US2946100A - Block graphite mold for continuous casting - Google Patents

Description

July 26, 1960 R. BAIER EI'AL BLOCK GRAPHITE MOLD FOR CONTINUOUS CASTING Filed Aug. 27, 1956 6 Sheets-Sheet 1 W Y 3 MW 5 mRA f N aw R mA HVm T 41%? III II 0 R m nM I I I I I I nnHnH HH| Y IIIII B July 26, 1960 R. BAIER ETAL BLOCK GRAPHITE MOLD FOR CONTINUOUS CASTING 6 Sheets-Sheet 2 Filed Aug. 27,

IN V EN TORS H MAW N Mu R mwmW R N Z14 MTT w w nww 6 Sheets-Sheet 3 Q I x M m mm flTIfll TlfiflTl IIrAFrfiLATTi TAUP \NN m m m m m Wu H- m i MWW m r Ti fi i H 1 m 2 G E5 N vw NW wfi w By JoH/v .5 TUflRT 6mm; JR.

ALBERT J PH/LL/PS ATTOAMFY July 26, 1960 BNER ETAL BLOCK GRAPHITE MOLD FOR CONTINUOUS CASTING Filed Aug. 27, 1956 -R. BAIER ETAL 2,946,100

BLOCK GRAPHITE MOLD FOR CONTINUOUS CASTING e sheets-sheet 5 July 26, 1960 Filed Aug. 27, 1956 July 26, 1960 R. BAIER ETAL 0 BLOCK GRAPHITE MOLD FOR CONTINUOUS CASTING Filed Aug. 27, 1956 6 Sheets-Sheet 6 mmvrozzs R/L'HARD 15/1/51? y Joy/v6 TU/l RTSMAREJR.

ALBERT J. PH/LL/Ps M W ATTORNEY Unite! Stats BLOCK GRAPHITE MOLD FOR TJONTINUOUS CASTING Filed Aug. 27, 1956, Ser. No. 606,518

16 Claims. (Cl. 22-573) The invention relates to molds and to their use for casting metal, and more particularly to molds for the continuous casting of copper cakes.

According to one preferred form of the invention, the mold comprises a composite graphite block made up of two half sections of graphite block clamped together. Each section contains half of a rectangular mold pocket which has an open top to receive the molten metal and an open bottom from which the congealed casting emerges.

Surrounding the mold pocket are a series of vertical drilled passages within which are disposed oversize copper tubes having closed upper ends. These copper tubes have compression fits with the graphite to promote excellent heat transfer, with special provision for preventing rupture of the graphite when the metal tube expands under casting conditions. Disposed within the copper tubes are inner tubes which are supplied with cooling water. The upper ends of the inner tubes fall short of the closed upper ends of the outer tubes causing the water to return downwardly in the space between tubes and to discharge into the water tank under the mold which receives the congealed casting.

The graphite blocks are housed in a metal box or frame comprising side plates with half section water manifolds at the bottom on which the graphite blocks rest. Each manifold has a gusset plate at each end providing a pair of end plates at each end of the graphite blocks. Horizontal bolts pass through the side plates at their ends to clamp the graphite blocks together.

The supporting manifolds under the blocks have return bends for feeding the inner cooling tubes with water. The manifolds also supply three series of water sprays at different levels for cooling the emerging casting.

The top level spray is located within the lower end of the mold pocket which is provided with a series of recesses separated by ribs which support the emerging casting. The sprays are applied within the recesses between the ribs against the surface of the casting before it leaves the mold, thus cooling the surface of the casting to a temperature below the plastic range While so supported.

The angle of impingement of the sprays is less than 30 from the vertical to create a downward venturi effect to prevent movement of water up the mold wall to elevations higher than the spray locations.

To increase cooling and to improve the surface of the casting, the graphite walls of the mold pocket are specially contoured or tapered. The tapers converge downwardly to. follow the shrinkage of the solidified casting.

General objects of the invention are to cast metals, particularly copper, at greatly increased rates; to cast cakes of larger cross section; to produce castings having superior surface and internal characteristics; to cast both oxygen-bearing coppers and coppers free of oxygen in commercial quantities in the same mold; to produce a mold for continuous casting having one or more of the above features of construction, and capable of accomplishing one or more of the aforesaid objects.

Patented July 26, 1960 Other objects and features of the invention will be more apparent from the following description when considered with the accompanying drawings in which:

Fig. 1 is a vertical elevation of the casting system, with parts of theholding furnace and pouring ladle shown in section; v

Fig. 2 is a side elevation of the mold and funnel assembly, with parts shown in section;

Fig. 3 is a top plan view of the mold with parts shown in section;

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

Fig. 5 is an enlarged vertical section through the water manifold, taken on the line 5-5 of Fig. 4, showing the water manifold and various connections thereto;

Fig. 6 is a fragmentary plan view of the end of a manifold, with the graphite block removed;

Fig. 7 is a section, on the line 77 of Fig. 2, taken through the T-shaped pouring nozzle; 1

Fig. 8 is a fragmentary side elevation, partly in section, of the upper ends of the cooling tubes, taken on the line 8-8 of Fig. 9; V

Fig. 9 is a transverse section through the upper ends of the cooling tubes, taken on the line 9-9 of Fig. 8;

Fig. 10 is a fragmentary side elevation of the mold, showing how the upper spray tubes are clamped to the upper face of the manifold;

Fig. 11 is a diagram illustrating the position of the several spray nozzles with respect to the mold and to the cake being cast; and

Fig. 12 is an isometric diagrammatic representation of the mold, illustrating the three levels of water sprays and the relationship of the tubes, graphite block and water manifold to each other and to the cake casting.

In the accompanying drawings and in the description forming part of this specification, certain specific disclosure of the invention is made for purposes of explanation, but it will be understood that the details may be modified in various respects without departure from the broad aspect of the invention.

Referring to the drawings and more particularly to Fig. 1, the system of casting, utilizing the invention, will be first briefly outlined, after which more detailed description of the mold will be given.

A melting furnace (not shown) supplies holding furnace 10 with the molten metal to be cast. The furnace 10 supplies pouring ladle 11 which in turn supplies funnel-distributor 12; the latter supplies mold 13 which is mounted on mold platform 14 which in turn is mounted for vertical reciprocation on carriage 15.

Carriage 15 is movable horizontally on tracks 16 from over tank 20, to provide access to the product after it is cast, as hereinafter explained more in detail. It will be understod that a stationary working floor (not shown) is located on opposite sides of the tracks 16, at a level even with the tracks 16, on which workmen may walk during pouring.

For effecting the casting operation, a hydraulic starting and lowering mechanism is located within and under tank 20; this comprises a starting block 17 mounted on platform 18 which in turn is supported on piston 19 which has working relation with a hydraulic cylinder (not shown) located below water tank 20.

It will be understood that the platform 18, as shown in Fig. 1, is in approximately its uppermost position with the starting block 17 projected up inside the mold 13. The starting block forms the bottom closure of the mold when initiating the pour. As molten metal is fed into the mold, it freezes and the frozen product is lowered uniformly into the tank 20 by the hydraulic arrangement. The tank 20 may extend below the top, surface of the mold a distance corresponding to the denane 3 sired length of the cast product, which may be as much as 27 feet long; in such case the hydraulic cylinder arrangement must extend below the mold top more than twice this amount, or over 54 feet, to accommodate the piston 19 in its fully retracted position.

Alternately, the hydraulic lowering mechanism may be replaced by a conventional roll drive, cut-off mechanism and handling equipment.

The holding furnace shown is an upright low frequency Ajax furnace rotatable about horizontal axis 24-. It has removable covers 22 and 23 and pouring spout 25. It may receive molten metal through a launder or a bull ladle. In practice, it may be preferable to use a Scomet cylindrical off-center pouring furnace arranged to continuously receive and pour molten metal into a suitable pouring ladle. In other applications, two or more furnaces may be grouped so that, while one was pouring,

the others may be melting cold metal.

The pouring ladle 11 comprises a bowl 27, trough 28, and skim gate 29. The ladle is arranged to tilt about an axis adjacent funnel 12, as indicated by the dot and dash lines. For this purpose the ladle is supported upon a carriage 47 having guide rolls which follow a fixed arcuate guide device 48. A conventional adjustable device 49 supports a hydraulic mechanism 30 which is used to raise and lower the pouring ladle 11. Since the details of the particular holding furnace 10 and pouring ladle 11 form no part of the present invention, they will not be further described.

Referring now also toFig. 2, the funnel-distributor 12 comprises a bowl 31 having a refractory lining with an entrance notch 32 for receiving the trough 28 of ladle 11. Funnel 12 has an inverted refractory T-shaped distributor 33 with a vertical passage 35 feeding a horizontal passage 36. See also Fig. 7. Horizontal passage 36 has, at its bottom, a narrow slit 34. Instead of slit 34, a series of bottom holes may be provided. Funnel 12 is supported by bridging plates 37 resting on the side walls of mold 13.

The manner of conveying molten copper from the holding furnace 19 to the mold 13 will be briefly outlined. The pouring ladle 11 receives the metal stream from the holding furnace 10, accommodating any changes in position of the pouring furnace spout through its tilting arc. The ladle bowl 27 is covered with charcoal and it delivers metal from a point near the bottom under the skim gate 29 in the usual manner.

The manner of handling the hot metal will depend on the nature of the metal. In the case of tough pitch copper, for example, the metal stream may fall through air in passing from holding furnace 10 to pouring ladle 11 and in passing from pouring ladle 11 to funnel 12. This is generally suitable also for highly deoxidized coppers. However, with all coppers, and particularly with oxygen-free and low residual phosphorous deoxidized coppers, it may be advisable to use a reducing gas at these points to prevent oxygen absorption.

The most important function of the funnel-distributor 12 is to distribute the molten metal in the mold 13 in such way as to avoid hot spots, cold shuts, local sweats and other minor surface faults. In casting tough pitch copper it is particularly important to obtain a uniform stirring action at the molten surface level in the mold, to avoid the formation of heavy oxide scum which causes both surface defects and local interior islands of highoxygen copper in the cast product.

The above action is accomplished by submerging the clay-graphite distributing tube 33 just below the surface of the molten metal in the mold, as indicated particularly in Fig. 2. The multi-directional outlet flow through the ends of the horizontal passage 36 and through the bottom slit 34 provides the necessary distribution; the open ends provide stirring at the ends of the mold, while the narrow bottom slit restricts downward velocity component at the center so that all of the hot metal is not directed with high velocity at one point. A compact stream with high velocity could result in a very localized central hot spot, which would increase the depth of the freezing zone of the metal in the mold.

On the other hand, if the entire metal supply is delivered horizontally, the excessive horizontal velocity of the metal streams will cause undesirable cold shuts and laps on the freezing surface. Thus there is a critical relationship between the area of the two end horizontal holes and the bottom slot (or vertical drill holes) depend ing on the rate of casting and the cross sectional area of the cast product.

It is one of the objects of this invention to provide a design, and a method of construction, of said delivery device which will maintain this critical relationship in practice, despite the well known errosive effect of flowing molten metals, particularly tough pitch copper. We have found that clay-graphite is particularly advantageous for casting coppers.

During the continuous casting operation, the platform 18 may be lowered at a uniform speed which is variable at will. Accuracy may be maintained within a limit of one percent of constant speed by a special high precision hydraulic system (not shown).

In operation, the red hot cake casting, emerging from the mold is rapidly chilled by a series of pressurized water sprays described hereinafter, and the large volume of water is collected in tank 20. This water is removed at any desired level as by drain line 46. The water may be circulated by a circulation and pumping system, through a cooling device, and back to the water manifolds as described hereinafter.

It will be understood that, if desired, a series of molds may be mounted side by side. In such event, a single platform 18 (and hydraulic mechanism) may service all molds, a separate starting block 17 being provided for each mold.

In the description, certain metals, sizes, values and dimensions are given for purposes of illustration. These are given for convenience of disclosure only, it being understood that the teachings of the invention apply to other metals, sizes, values and dimensions. Unless otherwise stated, the following description applies to casting tough pitch and phosphorous deoxidized copper cakes having a cross section of about 4%" x 25".

The mounting for mold 13 will now be described (Fig. 1). The mold is supported on carriage 15 having four wheels 38 riding on two rails 16; thus the entire mold may be rolled out of the way to give access to the top of tank 20 in the casting pit and to the hydraulic mechanism for the removal of the cast product, after the pouring operation is completed.

The mold 13 is supported by a frame 14 which is vertically oscillated by a reciprocating mechanism. A suitable prime mover (omitted for simplicity) is mounted on carriage 15, which reciprocates connecting rod 39. Rod 39 is pivoted to a series of hell crank levers 40 on one side of the frame 14. A series of bell crank levers 41 are pivoted to the carriage on the other side of frame 14. Links 42 and 43 pivotally connect bell crank levers 40 and 41 to oscillatory frame 14. A connecting rod 44 connects bell crank levers 40 and 41. A series of guide posts 45 are supported on carriage 15, and slidably engage guides on frame 14 to insure vertical reciprocation of the mold in a substantialy vertical straight line.

Any suitable means may be provided to vary stroke and frequency of vertical reciprocation of the mold. For example, to vary stroke, the drive motor may have a crank arm whose length is adjustable. To vary frequency, motor speed may be changed. Neither frequency nor stroke is especially critical.

When casting coppers free of oxygen, it is desired to rotect the surface of the liquid metal from contact with oxygen. A preferred method, in the case of phosphorous deoxidized copper, is to use a graphite flake cover on the 6 top of the molten metal in the mold. The reciprocating action of the mold works the graphite flakes down the mold wall'where they finally emerge at the bottom and are washed away by the water sprays. However, other carbonaceous materials may be used, and for some purposes, air displacement by anon-oxidizing gas is all that is necessary. 7

When using molds having an appreciable taper 'as discussed below, the stroke cannot be excessively long since, on the up-stroke, there is the possibility of jamming the taper on the hot and weak crater shell of the embryo casting that is forming at the top of the freezing zone, and which, at this point, is at a maximum cross dimension; or conversely, on the down-stroke there is a possibility of producing clearance between the embryonic crater shell and the mold wall and thereby seriously affecting the rate of heat transfer.

In casting cakes, good results have been obtained by us, using a frequency range of about 70 to 180 strokes per minute and an amplitude of 1 to 4 mms. Obviously, the most suitable combination for any mold would be related to the cross section being cast and the amount of taper required and the casting rate, for the section size. For cakes, we have found that 180 strokes per minute with a 2 mm.- amplitude is quite satisfactory without being unduly critical. By stroke we mean a complete round trip movement of the mold from bottom position back to bottom position.

. Referring more particularly to Figs. 3-11, the mold will now be described.

The mold 13 is supported in a metal frame comprising two manifolds 50 extending the width of the cake and forming the bottom of the mold frame. The sides of the frame are formed by two verticalside plates 52 extending the width of the mold; and the ends of the frame are formed by two pairs of gusset plates 53, one pair at either end. Within this frame is disposed two half sections of a massive graphite block 51, 51. The frame is clamped together by a series of horizontal bolts 54 at either end of the mold. Nuts on the ends of bolts 54 clamp the graphite blocks 51, 51 tightly together.

The 'ends of the side plates 52 have steps 55 (Fig. 2)

resting on transverse bars 56 which in turn rest on transverse bars 57 attached to hangers 58 which are suspended from adjacent members of reciprocating frame 14. Thus the graphite blocks 51, 51 are supported in a boxlike metal structure which protects the relatively fragile graphite material. I Referring now to Figs. and 6, the manifolds 56, which form the bottom of the mold frame, have end legs 59 which face each other but which do not abut (Fig. 3). The graphite blocks 51, 51 have corresponding end extensions which do abut at 61.

It will be understood that the graphite blocks 51 are made from suitable commercial graphite and are machined to the shape indicated. The abutting surfaces 61 of the two blocks are machined so as to form a tight seal to prevent escape of the molten metal. The interior mold surfaces 96 are machined to provide generally flat planar vertical surfaces which vary from planes by the tapers and bulges hereinafter discussed. In horizontal cross section the mold surfaces are of generally oblong rectangular configuration with curved fillets 62 at the corners (Fig. 3). In practice, it has. been found necessary to bulge the horizontal configuration outwardly to compensate for the tendency for the casting to dish inwardly as the result of thermal warpage. The bulge is proportional to casting speed and cooling rate and the dimensions are chosen to result in a casting with substantially parallel sides.

The manifolds 50 are box-like structures built up of plates suitably fastened together. At the upper and inner corners of the manifolds are extension ledges 60 (Figs. l and 5) facing the interior of the mold. These ledges 60 project both from the main length of the manifold and from the endextensions thereof.

The manifolds 50 are each provided with an inlet passage 63 which intersects both the main part of the manifold and the extension thereof-see particularly Figs. 5 and 6. These inlets have flanges for connection with pipes which supply the manifolds with cold water. The

inlet passages 63 for the two manifolds 50 are both located at the same end of the mold. p

The manifolds 50 deliver water to the main cooling tubes 80 and to three levels of water sprays. For this purpose the manifolds have a series of top holes 64 in the main sections and offset ends; they have a series of bottom holes 65 for the cooling tubes in both the main sections and offset ends; their ledges have a series of drilled passages 66 for -the middle level sprays in both the main sections and offset end; the ledges contain holes 86 for the main cooling tubes in both main sections and ends.

The water delivery to the top level sprays will now be described-see particularly Figs. 4, 5 and 10.

The graphite blocks 51 have 'a series of horizontal passages in which are located cross tubes 68.. Each cross tube has a nozzle tip 67 having a downwardly directed discharge passage disposed at a 20 angle to the vertical. The cross tubes 68 connect with elbows 69 which are connected to fittings 7tl-see Fig. 10. Fittings 70 have annular recesses housing O-rings 71 which press against the adjacent face of the manifold 50 around the top openings 64. The fittings 70 are clamped against the manifold by a series of clamping bars 72 and bolts 73. The bars straddle adjacent fittings and the bolts 73 are disposed between.

, It will be noted that at the meeting faces 61 of the two graphite blocks 51 the openings for the end cross tubes 68 are made, half in one section and half in the other section ofthe-graphite; Also, see Fig. 3, the top openings 65 supplying these end cross tubes 68 are positioned in one manifold for the one end of the mold and in the other manifold for the other end of the mold, the cross tube 68 being appropriately bent to accommodate the elbows 69.

It will be noted that the graphite blocks 51 and side plates 52 have clearance spaces 75 for the elbows 69. It will be noted that the inner faces of the graphite blocks 51 have clearance bays 74 below the discharge of nozzles 67. These clearance bays 74 provide, in effect, vertical ribs which support the hot and pliable casting while the water sprays are directed between the ribs on the surface of the casting before it leaves the mold, thus cooling the surface below the plastic range while so supported. I

The bottom level of sprays and the cooling tubes are supplied from the bottom openings 65 in the manifolds. A series of return bends 70 (Fig. 4) connect with the inner vertical tubes and have lower spray holes 82. The return bends 7Q are connected to coupling members 78 which are clamped around the bottom openings 65 by a series of clamping bars 81 and bolts; these are similar to the clamping bars 72 and bolts 73 described above.

, The middle level sprays are provided by nozzle holes 84 drilled into the ledges 60 and connecting with the passages 66. The axes of the nozzle holes 84 have an angle with vertical of about 20.

The main cooling tubes will now be described. The outer cooling tubes 85 (Fig; 4) are loosely disposed in the upper ends of openings 86 in the ledges 60, and have special fits with the drilled openings in the graphite blocks 51 through which they pass. The inner tubes 80 are disposed inside of the outer tubes 85 and extend short of the top of the outer tubes (Fig. 8). The outer tubes 85 have top caps 88 silver soldered thereto.

The outer cooling tube 85 has a normal size which is oversize with respect to the opening in the graphite 51 in which it fits. The outer tube 85 is providedwith an inner longitudinal rib 87 which limits the force exerted by the copper tube on the graphite when the copper tube expands from heat under casting conditions.

The inner tube 80 has two longitudinal external ribs 91 and a longitudinal internal rib 92. Internal rib 92 surrounds internal rib 87, and the external ribs91 space the inner tube from the outer tube to form the water passages illustrated particularly in the drawing.

The relationship between the cooling tubes and the graphite blocks is most important. The outer copper tubes 85 are fitted oversize in the drilled and precisely reamed graphite holes at room temperature. The tubes being of copper will expand more than the graphite mold block at casting temperatures and thus improve initial contact pressure during the service period. In fact, the relative expansions of copper and graphite are so dissimilar that an ordinary unribbed hard drawn copper tube will fracture a graphite cylinder having a wall thickness of 7a to inch when they are assembled tightly and heated up to operating temperature range.

The longitudinal expansion rib 87 avoids placing undue stress on the graphite since the expansion of the tube is accommodated by elastic collapse of the rib under compression and thus the copper tube maintains the desired surface-to-surface fit with the graphite 51.

Thirty cooling tubes are used in the present mold, each being pressed into a carefully reamed and slightly undersize hole in the graphite block. So long as these tubes are kept sufficiently cool by water, that is, below their re-crystallization temperature, they will retain their temper and tight lit, and they will expand and contract in the service cycle without loss of elasticity due to annealing. There is no need to provide copper tubes having higher annealing temperatures than that of ordinary phosphorized copper.

It will be noted that the graphite blocks have enlarged clearance recesses 89 and 90 at the tops of the tubes to relieve the graphite blocks of stress at these points. Similarly, the holes in the graphite at the lower ends of the tubes are made slightly larger than at the mid-lengths of the tubes to relieve the lower ends of the graphite block from stress where there is no need for tight fit between cooling tubes and graphite block because of the relatively small amount of heat extracted through the graphite block at the lower ends of the tubes.

Thus the tubes assume a slightly larger diameter at their ends than at their middles, thus reducing any tendency of the tubes to creep longitudinally in their holes.

Thus, a great volume of water is fed into the lower ends of the inner tubes 80, which water overflows at the upper ends of the inner tubes and passes down between the tubes 80, 85 as indicated by the arrows. In order to obtain maximum heat transfer, the ribbed side of the tube 85 faces the back side of the mold wall so that the circular side faces the mold surface 96 (Fig. 8). The fit of the inner tube 80 within the outer tube 85 determines the dimensions of the return passage for the water which is shaped to provide maximum water flow over the smooth surface facing the molding space, and minimum fiow on the back side. These provisions accomplish both high velocity flow and economy of water, while providing maximum cooling efficiency.

To protect the top of the mold 13 and top tube caps 88 against mechanical injury and against injury by molten metal which might he accidentally spilled, a series of protecting plates, indicated in general by 94, are provided-see particularly Fig. 3. These plates 94 are held in place by a series of bolts threaded into the graphite.

For the purpose of increasing the cooling and improving the surface of the copper, the graphite walls of the molding space are especially contoured or tapered. The relatively easy machining and shaping of the graphite makes the graphite mold especially adaptable for dressing tapers;

In the present cake mold the graphite block is made in two halves bolted together, but it can also be manufactured from a single solid block of graphite in one piece. However, the multiple piece construction has certain advantages because it is easy to machine tapers and to provide water sprays.

The tapers converge downwardly to follow the shrinkage of the solidified casting and are related in degree to the casting dimensions. Since tapers are intended to improve cooling contact and must follow the shrinkage pattern of the cake rather closely, it follows that a slow casting rate which produces a well cooled cross section will permit the use of a steeper taper (i.e. at a larger angle to vertical) than a rapid casting rate where the shape is emerging from the mold at a higher temperature.

On the other hand, the usable speed range for any given taper is not so critical that a reasonable variation in speed cannot be permitted. Obviously, this range is greater at higher speeds where the cake always tends to clear the mold at a high temperature. For instance, tests show that at higher casting speeds a taper suitable for 13 inches per minute can be used up to at least 20 inches per minute; whereas, at slower casting speeds a taper suitable for 8 inches per minute, becomes unsuitable above about 10 inches per minute.

For a cake casting speed of 15 inches per minute, in the mold illustrated, the tapers being used approximate a total of .045 inch across the 4 /2 inch direction, and .250 inch across the 25 inch direction. Their aid to heat extraction can be followed readily by measuring the working temperatures down the mold wall with thermocouples. In straight sided molds, there is a sharp drop in wall temperature below the point where the cake shrinks away from contact. With proper tapers, the wall temperatures in these locations can be raised by as much as 300-700 F. with corresponding increase in heat removal.

Tapers are determined empirically from observations of their effect on the surface of the cake during the course of operation. Their effect on surface quality is important in all types of copper, since they provide a general smoothness that is not obtained in straight sided molds. With tough pitch copper, we doubt that a commercially acceptable cake surface can be made without them at desirably high casting rates, due to exudations of heavy CuCu O eutectic sweats which form if a clearance gap is permitted due to shrinkage of the casting from contact with the mold wall. Copper melts at 1083 C. and the CuCu O eutectic melts at 1065 C.

The above is especially true on the narrow sides of the cake due to contraction along the 25 inch dimension, which is very appreciable. Consequently, much greater tapers are needed in these locations than across the 4% inch width. Sweat formation is also encouraged by high casting rates which result in easy bleeding of the eutectic through the hotter shell that prevails under such conditions. In some cases we have also experienced rupture of the shell by remclting on the narrow end surfaces when casting without the benefit of sufiicient tapers.

We have found that tapers are an effective aid to increasing heat transfer, and that their use permits the casting of a smoother surface on which oxide sweats can be suppressed to a remarkable degree.

The combination of tapers and mold reciprocation results in unexpected advantages. As the casting moves downwardl', downward movement of the mold tends to move the mold wall away from the casting, and upward movement of the mold tends to move the mold wall more firmly into engagement with the shrinking casting.

On the downward stroke a slight bulging of the hot plastic shell will occur while, on the upward stroke, the plastic shell is slightly hot worked or deformed back to original dimension. We have found, by proper selection of length and frequency of stroke, in relation to the dimensions of taper, that a moderate amount of such hot forming of the plastic shell can be carried out with the unexpected result that the surface of the casting not only 9 does not rupture or tear, but acquires a burnished eflect and is much smoother than that obtained from straight sided molds where no such forming takes place. Also, it is clear that the force fit type of rubbing contact established on the up stroke is especially useful in obtaining exceptionally high rates of heat transfer while an average rubbing contact on the down stroke is maintained by the ability of the plastic shell to maintain contact with the mold wall.

It will be understood that the motion of reciprocation of the mold, in the form illustrated, is simple harmonic. That is to say, from a position at rest at the upper end of its stroke the mold will gradually accelerate. to its maximum speed half way down its stroke, after which it will gradually decelerate to its position at rest at the bottom of its stroke; whereupon the mold will similarly accelerate and decelerate to its upper position of rest. The above described condition of hot forming of the plastic shell will be accentuated when the maximum speed of downward motion of the mold is greater than the uniform downward motion of platform 18 and the cast product-provided the clearance between casting and mold wall, produced on the downward stroke, is not excessive.

The combination of direct molten metal contact with the bare graphite on one side, and that of the compressed cooling tubes on the other, provides not only an extremely efiicient heat transfer medium, but one that has exceptionally high capacity. This construction results in increasing casting speed to at least 20 tons per hour while simultaneously maintaining a maximum graphite temperature of 800 F. at the freezing zone. At such casting rates, the mold and sprays are removing a B.t.u. equivalent of 4800 horsepower. The heat being transferred through the graphite walls probably averages 750,000 B.t.u.s per square foot per hour.

To secure cooling of this order, the mold illustrated must employ about 1300 gallons per minute of water at approximately 35 p.s.i. Half of this quantity is distributed to each of the two rectangular headers at the bottom of the mold. Each header in turn supplies its line of cooling tubes and the three sets of high velocity sprays that impinge on the hot surface of the emerging casting. The incoming water to each main cooling tube is conducted to the top and returned down between the two tubes with a free discharge at the mold bottom into the tank 20.

The three sets of sprays illustrated are important participants in the total cooling. When casting tough pitch copper at the rate of 15 tons per hour (about 15 inches per minute with the given cake size), the bottom of the liquid V zone or crater 97 is about even with the bottom of the mold. Therefore, the highest sprays, which are located above the bottom of the mold, are impinging on a red hot surface with a small liquid core. Consequently, the sprays as a whole, remove most of the sensible heat and a small portion of the latent heat under such conditions, and this total is well over 50% of the overall heat extraction.

It will be noted from Figs. 11 and 12 that the sprays are arranged in a staggered pattern so that their sweep on the descending cake 98 provides a series of parallel stripes as indicated by the arrows 67, 84 and 82. These arrows bear the same reference characters as the nozzles which cause the sprays: upper sprays 67; middle sprays 84; and bottom sprays 82.

It is very desirable that the sprays operate with such high velocity and proper tangential direction that the cooling is effected by warming the water, not by generating appreciable steam. Low velocity sprays used in the uppermost position would result in steam at sufiicient pressure to force its passage upward in the mold between the casting and mold wall. This results in shallow scalloping of the surface of the cake, if the steam reaches the solidifying surface. Accordingly, both pressure and dil0 rection are used-to create a downward venturi actiofi which eliminates this effect.- 1

It will be noted that the upper sprays have opportunity to apply cooling while the cake is still supported by the mold wall ribs between bays74, thereby preventing bulg ing. In addition, this design greatly aids in keeping-the and particularly copper.- It is especially useful for cast-' ing oxygen-bearing copper such as tough pitch copper in any desired size; and for casting coppers free of oxygen such as oxygen-free or phosphorous deoxidized copper. Heretofore it has not been possible to continuously cast tough pitch copper commercially in cake form with the quality required by industry.

v The term oxygen-bearing copper, as used herein, is intended to include tough pitch copper as well as copper containing a lesser amount of oxygen; it is intended to include any copper in which oxygen is in available form for attacking the graphite if the reaction temperature of the graphite is exceeded.

On the other hand, the term copper free of oxygen," as used herein, is intended to cover those coppers known as phosphorous deoxidized copper containing both high phosphorous and low residual phosphorous, any other deoxidized copper such as copper deoxidized by lithium, boron, calcium, etc., and also those coppers referred to as oxygen free; in other words, any copper in which there is no oxygen available for attacking the graphite at its reaction temperature.

For casting coppers free of oxygen, it is preferred to maintain a protective layer of discrete particles of carbonaceous material, such as flake graphite, lamp black,-

pulverized anthracite, etc., floating on the surface of the molten metal in the mold. This cover acts both as a protective blanket to prevent oxygen absorption and as a moving mold wash to prevent adherence of phosphate slag or other extraneous material to themold wall. Consequently, reciprocation has a special purpose when casting coppers of this type. Oxygen bearing coppers act decidedly differently. Here, reactive carbon produces defects, and the use of a bare mold wall is preferable to the nuisance of trying to apply an inert mold dressing and maintaining a-uniform coating at all times.

Reciprocation using long strokes has the known advantage of presenting a progressively different cold mold surface to the incoming metal, thus integrating the zone of high heat removal over a longer length of mold wall than would be the case if it were stationary. Reciprocation and the taper also have the advantage of improving the surface of the casting as pointed out above. Thus the present mold provides high heat transfer capacity in the initial construction, the maintenance of the Working contacts over the operating temperature range and the provision of great, dimensional stability despite repeated thermal cycling, which is needed if a long mold life is to be achieved. Our mold is based Graphite has a very low coefiicient of expansionabout one-ninth that of copper. Thus, graphite has unusual resistance to thermal shock and will not crack when subjected to temperature extremes. Equally important, the small expansions undergone within repeated temperature cycles are accommodated elastically in the high quality grades and do not cause either spalling or heat checking of the mold surface, nor the haphazard warping of mold walls which so often results in bulges, hollow spots, loss of shape, etc., in molds made of copper. For these reasons, the dimensional stability of graphite is greatly superior to metals where a vast heat extraction rate has to be achieved with a small surface area.

The above mold has many advantages. Due to the absence of lubricating film, and due to the efiicient heat transfer, it can cast at a higher rate than an all-metal mold. The tapers can be applied more easily to the graphite wall than to an all metal mold. The mold can be enlarged or made smaller within limits by machining off either the mold space surfaces or the meeting surfaces where the two halves meet. The mold may be used for casting other shapes by changing the shape of the graphite wall defining the mold space, and by chan ing also the disposition of the cooling tubes.

Instead of the above-described ribbed circular expandible tube for creating an elastic press fit against the reamed opening in the graphite, the tube may be made oval or elliptical in cross section and slightly oversize. The tube is then forced into the graphite hole which makes the elliptical cross section more nearly a true circle. As the graphite and copper heat up during the casting operation, the expansion of the copper tube will change its shape causing it to move still further towards circular form and, at the same time, the area of contact between copper tube and graphite opening will increase and the constant pressure will also increase. The major axis of the ellipse formed by the elliptical cross section may be perpendicular to the surface of the mold pocket so as to have the area of best thermal contact between tube and graphite adjacent the mold pocket.

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 casting metal comprising a block of frangible material having a mold pocket, the walls of said block having passages therein, oversize metal tubes having compression fits in said passages, said metal tubes having longitudinally extending compression ribs to limit the expansive force, exerted by the tubes against the frangible material due to temperature rise during the casting operation, to a point safely below the rupture strength of the mold material.

2. A mold according to claim 1 in which said tubes constitute outer tubes and in which the ribs on said outer tubes project inwardly, said mold further comprising inner tubes disposed within said outer tubes, said inner tubes having longitudinally extending, inwardly projecting ribs nesting the ribs on said outer tubes, and additional, longitudinally extending, outwardly projecting ribs bearing against said outer tubes to space the main portions of the inner and outer tubes to provide a flow space therebetween for coolant.

3. A mold for continuously casting metals comprising a graphite block having a mold pocket open at the top to receive molten metal and open at the bottom to discharge the congealed casting, the lower portion of said mold pocket having a series of recesses forming a series ofribs therebetween, said ribs being co-extensive with the walls of the mold pocket, means for supplying said recesses with a fluid to contact the congealed casting be fore it emerges from said mold pocket, thus cooling the 12 surface of the casting below its plastic range while the casting" is being supported by said ribs.

4. A mold according to claim' 3 comprising nozzles in said recesses, the angle of impingement of spray from said nozzles being less than 30 from the vertical for the purpose of creating a downward venturi effect, thus preventing movement of water up the mold wall to elevations higher than the spray locations.

5. The mold according to claim 4 comprising further means for directing sprays below the mold in order to further cool the emerging casting.

6. In apparatus for continuously casting metals, a mold having a mold pocket open at the top to receive molten metal and open at the bottom to discharge the congealed casting, opposed longitudinal profile areas in the mold pocket converging toward the bottom of the mold to provide tapers and thus maintain substantial cooling contact between the shrinking casting and mold pocket wall throughout the effective length of the mold pocket and means for vertically reciprocating said mold.

7. Apparatus for casting metals according to claim 6 in which the maximum downward speed of the mold in its reciprocating cycle is greater than the downward speed of the congealed casting.

8. A mold for continuously casting metals having a mold pocket for receiving molten metal at one end and for discharging a congealed casting at the other end, the portion of the mold pocket adjacent the exit end having a plurality of recesses forming a plurality of projections therebetwcen, the tops of said projections describing surfaces coextensive with the walls of the mold pocket, and means for supplying said recesses with a fluid to contact the congealed casting before it emerges from the mold pocket, thus cooling the surface of the casting below its plastic range while the casting is being supported by said projections.

9. The method of continuously casting metal in a mold, said mold having-a mold pocket whose walls converge downstream with respect to metal flow through the mold, said method comprising feeding molten metal into the mold at such rate, in relation to the degree of taper, that the casting shrinks, as it moves downstream, at a rate corresponding to the degree of taper, whereby to maintain heat transmitting contact between casting and mold wall for a substantial length of the mold, and reciprocating the mold lengthwise of the casting.

10. The method of claim 9 in which the mold has an open top, maintaining a free surface of molten metal in the mold, and cooling the metal at such rate as to congcal the upper end of the casting into the shape of a crater shell having a relatively deep crater whose upper edge is in close proximity to said free surface, whereby to hot work said shell.

11. A mold for continuously casting metals comprising a graphite block having a mold pocket open at the top to receive molten metal and open at the bottom to dis-- charge the congealed casting, said bloc having walls with internal passages therein, ,mctal tubes in said passages, said tubes exerting elastic, expansive pressure against the walls of said passages to promote heat transfer therebetween, said tubes having longitudinally extending compression ribs to limit the expansive force exerted by the tubes against the graphite due to temperature rise during the casting operation to a point safely below the rupture strength of the mold material, and means for supplying coolant to said tubes.

12. A mold for continuously casting metals comprising a graphite block having a mold pocket open at the top to receive molten metal and open at the bottom to discharge the congealed casting, said block having walls with internal passages therein, metal tubes in said passages, said tubes exerting elastic, expansive pressure against the walls of said passages to promote heat transfer therebetween, second metal tubes disposed within said first-mentioned tubes and spaced therefrom to provide a flow space for the coolant, means for preferentially directing coolant to that part of the flow space between said first and second mentioned tubes which faces the mold pocket.

13. The mold according to claim 11 in which said tubes constitute outer tubes and in which the ribs on said tubes project inwardly, said mold further comprising inner tubes disposed within said outer tubes, said inner tubes having longitudinally extending, inwardly projecting ribs nesting the ribs on said outer tubes, and additional, longitudinally extending, outwardly projecting ribs bearing against said outer tubes to space the main portions of the inner and outer tubes to provide a flow space therebetween for the coolant.

14. A mold for continuously casting metals comprising a graphite block having a mold pocket open at the top to receive molten metal and open at the bottom to discharge the congealed casting, said block having walls with internal passages therein, metal tubes in said passages, said tubes exerting elastic, expansive pressure against the walls of said passages to promote heat transfer therebetween, said internal passages being relieved at each end of the tubes, causing the tubes to assume a slightly larger diam eter at their ends than at the mid-parts thereof.

15. A mold for continuously casting metals having a mold pocket open at the top for receiving molten metal and open at the bottom for discharging a congealed casting, the portion of the mold pocket adjacent the lower end having a plurality of recesses forming a plurality of projections therebetween, the tops of said projections describing surfaces coextensive with the walls of the mold pocket, nozzles for supplying said recesses with water to contact the congealed casting before it emerges from the mold pocket, thus cooling the surface of the casting below its plastic range while the casting is being supported by said projections, said nozzles being directed downwardly and at such angle that their streams impinge against the surface of the casting at an angle of less than 30 degrees with respect to vertical, thus preventing upward movement of water products.

16. A continuous casting mold for continuously casting metal, said mold comprising a graphite block having a mold pocket open at the top to receive molten metal and open at the bottom to discharge the congealed casting, said block having walls with internal straight machined passages therein, the surfaces of said passages being smooth, straight metal tubes lining said passages, the wall of said tubes being elastic and having sufficient temper to exert pressure against said smooth surfaces to promote heat transfer therebetween, said tubes expanding more than the graphite with temperature rise, thus maintaining heat transfer contact between said tubes and block, means for permitting the walls of said tubes to move relative to said smooth surfaces to relieve pressure on the graphite block exerted by the tubes due to thermal expansion of the tubes, and means for supplying coolant to said tubes.

References Cited in the file of this patent UNITED STATES PATENTS 1,346,333 Petinot July 13, 1920 1,393,195 Bradley Oct. 11, 1921 2,131,307 Behrendt Sept. 27, 1938 2,154,234 Eppensteiner Apr. 11, 1939 2,264,288 Betterton et a1 Dec. 2, 1941 2,410,837 Peters Nov. 12, 1946 2,613,411 Rossi Oct. 14, 1952 2,698,467 Tarquinee et a1. J an. 4, 1955 2,744,303 Dore May 8, 1956 2,747,244 Goss May 29, 1956 2,767,448 Harter et a1. Oct. 23, 1956 2,772,455 Easton et al. Dec. 4, 1956 2,835,940 Wieland May 27, 1958 2,904,860 Hazelett Sept. 22, 1959 FOREIGN PATENTS 588,618 Great Britain May 29, 1947 718,644 Great Britain Nov. 17, 1954 518,702 Canada Nov. 22, 1955

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