US2187720A - Method and apparatus for continuous metal casting - Google Patents

Description

Jan. 23, 1940. E. R. WILLIAMS 2,187,720

METHOD AND APPARATUS FOR CONTINUOUS METAL CASTING Filed Feb. 2, 1959 11a ma 1.26L l5 10? 12b 15b 5.

lV NTOR Edwardfi.

ATTORNEYS Patented Jan. 23, 1940 UNITED STATES METHOD AND APPARATUS FOR CON- TINUOUS METAL CASTING Edward R. Williams, Latrobe, Pa.,assignor, by mesne assignments, to himseli' and Julia Lee Cox Williams, Latrobe, Pa.

Application February 2, 1939, Serial No. 254,195

9 Claims.

My invention relates to method and apparatus for casting of both ferrous and non-ferrous metals in a definite shape and form and is particularly applicable to what is commonly re- 5 ferred to in the art as continuous casting. In-

asmuch as my invention is peculiarly applicable to continuous casting, it will be described in connection therewith.

In the art of continuous casting, va supply of i molten metal is continuously fed to one end of a mold cavity of suitable cross-section, the walls of which are kept at a temperature which will cause solidication of the poured metal by a circulating uid in contact with the outside of .3 the mold wall. The cast metal having a crosssection corresponding to that of the mold cavity is withdrawn from the opposite end without substantially interrupting the continuity of the ingot during the entire pour. It is thus possible i0 to produce ingots of any desired cross-section and of a length corresponding to the amount of metal available for pouring. Ingots so produced not only have superior properties but may also be cast in an economical and expeditious manner.

While my invention is particularly applicable to the continuous casting of metal ingots, it may also be advantageously employed in the casting of ingots by what is commonly referred toas in- 0 termittent operation. In intermittent operation,

ingots having a cross-section and length substantially the same as the mold cavity are produced by lling a previously prepared mold with molten metal which is allowed to solidify to at least 5 the point where it is self-supporting, at which time it is withdrawn from the mold. This cavity may be employed again and again for molding individual ingots of a length limited by the length of the mold cavity.

l This invention is an improvement over the invention disclosed in my United States Letters Patent No. 2,079,644, issued May 11, 1937, for Method and apparatus for continuous casting. While generally satisfactory/.results have been i obtained by following the teachings of the said patent, I have found that somewhat better results can be obtained by the method and apparatus which I will now describe.

In order to successfully cast metal continu-,f

l ously 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 skin must be maintained in heat transl ferring relation with the lateral walls of the mold cavity for a suitable period of time so that the shell will acquire sufllcient thickness and strength to resist, without rupture, the force to which it is subjected during the operation oi' moving it along the wall of the mold cavity. 5 To accomplish this result, I employ a mold having a mold cavity formed by a wall having high thermal conductivity and cause a fluid to be circulated outside of and in contact with the mold wall whereby the heat conducted therethrough lo may be rapidly swept away from the outer surface of the wall. By employing a mold tube having a thin Wall made from a material such as copper or brass having high thermal conductivity and supplying a cooling fluid to the external suru y face of these walls in a thin stream and at relatively high velocity, heat can be extracted from the metal at a sumciently rapid rate to permit very rapid solidication of the metal coming into Contact with the walls of the mold cavity so that 2 a skin of suilicient thickness and strength to permit withdrawal of the formed ingot will be rapidly formed.

I employ a thin wall molding tube open at both ends and made from a material such as copper or brass having high thermal conductivity. This tube is made as thin as structurally possible so as to rapidly conduct the heat from the poured metal to the cooling fluid. The tube is enclosed within a jacket member or casing to provide between the tube and the casing a shallow cooling chamber through which a cooling medium is circulated in intimate contact with the tube wall. By the term shallow cooling chamber" I mean a chamber the radial depth of which is as small as structurally and commercially possible and one which will not be readily clogged by excrescences which may form in the chamber or by particles which may be .present in the cooling fluid. I have found that a radial depth approximating or less than the thickness of the wall tube is satisfactory. 'I'he stream of cooling fluid of such dimensions that it will pass through the shallow cooling chamber will be designated as a shallow stream. An element which may be considered as the equivalent of a mold stool is inserted into the exit end of the tube and is movable relative to the tube in the direction of the withdrawal of the ingot. In the initial position this element supports the molten metal and provides in cooperation with the mold tube a mold cavity into which the molten metal is poured.

In order to obtain the necessary flow of cooling fluid through the shallow cooling chamber, it has heretofore been necessary to supply the fluid under. a fairly high pressure. The high pressure causes difliculty in making and maintaining satisfactory expansion joints between the thin walled molding tube and the casing and also makes it necessary in some instances to construct the molding tube of a thickness sufficient t0 resist the force which tends to distort the walls of the molding tube and/or force them inwardly toward the center of the tube. When a tube wall was employed which was thin enough to give high thermal conductivity of maximum efilciency, it was sometimes distorted by the high pressure exerted on it by the cooling fluid. In some instances the tube would be so distorted that one portion of the cooling chamber would be increased in radial depth to such an extent that the cooling fluid would be starved from another portion of the cooling chamber and the starved portion would not have sufiicient cooling effect to insure that the ingot would have a skin of the necessary thickness. Furthermore, any inward bulging or distortion of the tube would tend to bind the ingot and in some instances the force which would have to be exerted to move the ingot downwardly would be too great for the skin of the ingot to withstand. In any event, the apparatus using cooling fluid under pressure while satisfactory in some instances and under some conditions, was not as satisfactory as was desired in other instances. The tendency of the tube wall to bulge inwardly was particularly .objectionable when it was desired to pour an ingot in the form of a slab having a width which was greater than the thickness. It was also somewhat difcult to pour square ingots in a satisfactory manner at a desirable speed.

I have discovered that structural diiilculties and operating drawbacks disappear when the circulation of the cooling fluid through the cooling chamber is aided by a suction pump connected to the cooling chamber outlet instead of being forced through the chamber as heretofore solely by means connected in the fluid supply conduit. By locating a suction pump connected to the outlet conduit, I cause the fluid to be circulated under conditions which do not exert a force against the outer wall of the welding tube in a direction toward the longitudinal axis of sufficient intensityto distort the tube wall. I am thus able to construct molds of a desirable size and shape to insure a cooling chamber of predetermined radial depth. The difficulties in making a satisfactory expansion joint and troubles due to the bulging and distortion of the molding tube entirely disappear by the use of my invention. This is of special importance where a square molding tube is employed and particularly where the mold tube has a rectangular opening for the pouring of slabs. Furthermore, a tube of equal thickness is much stronger when employed in connection with fluid circulation aided by suction means than where positive pressure is alone used on the fluid supply to cause the circulation. Conversely a tube of equalstructural strength but having a higher heat conductivity can be formed with thinner walls of the same material.

In the accompanying drawing, in which I have shown for purposes of illustration only certain present preferred embodiments of my invention,

Figure 1 is a View partly in section, and more or less diagrammatic, showing one form of apparatus which is suitable for carrying out my invention;

Figure 2 is a transverse section along the line II-II of Figure 1;

Figure 3 is a transverse section of an apparatus having a cross-section different from that shown in Figure 2; and

Figure 4 is a transverse section of apparatus having a still different cross-section.

In the drawing, I0 represents a thin wall molding tube of desirable cross-section and fabricated from metal such as copper or brass having high thermal conductivity. The tube is open at both ends and is housed within a metal casing or jacket l I so as to provide a shallow cooling chamber I2 between the tube and the casing. The tube I0 is spaced from the casing II by spacing members I3 which may be separate from the casing and the tube or may be formed integrally with the casing or the tube. Provision of the spacing members insures that the shallow cooling cham# ber I2 will be of definite radial thickness. A stool element I4 is provided in the form of an ingot blank so that when it is inserted within the tube it will have a sliding fit therewith. At the be ginning of the/ pouring operation, the blank is located at such a position within the tube III as to provide a pouring cavity I5 at the top of the tube. The molten metal to be cast is delivered from the furnace by any suitable means such as a tiltable ladle I6 to the pouring box or funnel I'I secured adjacent the top of the tube. In the bottom of the pouring box I1 is an orice I8 so disposed that the molten metal will be discharged from the pouring box into the mold cavity I5 in the form of a continuous stream. The pouring box may have a tube extending from the orifice into the pouring cavity I5 and this tube may, if desired, extend below the level of the poured metal. In some instances the metal may be delivered from the furnace in which it is melted directly to the pouring box.

The molten metal poured into the cavity I5 is supported on the upper ingot blank or stool I4 and bonded thereto by suitable means such as disconnectable lugs I9. The blank I4 is made long enough so that when it is in its initial position within the tube III the lower end of the blank will be engaged by suitable withdrawing rolls 20. 'I'he rolls 20 are pressed against the blank and may be driven in any suitable manner, for example, by a variable speed motor (not shown) so that the speed of withdrawal of the blank I4 and ingot can be controlled at a rate so that the level of the molten metal in the pouring cavity I5 will remain substantially constant during the pour. The metal will be delivered to the pouring cavity I5 at such a rate that a skin of suiiicient thickness may form around the edges of the molten metal in contact with the molding tube to enable the forming ingot to be withdrawn without rupture of the skin wall. The rate of formation of the skin will depend on the ability of the apparatus to carry away the heat transferred from the molten metal in the tube I 0 through the tube and to the cooling fluid.

The rolls 20 or other rolls may be used to exert a pressure on the formed and partly solidified ingot sufiicient to reduce the cross-section thereof and thereby minimize the formation of piping and reduce the porosity of the ingot 'I'he rate of pouring of the metal and the withdrawal of the ingot are synchronized so that the level of the metal in the molding tube I0 will remain substantially constant, although it is not necessary that the level of the metal remain absolutely constant. Heat is withdrawn from the metal at such a rate as to allow a skin to form which is sulciently strong to permit the ingot to be withdrawn without rupture of the skin wall.

In orde-r to maintain a substantially constant temperature differential between the inner and outer surfaces of the molding tube I0 and to effectively remove the heat from the outer surface of the mold tube, a cooling fluid, for example water, is introduced at a desired tempera.

ture into an inlet chamber 22 through a pipe 2I leading from a suitable source of water supply (not shown). 'I'he inlet flow may be controlled by the valve 24 in the pipe 2|. The inlet chamber 22 is in the form of an annular recess which has an opening 25 therein arranged so as to uniformly direct the entering water through the cooling chamber I2. The water passing through the cooling chamber I2 absorbs and scours away the heat transferred through the wall of the molding tube I 0. The Water is then withdrawn from the bottom of thel chamber I2 through the discharge pipe 26 to which is attached the suction pump 21.

'I'he Water supply is of such a character and the suction pump 2l is of a capacity and so operated as to cause a flow of fluid through chamber I2 at such a rate and under such conditions that there is not sufficient pressure exerted against the outside Wall of tube Il) as to distort it to such an extent that it will interfere with the withdrawal of the ingot or effect the radial depth of the cooling chamber. 'I'he operation may even be such that there is less than atmospheric pressure exerted against the outer tube wall.

The tube I0 is made of a thickness and the rate of flow of the cooling water and the rate of Withdrawal of the ingot are of such order that the heat may be transferred from the molten metal in the molding tube to the water by which it is carried away at a rate which is substantially equal to the rate at which the heat is given up by the molten metal within the molding tube. I have found that a copper tube or a brass tube having a thickness of from one-sixteenth to onequarter inch is satisfactory. As an illustration I have used a round brass tube six inches in diameter, having a thickness of one-sixteenth inch and a length of eighteeninches. A Water chamber of approximately thirty-thousandths of an inch in radial diameter was found to be satisfactory. This radial water chamber may be thicker than thirty thousandths of an inch, a1- though I prefer not to substantially exceed a thickness of about one-quarter inch.

In Figure 3 I have illustrated a modification of my apparatus having a square molding' tube Illa and a casing IIa which surrounds the tube Illa and is separated by spacing members I3a to form the cooling chamber I2a. The casing IIa is formed in two parts which are bolted together.

In Figure 4 I have shown a molding tube Ib for molding rectangular ingots commonly referred to as slabs. 'I'he molding tube is surrounded by a casing I Ib and spaced therefrom by spacing members I3b to form a cooling chamber I2b. I have here illustrated the casing I0b as being continuous but it is obvious that it could be made as a split casing similar to the casing shown in connection with Figure 3.

The cooling medium, for example water, is delivered by the inlet pipe 2| at such a temperature and is circulated through the cooling chamstantially immediate solidication of the molten metal directly contacting the tube. After the shell moves downwardly, it continually gives up heat to the molding tube III with the result that the shell increases in thickness as it recedes from the pouring cavity of the tube.

By causing the cooling water to be acted upon by means of the suction pump 21 I prevent pressure from being exerted against the tube walls in a direction and amount which would deform the tube walls in the direction toward the center of the tube and at the same time a large quantity of water can be passed through the cooling chamber. The suction may be of an order to either cause a measurable decrease in pressure urging the tube inwardly or may be great enough to cause a pressure to be exerted against the inner wall of the tube so as to urge the wall outwardly and against the spacer members which separate the tube from the casing to form the cooling chamber. I-thus prevent the difficulties which I have outlined above and insure that the tube will not be subjected to the strain imposed upon it when water is forced at high pressure through thecooling chamber and will retain its original contour and the cooling chamber I2 will continue to be of a thickness determined by the width of the spacing members which separate the outside of the tube from the inside of the casing. 'I'his method of circulating the cooling uid is of particular importance when ingots such as shown in Figure 3 and Figure 4 are to be produced or ingots having irregular shapes. Furthermore, the molding tube is not subjected to the strains imposed upon it when water is forced at high pressure through the cooling chamber.

By the term ingot" I mean to refer to a mass of metal having any desired area of cross-sectional dimensions.

While I have described suitable apparatus for carrying out my invention and while I have described it in connection with continuous casting of metal, it will be apparent thatrother types of apparatus may be employed so long as the cooling fluid is sucked through the cooling chamber. My invention may also be employed with intermittent as well as continuous casting. It will be understood that various changes, omissions andaddltions may be made to the apparatus without departing from the spirit and scope of the invention as set forth in the following claims.

I claim:

1. In the method of casting metal in a molding tube of high thermal conductivity which is cooled by a sheet of liquid owing through a chamber and in contact with the outer wall of the tube, the step of supplying liquid to the chamber under pressure and controlling the pressure of the liquid exerted on the tube wall by means of suction exerted on the outflowing liquid.

l 2. In the method of casting metal into an ingot having a desired cross-section, which consists in pouring metal into the top of a. thin walled molding tube having high thermal conductivity and oi' introducing cooling liquid under pressure at one end of the chamber and exerting a suction on the liquid at the other end of the chamber of such magnitude that the pressure exerted by the liquid against the tube walls is insufficient to cause distortion of the tube.

3. 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 therebetween of shallow radial depth for at least a portion of its length, said chamber having an inlet and an outlet, means whereby the inlet end of the cooling chamber can be connected to a source of cooling liquid supply under pressure and means connected to the discharge end of the cooling chamber for aiding the circulation of the cooling liquid by suction through the cooling chamber. l

4. The combination with an apparatus of the class described having a thin wall molding tube and a conned iluid circulating chamber surrounding the exterior of the tube, of a source of water supply under pressure at one end of the chamber and a discharge passage at the other end of the chamber, and a suction pump connected with the discharge passage capable of aiding a high velocity flow of water through the chamber while maintaining a pressure therein, which is insuicient to distort the tube.

5. The comb'nation with an apparatus of the class described having a thin wall molding tube and a confined iluid circulating chamber surrounding the exterior of the tube, of a source of water supply under pressure at one end of the chamber and a discharge passage at the other end of the chamber, and suction means connected with the discharge passage capable of aiding a high velocity flow of water through the chamber while maintaining a pressure therein, which is insufficient to distort the tube.

6.. Metal casting apparatus of the type wherein molten metal is poured into one end of a molding tube and chilled sufciently to be progressively withdrawn from the other end as a formed ingot, comprising a supporting casing of rigid construction, a molding tube of high thermal conductivity and capable lof being deformed under pressure arranged interiorly of and spaced from said casing to provide a passage therebetween, means whereby liquid may be introduced into said passage, and a suction pump connected to the passage for withdrawing the liquid from the passage.

of cooling liquid connected to the passage and a suction pump for withdrawing the liquid from the passage.

8. Metal casting apparatus of the type wherein molten metal is poured into one end of a molding tube and chilled suiciently to be progressively withdrawn from the other end as a formed ingot, comprising a molding tube of high thermal conductivity and of such thickness as to enable heat to be transferred therethrough at a rate suillcient to cause the rapid formation of a skin of metal about the molten mass of metal in the tube, a casing surrounding the molding tube spaced therefrom to form a water passage outside the molding tube, an inlet to said water passage, a source of cooling liquid connected to said inlet, an outlet connection for the passage longitudinally separated from the inlet so that liquid travels longitudinally along the outside of the molding tube along the passage, a suction pump connected to' said outlet for maintaining a high velocity circulation of liquid in said passage, and spaced elements in the passage between the molding tube and casing forming abutments to brace the tube against the casing to resist the outward pressure of the metal in the molding tube but which are ineifective to secure the tube to the casing.

9. In the method of casting metal into an ingot vhaving a desired cross-section, which consists in pouring metal into the top of a molding tube having high thermal conductivity and passing through a passage surrounding the tube a stream of cooling liquid in contact with the outer surface of the tube, whereby said surface is maintained at a temperature such that a layer of solidified metal is rapidly formed around the outside of the poured metal and of sufficient strength( to permit drawng the metal so molded through the tube, the steps of supplying cooling liquid at one end of the passage and exerting suction on the liquid at the other end of the passage to induce the flow of the cooling liquid through the passage.

EDWARD R. WILLIAMS.

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