US3057937A

US3057937A - Electric arc furnaces

Info

Publication number: US3057937A
Application number: US700411A
Authority: US
Inventors: Shaw Clifford
Original assignee: Zirconal Processes Ltd
Current assignee: Zirconal Processes Ltd
Priority date: 1956-12-06
Filing date: 1957-12-03
Publication date: 1962-10-09
Anticipated expiration: 1979-10-09

Description

Oct. 9, 1962 c. SHAW ELECTRIC ARC FURNACES 2 Sheets-Sheet 1 Filed Dec. 3, 1957 FIG. 2

INVENTOR. CLIFFORD SHAW BY Haw,- M

ATTORNEYS Oct. 9, 1962 c. SHAW 3,057,937

ELECTRIC ARC FURNACES Filed Dec. 3, 1957 2 Sheets-Sheet 2 \X A M HI H 6 FIG. 4

26 Fifi-1 25 A 1 0 FIG. 5

o o 32 32 FIG. 6

INVENTOR. 33

CLIFFORD SHAW FIG. 7 HMMNM ATTORNEYS 3,057,937 ELECTRIC ARC FURNACES Clifford Shaw, Forest Hill, London, England, assignor to Zirconal Processes Ltd, Port Washington, N.Y., a corporation of New York Filed Dec. 3, 1957, Ser. No. 700,411 Claims priority, application Great Britain Dec. 6, 1956 Claims. (Cl. 13-35) This invention relates to electric arc furnaces, and has for its object to provide improvements therein which facilitate the setting up of the furnaces and increase their adaptability.

Electric arc furnaces comprise a lining of refractory material surrounded with insulating material and housed in a metal container, and it has been the practice to pack loose insulating material or shaped bricks of insulating material around a molded lining, which, since the lining must be located in the correct position in the container, calls for skilled operators and takes considerable time.

According to one aspect of the present invention, an electric arc furnace comprising a furnace lining of refractory material housed in a metal container from which it is spaced by a mass of heat insulating material, is characterized in that the insulating material is in the form of a rigid block molded around the furnace lining.

The rigid block is preferably directly located in the container by engagement of at least parts of its external surface with the container walls.

The lining may be formed with a filling neck providing an orifice of large cross-sectional area, an apertured plug being provided to fit in the said orifice and provide a pouring opening of smaller cross-section than the orifice in the filling neck.

According to another aspect of the invention, a method of producing an electric arc furnace of the kind in which a lining of refractory material is housed in a metal container from which it is spaced by a mass of heat insulating material, which method comprises the steps of forming the furnace by molding, supporting the said lining in a mold, filling the mold around the lining with a mixture of an insulating refractory material and a binder, and allowing the mixture to set to form a rigid block enclosing the lining.

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

FIG. 1 is a front elevation of an electric arc furnace structure embodying the invention;

FIG. 2 is a plan view of the lining and insulating block of the furnace structure shown in FIG. 1;

FIG. 3 is a composite view, the left hand half being a front view, and the right hand half a sectional elevation on the line 33 in FIG. 2, of the lining and insulating block;

FIG. 4 is a section on the line 4-4 of FIG. 2;

FIG. 5 is a section, similar to FIG. 4, showing a modification;

FIG. 6 is a sectional view of a pouring spout adapted for use with the construction shown in FIG. 5; and

FIG. 7 is a side elevation of an electric arc furnace structure similar to that shown in FIGURE 1 but having the container mounted for tilting in a different manner.

Referring to FIG. 1 of the drawings, the furnace structure therein shown as an example of the invention includes a cylindrical metal container 10 supported by suitable mounting means shown as two

hollow trunnions

11, 11 in a frame 12, the axis about which the container 10 turns in the frame 12 being horizontal. The axis of the container itself is perpendicular to its axis of rotation, and one end of the container is provided with a remov- States Patent ice able cover plate 13. Inside the container 10, as shown in dotted lines, there is mounted a lining 14 of refractory material, the lining being embedded in a block 15 of insulating material which is so shaped as to locate the lining 14 accurately in the container 10. The lining 14 and block 15 are formed with aligned

holes

30, 31, lying on the axis of the

hollow trunnions

11, 11 for the passage of carbon rods, 16, 16 between which the arc is formed, and suitable mechanism (not shown) is provided for advancing and withdrawing the carbon rods and rotating the furnace for pouring. An opening 17 is formed in the lining 14 and in the block 15, and registering with an opening in the plate 13, provides for charging the crucible and pouring the charge when melted.

The lining 14 and the block 15 comprise respectively a refractory material and an insulating refractory material, the said material in each case being mixed with an ethyl silicate and sufficient water to hydrolyze the silicate, together with an acid or basic gelling accelerator as described for example in British patent specification No. 716,394.

The refractory material for the lining 14 may be fused alumina, magnesia, Zirconia or chrome magnesite, and the refractory insulating material for the block 15 may be sillimanite or molochite.

The furnace lining 14, FIGS. 1 to 4, is formed by molding about a wax core, the core being supported in the mold by means of a rod or tube which also serves as a core for the holes 30 in the lining through which the carbon rods pass. The lining 14 is generally spherical in shape, with

external bosses

18, 18 around the holes for the carbon rods to increase its wall thickness at the points where the carbon rods pass through and so reduce the risk of fusion of the insulation around the carbon rods with possible resultant slagging of the charge, and another boss 19 surrounds the filling opening '17. The materials of which the lining is formed are mixed into a slurry and poured into the mold, the said mold being vibrated during pouring and the binder is then allowed to gel before the mold is stripped off. After the mold has been stripped, the wax core is removed by steam heating, the lining then being air dried, baked for a period of six hours at a tem perature up to 600 C., and furnaced, again for approximately 6 hours, at a temperature of 1350 to 1400 C.

The lining is then supported in another mold, again by means of the rod or tube passing through the holes to re-' ceive the carbon rods, and has formed around it the block 15 of insulating material. The material to form the block 15 is poured into the mold while the latter is vibrated, the binder is allowed to gel, and is then air dried for some days, after which it is furnaced at a temperature of 1250 to 1300 C. for a period of approximately six hours. As shown in the drawings this block 15 is generally cylindrical in shape, having an external diameter such that it fits closely in the container 10 and having cut-away portions at its ends forming shoulders 20 on opposite sides of

flat lands

21, 21 which are symmetrical about a diametral plane of the block. The distance between the

lands

21, 21 is such that the block fits snugly between the ends of the container 10. The curved wall of the block is formed with substantially semi-cylindrical grooves running longitudinally thereof, as shown at 22.

As shown in FIGS. 2 and 4, an additional hole 23 may be formed in the lining 14 and block 15, directed towards the center of the cavity enclosed by the lining, to permit inspection of the are when the furnace is in operation.

Furnaces according to the invention may be used to melt metal for pouring directly into molds clamped to the said furances, or for pouring into separate molds. The filling opening in the furnace lining 14 and block 15 may be of large diameter as shown at 24 in FIG. 5 to enable relatively large pieces of scrap metal to be inserted thereinto, a smaller and more conveinent orifice for pouring being provided by inserting a tubular plug 25 in the opening 24. The plug 25 is formed with a flange 26 which, when the plug is inserted-in the orifice 24, rests against the end plate 13 of the container 10. A mold may be clamped to the furnace by any suitable means so that its filling channel is disposed to mate with the orifice in the plug 25. If the charge in the furnace is to be used to fill one or more molds which are not clamped to the said furnace, an alternative form of plug such as that shown at 27 in FIG. 6 may be used, that plug having a pouring spout 28. A solid plug (not shown) may also be provided for completely closing the orifice 24.

It will be understood that the shape of the insulating block may be modified, the said block being, for example, in the form of a cylinder fitting closely in the container 10. The container may be mounted for tilting by means other than the hollow trunnions shown in FIG.

1, a suitable alternative method of mounting being shown in FIGURE 7. A pair of discs, one of which is shown at 31, are provided, one on each side of the container 10, the discs 31 being co-axial with the carbon rods and resting on pairs of rollers such as those shown at 32, 32, mounted on a fixed frame 33. The carbon rods and their feed mechanism which may be of the conventional screw-andnut type, operated by a handwheel 34, are housed in casings 35 rotating with the container 10 about the axis of the discs, and current is supplied to the carbon rods through leads such as 36.

What is claimed as new and desired to be secured by Letters Patent is:

1. The method of producing an electric arc furnace of the kind wherein a lining of refractory material is housed in a metal container from which it is spaced by a mass of heat insulating material, which method comprises the steps of forming the furnace lining by molding, supporting the said lining in a mold, filling the mold around the lining with a mixture of an insulating refractory material and a binder, and allowing the mixture to set to form a rigid one-piece block enclosing the lining.

2. The method according to claim 1 which comprises the further steps of preparing a wax core having the shape of the furnace cavity, supporting said core in a mold, forming the furnace lining by filling said mold with a mixture of discrete refractory material and a gelling binder, allowing the binder to gel, stripping the mold, melting out the wax core, drying and firing the lining, the said lining then being supported in the block-forming mold and the insulating block formed about it in the form of a one-piece block, and the said block being dried and fired after removal from the said mold.

3. The method according to claim 1 wherein the binder is a gelling binder which is allowed to gel after the filling of the block-forming mold.

4. The method of manufacturing a heat refractory block for insertion in a metal container of an electric arc furnace, said method comprising the steps of providing a mold core and supporting the same in a mold, molding a layer of hardening refractory material about said core, removing said core when said layer has hardened sufficiently to sustain its configuration, subjecting said layer to a drying and heat treatment to complete the hardening of the layer, the hardening layer forming an inner lining defining a furnace cavity, then placing and supporting said liner in another mold, and thereupon enveloping the liner with a layer of insulating hardening refractory material to form an outer liner having an outer configuration fitting the inner configuration of said container.

5. The method according to claim 4 and comprising the steps of supporting said mold core on rods in the mold and forming said first layer with bosses about said support rods, and then supporting the inner liner formed by said first layer in said other mold by rods disposed in alignment with said bosses, said support rods for the inner and outer lining constituting cores to form aligned holes through'the liner for passing electrodes of the furnace there-through.

References Cited in the file of this patent UNITED STATES PATENTS 54,204 Presbrey Apr. 24, 1866 1,201,224 Gillett et al. Oct. 10, 1916 1,201,225 Gillett Oct. 10, 1916 1,418,773 Booth June 6, 1922 1,531,811 Peterson Mar. 31, 1925 2,224,982 Morin Dec. 17, 1940 2,438,559 Hubbell Mar. 30, 1948 2,536,859 Tama Jan. 2, 1951 FOREIGN PATENTS 716,394 Great Britain Oct. 6, 1954