US1922034A - Protective device for electric induction furnaces - Google Patents

Description

Allg. 15, 1933- T. A. FEEHAN `1,922,034

PROTECTIVE DEVICE FOR ELECTRIC INDUCTION FURNACES n Filed Nov. 23, 1931 Wl' 277655 y [2n/ew for:

Patented Aug. 15, 1933 PROTECTIVE DEVICE FOR ELECTRIC I INDUCTION FURNACES Thomas Arthur Feehan,I Trenton, N. J., assig'nor to Ajax Electrothermc Corporation, Ajax Park, N. J., a Corporation of New Jersey Application November 23, 1931 Serial No. 576,815

2 claims. (ci. isi-26) The invention refers to protective means for induction electric furnaces and comprises f orm-v ing a hollow space outside of the melting chamber wall and inside of the energizing coil. The object is to by-pass any part of the charge which might leak through the furnace wall, before it has had a chance to reach the energizing coil and cause damage.

In describing my invention I have preferred to illustrate by the use of ve figures, these being sufficient adequatelyto describevthe construction claimed but subject to amplification or change to meet required conditions.

Figures 1 and 2 show topfand section elevation views of an induction furnace` equipped lwith a safety device according to my invention.-

Fig. 3 is an isometric drawing showing an individual brick adapted to form, with other similar bricks, the proper spacing Cshown in Figs. 1 and 2. Figs. 4 and 5 show alternate methods of lining construction which leave a protective space according to whatis claimed.

In the usual form of lining for induction electric furnaces a protective lining' is cemented flat against the coil. Sometimes a layer'of mica is next applied for insulation, andflnally .a powder refractory is hard-rammed between these outer layers and a crucible or metal form. Lately it has been advocated that the rst layer of cement be substituted by a layer of brick or even twolayers of brick with or without mica between. Practice has also varied as to whether a crucible would be used or Whether a lining would be sintered in place by ramming the refractory material between the outer layers and a conducting sleeve which might Ibe heated to sinter the lining and then melted down to form a part of the firstcharge. The point brought out is that substantially all linings thus far have been solid packed between energizing coil and charge.

Onel exception' to the above is noted in'Brace, U. S. Patent #1,823,873. In this patent a construction is claimed generally vsimilar in idea to my-own idea but with the exception that the patentee has placed his protective space immediately outside of the crucible wall. Since the placing of the space is of prime importance to my invention and since from my operating experience Ihave found it important that the space be'as I have shown, I cnsider that the patentee in the above case in no-way anticipates my invention. I' mention it as a matter of record.

In the lining methods with which I am familiar and to which my application applies, great stress has been centered upon the necessity for having charge. All crucibles are subject to crackingand wear. Instead, it is specified that granular refractory material be rammed in behind the crucible to back up any cracksv which might form. This backing material sinters enough to form a secondary crucible wall but remains granular or unsintered away from the charge. y

It is the above sintering of a granular packed mass which allows the sinter'ing of a lining in place without the use. of a crucible; theA use of a crucible even though it has initial cracks when placed, or the use of brickd inner linings or the patching and continued use of an old lining.

The inside lining which becomes hard and sintered is `subject to cracking from expansion and contration but dependence is placed on the vbacking to remain unsintered at least for a space between coil and charge.'

The cracking of the inside sintered Wall is of little importance when backed with unsintered material, as the crack cannot extend beyond the point where sintering stops. Hence the argument that any protective space left to by-pass leaking metal must eiectively be placed beyond the unsintered portion of they lining except where the crucible itself is depended upon not to crack and where it is replaced as soon as it does crack.

As cracks appear and are healed by sintering v of granular backing material, the sintered zone gradually creeps back until the whole lining becomes sintered. When this occurs, there is danger of metal running through. Unless there is some safety device to indicate this condition,

there is a possibility that the charge making contact with the inductor coil will cause its turns to become short circuited with afurther possi'- .bility ot causing a water leak and explosion before the power can be shut oil' andthe inductor coil cleared of cooling Water.

In my invention I guard against the leaking metal coming in contact with the coil by diverting .it toa drain at the last point in the refractory nected t an electromotive source or generat r, 2.

Capacitors, 3, are 4connectedv in parallel with the inductor coil foi-,resonance purposes. The coil is mounted in'supporting members or frames, 4, 5.

I have preferred to show, as an example, a lining which has been sintered in place, although I 6 might as well have shown one embodying a cruci ble of the pre-formed or brick masonry type.

Foundation pieces, 6, '1, are first inserted in the bottom of the furnace. They are formed so as to leave a free space, 8, substantially` over the 10 entire bottom portion of the furnace. They may be formed to give this clearance by molding pressure points as shown in Fig. 3 or by any other suitable means. A large central hole, 9, is left, \las shown, and is covered by a thin copper disc, l5 10. Bricks, 11, are then laid close against the coil and are luted thereto.

If preferred they may be'substituted by a solid tegrally with the brick, or in Fig. 5 where 15,

and 16 show a different method of leavingl the space using two bricks.

All brick work lining the coil is suitably of material having a low electrical conductivity and a high thermal conductivity. In this way the cooling effected by the cooling medium in the inductor coil is transferredto the inside brick layer ensuring a suitable temperature gradient between outside brick wall and furnace charge.

by-pass to said discharge opening.

Refractory material, 17, is then packed around a form or crucible and is sintered to form a crucible or container for the charge, 18. Anysuitable-f.

topping Cement, 19, is added t0 finish 0H the lining.

When a leak occurs in the refractory as shown at 20 the metal reaches the space, 13, and flows down through space, 8, to -a discharge orifice, 2l, and into any suitable container. 'I'he leak is quickly detected by the operator who takes steps 35 to empty the furnace and repair the lining.

Should the metal leak through the bottom of the furnace, the disc, 10, melts letting the metal out through the orifice 9` and 21.

Having thus described my invention so that othersv skilled in the art may be enabled to practice the same, what I desire to secure by Letters Patentis defined in what is claimed. f

1. In an induction electric furnace, an inductor coil, a Agranular packed ref ractory lining within said coil forming a hearth, spaced brick walls between the coil and the lining providing a bypass for leakage molten metal to prevent damage to the coil and av refractory base beneath said lining having a discharge opening and provided 10 with passageways leading from said by-passto said discharge opening.

' 2. In an induction electric furnace. an inductor coil, a granular packed refractory lining within said cou forming a. hearth, spaced refractory walls between the coil' and the lining providing a by-pass for leakage molten metal to prevent damage to the coil and a refractory base beneath said lining having a discharge opening Y and provided with passageways leading from said THOMAS ARTHUR FEEHAN.

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