US3393266A

US3393266A - Electric arc furnace

Info

Publication number: US3393266A
Application number: US558702A
Authority: US
Inventors: Peter J Wynne
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1966-06-20
Filing date: 1966-06-20
Publication date: 1968-07-16
Anticipated expiration: 1985-07-16

Description

July 16, 1968 P. J. WYNNE 3,393,266

ELECTRIC ARC FURNACE Filed June 20, 1966 Peter J Zg/vme BY United States Patent 3,393,266 ELECTRIC ARC FURNACE Peter J. Wynne, Pittsburgh, Pa., assignor to McGraw- Edison Company, Milwaukee, Wis., a corporation of Delaware Filed June 20, 1966, Ser. No. 558,702 6 Claims. (CI. 1331) ABSTRACT OF THE DISCLOSURE An arc melting furnace having a plurality of crucibles and a support means movable over each, electrode holding means for positioning an electrode within a respective crucible and closure means for sealing the crucible, and separate drive means for raising and lowering the electrode holding and closure means, wherein the mounting of the electrode holding drive means to the support means is located between the mounting of the closure drive means and the electrode.

This invention relates to electric arc furnaces and, more particularly, to furnaces of the type wherein a consumable electrode is melted in a vacuum or controlled atmosphere.

Consumable electrode electric arc furnaces have been widely used for such applications as the melting of refractory materials of which titanium is an example. Such furnaces, in general, include a sealed chamber wherein a consumable electrode is progressively melted under a controlled atmosphere and the resulting molten metal collected in a crucible to form an ingot. Melting is accomplished by means of an are which is drawn between the consumable electrode in the ingot and which is sustained by relatively large direct currents. The diameter of the electrode is somewhat smaller than that of the ingot so that as the ingot forms and the electrode length gradually decreases, it must be lowered in order to maintain the proper arc length for the desired melting conditions. For this purpose, a motor driven electrode ram is provided for feeding the electrode toward the ingot in accordance with the electrical conditions in the arc. After the electrode has been completely consumed, the ingot must be allowed to cool and then it is removed from the crucible prior to the initiation of another melting operation. Because a relatively long time is required for such ingots to cool, it is desirable that a single electrode drive and ram assembly be mounted for successive operation over several crucibles.

In prior art assemblies wherein a single electrode drive was employed with multiple crucibles, it was necessary to provide means for raising the drive assembly clear of the crucibles so that it could be moved from a position above one crucible to a position above another. In addition to the expense of such additional structure for raising the electrode drive, such prior art assemblies also required a substantial amount of space above the furnace.

One method for eliminating the above deficiencies in the prior art is disclosed in co-pending application Ser. No. 374,992, filed June 15, 1964, and assigned to the assignee of the instant invention. The apparatus disclosed in said co-pending application provided means for raising the upper portion of the furnace as well as the electrode clamp so that the electrode drive mechanism could be moved horizontally from a position above one crucible to a position above another. In this device the assembly for raising the upper portion of the furnace was disposed between the furnace body and the electrode drive mechanism, thereby limiting the electrode stroke.

It is an object of the invention to provide an arc melting furnace having a drive assembly which is horizontally movable from a position above one crucible to a position above another crucible wherein means is provided for 3,393,266 Patented July 16, 1968 "ice raising and lowering crucible closure means and which does not interfere with the stroke of theelectrode drive mechanism. I

This and other objects and advantages of the instant invention will become more apparent from the detailed description thereof taken with the accompanying drawing which is a side elevational view, partly in section, of a' consumable electrode electric arc furnace incorporating the instant invention.

In general terms, the invention comprises an arc melting furnace having a plurality of vessels adapted to receive an ingot formed by the melting of a consumable electrode therein, closure means selectively engageable with the upper ends of the vessels, an electrode drive assembly adapted to be alternately positioned above the vessels for supporting an electrode therein, the electrode drive assembly being constructed and arranged for movement between an elevated position to a lower position adjacent the closure means, and second drive means spaced from the path of the electrode drive assembly for raising and lowering the closure means vertically relative to the vessels.

Referring now to the drawings in greater detail, a consumable electrode electric arc melting furnace is designated by the reference numeral 10 and has a crucible section 11, a middle section 12 and an electrode drive assembly 13.

The crucible section 11 includes an outer substantially cylindrical shell 15 having a bottom closure member 16 which is affixed thereto in a hermetically sealed relation by means of bolts 18 to provide a cooling jacket for a crucible 22 disposed therein and which receives an ingot 23 formed from the metal being melted. The shell 15 is provided with a cooling fluid inlet pipe 24 and an outlet pipe 25. A horizontal mounting plate 26 is supported ad-' jacent the upper end of the shell 15 by vertical columns 28 and has a central aperture 29 for receiving the upper end of the crucible 22. A flange 32 extends outwardly from the upper end of the crucible 22 and is afiixed to the upper surface of the mounting plate 26 by bolts 34.

The middle section 12 of the furnace 10 includes a lower middle section 36, an upper middle section 37, and an upper middle drive assembly 38. The lower middle section 36 has a generally cylindrical configuration coradial with the crucible 22 and is aflixed to the upper end thereof by a flange 39 extending outwardly from its lower end and overlaying the flange 32 on the crucible 22 and which is held thereagainst by the bolts 34. A second flange 41 extends outwardly from the upper end of the lower middle section 36 and is engaged by a corresponding flange 42 on the lower end of the inverted, cup-shaped upper middle section 37. Bolts 43 secure the flanges 41 and 42 and compress a gasket 44 therebetween to insure a fluid tight joint. The upper middle section 37 forms a closure for the hollow assembly 45 comprising the crucible 22, the lower middle section 36, and the upper middle section 37 An electrode 46 is disposed within the hollow assembly 45 and has a stub 48 integrally formed at its upper end for releasable attachment to the bottom of a hollow electrode ram 49 by a clamp 50. The electrode ram 49 slidably passes through a sealing bushing 56 which provides a fluid tight seal for the enclosure 45 and, in addition, electrically insulates the electrode ram 49 from the upper middle section 37. A pipe 57 is connected to and communicates with the interior of the enclosure 45 for placing the latter in communication with an evacuator or source of inert gas if a partial vacuum or inert gas atmosphere is required during the melting operation.

A movable support assembly 58 is provided for supporting the electrode drive assembly 13 and the upper middle section drive assembly 38 and includes a generally triangular top plate at the upper ends of generally

vertical columns

61, 62 and 63. The

columns

61 and 62 are supported at their lower ends by roller assemblies 64 which engage a curved track 65 mounted on the upper surface of the plate 26 While the lower end of the column 63 engages a rotary hydraulic cylinder 66 which purpose will be explained in greater detail herein below.

The plate 60 supports the upper middle section drive assembly 38 while a second plate 68 is aifixed to the

columns

61 and 63 and vertically below the plate 60 for supporting the electrode drive assembly 13.

The electrode drive assembly 13 includes a drive motor 70, a screw shaft 71 and a ram head 72, which is aflixed to the upper end of the ram 49 in which carries a nut 74 for threadably engaging the screw shaft 71. The ram head 72 also carries a pair of laterally extending arms 75 each of which carries a coupling member 76 for slidably engaging one of a pair of vertical guide rods 77 which are secured at their upper ends to the plate 68 and whose lower ehds are slidably received in guide members 78 which are secured to the upper middle section 37.

The motor 70 is suitably mounted on the plate 68 while the screw shaft 71 extends vertically downward through aperture 80 in the plate 68, threadably engages the nut 74, and extends into the hollow interior of the electrode ram 49. A pinion 81 is carried on the output shaft 82 of motor 70 and engages a gear 84 fixed to the upper end of the screw shaft 71 and rotatably mounted about the aperture 80 in the plate 68 by a suitable bearing assembly 85.

Electrical energy is supplied to the electrode 46 through a terminal 88 mounted on the ram head 72 and which is constructed and arranged to receive a flexible conductor 89. Current flows from the ram head 72 through the electrode ram 49, the clamp 50, the stub 48 and to the electrode 46. Insulating bushings 90, of any suitable material, electrically insulate the guide rods 77 from the coupling members 76.

The upper middle section drive assembly 38 includes a motor 92 suitably mounted on the plate 60 and a pair of screw shafts 93 which extend through openings 94 in the plate 60 and which are engaged at their upper ends by one of a pair of gear assemblies 95. Each of the gear assemblies 95 are also engaged by one o'f a-pair of oppositely extending motor output shafts 96" so that each of the screw shafts 93 will rotate when the motor 92 is energized. I

The upper middle section drive assembly 38 also includes a pair of oppositely directed arms 99 fixed to the bushing 56 carried by the upper end of the upper middle section 37. The outer ends of the arms 99 are suitably aflixed to the lower end of one of a pair of tubular members 100 which extend vertically upward in a coaxial relation to the screw shafts 93. In addition a nut 102 is fixedly mounted at the upper ends of each of the tubular members 100 and threadably engages the corresponding one of the screw shafts 93.

The electrode drive assembly motor 70 may be a reversible, variable speed, DC. motor which is controlled in accordance with the electrode voltage in current conditions. The motor control, which is not shown but which is well known in the art, causes the motor 76 to rotate in a direction which maintains the are between the electrode 46 and the ingot 23 at a relatively uniform length. Thus, when the arc length is too short, the motor will rotate in a first direction to raise the electrode 46, and when the arc length is too long, the motor 70 will rotate in an opposite direction to lower the electrode 46. However, since the electrode 46 has a s lightly smaller diameter than the crucible 22, the general direction of movement of the electrode will be downward during a melting operation.

More specifically, it can be seen that rotation of the motor 70 will rotate the screw shaft 71 through the agency of the pinion 81 and the gear 84. As the screw shaft 71 rotates, relative movement will be produced between it and the nut 74 fixed to the ram head 70. This will cause the ram head 70 to move in a direction governed by the direction of rotation of the screw shaft 71 and this will in turn be transmitted to the electrode 46 through the ram 49.

After the electrode 46 has been melted so that substantially only the stub 48 remains, the ram head 72 will bein its phantom position adjacent the bushing 76. The motor 70 is then driven in a direction which raises the clamp 50 to its uppermost position in the chamber 45 which also elevates the ram head '72 to its full position adjacent the plate 68. The bolts 43, which secure the upper middle section 37 to the lower middle section 36, are then removed to release the upper middle section 37 from the lower middle section 36. The motor 92 is then operated to rotate each of the screw shafts 93 through the gear assemblies 95. This produces relative movement between the screw shafts 93 and the nuts 102 afiixed in the upper ends of the tubular members 100. The tubular members 100 are thereby moved vertically upwardly toward the plate 60 fro-m a position shown by full lines to a position shown by phantom lines to raise the upper middle section 37 through the agency of the arms 99 and the bushing 56 to the position shown by phantom lines.

It can be seen that because the upper middle section drive assembly 38 is mounted above the electrode drive assembly 13, the ram head 72. may move from an initial position shown by full lines during a melting operation to its position shown by phantom lines which is adjacent the upper middle section 37 without interference by the upper middle section drive assembly 38. This substantially reduces the total space required for the assembly over prior art devices wherein the total height was equal to the ram stroke, plus the distance that the upper middle section was required to be raised, plus the height of the drive assemblies 13 and 38. In the disclosed device, on the other hand, because the upper middle section and the ram assembly, in effect, move through the same space, no additional furnace height is required to allow for movement of the upper middle section 37.

When the upper middle section 37 and the ram head 72 are in their elevated positions, the clamp 50 is released and the stub 48 removed, after which the rotary hydraulic cylinder 66 is actuated to rotate the support assembly 58 from a position above the crucible 22 to a position above an alternate crucible (not shown) as the roller assemblies 64 move on the track 65. After the electrode drive assembly 13 has been positioned above the alternate crucible, the electrode ram head 72 is lowered until the clamp 50 is in a position to be secured to the stub of the alternate electrode which has been previously disposed within the alternate crucible. The motor 92 is then operated in a direction which will lower the upper middle section 37 until its lower flange 42 engages the flange on the upper middle section of the alternate crucible. The bolts 43 are then re-inserted and closure of the alternate crucible is achieved.

In addition a cover plate, not shown, but which has a shape similar to the upper middle section 37, may then be placed over the lower middle section 36 and secured thereto by bolts 43 so as to reseal the enclosure 45 whereby the ingot 23 may be cooled in a controlled atmosphere.

While only .a single embodiment of the invention has been illustrated and described, other modifications thereof will become apparent to those skilled in the art once the invention is known. In addition while the invention has been described with respect to one particular type of electric arc furnace those skilled in the art will appreciate that it has application to other types of controlled atmosphere electric arc furnaces as well. Accordingly, it is not intended that the invention be limited by the foregoing description but only by the scope of the appended claims.

I claim:

1. In an arc melting furnace having a plurality of crucibles each adapted to receive and melt a consumable electrode to define an ingot therein, a ram having means on a lower end thereof to hold the electrode within the respective crucible, and closure means for the crucible, the combination comprising support means, means mounting the support means to move horizontally between alternate position above the respective crucibles, drive mechanism mounted between the support means and the ram for raising and lowering the ram relativeto the crucibles, said closure means being disposed in sealed sliding relationship to the ram and adapted in the alternate position of the support means to be removably selectively secured to the upper end of the respective crucible for sealing the same, drive means mounted between the support means and the closure means operable to raise and lower said closure means and to hold said closure means spaced above the respective crucible to permit the support means to be moved between the alternate positions, and the drive mechanism being mounted to the support means at a location between the electrode and where the drive means is mounted to the support means.

2. In an arc melting furnace according to claim 1, wherein said drive mechanism include-s a threaded shaft and a means to rotate the shaft, and wherein the shaft is rotatably mounted but axially fixed relative to one of the support means or ram and is threadably engaged to the other of the support means or ram, so that shaft rotation raises or lowers the ram relative to the crucible units.

3. In an arc melting furnace according to claim 2,

wherein the ram is hollow and freely receives varying portions of the shaft, and wherein the shaft is threaded relative to the ram and is axially fixed relative to the support means.

4. In an arc melting furnace according to claim 1, wherein said drive means includes a threaded shaft and a means to rotate the shaft, and wherein the shaft is rotatably mounted but axially fixed relative to one of the support means or closure means and is threadably engaged to the other of the support means or closure means. so that shaft rotation raises or lowers the closure means as required.

5. In an arc melting furnace according to claim 2, wherein said drive means includes a threaded shaft and a means to rotate the shaft, and wherein the shaft is rotatably mounted but axially fixed relative to one of the support means or closure means and is threadably engaged to the other of the support means or closure means, so thr-at shaft rotation raises or lowers the closure means as required.

6. In an arc melting furnace according to claim 5, wherein each shaft is axially fixed relative to the support means.

References Cited UNITED STATES PATENTS 6/1965 Gruber et al 1331 4/1966 Wooding 13-31