US3061655A

US3061655A - Electric arc furnaces

Info

Publication number: US3061655A
Application number: US773350A
Authority: US
Inventors: Shaw Clifford
Original assignee: Shaw Process Dev Corp
Current assignee: Shaw Process Dev Corp
Priority date: 1958-11-12
Filing date: 1958-11-12
Publication date: 1962-10-30
Anticipated expiration: 1979-10-30

Description

Oct. 30, 1962 C c. SHAW 3, 6 55 ELECTRIC ARC FURNACES Filed Nov. 12, 1958 5 Sheets-Sheet 1 INVENTOR Caz/ am: .5710

Y M M ATTORNEY Oct..30, 1962 c. SHAW ELECTRIC ARC FURNACES 5 Sheets-Sheet 3 Filed Nov. 12, 1958 IN VEN TOR (Zn-Tom Jaw BY Ham M M.

ATTORNEYS Oct. 30, 1962 c. SHAW 3,061,655

ELECTRIC ARC FURNACES Filed Nov. 12, 158 5 sheets-sheet 4 33 I II FIG. 6

FIG. 7

INVENTOR.

CLIFFORD SHAW i' MW Oct. 30, 1962 c. SHAW 3,061,655

ELECTRIC ARC FURNACES Filed Nov. 12, 1958 5 Sheets-Sheet 5 T- I t'' LMJ Fl G. 8

INVENTOR.

A T 1-0 RNEYJ United States Patent Ofifice 3,061,655 Patented Oct. 30, 1962 3,061,655 ELECTRIQ ARC FURNACES Clifford Shaw, London, England, assignor to Shaw Process Development Corp, Port Washington, N.Y., a corporation of New York Filed Nov. 12, 1958, Ser. No. 773,350 9 Claims. (Cl. 1331) This invention relates to electric arc furnaces for melting metal for the purpose of making castings.

Electric arc furnaces for this purpose are known in which a crucible is mounted for rotation about a horizontal axis to enable melted metal to be poured therefrom, the crucible being housed in a casing to which can be secured the mould into which the charge of metal is to be poured, and the casing and mould being rotatable with the crucible. It is sometimes essential that the melting and pouring of the metal shall take place under vacuum, and consequently the crucible casing, and a mould cover, have been arranged to form together a closed space from which air can be evacuated. Hitherto, however, the carbon rods between which the arc is formed have been mounted in stationary tubes about which the crucible rotated, and, in order to maintain a vacuum in the enclosed space, it has been necessary to provide glands around the tubes, and the provision of glands which were satisfactory under the conditions existing has been a difficult problem.

The object of the present invention is to provide an improved electric arc furnace for the purpose described, which is free from many of the disadvantages of the previously known furnaces.

According to the present invention, in an electric arc furnace including a crucible mounted in a casing rotatable about a horizontal axis and having provision for the attachment thereto, in an airtight manner, of a mould cover the carbon rods between which the arc is formed, and adjusting gear for the said carbon rods, are wholly enclosed in auxiliary casings forming a common enclosed space with the crucible casing and rotatable therewith.

Cooling means may be provided for preventing transmission of excessive heat from the crucible to the auxiliary casings, said cooling means comprising coolant chambers surrounding the ends of the auxiliary casings adjacent the crucible casing, and means for circulating a liquid coolant through the said chambers.

The carbon rods may be mounted in travelling blocks slidable on guide rods to move the said rods in and out of the furnace, the rods extending through bores in the said blocks and being clamped therein 'by wedge members mounted in tapered longitudinal grooves in the walls of the said bores.

Cooling means may be provided in association with the adjusting gear for the carbon rods, the guide rods conveniently being tubular and being arranged in a circuit for cooling liquid.

The invention is hereinafter described with reference to the accompanying drawings, in which:

FIGURE 1 is a front elevation of a form of arc furnace according to the invention;

FIGURE 2 is a side elevation of the furnace shown in FIGURE 1;

FIGURE 3 is a partial sectional elevation, on an enlarged scale, on the line 33 of FIGURE 2;

FIGURE 4 is a sectional elevation on the line 4-4 of FIGURE 3;

FIGURE 5 is a sectional elevation of a detail;

FIGURE 6 is a fragmentary section side view of a modification of FIG. 3;

FIGURE 7 is a sectional plan view of FIGURE 6; and

FIGURE 8 is a rear elevation of the furnace showing a modification of the air withdrawal arrangement of FIGURE 2.

Referring to FIGURES 1 and 2 of the drawings, a cylindrical crucible casing 10 has secured thereto, at each end of a diameter thereof substantially at the middle of its length, a cylindrical sleeve 11. To the ends of the sleeves 11 remote from the crucible casing are secured discs 12 which extend radially outwardly beyond the sleeves 11, and rest at their edges on pairs of rollers 13 mounted on a stand 14, so that the crucible casing is 1'0- tatable about a horizontal axis passing through the centres of the discs. To each of the discs 12 there is detachably secured an auxiliary casing 15 extending therefrom in the direction of the axis of rotation and having a radial extension 16 on one side. Each of the auxiliary casings 15 encloses one of the carbon rods between which the arc is formed in the crucible, together with mechanism for moving the said carbon rod longitudinally, which mechanism will be hereinafter described. A handwheel 17 at the outer end of each auxiliary casing 15 is provided to operate the said mechanism.

One end of the crucible casing 10 is flanged externally at 18, and a bell-shaped cover 19 is arranged for clamping to the said flange to enclose a mould 95, the mould being itself clamped to the crucible casing as hereinafter described. The other end of the crucible casing 10 is permanently closed and is provided with a boss 20 formed with a screw-threaded socket to receive the screw-threaded end of a rod 21 carrying a counterweight 22 such that the Whole assembly is substantially balanced about its axis of rotation. Each of the auxiliary casings 15 is provided with a radially-extending handle 23 to facilitate turning of the assembly.

Referring now to FIGURE 3, the crucible 24 is enclosed in a block 25 of insulating refractory material which fits in the crucible casing 10 and locates the crucible accurately therein, the crucible 24 and block .25 being retained in the casing 10 by a plate 26 secured by screws 27 (FIGURES 1 and 2) to the flange 18. The plate 26 is apertured to provide a filling and pouring passage (not shown) and also a sighting passage aligned with a sighting aperture at 28 in the cover 19 and with the position of the arc. Spaced inwardly from each sleeve 11 is a co-axial sleeve 29 which forms, with the said sleeve 11, the disc 12, and the wall of the crucible casing 10, an annular chamber 31 through which cooling liquid is circulated by a pump and suitable conduits to reduce the transference of heat from the crucible casing 10 to the auxiliary casings 15.

In each auxiliary casing 15 there are mounted a pair of parallel guide rods 3-2 (FIGURE 4), one of the guide rods being also shown in FIGURE 3. The rods 32 extend parallel to the axis about which the assembly is rotatable, and they support slidably a travelling block 33 (FIG- URES 3 and 4) of generally triangular shape, the guide rods 32 passing through the block 33 adjacent two corners thereof. "Hie guide rods 32 are electrically insulated from the auxiliary casingv 15 at both ends, for example by bushes of insulating material. A screw-threaded rod 34 is mounted in the auxiliary casing 15 parallel to the guide rods 32, and is also electrically insulated from the said casing, the rod 34 passing through a screw-threaded hole adjacent the third corner of the block 33. Each of the screw-threaded rods 34 has a plain portion 35 extending through an opening in an end plate 36 closing the outer end of the auxiliary casing 15 in which that rod is mounted, and has one of the handwheels 17 mounted on its outer end, with the interposition of an insulating bush 37.

A packing 38 surrounding the plain portion 35 of the rod 34 is comprised by a gland 39 of electrically insulating material tightened down on to the packing 38 by nuts 41 engaging studs 42 passing through a metal plate 43 bearing on a shoulder on the gland.

The traveling block 33 is hollow, being formed by two substantially triangular plates 44, 44 between which are welded three metal bushes 4'5, 46 and 47 (FIGURE 4) two of these

bushes

45 and 46 providing the apertures for the guide rods 32, and the bush 47, which is internally screw-threaded, receiving the screw-threaded rod 34. A fourth bush 48 extending between the plates 44, 44' substantially at their centres is adapted to receive the outer end of a carbon rod 49 which extends through the crucible casing and through the wall of the crucible 24 into the interior of the latter. A tapered longitudinal groove 51 is formed in the wall of the bore of the bush 48 to receive a tapered key 52 adapted to grip the carbon rod 49 in the said bore. The key 52 is formed with a radially outwardly projecting lug 53 at its thicker end, the lug being notched, and a screw 54, engaging in a screwthreaded hole in one of the plates 44 of the block 33, is grooved circumferentially at 55. The groove 55 in the screw fits into the notch in the lug 53, so that the wedge can be moved in and out by rotating the screw 54.

The end plates 36 are formed with circular apertures 56 closed by screw-caps 57 provided with packing rings 58 to ensure a substantially fluid-tight closure of the apertures 56. The caps 57, when removed, expose the ends of the carbon rods 49 and the heads of the screws 54, so that the carbon rods can be readily removed, replaced and clamped in position.

The space in the travelling blocks 33 between the plates 44, 44 is closed by metal strips 59 welded in position, thus providing closed chambers in the said blocks to receive cooling liquid which absorbs and carries away some of the heat from the carbon rods. The radial extensions 16 of the auxiliary casings are closed at their ends by plates 61 of electrically insulating material, each such plate 61 having mounted in it two

pipe connections

62, 62 from each of which a flexible pipe 63 (FIGURE 3) leads to a further connection 64 on the travelling block 33 in the corresponding casing 15. The connectors 62 are connected externally, by further flexible pipes 65 (FIGURE 2) to the pump already referred to which circulates cooling liquid through the chambers 31. There is also mounted in each plate 61 a binding post 66 from which a flexible conductor 67 preferably of metal braid, leads to the block 33, the binding posts 66 being connected to opposite poles of a source of electric current. The pipes 63 and the conductor 67, being flexible, allow of move 'ment of the block 33 along the guide rods 32.

In an alternative arrangement shown in FIGURES 6 i and 7, the block 33 does not receive cooling liquid and is solid, the guide rods 32 being tubular and connected to one another at their inner ends by a pipe 32a. One of the tubular rods 32 is connected at its outer end to a coolant supply pipe 32b, the other being connected at its outer end to a return pipe 32c the inner end of which communicate with a water jacket 32d surrounding the carbon rod 34.-

To provide means for securing a mould to the crucible casing the plate 26 has mounted on it, adjacent its periphery, two or more pillars, one of which is shown at 68 in FIGURE 3, each of the pillars 68 carrying, at its end remote from the plate 26, a cylindrical head member 69 having formedin it a series of axially spaced circumferential grooves. A dished metal plate 71 havinga diameter-such that its edge can engage in the grooves in the head members 69 is notched at its edge in such positions that, by aligning the notches with the pillars, it can be inserted between the heads and then partially rotated to engage its edge with any selected grooves in the heads. A flat metal plate 72, slidably mounted relative to the dished plate 71 by means of a central stem 73 on the flat plate engagingin a sleeve 74 on the dished plate, is positioned on the side of the latter nearer to the crucible casing, a coiled compression spring 75 being mounted between the two plates 71 and 72 to urge them apart. A pair of pillars are fixed to the flat plate 72, one on each side of the stem 73, one of the pillars being shown at 76 in FIGURE 3, the pillars 76 extending through openings in the dished plate 71. A pivot pin 77 journalled in the pillars 76 has mounted on it a cam 78 rotatable about the pivot pin by means of a handle 79, the contour of the cam 78 being such that if the handle 79 is turned to a position in which it is perpendicular to the plates 71 and 72 the spring 75 is compressed and the flat plate 72 is drawn towards the dished plate 71, whereas movement of the handle 79 to a position in which it lies parallel to the plates 71, 72, as shown in FIGURE 3, allows the spring 75 to extend.

A mould to receive metal to be melted in the crucible 24 can thus be clamped in position against the plate 26 by setting the cam 78 to retract the flat plate 72 relative to the dished plate 71, positioning the dished plate 71 with its edge engaging in appropriate grooves in the heads 69 so that the flat plate 72 lies close to the bottom of the mould, and moving the cam 78 to allow the flat plate 72 to engage the bottom of the mould. The mould 95 is formed with a filling orifice 95a registering with the pouring passage 24a in the crucible. The dished plate 71 serves as an adjustable reaction plate for the spring 75, whilst the plate 72 acts as a clamping plate for the mould.

The bell-shaped cover 19 has a relatively sharp edge 81 which rests on a deformable sealing ring 82 mounted in a rebate around the edge of the plate 26, and is held in position by clamp units 83 one of which is shown in detail in FIGURE 5. The clamp unit comprises a stud 84 carried by a block 85 pivotally mounted in abracket 86 secured to the underside of the flange 18, and a nut 87 on the stud, the cover 19 being provided with slottted lugs 88 with which the studs 84 are engaged by turning them about their pivots before the nuts 87 are tightened.

The depth of the cover 19 is such that, in any position of the dished plate 71 relative to the grooved head members 69, the handle 79 is unable to move to the mouldreleasing position if the cover is on. The cover 19 is provided with lifting handles 89.

The interior of the furnace is connected by a suitable conduit, such as that shown at 9-1 in FIGURES 1 and 2, to an evaluator (not shown) so that the interior of the furnace can be evacuated. The conduit 91 is shown as being connected to one of the auxiliary casings 15, but if preferred, the air may be withdrawn direct from the interior of the bell-shaped cover 19 through conduits extending upwardly through the flange 18 and plate 26. FIGURE 8 shows such an alternative arrangement for withdrawing air from the interior of the furnace. According to this arrangement the air is withdrawn direct from the interior of the bell-shaped cover 19' through conduits 93 extending upwardly through plate 26, the pipes being connected by further pipes 94 to the evacuator (not shown). A vacuum gauge 92 is provided to indicate the pressure in the furnace.

For loading, the furnace is positioned with the plate 26 at the top, the counterweight 22 tending to hold it in that position. With the bell-shaped cover 19 removed, the crucible is charged, the mould being then placed in position and clamped, and the cover 19 being then clamped in position. The current is then switched on and the arc struck to beat and melt the charge. When the charge is melted, the whole assembly is inverted to cause the charge to flow into the mould.

The whole of the interior of the furnace is evacuated prior to the melting operation, and if a reducing atmosphere is required, a suitable gas is fed in after the air has been withdrawn.

The invention provides an electric arc furnace in which by arranging the whole of the carbon rods within a space which can be evacuated, the necessity for providing an airtight seal through which the said rods can slide is avoided, and adequate sealing of the evacuated space is more readily and economically provided.

I claim:

1. A vacuum furnace for melting metal by an electric arc, said furnace comprising a main casing, two closed auxiliary casings secured airtight to the main casing and radially extending from opposite side Walls thereof; a crucible mounted within the main casing, a carbon rod mounted with its entire length longitudinally slidable within each of said auxiliary casings and extending from the respective casing through the respective main casing wall into the crucible, operating means for sliding said rods into and out of an are producing position in reference to each other, a mold cover airtight attachable upon the top of said main casing, and support means supporting the main casing, the auxiliary casings and the mold cover pivotal as a unit about a horizontal axis.

2. A furnace according to claim 1 and comprising cooling jackets surrounding the auxiliary casing portions adjacent to the main casing, and means for circulating a coolant through said jackets to reduce the transfer of heat from the crucible to the auxiliary casings.

3. A furnace according to claim 1 and comprising in each auxiliary casing at least one guide rod mounted parallel with the respective carbon rod, and a travelling block slidable on the guide rod and releasably keyed to the carbon rod for joint longitudinal displacement of the traveling block and the carbon rod along the guide rod, said carbon rod operating means being drivingly coupled with said traveling blocks for independently displacing the latter from the outside of the auxiliary casings.

4. A furnace according to claim 3 wherein said carbon rod operating means comprises in each auxiliary casing a threaded rod rotatably mounted parallel to said carbon rod and said guide rod and threaded through the traveling block, and actuating means located outside each auxiliary casing and coupled to the respective threaded rod for rorating the same whereby the respective block and with it the respective carbon rod are correspondingly displaced within the auxiliary casing.

5. A furnace according to claim 3 wherein said guide rods are hollow and means are provided for circulating a coolant through said rods.

6. A furnace according to claim 1 and comprising cooling means disposed in close heat transferring relationship with said rod operating means for dissipating the heat transferred to said means from the rods.

7. A furnace according to claim 1 and comprising in each auxiliary casing at least one guide rod mounted parallel with the respective carbon rod, and a hollow traveling block slidable on the guide rod and releasably keyed to the carbon rod for joint longitudinal displacement of the traveling block and the carbon rod along the guide rod, said carbon rod operating means being drivingly coupled with said traveling blocks for independently displacing the same from the outside of the auxiliary casings, and further comprising means for circulating a coolant through said hollow traveling blocks.

8. A furnace according to claim 1 and comprising mold clamping means for detachably securing a mold to the main casing, said clamping means including upright pillars mounted on the main casing in circumferential arrangement, a reaction plate engageable with said pillars in a selected one of several positions of different spacings from the top of the main casing, a clamping plate resiliently urged away from said reaction plate to exert clamping pressure upon a mold placed between the plate and the top of the main casing, and means coacting with said clamping plate for pulling the same toward the reaction plate against said resilient action.

9. A furnace according to claim 8 wherein said pillars mount heads having longitudinally spaced circumferenial grooves, and wherein said reaction plate has a diameter overlapping the heads of said pillars and is notched along its peripheral rim, the notches being circumferentially spaced to correspond with the circumferential spacing of said pillars.

References Cited in the file of this patent UNITED STATES PATENTS 688,393 Contardo Dec. 10, 1901 949,511 Weeks Feb. 15, 1910 1,310,079 Hechenbleickner July 15, 1919 1,926,573 Willcox Sept. 12, 1933