US2079644A - Method and apparatus for continuous casting - Google Patents

Description

-May 11, 1937. E. R. WILLIAMS METHOD AND APPARATUS FOR CONTINUOUS CASTING Filed May 5, 1936 INVENTOR 5M 16.

r I rm Patented May-11,1937

, umrso srArss v I I AND APPARATUfi FOE S CASTING Edward R. Williams, Latrobe, Fm, assignor, by

wardlt. amsamf mesne assignments, to Ed I Julia Ileev ox Williams, both of Latrdbc. Pa. Application May 5, 1936, Serial No. 77,971

7 Claims.

My invention relates to method and apparatus for continuous casting in a definite shape and form of both ferrous and non-ferrous metals, and is particularly applicable to what is hereinafter referred to as continuous casting. ply of molten metal may be continuously fed to one end of a mold and the cast ingot be withdrawn from the opposite end of the mold without interrupting the continuity of the ingot during the entire process, thereby allowing ingots of in-' definite length and having superior properties to be cast. I

In casting metal the usual procedure employed is what may be termed intermittent, wherein the previously prepared mold is filled with molten metal which is allowed to solidify within the mold cavity and is then withdrawn therefrom. This cavity, unless the mold is of the temporary type sometimes employed, may be again used in carrying out the procedure.

This application is a ccntinuation-in-part of my application Serial No. 715,433, filed March 14, 1934, which is a ccntinuation invpart of my application Serial No. 650,595, filed January 7, 1933.

The present, commonly used, methods of casting metal ingots from which various shapes are later to be rolled or forged are not entirely satisfactory because of defects which appear on the butt of the ingot along the sides of the ingot and the pipe or cavity which forms at the top. Further treatment of such ingots to prepare the ingots for further working are expensive and necessary. For example, surface imperfections have to be chipped orground out before further operations are performed on the ingot and the pipes or cavities which form at the top of the ingot due to uneven contraction of the molten metal during the casting operation have to be cut off and this necessitates that from ten to twenty percent of the top of each. ingot has to be cropped off and discarded. To overcome these and other defects it is desirable to form the ingot so that surface imperfections and pipes are obviated, and various continuous casting operations have been suggested from time to time, but in so far as I am aware no procedure or apparatus has been heretofore developed which is commercially acceptable. This is due to'the failure to solve the problem of heat removal from the metal as it is received and formed in the mold cavity.

By my invention it is possible to extract heat from molten metal during thecasting operation at a relatively high rate so that the casting operation is improved, simplified and expedited 'whetherit be a continuous or'intermittent oper-' The sup- 'ation. I have found that the solution of the problem of continuous casting depends upon proper heat removal from the metal which has been poured. In order to successfully accomplish continuous casting at a commercially acceptable rate it is necessary to almost instantaneously congeal the molten metal contacting the lateral walls of the mold cavity so as to form a thin shell or skin, and this shell must be maintained in heat.- transferring relation with the lateral wall of the mold cavity for a substantial period of time and it must be so formed and of such thickness that it is of sumcient strength to'resist, without rupture, such force as his subjected to during the operation of moving it along the wall of the mold cavity, in order to provide for the continuous casting operation. By the use of my method and apparatus it is possible to produce a homogeneous ingot of indefinite length without butt irregularities, surface imperfections or pipes or cavities.

I employ a mold having a mold cavity provided with a wall having high thermal conductivity and means outside the mold wall whereby the heat conducted therethrough may be rapidly scoured away from the outer surface of the wall and dissipated. By employing a thin mold wall having high thermal conductivity and supplying a cooling fluid to the external surfaces of these walls at such a velocity and at such a pressure to insure that the fluid will neither be vaporized nor give off gases in contact with the walls I cannot only extract the necessary heat to accomhaving a relatively high thermal conductivity,

such as copper. This tube should be as thin as structurally possible. The tube is enclosed within a 'jacket member or casing to provide therebetwe'en a shallow cooling chamber through which a cooling medium is circulated in intimate contact with the tube. By the term shallow cooling chamber I mean to. designate a chamber the radial depth of which is as small as structurally possible so, that the chamber will not be readily clogged by excrescences which are liable to form in the chamber. I have found that the radial depth approximately the thickness of the wall tube is satisfactory and is comparatively simple to construct. The stream of cooling fiuid' considered as the equivalent of a mold stool is inserted into one end of the tube and is movable with relation thereto. In its initial position this element supports the molten metal and provides with the mold tube a mold cavity into which the molten metal is introduced.

When a liquid such as water is employed as the cooling medium it is desirable to obtain it from a low temperature source, or, again, it may be artificially cooled. It is also desirable to deliver the liquid to the cooling chamber under suflicient pressure to maintain the water unvaporized along the tube.

It will be apparent that the stool element provides a heat absorbing agent and that the metal directly contacting with it will solidify more' .or less rapidly and the arrangement must be such as 'to insure this condition. The stool is withdrawn at a rate depending on the rate of introducing metal into the mold cavity, and this, in turn, depends on the rate of heat dissipation. The metal previously introduced moves with the stool and is thereby subjected to the cooling effect of the portions of the tube uncovered by the receding stool. The thickness of the solidified shell is thus increased as the formed ingot moves along the tube, and it is desirable to have paratus' which is suitable for carrying out my.

the tube of such length that the shell so formed will reach such a thickness before being withdrawn from the tube that it will retain such metal as remains in molten condition and will not be ruptured by the force necessary to withdraw it from the mold, nor melted through by the molten metal in the center. It is obvious that the cooling operation may be continued even after the cast metal leaves the tube and that, therefore, auxiliary means may be employed for cooling this portionof the casting.

One of the advantages of my invention is that the metal can be cast in such a form and in such a length as to obviate-the necessity of employing the usual preliminary hot rolling operations as ordinarily termed the roughing down operation. For example, the metal may be cast in the form of a billet ingot or a slab ingot of desired and convenient dimensions. This is of advantage where the ingots are to be subjectedto further working, for example, in a continuous mill, and one of the objects of my invention is to produce ingots in such form as will minimize hot rolling operations.

In the accompanying drawing I have illustrated a present preferred embodiment of my invention. In the drawing- Figure 1 is a view, partly in section and more or less diagrammatic, showing one form of apinvention; v

Figure-2 is a cross section along the line 11-11 of Figure 1;

Figure 3 is a transverse section showing a slightly modifledform of a detail of the apparatus; and

Figure 4 is a section of an apparatus suitable for casting metal in slab form.

In the drawing l5 represents a. thin walled molding tube of cylindrical form which is open at both ends and is housed within a casing or jacket IS in such a way as to provide a relatively narrow or shallow cooling chamber or jacket space i! between it and the casing It. The tube I 5 has a ring-like series of lugs l8 which bear against the casing is and serve to support the tube therein and insure a water passage between the casing and'the tube. A stool element IS in the form of an ingot blank is located within and has a sliding lit with tube I5. At the beginning of the' .pouring operation the blank is located 'at such a position within the tube as to provide a. pouring cavity at the top thereof. Molten metal to be cast is delivered from th: furnace by any suitable means such as a tiltable ladle 2| and is received by a pouring box 22 secured adjacent the top of the apparatus. In the bottom of thepouring box is an orifice 23, so arranged that the molten metal will be discharged into the'mold cavity 20 in the form of a continuous stream.*-The molten metal poured into the cavity 20 is supported on the upper end of the ingot blank or stool I9 and for the purpose oi forming a bond between the bottom of the molten metal as it congeals and the top of the ingot blank IS, a series of lugs 24 are mounted in recesses 25 formed in the end of the ingot blank. These lugs project into the mold cavity 20 and are held in position in the recesses 25 by means of a pin 26 which extends through a transverse opening in the end of the ingot blank l9 and through openings 21 in the ends of the lugs 24. In order to maintain a substantially constant temperature differential between the inner and outer surfaces of the molding tube and to effectually remove the heat from the outer surface of the mold tubefl5, a coolingmedium such as water is introduced into the chamber l1 through a pipe 28 leading from a suitable source of water supply. Pipe 28 discharges into an annular recess 29 arranged so as to uniformly direct the water enalong the outer surface of tube I5. The liquid passing through chamber i1 absorbs and scours away the heat transferred through the wall of the tube l5 and is withdrawn from the bottom of the chamber through a discharge pipe 3|.

In order that the ingot blank or stool and the ingot being formed in the molding tube l5 may be readily and continuously removedltherefrom, the blank I! is preferably of such a length that when it is in its initial position within the tube IS the lower end of the blank-may be engaged by a suitable extracting or withdrawing mechanism such as toothed rollers 32. The rollers 32- tering the annular recess 29 through chamber I I a variable speed motor (not'shown) so that the speed of withdrawal of the blank i9 and the ingot can always be controlled at a rate so that the level of the molten metal in the pouring cavity 20 will remain approximately constant during the pour. It will thus be apparent that the pouring orifice 23 is of such a size that the metal will be deliveredto the pouring cavity at a rate such that. thenecessary skin may form around the edges of the molten metal in contact with the molding -tube,;so that the forming ingot may be withdrawn-without rupture of the skin wall thus formed; .The rate, of formation of the skin will depend upon the ability of the apparatus to carry away the heat transferred from the molten metal in the pouring cavity 20 through the molding tube copper or brass because of the high thermal conductivity of such metals and is made of such thickness that it will have a thermal conductivity sufficient to transfer the heat in the molten metal in the cavity to the chamber I! at a rate substantially equal to the rate at which the heat is given up by the molten metal within the mold cavity. I have discovered that the mold tube should be made of a metal having a high thermal conductivity and as thin as is structurally possible. In this connection I have used and found satisfactory a copper tube having a thickness of approximately inch.

The length of the tube I 5 depends upon the heat content of the metal being poured and the desired lineal speed of withdrawal of the solidifying metal from the discharge end of the tube. The tube should be of a length suflicient to allow the metal to be in contact therewith for such a period of time as will cause the shell or skin which solidifies around the metal to be of sufficient thickness and strength to maintain the still molten metal within its confines as it emerges from the endof the tube without the need of supporting walls. I have found that a round copper molding tube approximately 6 inches in diameter and having a length of approximately 30 inches is sufiicient for the casting of steel.

It is absolutely essential that the heat be scoured away from the outer wall of the molding tube as fast as it is conducted through the molding tube from the molten metal. It is also essential that the water be maintained in intimate contact with the wall of the tube without the formation therebetween of steam or vapor, or the liberation of gases. I have discovered that this cooling chamber should be of a radial thickness as small as is structurally possible, and I have successfully used my apparatus with a water chamber of a thickness of about 1 of an inch, which is approximately the thickness of the molding tube employed. However, it will be understood that this water chamber can be of a radial thickness less than of an inch and so also the thickness bf the molding tube can be less than 1 g of an inch. Structural possibilities and operating conditions will determine the thickness of the of an inch or less for the whole length of the molding tube, but it is essential that a very thin water-passage be maintained around the molding cavity and adjacent the top portion of the apparatus. Toward the bottom of the apparatus, however, the cooling chamber may have a greater radial thickness and this will serve somewhat to reduce the pressure necessary to force the water through the chamber.

Below the mold tube an auxiliary cooling means may be provided for completing the solidification of the ingot before it is cut to length. The auxiliary cooling means may be of any desired form such as an annular pipe 33 positioned at the discharge end of the tube i5 and having a series of nozzle orifices 34 therein for directing a cooling fluid such as water against the solidified surface of the ingot as it emerges from the discharge end of the tube. The pipe 34 is connected by means of a pipe 35 to a suitable source of water supply.

In Figure 3, I have illustrated a modification of my apparatus, in which means are provided for increasing the velocity of the cooling fluid in the cooling or jacket chamber l1 without increasing the quantity of fiow. In this modification the outer surface of the molding wall 15' is grooved to form a series of spaced ribs 36 which extend longitudinally of the tube and bear against the inner surface of the casing it, thus supporting the tube on the casing, reinforcing it longitudinally and increasing its external radiating surface. The ribs may be formed integral with the molding tube or may be attached thereto in any manner such as by brazing or welding. The spaces or grooves 31 between the ribs 36 form passageways extending lengthwise of the tube l5 and which are approximately equal in depth but may be less than the efiective thickness of the molding wall. As a result of the shallowness of the grooves 31, the cooling fluid is conveyed therethrough from the inlet pipe 28 to the outlet or discharge pipe 3| at a high velocity due to the restricted area of the water passages. Such a high velocity is of great aid in carrying away or scouring the heat from the outer surfaces of the molding wall H5. The mold tube may have this construction throughout the full length of the apparatus or this construction may extend for about one-half of the length of the molding tube, in which case the lower portion of the molding tube may be made of uniform cross section and the water passage thickness increased, similarly to the construction illustrated in Figure 1.

In Figure 4 I have shown a cross section of an apparatus similar to that shown in Figure 1 but of different cross section to enable slabs or rectangular shaped ingots to be poured. In this form of apparatus the thin walled molding tube l5a is maintained in spaced apart relation to the casing Isa to provide a shallow cooling chamber Ila therebetween. To reinforce the walls of the molding tube the wedge shaped ribs 38 are secured to tube l5a as by welding or brazing, or they may be formed integral therewith. The base of the wedges fit in slots 39 formed in the casing Ila. In other respects the arrangement may be as shown in Figure 1 hereinabove described.

22 in a substantially constant stream and in such quantities as to maintain a constant flow of molten metal through the orifice 23 into the mold cavity 20. This flow through the orifice should be at such a rate as to occasion the introduction of an uninterrupted stream into the cavity, i. e. a continuous stream as distinguished from a drop by drop stream. Upon initially starting the apparatus, the cavity 20 above the stool I9 is filled to a predetermined level, it being understood that during this filling operation the refrigerating or cooling medium is within and is being delivered through the jacket chamber H in direct contact with the outer surface of the mold tube l5. When the metal within the mold cavity has reached the predetermined level, the blank is withdrawn at such a rate as to maintain the metal level substantially constant within the cavity.

The refrigerating medium is delivered at such a temperature and rate of flow that the differential of temperature between the inner and outer surfaces of the tube I5 is such as to not with relation to any transverse section of the ingot the mass of unsolidifled metal gradually decreases as the ingot is withdrawn from the metal admission end of the tube and the molten metal which is maintained within the interior of the ingot prevents the formation of shrinkage cavities. The initial solidification of the metal in the mold cavity and along the top of the stool is shown at M.

The pressure necessary to prevent vaporization of the cooling liquid varies with the ingot speed and the heat content of the molten metal being poured, and I have found that when pouring a low heat-content metal the apparatus will work perfectly when a cooling liquid, such as water, is introduced into the chamber I! under a head pressureof about 35 to 45 pounds per square inch. With metals having a high heat content and where the casting is withdrawn from the tube l5 at a high lineal speed, the head pressure of the cooling liquid must be increased materially and may be as high as 150 pounds or more per square inch. For example, I have found in casting aluminum in a brass molding wall of circular shape 6 inches in diameter. and having a wall thickness of approximately of an inch and a cooling chamber approximately of an inch in radial thickness that a solidified skin will be formed almost instantly adjacent the inner wall of the tube which is of suflicient thickness and strength to support the pool of still molten metal within its confines and will contract sufficiently to reduce its frictional engagement with the tube, so as to -permit the ingot to be withdrawn, when the outer surface of the tube is continuously washed with water supplied at a rate of 30 to 35 gallons per minute under a head pressure of 30 to 40 pounds per square inch at water main temperature. Under such conditions, I have been able to withdraw the solidified metal from the molding tube l5 at commercial lineal speeds.

When steel and other metals having a high heat content are being cast in the apparatus above set forth with the volume of water passing through the cooling chamber I'I remaining the same, that is, 30 to 35 gallons per minute, I have found that the head pressure of the water must be increased materially and pressures of 75 to pounds or more may be required to prevent the water from vaporizing and to secure sufficient cooling to form a solidified skin adjacent the mold wall with suflicient rapidity to permit the ingot to be continuously withdrawn from the tube at commercial lineal speeds.

' In the apparatus illustrated and described, the pouring box 22 is shown as having an orifice 23 in the bottom thereof through which the molten metal issues in an open stream, but it will be understood that the orifice may be provided with a downwardly projecting nozzle (not shown) which extends into the interior of the mold cavity 20 below the normal level of the molten metal within the cavity blank. Such a nozzle may be beneficially employed when certain molten metals which oxidize rapidly are being cast, and it will also tend to decrease turbulence within the pool.

It is impossible to definitely designate the desirable liquid pressure and the velocity of liquid flow through the jacket for all the varying conditions which may be encountered in casting metals, but, asabove stated, the pressure and the velocity of flow should be such that under the temperature conditions encountered, the water will neither vaporize within the jacket nor give off such gases as it may carry, when coming in contact with the hot surface of the molding tube. Where a cooling medium other than a liquid is employed in the jacket surrounding the molding tube, this medium should be introduced into the jacket space at such a temperature, insuch quantities, and at such velocity as will not only insure a substantiallyv instantaneous solidification of the molten metal contacting with the tube, but will also cause sufficient contraction or shrinkage of the metal thus solidified to break or materially lessen the frictional contact between it and the tube. It is also desirable to maintain a flow of the cooling medium through the jacket space in such a way that the coldest medium within that space contacts with the hottest portion of the molding tube.

While I have described one apparatus for carrying out my invention and while I have described the invention in connection with continuous casting, it will be apparent that other types of apparatus may be employed and that the procedure here outlined may also be effectively employed in connection with intermittent as well as continuous casting. It will be apparent from the foregoing that the present invention particularly contemplates a procedure for the rapid removal of heat during a casting operation, and this procedure in its broad application can be made use of either in continuous or intermittent casting. It will also be understood that various changes, omissions, and additions may be made to that procedure without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. The method of continuously casting metal into ingot form which consists in continuously pouring metal into the top of a molding tube having high thermal conductivity and passing a shallow stream of cooling fluid at high velocity along the outer surface of said tube and in contact therewith whereby said surface is maintained at a temperature such that a layer of solidified metalis almost immediately formed around the outside of the metal so poured of suificient strength to permit drawing the metal so molded downwardly through the tube.

2. The method of continuously casting metal into ingot form which consists in continuously pouring metal into the top of a molding tube having high thermal conductivity and passing a shallow stream of cooling fluid at high velocity along the outer surface of said tube andin contact therewith and at such pressure as to prevent a film of vapor from forming between the outer surface of the tube and the shallow stream, whereby said surface is maintained at atemperature such that a layer of solidified metal is almost immediately formed around the outside of the metal so poured of sufficient strength to permit drawing the metal so molded downwardly through the tube.

3. The method of continuously casting metal into ingot form which consists in continuously pouring metal into the top of a molding tube having high thermal conductivity and passing a shallow stream of cooling fluid at high velocity along the outer surface of said tube and in contact therewith and at such pressure as to prevent a film of vapor from forming between the outer surface of the tube and the shallow stream, whereby said surface is maintained at a tempera ture such that a layer of solidified metal is almost immediately formed around the outside of the metal so poured of sufficient strength to permit drawing the metal so molded downwardly through the tube, and subjecting the molded metal adjacent the tube exit to the action of a cooling fluid.

4. The method of cooling theouter surface of a thin confining wall of a mold which consists in subjecting the outer surface of such' wall to the scrubbing action of a shallow stream of cooling fluid forced at high velocity along said wall, main-' taining said fluid under suflicient pressure to prevent vaporization thereof adjacent said wall and delivering such fluid in sufllcient volume to preclude an appreciable temperature rise therein, whereby a temperature differential is produced between the inner and outer surfaces of said wall which will substantially instantaneously solidify a skin of metal adjacent the inner surface of said wall as rapidly as it comes in contact therewith.

5. The method of casting molten metal which consists in delivering molten metal in a substantially continuous stream to a stationary thin walled molding tube of high thermal conductivity,

continuously subjecting the outer surfaceof said tube to the action of a shallow stream of cooling fluid delivered under such pressure as to cause the fluid to travel at a high velocity along the outer surface of the tube and toprevent vaporization of the fluid along the tube whereby the heat from the molten metal is rapidly transferred to r and carried away by the fluid, thus causing the molten metal adjacent the said wall to congeal.

6. In apparatus for casting molten metal comprising a thin wall molding tube having a thin wall for at least a portion of its length, a casing surrounding said tube and spaced therefrom to form a cooling chamber therebetweenof shallow radial depth for at least a portion of its length, means for circulating fluid along the outer surface of said tube at high velocity and at pressures sufliciently high to prevent vaporization of the fluid in contact with the outer surface of the end of the tube for spraying fluid on the formed ingot after it has emerged from the tube, and means beyond said tube for drawing the ingot out of and away from said tube.

EDWARD R. wmmmvrs.

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