Technical Field

This invention relates to a process and apparatus for casting rounds, slabs, and the like from high melting point metals and is particularly concerned with the direct casting of semi-finished steel products.

Background Art

The conventional way to manufacture "semi-finished" steel products, such as rounds, slabs, blooms, and billets, is to pour molten steel into an ingot and then roll the ingot down into a round, slab, bloom, or billet in a rolling mill. The semi-finished products are then made into bars, tubes, sheet, strip, or the like, which are called "finished prod¬ ucts."

It may require up to twenty-five or more passes through various rolling mills to transform an ingot into a semi-finished product. The reduction in cross-sectional area from an ingot to a semi-finished product is at least four to one. A great deal of energy, as well as expensive capital equipment, is thus required to reduce the ingot to semi¬ finished product forms.

A more modern technique for making slabs and other semi-finished products is the continuous casting process whereby molten steel is poured into a tundish, from there into bottomless, cooled vertical molds, and then withdrawn by

rolls or other mechanisms in a continuous length. Pieces are cut off from this continuous length to give slabs, blooms, or billets as desired, in accordance with the shape of the ver¬ tical mold. Although deceptively simple in principle, this technique has, in practice, many inherent difficulties. Con¬ tinuous casting equipment is bulky and requires a large amount of space for each installation. The capital invest¬ ment is enormous, and the process is not suitable for low volume production.

Although slabs and billets can be cast by the con¬ tinuous casting process, the casting of rounds by continuous casting has not proved satisfactory because rounds have the least surface area per unit of volume and are difficult to cool and otherwise handle in a satisfactory manner in a con¬ tinuous casting process.

Another technique for making slabs, particularly stainless steel slabs, is the bottom pressure pouring method described in my U. S. Patent No. 3,196,503. According to this technique, a ladle filled with molten steel is placed in a pressure vessel which is sealed with a lid. A pouring tube extends through the lid down to within approximately 4 to 6 inches (10 to 15 cm) from the bottom of the ladle. The top part of the pouring tube is mechanically connected to the filling end of the slab casting mold. Air pressure within the vessel causes the molten steel to rise through the pour¬ ing tube and enter the slab mold at the lower end, the mold being at a slight tilt. The equipment is expensive, and there are problems with inclusions, since the top portion of the slab to which inclusions normally rise is the first por¬ tion to become cool.

It is well known that ferrous metals can be cast directly into commercial products in sand molds. It has not, however, generally been possible to cast them directly into commercial products in a permanent mold because the molten

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ferrous metal welds to and/or erodes the sidewalls of the mold and, if there is any vertical drop, the forces of the falling molten metal can damage, or even knock out, the bottom of the mold.

Disclosure of Invention

An object of the present invention is to provide a new and useful process for the direct casting of semi¬ finished steel products and similar products of other high- melting-point metals, particularly rounds and slabs.

Another object of the present invention is to pro¬ vide an efficient and inexpensive process and apparatus for the direct casting of semi-finished products which have low levels of impurities and superior grain structure and surface characteristics.

In accordance with the present invention, semi¬ finished steel products are cast directly into a permanent mold provided with a special movable plunger which is rapidly lowered into the mold as the mold is filled with molten metal and then is quickly forced upwardly as the molten metal solidifies to lift the casting slightly from the mold as it cools. This lifting puts the casting in compression and reduces cracking.

A reservoir of molten metal is provided over the casting cavity and is kept substantially full as the plunger descends into the mold. The reservoir also acts as a feed head of molten metal as the casting cools.

The mold has a casting cavity with a constant cross section which corresponds to that of the product being cast. The plunger has the same cross section as the mold and makes a sliding, molten-metalprσof seal with the sidewalls of the

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mold. The top of the plunger is surrounded with a thin band of steel and the space inside of the band is filled with core sand and then cured in place. The plunger descends at rates of 1/2 to 4 inches per second (1.3 to 10 cm/sec) . The plun¬ ger is preferably lowered and raised by a screw jack driven by an air motor.

The molds for rounds are preferably made of inner and outer steel sleeves which are separated by a layer of sand. The molds for slabs and other flat products are pref¬ erably made of side blocks and slotted steel end blocks which are reinforced with strongbacks. The molds can be reused many times and can be adapted to pour single rounds or slabs, or multiple rounds or slabs, or the like, as desired.

The present invention thus provides a process and apparatus for casting ferrous and other high melting point metals directly into rounds, slabs, and other semi-finished products in relatively inexpensive equipment with low produc¬ tion costs and high production rates, maximizes the yield from the molten metal being poured, minimizes the losses, and produces semi-finished products with improved surface quality and grain structure.

Using the present invention, slabs may be made with¬ out utilizing additional energy to reheat the steel or ingot

such as is necessary to operate a rolling mill, thus conserv¬ ing energy and saving substantial expense. The present in¬ vention is especially adaptable to the production of cast products in relatively small volumes, such as the production of stainless steel products, where continuous casting could not be employed because of the large output necessary and lack of flexibility.

The present invention provides cast products of excellent quality. The molten metal passes into a mold with minimal contact with air, so that oxidation of the metal is minimized. The quality of the surface of the product is improved because the upward force from the plunger on the casting minimizes the air gap between the casting and the mold and reduces areas of adhesion. Splashes, buckles, wrinkles, and cold shots are eliminated because the metal does not drop any substantial distance. Inclusions rise to the top of the cast product and are easily cropped off. The flow of metal by gravity follows the natural convection pat¬ terns of the system, in contrast to the flow patterns pro¬ duced in bottom pressure casting, because in the present invention the hot metal is fed into the top of the mold and the hot metal rises to the top of the mold.

The process and apparatus of this invention may be used to cast products from any of the ferrous metals includ¬ ing stainless steel and from other high-melting-point metals, such as nickel, copper, and titanium.

Brief Description of Drawings

FIG. 1 is a side elevational view, in section, of a mold for casting rounds using the process and apparatus of the invention;

FIG. 2 is an enlarged, side sectional view of the plunger of FIG. 1;

FIG. 3 is a top plan view, partially in section, of the plunger and top of the mold, taken along line 3-3 of FIG. 2;

FIG. 4 is a side sectional view similar to FIG. 1, illustrating the casting process for rounds with the plunger about halfway down;

FIG. 5 is a side sectional view similar to FIG. 4 showing the plunger all the way down and the mold cavity filled with molten metal;

FIG. 6 is a side sectional view similar to FIGS. 4 and 5 showing the cast round and pouring cup lifted slightly from the mold as the cast round cools;

FIG. 7 is a plan view of the shim band showing the slits which facilitate wrapping it about the circumference of the retaining plate.

FIG. 8 is an enlarged side sectional view of a mold showing another embodiment of this invention for casting hol¬ low rounds;

FIG. ^' 9 is an end elevational view, with portions in section, of a mold showing another embodiment of this inven¬ tion for casting a single slab;

FIG. 10 is a top plan view of the single slab mold of FIG. 9;

FIG. 11 is a side sectional view of the single slab mold taken along line 11-11 of FIG. 9;

FIG . 12 is an enlarged top plan view of a portion of the pouring cup and plunger for the single slab mold of FIG .

9 ;

FIG. 13 is an enlarged side elevational view of a portion of the pouring cup and plunger for the single slab mold of FIG. 9, taken along line 13-13 of FIG. 12;

FIG. 14 is an end elevational view of a portion of the pouring cup and plunger for the single slab mold of FIG. 9, taken along line 14-14 of FIG. 13;

FIG. 15 is a plan view of the screw jack motors and air supply system for the plungers of the single slab mold of FIG. 9; and

FIG. 16 is a series of perspective views, illustrat¬ ing some of the .semi-finished products which may be poured in accordance with this invention, namely, a round, a thick- walled hollow round, a thin-walled hollow round, a bloom, a slab, and a thin slab.

Modes for Carrying out the Invention

- A preferred embodiment of an apparatus of the pres¬ ent invention for casting rounds and an illustration of the process of the present invention are shown in FIGS. 1 to 6. Referring to FIG. 1, there is shown a permanent mold 20 com¬ prising an inner tubular sleeve 21 and a concentric, spaced- apart, outer tubular sleeve 22, both sleeves being circular in cross-section, with sand 23 filling in the intermediate space 24. The inside wall 25 of the inner sleeve 21 defines the sides of a casting cavity 26. A plunger 27 affixed to a lifting screw 28 is lowered and elevated in the casting cavity 26 by a screw jack 29 at the bottom of the apparatus.

An air motor 31 drives the screw jack 29 and causes the lift¬ ing screw 28 to lower and raise the plunger 27 at controlled rates as required.

A pouring cup 33 is placed on top of the mold over the inner sleeve 21 and a ladle 34 is provided above the cup 33 for releasing molten metal 35 into the pouring cup, as shown in FIG. 4. At the beginning of a pour, the plunger 27 is in the top of the casting cavity 26, as shown in FIG. 1. When the molten metal 35 is released into the pouring cup 33, the plunger 27 is lowered at a controlled rate toward the bottom of the mold so that at the end of its descent, as shown in FIG..5, the molten metal 35 fills the casting cavity 26. When the molten metal cools, there is formed a round or other semi-finished product with a feed head 36 which is cut off.

Referring now in more detail to the mold 20, the outer sleeve 22 rests on a circular base plate 38 inside an annular collar 39 to which the outer sleeve is welded. The collar 39 in turn is secured by nuts 40 and tie-down studs 41 to the base plate 38, so that it can be disassembled if desired. At the top of the mold is an annular top plate 42 to which the top of the outer sleeve 22 is welded. The top plate 42 is provided with a center circular opening 43 with a diameter slightly larger than the outer diameter of the inner sleeve 21 and an upper circular countersunk groove or channel 44 into which fits an annular ring 45 (FIG. 2) . The top exterior of the inner sleeve 21 is welded to the inside of the ring 45 so that the combination can be placed in the opening 43 and suspended from the top plate 42 by engagement of the ring 45 in the channel 44. The bottom of the inner sleeve 21 is not restrained and can expand downwardly without buckling or jamming as it absorbs heat from molten metal.

Secured by bolts 47 to the bottom of the inner sleeve 21 and inside the outer sleeve 22 is a round plate

48. The round plate 48 has a layer of asbestos packing or steel wool 49 between it and the sand 23 which fills the space 24 between the outside of the inner sleeve 21 and the inside of the outer sleeve 22. There is clearance between the outer circumference of the round plate 48 and the inside surface of the outer sleeve 22. The asbestos packing 49 pre¬ vents the sand 23 from running out and interfering with the necessary downward expansion of the inner sleeve 21.

The surface of the inside wall 25 of the inner sleeve 21 is preferably honed or otherwise made smooth and regular. The inner sleeve 21 should be at least about 1-1/4 inches (3.2 cm) thick and is substantially thicker than the outer sleeve 22 since it must maintain its strength and integrity upon direct exposure to molten metal. At the same time, the inner sleeve 21 should be as thin as possible to avoid thermal gradient and hanger crack problems.

As noted, the space 24 between the inner sleeve 21 and outer sleeve 22 is filled with sand 23, which is packed into that space to support and strengthen the inner sleeve. The space 24 may also be filled with other filler materials, such as steel shot or grit, and the like. Preferably, the filler is of varying size and is not a good conductor of heat.

The plunger 27 is shown in greater detail in FIGS. 2 and 3 and comprises a heavy steel swivel plate 50 which is attached to the top of the lifting screw 28 and is held in a recess 51 in a heavy steel cylindrical block or piston 52 by a ring 53 which is secured to the bottom of the piston by bolts 54. Above the piston 52 is a circular retaining plate 56 which is bolted to the top of the piston with bolts 57. A shim band 58 of steel about 0.015 inch (0.38 mm) thick such as is used for shims extends circumferentially around and axially above the top of the piston 52.

This shim band 58 is attached to the plunger piston 52 by means of nails 60 which extend through holes 61 in the

retaining plate 56, through holes 62 drilled into the shim band, and through holes 63 in the piston. The lower portion 58a of the shim band is provided with a multiplicity of slits 64 (FIG. 7) about 1 inch (2.5 cm) deep and about 1/2 inch (1.3 cm) apart, and the lower portion is then annealed and bent at a 90° angle to the other or upper portion 58b of the shim band. The shim band 58 is disposed about the cir¬ cumference of the retaining plate 56 and the plate is placed on top of the piston 52 and bolted to the piston with bolts

57 which are tightened up at least finger-tight. This causes the holes 61 in the plate 56 to line up with the holes 63 in the piston 52. The nails 60 provide a positive means of holding or retaining the shim band 58 on the piston 52 as the piston descends.

The shim band 58 is positioned against the wall 25 of the inner sleeve 21 and smoothed out against it before the holes 62 are drilled. The bolts 57 may be tightened up fur¬ ther if desired once the shim band 58 is so positioned.

The shim band 58 may be made of steel or other rela¬ tively thin, flexible, resilient and strong metal which can withstand the high temperatures involved in this process. A suitable thickness for a steel shim band is about 0.015 inch. The thickness may range from as little as 0.005 inch (0.13 mm) up to about 0.035 inch (0.89 mm).

Silica sand 65 mixed with a suitable core binder is then rammed into the space above the retaining plate 56 up to within about 1/8 inch (0.32 cm) of the top of the shim band

58 to form a refractory cap or cover 66 for the plunger 27. The shape of the cover 66 is preferably concave as shown in FIG. 2 so that the sand is higher on the sides and lower in the middle. A rammer having a diameter which is slightly smaller than the diameter of the inner sleeve 21 and a curved forward surface readily forms this shape. The top of the shim band 58 should extend at least about 1/8 inch (0.32 cm)

above the top of the sand 65 so that the sand cannot rub off against the inside wall 25 of the inner sleeve and cause dirt and/or cracks in the casting. The sand 65 is then cured by a carbon dioxide gas or "no bake" system or otherwise to form a hard refractory mold ^' ed-in-place cap 66 on the piston plunger 27. After curing, any loose sand should be blown or brushed off the cap 66 and the inside wall 25 of the inner sleeve. The refractory core sand cap or cover 66 for the plunger 27 has to be made up in place as described for each cast. The piston 52 and the retaining plate 56 can be used over again. A new shim band 58 is preferably used for each cast.

There should be openings and clearances downwardly from the refractory cover 66 so that any gases generated by ^* contact between the cover and the molten metal can escape downwardly and are not forced upwardly through the molten metal. The cover 65 is porous so that any gases blow down¬ wardly through it, through nail holes 61 in plate 56, through the clearance between plate 56 and piston 52, and through the clearance between the inside wall 25 and piston 52 into the inside of the mold.

The plunger 27 formed as described above makes a sliding, molten-metalproof seal with the inside wall 25 of the inner sleeve 21 and has the same cross-sectional shape as the casting cavity 26 and product being cast. The term "molten-metalproof seal" signifies that molten metal does not flow past the plunger or, if a small amount does flow past the plunger, it is not enough to jam the plunger or in any way damage the means for lowering and raising the plunger.

The lifting screw 28 and screw jack 29 are prefer¬ ably a ball jack or screw jack such as shown in U. S. Patent No. 3,323,777, and constitute the means for lowering and raising the plunger 27. Preferably, there are ball bearings in the worm gear in the housing 32 to provide what is called a ball bearing screw jack. Also, there should be swivel

means somewhere in the connection between the lifting screw 28 and the plunger 27 so that there is no tendency to rotate the plunger when the screw jack is activated to lower or raise the plunger. In the floor supporting the mold there must be a bore hole 67 with a depth at least equal to the travel of the plunger 27 in order to accommodate the lifting screw 28 as it lowers the plunger downwardly into the mold. The screw jack 29 is like either of the two screw jacks shown in FIG. 15 and described hereinafter.

Mounted at the top of the mold 20 over the molding cavity 26 is the pouring cup 33 (FIG. 1) which comprises a cylindrical metal can 69 or section of steel pipe which is filled with shaped, bonded refractory core sand 70. The sand 70 is rammed in place around a frusto-conical plug of suit¬ able shape with the small end up and then cured. The sand 70 may have a silicate binder system which is cured with a car¬ bon dioxide, a "no bake" system, or a system in which a resinous binder is set by a catalyst and is cured with heat. Sharp silica sand such as used in foundries for cores may be used for this purpose.

The pouring cup 33 directs molten metal into the casting cavity 26 and forms reservoir or feed head 36 of molten metal above the plunger 27 as the plunger descends and as the casting cools. In accordance with the known princi¬ ples of the design of risers used in steel castings, the pouring cup 33 may be designed with the smallest cross sec¬ tional area at the top and with the area increasing as the cup extends downwardly, as shown. Pouring cups with the greatest cross sectional area at the top may also be used. The pouring cup 33 should be kept substantially full of molten metal throughout the pour and should be substantially full before the plunger 27 starts down. A probe or sensor 76 may be draped over the top of the pouring cup 33 so that when molten metal reaches the tip of the sensor, it shorts out a

circuit and causes the screw jack air motor 31 to start the plunger 27 down.

At the beginning of a pour, the plunger 27 should be as close to the top of the mold as possible and preferably within less than 3 inches (7.6 cm) of the top of the mold 20 and as close to the bottom of the pouring cup 33 as is pos¬ sible so as to minimize the distance through which the molten metal falls.

The ladle 34 has a lining 78 of suitable refractory material and is provided with a bottom opening 77 closed by a removable stopper 79. The ladle 34 can have a slide gate in place of the stopper 79 or the steel can be lip poured. When the stopper 79 is lifted, the molten metal flows out through a spout 80 beneath the bottom opening 77, as shown in FIG. 4.

The process of the present invention is illustrated in FIGS. 1, 4, 5, and 6. In FIG. 1, the ladle 34 is above the top of the mold with the stopper 79 closed to retain molten metal in the ladle 34. The plunger 27 is at its starting position at the top of the casting cavity 26.

In FIG. 4, the stopper 79 has been lifted and molten metal 35, such as steel or stainless steel or nickel, is being fed into the pouring cup 33 from the ladle 34 as the plunger 27 descends. Molten metal 35 fills the casting cavity 26 above the plunger 27 and substantially fills the pouring cup 33. The ladle operator should try to pour molten metal into the pouring cup 33 at approximately the same rate that it runs into the casting cavity 26 and maintain a good supply of molten metal in the pouring cup.

The plunger 28 is lowered at a rate of about 1/2 to 4 inches per second (1.3 cm/sec to 10.2 cm/sec) with a pre¬ ferred rate for rounds of about 1-1/2 to 2-1/2 inches per second (3.8 to 6.35 cm/sec), depending upon the size of the pouring cup 33 and the size of the product and other factors which will be apparent to those skilled in the art. A 10-foot (3-meter) round can be cast in about 50 to 80 seconds.

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Long rounds, up to say 40 feet (12 meters) long, may be cast in accordance with this process, in which event it may be desirable to vary the rate of descent of the plunger in the course of the pour.

In FIG. 5, the plunger 27 has completed its descent, forming a round casting 30. Anti-piping or insulating mater¬ ial 83, such as Ferrux material made by Foseco, Inc., is spread over the top of the metal 35 in the pouring cup 33 to keep the metal in molten condition and to permit it to feed downwardly into the casting under atmospheric pressure as the casting cools. If desired or found necessary, an exothermic material may also be used for this purpose.

In FIG. 6, the plunger has been raised to lift the casting 30 and pouring cup 33 out of the mold 20 a short dis¬ tance B which is at least about 3/4 inch (1.9 cm) and can be up to 3 or 4 inches (7.6 to 10.2 cm) . The plunger 27 is held in this position as the casting cools and shrinks, and may be raised a second or third time to accommodate the shrinkage and prevent the bottom of the pouring cup 33 from coming to rest upon the top of the mold 20. It is important that a lifting force be applied to the bottom of the casting as it cools so as to maintain contact between the solidifying cast¬ ing 30 and. the inside wall 25 of the mold, break any areas of adhesion between the mold wall and casting surface, and delay the formation of an air gap. The hydrostatic pressure forces of the molten metal are thus taken up by the plunger and the development of horizontal and vertical hanger cracks pre¬ vented. The longer the period of time that the sides of the solidifying casting can be held against the mold wall, the cooler the casting will become, the finer its grain struc¬ ture, and the better its surface.

The upwardly directed lifting force is accomplished by reversing the plunger 27 for a short period until the pouring cup 33 begins to lift off the top of the mold 20.

The plunger 27 is then stopped, the casting 30 is allowed to shrink, and the pouring cup 33 may resettle onto the top of the mold 20. The plunger 27 is again moved upwardly and the upwardly directed force is reapplied until the pouring cup 33 again begins to lift from the top of the mold 20. This pro¬ cedure may be repeated two or three or more times as needed until the shrinkage of the casting 30 is completed. The lifting or reversal step may be commenced immediately after the plunger 27 reaches the bottom of the mold, and preferably is begun within about a minute after the plunger reaches the bottom of its cycle.

For the final step in the process, the riser or feed head 36 formed in the pouring cup 33 is removed from the round casting 30 by burning off or otherwise cropping at the top of the casting, and the finished round is lifted from the mold by appropriate lifting means such as tongs carried by a crane and while simultaneously being pushed from the bottom by the plunger 27. At this point, the cast product has sub¬ stantially solidified and has cooled and contracted away from the inside wall 25 of the mold so that it can be stripped from the mold.

In order to discourage or prevent welding of the molten metal to the inner sleeve 21, a coating of zircon oxide 55 or other suitable anti-weld agent may be applied to

the top 37 of the inner sleeve 21 and to the inside wall 25 of the inner sleeve down to the plunger in its uppermost position.

For steel molds, it is desirable to form and main¬ tain an oxide coating on the inside wall 25 which acts as an insulative layer between the molten metal 35 and the inner sleeve 21. The oxide forms rapidly in the temperature range of from about 1700° F to 2000° F (about 930° C to 1090° C) and for this reason, a sand with relatively good insulative properties, such as silica sand 23, is used in the space 24 between the inner sleeve 21 and outer sleeve 22 so that the inner sleeve reaches the temperatures to form the oxide. Within obvious design limits, the inner sleeve 21 is also preferably made to be relatively thin from wall to wall so as to reach the temperatures at which the insulative oxide is formed quickly when exposed to the molten metal. An added advantage of a thin inner sleeve is that a hotter sleeve ex¬ pands more and thereby relieves pressures on the casting. For an eight-inch (20.3 cm) round, the inner sleeve 21 should be about 1-1/2 inch (3.8 cm) thick.

In order to permit the inner sleeve 21 to reach the temperatures at which the insulative oxide layer is formed on its inside surface, the weight of the inner sleeve should preferably be about 1-1/4 to about 1-1/2 times that of the product being cast therein.

If desired, air can be blown through the silica sand 23 to cool it down should it reach temperatures above 2000° F (1090°C) and begin to lose its strength and structural integrity. If it becomes desirable to increase the heat con¬ ductivity of the material in the space 24 between the inner and outer sleeves, steel grit or shot or similar material can be mixed in with the sand.

The means for providing the controlled vertical movement of the plunger 27 may be any suitable mechanical,

pneumatic, or electrical means other than the screw jack arrangement shown. A rod may be affixed to the plunger 27 at the top and to a piston in a cylinder at the bottom and powered pneumatically or by steam. A rack and pinion gear arrangement may be used with pneumatic or electric motors. Hydraulic systems are not favored because of fire hazards.

FIG. 8 illustrates an embodiment of this invention for the manufacture of hollow rounds. The permanent mold 20 is the same as that used in FIGS. 1-6. The plunger 100 is similar to the plunger 27 of FIGS. 1-6 in that it has a piston 101 and a shim band 102 which is filled with cured core sand 103 to form a cover 104 for the plunger.

In order to make a hollow round, there is attached to the plunger 100 a core 106 which is slightly greater in length than the length of the round being cast plus the height of a pouring cup 105. The core 106 is constrained and guided above the pouring cup 105 by a jig 107. The core 106 comprises a hollow steel tube 108 filled with dry silica sand 109. The bottom of the core 106 is welded to a retaining plate 110 of the plunger 100. The plate 110 is in turn bolted to the plunger piston 101 by means of four bolts 111 which are evenly distributed about the plate 110 in each quadrant thereof. As will be apparent to those skilled in the art, other means of attaching the core to the plunger may be employed.

A ceramic sleeve 113 extends over the core 106 from the jig 107 to protect the core from the impact of the molten metal 35 and also to act as a guide for the core. Molten metal 35 which is poured into a refractory brick-lined pour¬ ing trough 114 runs into and fills the pouring cup 105. The ^' ceramic sleeve 113 is adjustable and of sufficient length to protect the core 106 from the molten metal. The molten steel 35 may also be run into the mold above the plunger 100 with a side or bottom gate arrangement.

The means for positioning the jig 107 comprises a pair of lugs 117 and 118 which are welded to the can 69 of the pouring cup 105 and which support a vertical rod 119. A horizontal member 120 is welded to the top of the rod 119 and holds the jig 107 and ceramic sleeve 113 at one end over the center of the casting cavity 26. A bolt 121 in the lug 118 holds the rod in an adjustable manner.

The plunger 100 is lowered at about the same rate as that for rounds, or a little more rapidly because the metal cools a little more rapidly. Depending upon sizes and con¬ figurations, it may not be necessary to apply a reverse forg¬ ing or lifting force at the end of the descent of the plunger 100 in order to avoid hanger cracks and the like. The plun¬ ger 100 may be used to strip the product from the mold after the casting has substantially solidified and cooled enough to shrink away from the inside wall 25 of the mold.

The core 106 should be considered to be expendable and should not be reused. The core 106 can be stripped from the casting after the casting has been stripped from the mold.

Other forms of cores may be used to cast hollow rounds. A solid ceramic core, for example, may be used. A rod-reinforced and/or binder core may be used. The kind of core will depend upon a number of practical factors which will be apparent to those skilled in the art.

Using the same general arrangement, it is also con¬ templated that a steel-reinforced copper round can be cast which may then be rolled and possibly drawn into steel- reinforced copper wire. A steel rod would be mounted on the plunger in place of the core element 106 and copper poured around it. As a further modification, a plurality of steel rods could be mounted on the plunger, guided by a suitable jig at the top, and a steel-reinforced copper round thereby cast with a multiplicity of reinforcements in it.

In the same manner, other reinforced or combination metal products may be cast of other high melting point met¬ als. For example, the element 106 could be of larger diame¬ ter and of steel and stainless steel poured around it to make a clad round with stainless steel on the outside and a low carbon steel core on the inside.

FIGS. 9-15 show another embodiment of the invention for the production of slabs. Referring to FIG. 9, a mold 150 comprises two identical side blocks or side sections 151 and 152 which are supported in a parallel, vertical, upright position on a stool or base plate 153 and positively main¬ tained in that position by a multiplicity of hydraulic rams

154 which press against the outside surfaces of the side blocks. The assembly is preferably placed in a concrete pit

155 and the hydraulic cylinder and piston mechanism or rams 154 are affixed to the sidewalls of that pit.

As shown in FIG. 10, the side blocks 151 and 152 are separated and spaced apart by two pairs of identical vertical end blocks 157, 158, 159, and 160. For one pour, the end blocks 157 and 158 separate the side blocks 151 and 152 and, together with a plunger 161, define one slab casting cavity

162. For the next pour, the side block 151 is lifted over the side block 152 and set down on the other side of it, as shown by the side block 151' in broken lines in FIG. 10. In that combination, the side blocks 152 and 151' are separated by the end blocks 159 and 160 and, together with a plunger

163, define a second slab casting cavity 164. A lifting crane is attached to pad eyes 165 (FIG. 12) on each side block to lift and place it, as above described.

The purpose of moving the side block 151 in this manner is to alternately expose the faces of each block 151 and 152 to molten metal on sequential pours so that thermal stresses are neutralized and are not built up from having only one face of the side blocks exposed to the heat of the

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molten metal. The side blocks would warp and crack like ingot molds if exposed to the extreme heat of the molten metal on only one face.

The side blocks 151 and 152 are preferably made of cast iron about 10 to 12 inches (25 to 30 cm) thick with machined faces so as to be flat and smooth. Cast iron side blocks are preferred for large slabs. For small slabs, bil¬ lets, and blooms, slotted steel, strongback reinforced side blocks, such as shown in my U. S. Patent No. 3,948,311, may be used.

Each of the end blocks 157-160 is identical and will be described with reference to end block 157. As best shown in FIGS. 12 and 13, the end block 157 is made of a narrow steel plate 168 about 4 inches (10 cm) thick with a plurality of regularly spaced, horizontal slots 169 in the outer sur¬ face thereof. An "I" beam strongback 170 is bolted onto the outer or back surface of the plate 168 with a series of Nelson studs 171 which are welded to the plate and extend through holes 172 in the "I" beam. A plurality of cylindri¬ cal rollers 173 are disposed horizontally in a U-shaped, elongated channel member 174 above and below each stud 171 to permit any necessary movement and adjustment when the molten metal contacts the hot face of the plate 168 and causes it to expand. The slots 169 accommodate any such expansion which the "I" beam strongback 170 resists. Each Nelson stud 171 has a nut 175 which clamps the channel member 174 against the rollers 173. There is generous clearance in the holes 172 in the "I" beam strongback through which the Nelson studs 171 extend in order to avoid any binding. Each end block is assembled by horizontally placing the plate 168 and the "I" beam strongback 170, distributing the rollers 173, placing the channel member 174 over the rollers, and bolting the unit together by placing the nuts 175 on the ends of the studs 171. If desired, the rollers 173 can be held on axis pins or brackets in the channel member 174.

C"

The end blocks 157-160 are attached to the edge of the side block 152 which is not lifted, so as to be adjust¬ able in and out and to provide slabs of varying widths. Referring to FIG. 10, three brackets 177 are welded to each end of the side block 152.- The upper and lower brackets 177 are identical, and a horizontally extending plate 178 is welded to each of these brackets. A housing 179 is mounted on each end of the upper and lower brackets 177 adjacent to one of the end blocks 157-160. Referring to FIG. 11, at least two positioning screws 180 are attached to each end block. Each positioning screw 180 passes through one of the housings 179 in which there is a worm gear driven by a worm gear drive shaft 181. One of the drive shafts 181 drives the worm gears for both positioning screws 180 attached to each end block. A handwheel 182 operates a second worm gear in another housing 183 to rotate the worm gear drive shaft 181 and cause both positioning screws 180 to move in and out the end block to which they are affixed. There is thus a hand¬ wheel 182 for each end block 157-160. The handwheels 182 extend from housings 183 which are mounted in side-by-side pairs on a plate 184 (FIG. 9) , which is welded to the inter¬ mediate bracket 177. Obviously, other means of positioning and adjusting the end blocks may be employed.

Since the plungers 161 and 163 are identical, and since only one plunger is used at a time, both plungers will be described in detail with reference only to the plunger 161. With reference to FIG. 11, the plunger 161 for the single slab mold comprises a block 187 affixed to and sup¬ ported by two lifting screws 188 and 189. The block 187 cor¬ responds to the piston 52 of the plunger 27 of FIG. 2. With reference to FIGS. 12-14, a shim band 192 is L-shaped in cross section and the lower leg is disposed in a peripheral, horizontal slot 190 in the block 187. Holes 191 in the block 187 receive nails 194 which also go through holes 196 drilled

into the shim band 192 after the shim band has been suitably positioned against the inside walls of the mold 150. Curable core sand 193 is packed into the space above the block 150 within the shim band 192 and cured to form a flat, expendable refractory cover 195 for the plunger 161.-

The base plate 153 FIG. 11) is preferably provided with holes 197 each large enough to accommodate one of the lifting screws 188 or 189 but not the plunger 161, so that the plunger always stays above the bottom edge of the side blocks 157-160 and does not have to be realigned with them for each pour.

In order to facilitate the manufacture of slabs of different widths, the plunger block 187 is formed of a center section 198 and two end sections 199, as shown in FIG. 11. The size of the plunger 161 can be modified by removing one or both of the end sections 199 from the center section 198. As shown in FIG. 13, each of the end sections 199 is bolted with a horizontal bolt 200 to the center section 198. Round threaded couplings 201 are bolted to the ends of the bottom of the center section 198 and attached to the top of the lifting screws 188 and 189 to affix the plunger 161 to the lifting screws.

The arrangements to cover the top of the mold and provide an integrated pouring cup are shown in FIGS. 11-14. A pouring cup 203 comprises a can 204 inside of which is a ceramic sleeve 208. The top of the casting cavity 162 is covered with a layer 210 of core sand which is packed into a thin metal trough 211 supported from below by the plunger 161 and is then cured. A ceramic sleeve 212 is placed on the metal trough 211 prior to formation of the sand layer 210 and is then surrounded with packed sand which is provided with a binder as previously, described. A hole 213, of perhaps 1 inch (2.5 cm) in diameter, is made in the metal trough 211 so that when molten metal is placed in the sleeve 212, it will

quickly burn out the hole 213 and flow unrestrictedly into the casting cavity 162 above the plunger 161. Obviously, other arrangements to cover the top of the casting cavity and provide a reservoir of molten metal over the cavity and access to the cavity may be employed. For instance, metal plates may be supported by the side blocks 151 and 152 and a pouring cup placed between them.

Before a pour, the plunger 161 should be lowered away from direct contact with the bottom of the metal trough 211 which supports the core sand layer 210 a distance of at least 1/2 inch (1.3 cm). This provides space between the refractory core-sand on the plunger 161 and the metal trough 211 through which molten metal can flow.

The plunger 161 is lowered and raised by a pair of screw jacks 216 and 217 connected to the lifting screws 188 and 189, as shown in FIG. 11. An identical pair of screw jacks 218 and 219 lower and raise the plunger 163 (FIG. 10) . There is thus one plunger and one pair of screw jacks for each casting cavity so that the same pair of screw jacks are used for every other pour.

The controls for each of the screw jacks 216-219 are identical and will be described with reference only to the screw jacks 216 and 217. As shown in FIG. 15, an air motor 220 causes a shaft 221 to rotate, which causes worms 222 and 223 mounted on opposite ends of the shaft 221 to engage worm gears 228 and 229 and elevate or lower the respective lifting screws 188 and 189. The air motor 220 is reversible with a variable speed. At one end of the shaft 221 is a top and bottom limit switch 224 which is actuated by the shaft. The limit switch 224 is electrically connected to a solenoid 225 which operates a four-way valve 226 and which is connected to suitable electrical controls so that the valve 226 may be operated to move the lifting screws 188 and 189 up and down. A solenoid-operated brake 227 is mounted on the end of the

quickly burn out the hole 213 and flow unrestrictedly into the casting cavity 162 above the plunger 161. Obviously, other arrangements to cover the top of the casting cavity and provide a reservoir of molten metal over the cavity and access to the cavity may be employed. For instance, metal plates may be supported by the side blocks 151 and 152 and a pouring cup placed between them.

Before a pour, the plunger 161 should be lowered away from direct contact with the bottom of the metal trough 211 which supports the core sand layer 210 a distance of at least 1/2 inch (1.3 cm). This provides space between the refractory core-sand on the plunger 161 and the metal trough 211 through which molten metal can flow.

The plunger 161 is lowered and raised by a pair of screw jacks 216 and 217 connected to the lifting screws 188 and 189, as shown in FIG. 11. An identical pair of screw jacks 218 and 219 lower and raise the plunger 163 (FIG. 10) . There is thus one plunger and one pair of screw jacks for each casting cavity so that the same pair of screw jacks are used for every other pour.

The controls for each of the screw jacks 216-219 are identical and will be described with reference only to the screw jacks 216 and 217. As shown in FIG. 15, an air motor 220 causes a shaft 221 to rotate, which causes worms 222 and 223 mounted on opposite ends of the shaft 221 to engage worm gears 228 and 229 and elevate, or lower the respective lifting screws 188 and 189. The air motor 220 is reversible with a variable speed. At one end of the shaft 221 is a top and bottom limit switch 224 which is actuated by the shaft. The limit switch 224 is electrically connected to a solenoid 225 which operates a four-way valve 226 and which is connected to suitable electrical controls so that the valve 226 may be operated to move the lifting screws 188 and 189 up and down. A solenoid-operated brake 227 is mounted on the end of the

shaft 221 opposite the limit switch 224, and is electrically connected to the limit switch and controlled thereby. When the limit switch 224 senses that the plunger 161 is at the top or bottom limit of its travel, the switch automatically operates the valve 226 and actuates the brake 227 to halt the plunger.

One advantage of using an air motor as the source of power for driving the screw jacks is that when the plunger is caused to lift at the end of its descent to apply a forging force, the air motor will not stall and will provide substan¬ tial lifting force at very slow or no revolutions of the worm drive shaft 221.

A probe or sensor 230 (FIG. 9) is placed in the pouring cup 203 and set so that when the pouring cup is sub¬ stantially full of molten metal, it will start the plunger downward.

The pit 155 in which the mold 150 is set is provided with vertical plates 232 (FIG. 9) to which the rams 154 are affixed; the plates extend above the ground level approxi¬ mately one-third of the distance of the depth of the pit. The above-ground portions of the plates 232 are buttressed by vertical backing plates 233, which are set at right angles to the pit plates 232 and mounted on horizontal mounting plates 234. The hydraulic fluid supply and controls for the rams 154 are placed out of and away from the pit. The rams 154 press the assembly of side blocks 151 and 152 and end blocks 157-160 tightly together for each pour and are released when the upward forging force from the plunger 161 is discontinued,

As shown in FIG. 11, the screw jacks 216, 217, 218, and 219 are mounted on a plate 236 in the bottom of the pit. A pipelined bore hole 237 is provided in the ground immedi¬ ately beneath the lifting screw of each screw jack to accom¬ modate its respective lifting screw as the plunger is lowered,

Slabs are cast in the apparatus of FIGS. 9-15 in ac¬ cordance with the same process as that used for the rounds. The plunger 161 is raised to the top of the casting cavity 162 and formed with the shim band 192 and the top cover 195, as previously described, so as to have a sliding molten- metalproof seal with the inside walls of the casting cavity 162. The pouring cup 203 or reservoir for the molten metal is placed and/or formed over the casting cavity 162. Molten metal 35 is poured from the ladle 34 into the pouring cup 203, and when the pouring cup is substantially full, the plunger 161 is caused to descend at a rate of about 1/2 to 4 inches per second (1.3 to 10 cm/sec) until it reaches the bottom portion of the casting cavity, at which point it stops descending and begins to push upward with at least a fσrging force, and preferably a lifting force, on the solidifying slab. The slab is pushed upwardly, lifting the pouring cup 203 off the top of the mold 150. The upward movement of the plunger 161 is then halted momentarily, and as the casting shrinks the pouring cup 203 tends to settle back into place on top of the mold 150. The upwardly directed lifting force is then re-applied as before to keep the pouring cup 203 up off the top of the mold 150 and to keep the cooling metal in compression. Then, after another 10 to 15 minutes, the cast slab cools and can be stripped or ejected from the mold by releasing the pressure in the hydraulic rams 154 and raising the plunger 161. The feed head formed in the pouring cup 203 may be burned off while the casting is in the mold, or the casting may be lifted from the mold and cut off at a separate location.

For the next pour, one side block (in the case of the apparatus of FIGS. 9-15, the side block 151) is lifted over the other side block (the side block 152) and reassem¬ bled to provide a second casting cavity 164 in which the hot face exposed to the molten metal for each side block 151 and

152 is opposite from the one of the previous pour. The plun¬ ger 163 is operated in the manner just described with respect to plunger 161 in cavity 162.

-FIG. 16 shows the various products and shapes which may be manufactured in accordance with this invention. FIG. 16A shows a round 241 which may be made in the apparatus of FIGS. 1-7. A round is cylindrical, 4 to 20 inches (10 to 50 cm) in diameter and 10 to 30 feet (3 to 9 meters) long. FIG. 16B shows a thick-walled hollow round 242 which may be made in the apparatus of FIG. 8. FIG. 16C shows a thin-walled hollow round 243 which may be made in the same apparatus. FIG. 16D shows a billet or bloom which may be made in the apparatus of FIGS. 9-15. A billet is usually square, in the range of 2 by 2 inches (5 by 5 cm) up to 15 by 15 inches (38 by 38 cm) , and at least 10 feet (3 meters) long. A bloom is usually square, in the range of 6 by 6 inches (15 by 15 cm) up to 12 by 12 inches (30 by 30 cm) , and at least 10 feet (3 meters) long. Both billets and blooms can also be rectangu¬ lar. FIG. 16E shows a slab 245 which may be made in the apparatus of FIGS. 9-15. A slab is a relatively flat, oblong rectangle with a width of from 24 to 80 inches (60 to 203 cm) or more, a length of from 10 to 30 feet (3 to 9 meters), and a thickness of from 2 to 10 inches (5 to 25 cm) . A plate is like a slab except that it is thinner. FIG. 16F shows a plate 246 which may be made in the apparatus of FIGS. 9-15. FIG. 16G shows a headed round 239 which may be made in the apparatus of FIGS. 1-7. The head 240 is provided for in the pouring cup. In effect, a large pouring cup is provided with a lower portion which is made to form the head 240 with the remaining upper portion forming a feed head in the pouring cup which is cut off. The present method of manufacturing such products is to upset a round to form the head.

As will be apparent to those skilled in the art, other semi-finished products may be made in accordance with

the process and apparatus of the present invention. It is believed that even irregular shapes such as "dogbones" can be made in accordance with this invention.

As noted, the pouring cups, refractory covers for the plunger, covering for the slab molds, and cores for the hollow round are made from sand/binder mixtures such as are used in foundries to make cores. One sodium silicate binder/carbon dioxide gas system is Carsil 700, sold by the Foseco Foundry Products Group in Cleveland, Ohio, U.S.A. Another system is a "no bake" system in which a sodium sili¬ cate binder is set up with a catalyst or chemical hardening agent, not carbon dioxide gas, such as is sold by the Thiem Division of Koppers Company in Milwaukee, Wisconsin, U.S.A. under the name Thiem Che Bond 31. Other foundry core making systems may also be used, preferably with inorganic binders such as fire clay. Western bentonite, Portland cement, or iron oxide. Resinous binders, such as phenolic resins, evolve a lot of gas and are less desirable.

In systems which evolve water in the curing process, it is advisable to "torch" the refractory cover and/or pour¬ ing cup in order to drive off this water. This can be done with a soldering or welding torch with care so as not to harm the cured core sand.

It is contemplated that other forms of plungers and which have a refractory cover and a shim band or the equiva¬ lent and make a molten metal-proof sliding seal with the sidewalls of the mold may be used in accordance with my invention, as will be apparent to those skilled in the art.

Preformed ceramic discs or blocks may be substituted for some of the sand, but should preferably be embedded in sand so that there is a buffer layer of sand between the shim band and the ceramic disc or block of at least about 1/2 inch (1.27 cm) . The reason for this is that most ceramics have high coefficients of expansion and may expand against the shim band and bind or prevent the plunger from being lowered.

The forces acting on the shim band are substantial and it must be well secured to the plunger. In place of the FIG. 7 shim band, a suitable shim band may be made by welding a row of Nelson studs to the band, which will serve to hold it in place and avoid the necessity of slitting and bending it. The studs are welded at right angles to one flat side of the band in a row which extends the length of the band about a one-third width distance in from one edge. In order to assemble the shim band with the plunger piston or plunger block, the shim band is disposed vertically, with the studs extending horizontally from the lower portion of the shim band and resting on the piston or block. A metal retaining plate clamps and holds the studs onto the plunger piston or block and in this way holds the shim band. The cured-in- place refractory cover is over the retaining plate.

Bottom pouring ladles have been shown for filling the molds with molten metal because they provide the minimum exposure of the molten metal to the atmosphere gases. In some instances, lip pouring may prove to be preferable because a greater volume of metal can be poured in a shorter period of time.

As noted, a substantial lifting force should be applied to the bottom of the casting very quickly after the plunger has reached the limit of its descent or stroke so that the tensile forces which build up in a casting as it cools are greatly minimized or eliminated, and the casting preferably is put in compression. When the casting is lifted slightly out of the mold, it is clearly in compression under its own weight plus the weight of the pouring cup.

If the casting is not lifted out of the mold, the lifting force should be equivalent to at least half, and preferably at least two-thirds, of the weight of the cast¬ ing. Once the plunger stops its descent, the timing for the application of the upward lifting force may vary with the

type of metal being cast, the type of product being cast, and the tendency of the solidifying metal to adhere to the inside walls of the mold. Likewise, the amounts of the lifting force may vary with the same factors. For some products such as hollow rounds or small slabs, the application of a lifting force at the end of the pour may not be necessary. It is believed, however, that the application of a lifting force at the end of the pour universally improves the surface of the casting and the grain structure of the casting.

The molds for making products in accordance with the process of this invention are preferably made of steel or cast iron. The molds may be made of other materials, how¬ ever, such as copper or graphite. Copper molds must be water-cooled and graphite is very expensive.

Even though steel and cast iron molds may be reused many times, they are not indestructible. They are neverthe¬ less characterized herein as "permanent molds" to distinguish from molds which are destroyed with each pour or molds which might last for a relatively limited number of pours, such as ingot molds.

The molds may be water-cooled, if desired, to speed up the cycle. Even though it takes a little longer cycle, however, air cooling is preferred because it does not involve the mess and complications of water cooling. The molds of FIGS. 1-8 can be air-cooled by blowing air through the sand.

For the round molds in particular, it is contemplat¬ ed that the inside wall surface may be honed regularly in order to keep it smooth and clean. The inside surfaces of the slab molds may be cleaned by grinding or wire brushing from time to time.

For the most part, it is contemplated that this invention will be used for the manufacture of semi-finished ferrous products, low carbon steels, and the various stain¬ less steels. It may be used in the manufacture of products

of other high melting point metals such as nickel. More generically, it is believed that this invention has applica¬ tion in the casting of any product of uniform cross section of any metal with a melting point of over 1000° C. This would include, for example, copper products. It should be understood, however, that a process which can cast ferrous metal products can probably cast copper products because cop¬ per is a lower melting, easier-to-handle metal. The reverse rule does not apply, that is, a process which can cast copper products probably cannot cast ferrous metal products.

As is inherent in the nature of this process and should be obvious from the foregoing description, the prod¬ ucts must have a constant cross-sectional shape or configura¬ tion which corresponds to that of the mold and that of the plunger. The length of the product may be varied at will by the stroke of the plunger. If a short product is desired, the descent of the plunger can be halted above the bottom of the mold and the product length is thus determined by the limit of the descent or stroke of the plunger. It is contem¬ plated that relatively long rounds, blooms and billets may be cast by my process, up to 40 feet (12 meters) or more in length.