longitudinal portions of such soft exterior surface of such hot-formed casting while laterally confined.

6. The method of continuously casting molten metal which comprises extracting heat gradually from successive longitudinal portions of a laterally confined, longitudinally flowing stream of molten metal of substantially uniform cross-section size and shape to form a continuous hot-formed casting in self-sustaining state which has a soft exterior surface, passing the laterally confined, hotformed casting through a high frequency induction heating field to heat to melt at least a substantial portion thereof only the exterior surface of the casting to slippery condition, and trowelling the slippery exterior surface of the hot-formed casting as the latter continues to ilow as a self-sustaining, laterally confined, longitudinally flowing stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,657,132 Merle Jan. 24, 1928 2,209,968 Gould et a1. Aug. 6, 1940 2,225,424 Schwarzkopf Dec. 17, 1940 2,473,221 Rossi June 14, 1949 2,496,235 Rossi Jan. 31, 1950 2,565,959 Francis et al. Aug. 28, 1951 2,567,525 Morris Sept. 11, 1951 2,569,150 Brennan Sept. 25, 1951 2,590,311 Harter et al -2 Mar. 25, 1952 2,698,467 Tarquinee et a1. Jan. 4, 1955 FOREIGN PATENTS 504,519 Great Britain Apr. 26, 1.939

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