US2835940A - Mold and method for continuously casting cakes - Google Patents

Description

MOLD AND METHOD FOR CONTINUOUSLY CASTING CAKES Filed July 18. 1956 H. G. P. WIELAND 3 Sheets-Sheet 1 HH H rlll. H l U w R May 27, 1958 Y FIQ Illllll'lll May 27, 1958 H. C. WIELAND MOLD AND METHOD FOR CONTINUOUSLY CASTING CAKES Filed July 18, 1956 3 Sheets-Sheet 2 .w v Illll l l l I l I l l i l l l l l I l l II w 3 & \m

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V MW W\\ MWMWQ ATTORNEX May 27, 1958 H. C. P. WIELANDv MOLD AND METHOD FOR CONTINUOUS LY CASTING CAKES Filed July 18, 1956 3 Sheets-Sheet 3 INVENTOR: /7A/vs C. P IV/ELA/m Zwzm ,4 T TGRNEY The invention relates to the continuous casting of metal products having polygonal cross-section and, more particularly, to the continuous casting of metal products whose cross-section is rectangular or oblong, adapted to be subsequently cut into cakes.

A general object of the invention is to provide a mold having a graphite liner for continuously casting metal products of polygonal or oblong cross-section, in which the graphite has long life, and which does not require the use of inert gas to prevent oxidation of the graphite to obtain an acceptable cast product.

According to a preferred form of the invention, the mold comprises a water-cooled jacket and graphite liner, having a mold casting space which is oblong in crosssection. The jacket comprises an inner shell of copper and an outer shell of steel. These shells are connected only at the top and bottom to form the water space. The jacket is made up of separate members connected together by packed joints. The liner comprises a set of flat, relatively thin, graphite plates independently secured to the walls of the copper shell. The upper and lower ends of the mold are provided with beveledledges, and the upper and lower edges of the graphite plates are beveled and held by such beveled ledges. The side liner plates corresponding to the width of the cake have clearance spaces at their ends to permit horizontal expansion. This type of mold will continuously cast copper cakes, particularly in the large sizes, as, for example, cakes approximately 20 wide by /2" thick, although not limited to such product or size.

Other objects and features of the invention will be more apparent from the following description when considered with the following drawings in which:

Fig. l is a diagrammatic elevation with parts in section, illustrating a continuous casting process according to the invention;

Fig. 2 is a diagrammatic elevation taken at right, angles to Fig. 1;

Fig. 3 is a plan view of the cake mold, partly in section, illustrating structural detail;

Fig. 4 is a vertical section, taken on the line 4-4 of Fig. 3;

Fig. 5 is a vertical section, taken on the line 55 of Fig. 4;

Fig. 6 is a detail illustrating a corner construction, taken on the line 6-6 of Fig. 4.

In the following description and in the claims, various details will be identified by specific names for convenience, but they are intended to be as generic in their application as the art will permit.

Like reference characters denote like parts in the several figures of the drawings.

Referring now to the drawings, and more particularly to Figs. 1 and 2, the general system will first be briefly described. In these figures, parts are shown largely diagrammatically for simplicity. The system comprises, in general, a vertically reciprocable mold 10 fed by a furnace 11 which supplies molten metal to the mold. The oblong casting bar issues from the bottom of the mold through a tank 12 containing water. Power-driven rolls 13 lower the casting. A circular saw 14 cuts the oblong casting bar into lengths forming cakes.

The furnace 11 may be a tilting low-frequency furnace pivoted on fulcrum 15 and adjusted by hydraulic cylinder tates Patent 6 "ice 16. A spout 22 of alloy steel is secured to the furnace wall. The spout has a T-shaped branch discharge 23. A valve 17 controls the flow of molten metal into the spout 22. The valve 17 has a support 18 with which the valve spindle has screw threaded engagement. A hand wheel 19 screws the valve disk up and down to control the metal flow. The spout 22 may be electrically heated to prevent freezing of the metal stream, and may be lined with a suitable refractory such as steatite.

The'mold 10 comprises, in general, a water-cooled jacket 25 having a graphite liner 26. The mold is supported by a reciprocable platform or frame indicated, in general, by 27.

The reicprocating mechanism comprises a set of four bell crank levers 28 pivoted to a stationary support by pivots 29. Tie rods 30 connect the pairs of bell cranks 28. Links 34 connect the bell cranks to the frame 27. A motor 32 drives a crank 31 connected by connecting rods 33 to the bell cranks 28.

The motor 32 may be of variable speed, or some other device may be provided, to control the number of vertical strokes per minute imparted to the mold 10. By

. adjusting the length of the lever arms, or eccentricity of the crank 31, the length of the stroke may be varied.

Tank 12 surrounds the cast cake where it leaves the mold. The tank may be supported in stationary position, or it may be secured to the support 27 to reciprocate therewith. A rubber water seal 38 is provided which works against the casting. The level of the water in the tank 12 is preferably kept at a level of about 1 above the bottom of the mold. This expedient provides cooling means over the entire length of the casting and prevents oxidation of the cast surface. The bar casting is cooled sufiiciently by the time it leaves the bottom of the tank so that no overheating of the rubber seal is encountered.

Cooling water is supplied to the water jacket by supply pipes 39. Outlet pipes 40 conduct the cooling water from the jacket. The cooling water overflows thetop of the tank, as indicated. Regulation of the overflow from the tank by weir 41 determines the height of the water in the tank with respect to the mold bottom.

In operation ,the drive rolls 13 move at such speed that the casting bar is sufficiently solidified when it leaves the mold to prevent breakthrough of the molten metal. The valve 17 is adjusted to feed molten metal to the mold at a speed corresponding to the rate of withdrawal of the casting. Metal is added from time to time to the furnace 11. To stop the flow of metal from the furnace, the hydraulic cylinder 16 is adjusted to move the furnace downwardly in the direction of the arrow A so as to place the seat of the valve 17 above the level of molten metal in the furnace. The congealing metal freezes in the form of the usual crater shell 20 having edge 42.

Referring now to Figs. 3 to 6, the mold will now be described in detail. The mold 10' corresponds to the mold 10. Jacket 25 corresponds to jacket 25, and the liner 26' corresponds to the liner 26.

Jacket 25 is made up of an inner copper shell and an outer steel shell. The inner copper shell comprises a pair of vertical copper side plates 43 and a pair of vertical copper end plates 44. The side plates 43 have recesses 45 and the end plates 44 have tongues 46 fitting into the recesses 45 with gaskets 35 interposed. A series of horizontal bolts 47 clamp the vertical plates together to form a water-tight seal.

The steel outer shell comprises side plates 48 and end Patented May 27, 1958 on the inner copper plates and against the bars 50 and 54 attached to the outer steel wall with suitable gaskets 36, 37 interposed. A set of vertical bolts 53 clamp the frame members 52 and 51 together to provide a water-tight jacket space.

Water is supplied by a set of two lower inlet pipes 57 and 58 arranged at diagonally opposite corners of the mold. Outlet pipes 59 and 60 are at the top of the molds directly over the inlet pipes. This arrangement helps provide a rotary circulation to the cooling water.

The liner 26' comprises four individual graphite sheets or plates, the side plates being indicated by 65 and the end plates by 66. The lower end of the copper wall has a projecting flange or ledge 64 forming a V-shaped recess. Each of the liner plates 65, 66, has a lower beveled edge fitting into the recess.

The liner may be fabricatedof any grade or quality of graphite including materials containing graphite such as graphite coated carbons which are not wetted by the molten metal being cast.

The upper ends of the liner plates 65, 66 are similarly beveled and are held in position by a frame member 67 having a dependent rib or ledge 68 forming, with the adjacent copper wall, a V-shaped recess to receive the beveled upper edges of the liner plates 65, 66.

It will be noted that the liner plates 65, 66 are of such thickness with respect to the adjoining ledges 64 and 68 as to project inwardly into the mold space beyond these parts. Thus, the casting may leave the mold without engaging the lower edge of the copper wall of the jacket.

Adequate provision for linear expansion of the side liner plates 65 is provided by making them somewhat shorter than the corresponding jacket wall against which they rest, leaving expansion spaces 69 at the ends of the liner plates 65. End liner plates 66, on the other hand, being substantially shorter, snugly abut the side liner plates 65. Since the side plates 65 are substantially longer than the end plates 66, provision for expansion of the side plates 65 must be made. However, in view of the relatively short transverse dimension of the end plates 66, it is not necessary to provide here for expansion. In cases where the end plates have longer transverse dzmension, similar provision for expansion may be made.

The size, shape, and composition of the product, that can be cast according to the invention, may vary widely. These characteristics are somewhat interdependent, and will depend further upon the characteristics it is desired the product to have.

The following is given as one example of an actual installation that has been used commercially. This example r is given for purposes of illustration only, and not by way of limitation.

The cast bar was of phosphorized de-oxidized copper. It had a cross-section of approximately 20" wide by 4 /2" thick. The thickness of the copper walls 43, 44 (where they are co-extensive with the liners) was about 1 (26.5 mm). The thickness of the liners was approximately /4" (6 mm.). The axial dimension (lengthwise of the mold) of the liner plates was approximately 12''. The mold had a reciprocation stroke of about 0.16" (4 mm.) and a frequency of reciprocation of about 60 cycles per minute. Figs. 3 and 4 of the drawing are approximately to scale.

The longer liner plates 65 were about 0.08" (2 mm.) shorter than the inside transverse dimension of the mold to provide an expansion space 69 at each end; thus room for expansion of the liner plates was provided of about 0.04" (1 mm.) at each end. The shorter liner end plates 66 had no provision for expansion since they were fitted with a light push fit between the longer liner side plates. The shorter end plates 66 having a dimension transverse of the mold of about 4 /2", are so short that expansion clearances were not required. The longer side plates 65 which are about 20" long required the expansion clearance.

The pouring, and speed of withdrawal of the cast product, was so arranged that the level of molten metal in the mold was maintained at about 1" below the upper edge of the graphite liner. The thin edge 42 of the crater 20 formed by the congealing metal was maintained about at the surface of the molten metal. The bottom of the crater was estimated to be near the lower edge of the mold.

A cover of flake graphite was maintained on the surface of the molten metal in the mold and casting speed was about five short tons per hour.

The present invention provides not only high heat transfer from the casting below the mold by the water bath 12 but also through the mold itself. High heat transfer through the mold is obtained by maintaining close surface-to-surface contact between liner and jacketmade possible by special features of construction of the copper jacket and of the graphite liner, and special relationships between these parts. Sufiicient heat transfer is obtained to keep the temperature of the graphite liner sufliciently low to minimize oxidation under the particular conditions of use. No special non-oxidizing atmosphere is necessary.

It is well known that graphite has a number of advantages for continuous casting. Graphite has high thermal conductivity; it is not wetted by most metals, particularly copper and copper alloys; it is easily machined; it is low priced; it has good mechanical strength and is somewhat flexible; it has a low co-efficient of expansion of about one-ninth that of copper.

The thermal conductivity of graphite is about 40% of the thermal conductivity of copper. The thermal conductivity of copper, graphite, and air are as follows. These are given in B. t. u.s per hour, per degree F., per square foot of area, per inch in thickness. Copper 2650; graphite 900; air 0.165.

These figures show that .001 of an inch of air space is equivalent to about 16" of copper and to about 5%" of graphite so far as thermal conductivity is concerned. The effect of losing liner-to-jacket contact is thus clearly evident.

Graphite begins to oxidize at an incipient oxidation temperature of about 750 F. (400 C.). However, for all practical purposes, even though the liner be exposed to oxygen-bearing metal being cast, or to the atmosphere, satisfactory life of the graphite liner is obtained so long as the graphite liner is kept below about 600 C. (1112 F.). Thus oxygen-bearing copper, such as tough pitch copper, may be cast without the flake graphite cover floating on the surface of the molten metal in the mold so long as the temperature of the graphite liner is maintained below 600 C.

However, if the graphite liner is not exposed to oxygen from either the metal being cast or from atmosphere, the temperature of the graphite liner may be permitted to rise above 600 C. Thus, coppers free of oxygen, such as phosphorous deoxidized copper, may be cast with graphite liner temperatures as high as 1400 F. (760 C.) without undue loss of graphite from oxidation, provided a carbonaceous cover is used on the surface of the molten metal in the mold.

It will be noted that the liner plates are relatively thin and flexible; and they are mounted independently of each other, so that each is free to move, or adjust, with respect to the others, and to the jacket, under the various conditions of temperature and pressure due to the molten metal.

It will also be noted that the inner copper shell and the outer iron shell are unconnected except at the top and bottom of the mold. It will be further noted that the several side and end plates 43, 44 of the copper shell are separate pieces, and that they are connected by articulate joints having packing; also, these plates are connected to the lower and upper frames 51, 52, through joints having packing. This gives the walls of the copper shell a certain freedom to adjust, to flex, or warp, under the inasaaaao fluence of the temperature of the molten metal, without interference from each other, or from the outer shell which is of a dissimilar metal having different physical properties such as coefficient of expansion, etc.

Due to the difference in temperature on the liner facc contacting the molten metal and the liner face contacting the copper shell, the graphite liner will bow inwardly; that is to say, the parts of the liner plates in contact with the molten metal will move toward the molten metal. Thus, both horizontal and vertical lines drawn through the centers of the liner faces contacting the molten metal will become convex toward the molten metal.

Due to the diiference in temperature of the copper shell face contacting the graphite liner and the copper shell face contacting the cooling water, the copper jacket plates will 'bow generally in the same direction as the graphite liner plates. Thus, there is a tendency for the liner and copper shell to warp or distort in parallelism due to temperature differentials, and thus maintain face-to-face contact. In addition, the hydrostatic pressure of the molten metal in the mold presses the comparatively thin liner back against the copper shell, and thus aids in preserving the contact.

As the molten metal congeals, it forms a crater shell 20, as is well known; the metal freezes first where it contacts the relatively cool walls of the mold, and freezes last in the center of the mold space. The metal contacting the side walls will freeze very quickly so that the edge 42 of the crater shell will be in close proximity to the level of the molten metal in the mold. The crater edge will first freeze into a skin of soft, or mushy, consistency. This weak, newly-formed skin of the embryonic casting will not have suificient strength to be selfsupporting for some distance below the crater edge.

As the metal freezes sufiiciently to become self-supporting, it shrinks and pulls away from the graphite liner, thus reducing heat transfer from the casting to the liner. In the specific example given above, it is estimated that the pulling away of the casting from the graphite liner took place at about 4 or 5 inches below the top edge of the graphite. Most of the heat transfer takes place at the area where the poured metal is either completely molten or is passing through the soft or mushy stage. Most of the bowing of the side and end plates of the mold takes place at this area.

Despite such local distortion, the unique construction of the jacket, the manner of mounting the thin flexible graphite liner plates, permits the maintenance of intimate contact between liner and jacket needed to obtain high rate of heat transfer.

The system, according to the invention, has been used to cast cakes of varying cross-sectional shape and size and having various well known compositions as, for example, phosphorized copper containing residual phosphorous, high conductivity, low residual phosphorized copper, and tough pitch copper. If desired, the water tank may be omitted and replaced with a Water spray.

The term continuous casting as used herein is intended to mean the making of cast products which are indefinite in length with respect to the axial dimension of the mold. That is to say, the term is not to be limited to any length of product cast between successive starts. For example, the cast oblong product may be comparatively long, making possible the cutting of a single casting into many cakes. Or, the cast product may be relatively shortonly long enough for one, or possibly two or three cakes, to be made from the product.

The present invention makes possible the casting of cakes without requiring inert gas to prevent oxidation of the graphite. However, when casting copper free of oxygen such as oxygen-free or deoxidized coppers, it is advantageous to employ the protective cover of finely divided carbonaceous material on top of the free surface of the molten metal in the mold. When casting oxygenbearing coppers, such as tough pitch copper, the protective cover of carbonaceous material must not be used. At the same time, the metal is cooled sufficiently slowly to prevent development of undesirable properties in the cast product.

The temperature of the graphite liner may be measured in any desirable or convenient manner. For example, holes may be drilled vertically down through the top frame member 67 into the top edge of the liner, lengthwise of the mold and midway across the liner thickness. Such holes may be drilled at any desired points in any one or more of the four liner plates. A thermocouple may be inserted in each hole and moved up and down to measure the temperature along the length of the liner. In this way the hottest point of the liner can be conveniently measured. Maximum temperature usually occurs in the area where the molten metal contacts the graphite liner and where the edge of the crater shell is passing through its embryonic stage. The holes are sufficiently large so that the distance between the hole and the casting surface can be made as small :as is consistent with .the strength of the graphite.

While certain novel features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A mold for continuously casting metal, said mold having an open top into which molten metal is fed, and an open bottom from which the cast product is continuously withdrawn, said mold having a casting space polygonal in cross-section, said mold comprising a metal jacket and a graphite liner, said jacket having walls, said liner comprising plates, at least one for each jacket wall, means for mounting the liner plates against their respective jacket walls to permit the liner plates to adjust independently of each other so as to maintain substantial surface contact with their respective jacket walls.

2. A mold according to claim 1 in which the jacket walls are unrestrained from flexing at the areas Where the molten metal congeals and the liner plates may flex correspondingly at said congealing areas.

3. A mold according to claim 2 in which said jacket comprises an inner shell contacting the liner and an outer shell surrounding said inner shell, means connecting said shells *articularly and only at top and bottom to provide a jacket space for circulation of a coolant.

4. A mold according to claim 1 in which said liner mounting means are confined to the top and bottom of the liner plates.

5. A mold according to claim 4 in which said liner mounting means comprises inwardly projecting ledges on said jacket walls at top and bottom, said ledges having V-shaped recesses facing each other, the upper and lower edges of said liner plates being beveled to fit in said V-shaped recesses.

6. A mold according to claim 1 in which the crosssection of the casting space is oblong, and in which the vertical edges of the longer side liner plates have edge clearance with the shorter end walls of the jacket to allow for expansion of the longer side liner plates.

References fited in the file of this patent UNITED STATES PATENTS 1,850,060 Haws Mar. 15, 1932 1,988,425 Summey Jan. 15, 1935 2,305,477 Junghans Dec. 15, 1942 2,376,518 Spence May 22, 1945 2,510,100 Goss lune 6, 1950 2,527,545 Goss Oct. 31, 1950 FOREIGN PATENTS 705,856 Great Britain Mar. 17, 1954

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