US3382912A

US3382912A - Apparatus for conserving heat, degassing and casting molten metal

Info

Publication number: US3382912A
Application number: US412033A
Authority: US
Inventors: Jr Herbert S Philbrick
Original assignee: John Mohr and Sons
Current assignee: John Mohr and Sons
Priority date: 1964-11-18
Filing date: 1964-11-18
Publication date: 1968-05-14
Anticipated expiration: 1985-05-14

Description

y 1968 H s. PHILBRICK, JR 3,382,912

APPARATUS FOR CONSERVlNG HEAT, DEGASSING AND CASTING MOLTBN METAL Filed Nov. 18, 1964 2 Sheets-Sheet l y 1968 H. s. PHILBRICK, JR 3,382,912

APPARATUS FOR CONSERVING HEAT, DEGASSING AND CASTING MOLTEN METAL Filed Nov. 18, 1964 2 Sheets-Sheet 2 I N VEN TOR.

United States Patent 3,382,912 APPARATUS FOR CONSERVING HEAT, DEGAS- SING AND CASTING MOLTEN METAL Herbert S. Philbrick, Jr., Chicago, Ill., assignor to John Mohr and Sons, Chicago, 11]., a corporation of Illinois Filed Nov. 18, 1964, Ser. No. 412,033 7 Claims. (Cl. 164-254) ABSTRACT OF THE DISCLOSURE A method of degassing and casting molten metal including the steps of subjecting molten metal contained in a receptacle to a vacuum, applying a positive pressure against the surface of the molten metal to force said metal out of the receptacle and into a molding apparatus, and reducing the radiant heat loss from the surface of the molten metal during the above steps by positioning a radiant heater above the surface of the molten metal to direct radiant heat to a substantial portion of the surface of the molten metal.

An apparatus for degassing and casting molten metal having a first tank part adapted to receive a receptacle containing the molten metal and close in seal-ing engagement with both a second and third tank part to form hermetically sealed enclosures for the receptacle. The first tank part contains conduits which may be placed in communication with a source of vacuum and a source of fluid pressure. The second and third tank parts respectively carry on inductively heated radiant heater adapted to be positioned above the surface of the molten metal when either such tank part is engaged with the first tank part; the thrid tank part also carries a tube which extends into the molten metal and communicates with a molding apparatus so that when the enclosure is pressurized, the molten metal is forced through the tube and into the molding apparatus.

This invention relates to improvements in the casting of shaped forms, particularly semi-finished forms, and particularly to a method of and apparatus for conserving heat in the casting process whereby a better product is produced at a lower cost than with conventional processes.

The invention has particular application to the casting of slabs by pressure pouring, though with relatively slight modification it could be adapted to the continuous casting process.

The pressure pouring process became commercially important in the l950s. Originally the process was applied to the casting of railroad car wheels, but in recent years efforts have been made to apply it to a wider and wider range of products. Among the numerous advantages of the pressure pouring process may be enumerated the following:

(1) It is possible to cast to very close tolerances.

(2) The process eliminates much casting surface conditioning and machining.

(3) The :mol-d life is extremely long, as contrasted to conventional green sand practices.

(4) The molds may be filled quickly, and the casting cooled relatively rapidly since usually a graphite mold is employed. This factor, in addition to contributing to low cost and high production, makes the process attractive from an automated standpoint.

(5) The process has a lower capital cost over conventional pouring processes due to elimination of many additional steps, such as ingot casting, the use of soaking pits, and primary rolling.

(6) The process requires a relatively small area in the plant.

(7) The process provides extremely high yields, published results indicating that yields of 95% are not uncommon, as contrasted to about in conventional forming processes.

(8) The process may be easily adapted to castings of varying sizes and, within limits, varying chemical compositions.

At the present time, slabs of up to seven inches in thickness, 5 8 inches in width and 28 feet long and weighing anywhere from six to twenty tons have been reported. The steels cast, however, have so far been largely limited, on a commercial basis at least, to relatively high alloy steels, such as stainless steels. For further background information, reference is made to the article Pressure Pouring of Stainless Steel Slabs by Drever et al., in the December 1963 issue of Iron and Steel Engineer.

The continuous casting process has many of the advantages discussed above in connection with the pressure pouring process. Again, however, the continuous casting process has been applied primarily only to the relatively high alloy steels, including stainless steels.

So far as is now know-n, neither the pressure pouring nor the continuous casting process has been commercially applied to any considerable extent to low carbon steels, which steels form the large tonnage of steels which are cast in semi-finished form.

Perhaps the most restrictive factor limiting the application of the pressure pouring and continuous casting processes to the low carbon steels has been the inability to consistently maintain the desired quality in the steel. Since low carbon steels contain relatively large amounts of deleterious gases, as contrasted to higher carbon and alloy steels, the casting is subject to defects resulting from too high a final included gas content. To remedy the situation the steel may be vacuum degassed. This procedure reduces the final included deleterious gas content to tolerable limits but, when used in conjunction with the continuous casting and pressure pouring processes, with their relatively long equipment handling time as contrasted to conventional ingot casting, may cause problems due to loss of temperature.

Accordingly, a primary object of this invention is to provide a method for pressure pouring and continuously casting large tonnages of acceptable quality low carbon steel, particularly in semi-finished forms such as slabs.

Another object is to provide a system for carrying out the abovedescribed method.

Still another object is to provide a method for conserving heat in a molten metal receptacle, in which molten metal is held and/ or treated for a period of time sufiicient to enable the molten metal to be vacuum degassed and thereafter utilized in a continuous casting, pressure pouring or other metal forming process.

Yet another object is to provide structure suitable for practicing the above-mentioned process.

Other objects and advantages of the invention will be apparent upon reading the following description of the invention.

The invention is illustrated more or less diagrammatically in the accompanying drawings, wherein:

FIGURE 1 is a sectional, elevational view of an apparatus for carrying out the method of this application illustrating the vacuum degassing phase of the invention; and

FIGURE 2 is a similar sectional view illustrating the pouring phase of the invention.

Like reference numerals will he used to refer to like parts throughout the following description of the drawings.

Referring to the figures, it will be noted that the invention has been illustrated in conjunction with a pressure pouring process. This has been done for convenience of illustration and description only, the basic invention being applicable to both pressure pouring, continuous casting and perhaps other forming processes.

A pit is indicated at 10. The pit accommodates a tank 11 having a stationary lower portion 12 and a movable upper portion 13. The stationary lower portion is supported above the pit floor by any suitable structural means 14, the details of which are not essential to an understanding of the invention. The bottom of the tank is lined with a layer of refractory 16 and a ladle supporting structure is indicated generally at 17.

The molten metal receptacle, in this instance a conventional shop ladle, is indicated generally at 20. The ladle is of usual construction, having a steel exterior shell 21 which is lined with refractory 22. A depression 23 is formed in the refractory covering the bottom for a purpose which will appear hereinafter. The ladle may be lifted and lowered into and out of the lower stationary portion 12 by trunnions 24, 25. The upper edge portion of the lower tank shell portion 12 terminates in a sealing ring 26, which carries an O-ring seal 27 in an upwardly open aperture in the upper planar face thereof. The seal ring has a plurality of flanges 28, 29 which extend radially outwardly a short distance from the tank wall for a purpose which will appear hereinafter.

The upper movable portion 13 of the tank terminates, at its lowermost edge, in a seal ring 32 which mates with lower seal ring 26. A plurality of brackets 33, 34 are welded to the interior of the upper shell 13. These brackets support a ladle cover indicated generally at 35.

The ladle cover consists essentially of a steel shell 36 having a refractory lining 37 which is baked or otherwise held in place against the steel shell by any suitable means such as

clips

38 and 39. An innermost facing of graphite is indicated at 40. An induction heating coil is indicated at 41 embedded in the refractory behind the graphite shell or heating surface. The graphite shell is continuous to provide electrical continuity. Heating of the graphite shell is caused by electrical currents induced in the shell by the changing magnetic field of the induction heating coils. A plurality of suspending brackets 43, 44 are welded or otherwise suitably secured to the exterior surface of shell 36 and are in turn bolted or otherwise suitably connected to the brackets 33, 34, so as to be carried by and movable with the upper movable section 13 of the tank.

It will be noted that the tank cover is formed substantially as a frustum of a cone. In this way, heat transferred to the heating surface 40 is radiated downwardly over at least a substantial portion of the surface of the melt. In the illustrated embodiment, somewhere between about /3 to about /2 of the area of the melt is located directly beneath the heating surface 40.

A viewing port is indicated generally at 46. The port may have any convenient mechanism 47 for operating a window clearing assembly 48 whereby the surface of the melt may be observed during treatment.

A nozzle structure is indicated at 50. The nozzle terminates in a bearing ring 51 having a sealing groove and O-ring seal 52 formed in the upper surface thereof. A charge material hopper is indicated generally at 53. The hopper may contain alloys and/ or slag forming materials which it is desired to add to the melt, perhaps late in the degassing cycle. An annular plate 54, which is reinforced with a plurality of triangular face plates 55, is disposed in flat bearing engagement against the seal ring 51 to form a vacuum-tight seal therewith. The top of the hopper is closed by a cover plate 56, which again rests in vacuumtight engagement with a seal ring 57. A bottom closure 59 is held in place by a releasing mechanism 60 which is tripped by rotating lever 61.

Lifting eyes 63 and 64 enable the tank cover 13 to be lifted and lowered from an overhead crane. It will be appreciated, however, that other means may be provided for lifting and lowering the vacuum cover, including lift and swing devices which are well known in the art.

Means for inducing an agitation within the melt which brings undegassed portions of the melt to the surface so as to be exposed to the vacuum are indicated at 66. In this instance, the means consists of an induction coil system which encircles the ladle. When operated, the coils set up a circulation within the melt which may, for example, be substantially as shown by the arrows in the melt. Alternately, a purging gas may be admitted to the melt through plugs or other means in the bottom or sides of the ladle, the gas being a gas which is inert with respect to the molten metal undergoing treatment.

A connection to a source of vacuum is indicated generally at 67; v

In FIGURE 2, the system'is shown during a second phase of operation. In this phase degassing has been completed and the vacuum cover 13 removed. A second cover 70 has been lowered into place on the lower stationary portion of the tank, the cover 70 being in this instance more accurately described as a pressure pouring cover. The cover carries a plurality of clamping brackets 71, each of which has a clamping lever 72 rotatably mounted therein as by shaft 73. The clamping levers are aligned with flanges 28. A ram 74, which is carried by the lower stationary portion 12 of the tank, forces the clamping lever into engagement with the brackets upon expulsion of its piston rod 75. Since the pressure in the tank during the pouring portion of the cycle will be greater than atmospheric pressure, the clamping forces are necessary to maintain the upper and lower tank portions in pressure-tight engagement with one another.

The pressure cover carries a heat shield 75 which overlies a substantially portion of the surface of the melt. The heat shield consists essentially of a layer of refractory 76 in which are embedded a plurality of hooks 77 which maintain the refractory in engagement with the outer shell 78 of the shield. The shield is supported from the inner face of the pressure cover by a plurality of supporting brackets 79, 79 spaced at convenient intervals about the periphery of the shield.

The shield is apertured as at 80 to receive a ceramic pouring tube assembly indicated generally at 81. The pouring sleeve assembly consists essentially of an elongated ceramic or refractory tube 82 which projects downwardly into the melt a distance sufficient to terminate at substantially the nominal bottom level 83 of the melt. An annular flange 84 is suitably secured to the upper end of the pouring tube, the flange making a pressure-tight engagement with the bearing surface 85 which encircles the aperture 80.

A mold is indicated generally at 87. The mold may be of any convenient size. In this instance, a mold suitable for forming a slab has been illustrated, but it will be understood that it is within the scope of the invention to utilize molds of differing sizes.

A conduit for the admission of a pressure pouring fluid is indicated at 89. If desired, the valving and piping systems may be so arranged that the vacuum conduit 67 may be used alternately as a vacuum conduit and a pressure fluid conduit.

The use and operation of the invention are as follows:

The invention will be described in connection with the ciaslting of a semi-finished form known to the trade as a s a At the start of operation the tank cover 13 of FIGURE 1 is removed and the lower stationary portion 12 of the tank awaits placement of a molten receptacle therein.

Molten metal from a suitable source, most usually an electric furnace, is tapped into ladle 20 which is then placed by a crane or other suitable means onto supporting platform 17 in lower tank portion 12. The vacuum cover 13 is then lowered into position and bearing ring 32 makes engagement with sealing flange 26. Guide means 86 quickly aligns the tank cover with the tank bottom so that clamping time is reduced to a minimum. Once a sealed connection is made between the opposed, abutting faces of the sealing ring 26 and bearing ring 32, a vacuum is drawn through conduit 67. The melt may be degassed either solely by the action of the vacuum or by a combination of the vacuum and auxiliary agitation means, such as the induction heating coil 66 or a purging gas.

As the metal is treated the electric induction coil 41 is energized. The coil heats the graphite cone surface 40 to an elevated temperature which may be somewhere between 3000 and 4000 F., graphite having a reasonably long life at 3500. The heat radiated from the heating surface 40 toward the melt may be sutficient to completely counteract the radiant heat lost from the surface of the melt. When this condition occurs, the only heat loss from'the melt will be that lost through the ladle walls. After the melt is degassed to a desired extent, handle 61 may be rotated to open bottom 59 of the charge material addition hopper to add desired materials to the melt whemthe vacuum in the tank is broken and atmospheric pressure restored in the tank. Usually an inert gas, such as nitrogen, is bled into the tank in order to provide a protective atmosphere above the surface of the melt.

As soon as atmospheric pressure is reached in the tank, the movable vacuum cover 13 is removed and a pressure cover=70 installed in its place. The pouring tube assembly 81 may be separately added, or it may be carried with the pressure cover. Ram 74 is actuated to pressure tightly secure the pressure cover to the stationary tank portion 12. Once a pressure tight connection has been made, a pressure pouring fluid such as air is admitted through conduit 89. The pressure in the tank is then raised sufiiciently high to force molten metal upwardly through ceramic pouring tube 82 into mold 87. Alternately, of course, the molten metal may be admitted into suitable continuous casting apparatus.

In any event, molten metal will be at a temperature suitable for pressure pouring at the end of the degassing phaseof the cycle. As is well known in the art, one of the drawbacks of degassing which must be compensated for is the increased temperature loss it induces due to the greater length of exposure of the molten metal between tapping and teeming as contrasted to a conventional ingot pouring process. The graphite heating surface 40 supplies sufiicient heat to counteract the radiant heat loss from the surface. Because of the additional time for degassing provided by the cone, it is possible to thoroughly degas the metal before additions of de-oxidizers such as aluminum and silicon, or other charge materials are made from hopper 53. For example, low carbon steel contains a tremendous quantity of hydrogen, oxygen and nitrogen and a considerable period of time is needed in order to remove these gases from the melt prior to further processing. When the temperature of the melt is maintained substantially constant during the degassing phase, adequate time is provided to remove the included deleterious gases, and thereafter making charge material additions prior to pressure pouring or continuous casting at a safe temperature.

Although a preferred embodiment of the invention has been illustrated and described, and an alternative embodiment described, it will at once be apparent to those skilled in the art that various changes and modifications may be made within the spirit and scope of the invention. Accordingly, it is intended that the scope of the invention be limited not by the above description, but solely by the scope of the hereafter appended claims when construed in light of the pertinent prior art.

I claim: 1. Apparatus for conserving heat in a receptacle, said apparatus including, in combination an electric coil, the lower portion of which is generally similar in contour to the configuration of metal holding receptacle with which it is to be used,

structure for maintaining the coil in a fixed position with respect to the receptacle for at least selected periods of time,

said structure maintaining the coil elevated with respect to the surface of a melt in the receptacle, and

a heating surface disposed between the surface of the melt in the receptacle and the electric coil, and in heat inductive relation with the coil,

said heating surface being disposed in a position to direct radiant heat generated by the electric coil toward a substantial portion of the surface of the melt.

2. The apparatus of claim 1 further characterized in that the heating surface is peripherally continuous to a substantial depth to thereby expose an uninterrupted heating surface to the surface of the melt and to have the maximum currents induced therein.

3. The apparatus of claim 2 further characterized in that the heating surface is composed substantially entirely of graphite.

4. The apparatus of claim 3 further characterized in that the heating surface is formed generally as a frustum of a cone, the lower edge of the heating surface being substantially co-terminous with a similarly contoured surface of the receptacle.

5. A system for casting shaped forms, such as slabs, said system including, in combination:

a receptacle for holding molten metal;

means for subjecting the molten metal to a vacuum sufficiently low to elfectively degas it, said means including a first cover sufficiently large to form a vacuum space above the molten metal in the receptacle and means for moving said first cover into and out of general alignment with the receptacle;

means carried by said first cover for conserving heat during exposure to the vacuum, said heat conserving means including a heating surface and means for heating it and directing radiant heat against the surface of the molten metal in the receptacle;

a mold; and

means for directing the molten metal into the mold,

said directing means including, a second cover sufiiciently large to form a control environment above the molten metal in the receptacle, means for moving the second cover into and out of position above the receptacle, means forming a molten metal flow path from the metal in the receptacle through the control environment cover, and into the mold, and means for exerting a positive force on the molten metal in the receptacle whereby the molten metal may be directed under pressure into the mold.

6. An apparatus for degassing and casting molten metal contained in a ladle, said apparatus including, in combination,

a tank adapted to receive the ladle,

a first cover adapted for movement into and out of sealing engagement with said tank,

means for connecting said sealed tank to a source of vacuum to enable degassing of the molten metal,

first heating means carried by said first cover for radiating heat onto a substantial portion of a surface of the molten metal,

a second cover adapted for movement into and out of engagement with said tank,

a tube extending through said second cover into said molten metal and communicating with a mold cavity externally of said second cover, with said second cover adapted to form a sealed chamber tbove said ladle, and

means for connecting said sealed chamber to a source of superatmospheric pressure to thereby force the molten metal out of said ladle and into said mold cavity.

7. The structure of claim 6 further characterized in that said second cover carries second heating means adapted to radiate heat onto a substantial portion of a surface of the molten metal.

(References on following page) References Cited UNlTED STATES PATENTS Meyers et a1. 249-78 Thompson 22-73 Johnson -24978 0 Olsen 22-200 X Brennan 22-'73 X Sylvester 22-69 Finkl 22--73 X Sickbert 22- 57.2 Hokanson 7549 X Stenkvist 22-73 X 8, FOREIGN, RAJENIS 344,947 3/1931 (1166113111 1 930,373 .,7/1963 Great Britain. 325,179 12/1957 Switzerland.

OTHER REFERENCES Metal Progress, High VacuumDegassing with Induction Stirring Makes Cleaner Steels, August 1963, pp. 88-91, TS 300 M587.