US1889362A - Electric resistance furnace - Google Patents

Description

Patented Nov. 29, 1932 UNITED STATES PATENT OFFICE LENNABT p HGEL, OF VASTERAS, SWEDEN, ASSIGNOB TO ALLMANNA SVENSXA ELEXTBISKA AKTIEBOLAGET, 0F VASTERAB, SWEDEN, A. CORPORATION 0F SWEDEN ELECTRIC RESISTANCE FUBNACE Application illed September 23, 1931, Serial No. 584,575, and in Sweden June 14, 1929.

Metallic heating elements for resistance furnaces have hitherto generally been made of round wire which has most frequently been helically wound. The circular section, however, odors the smallest possible radiating surface in proportion to the weight and results therefore in a very inefficient utilization of the material. It has also been previously proposed to make heating elements in general in the form of straight or corrugated bands, which have in such cases been mounted edgewise on a plate, in which they have been entirely or partially embedded. If a furnace be constructed by means of such plates there is, however, no essential improvement of the radiating action of the element in relation to that of the round wire, as the broad surfaces mainly radiate heat to one another and only to a small extent to the rest of the furnace contents.

According to the invention, heating elements consisting of corrugated bands are arranged substantially free alon the walls of the furnace with one broad si e of the band facing the interior of the furnace, whereby at i.' asttlie entire radiation from this side is directly utilized by the furnace. For instance the band elements may be arranged on shelves or in grooves in the side walls of the furnace, the shelves or groove sides having outside the elements projections for retaining them. In order to utilize the radiation from both sides of the band, it can be placed at some distance from the furnace wall in open grooves ci larger width than the band and of appropriate section for acting as relectors.

The corrugated band shape of there-sistance elements is particularly useful when applied to certain alloys which endure a very high temperature. Such alloys have a very coarse crystallinic structure, and at high temperature there may be a displacement between the crystal .surfaces resulting into deformation. If the metal then is in the shape of hclically wound wire., the deformation may cause short-circuit between turns, but in corrugated bands this danger is practically eX- eluded.

Three methods of carrying out the invention by way of example are diagrammatically illustrated in the accompanying drawing in which Figure 1 shows a furnace in crosssection, Figure 2 a vertical longitudinal section on the line A--A in Figure 1, Figure 3 a detail of another method of construction in cross-section, Figure 4 a horizontal section corresponding to Figure 3, and Figure 5 a cross-section of a third form of the grooves for the band.

In Figures 1 and 2 there are placed in open grooves in the brick walls 1 of the furnace, corrugated bands 2 which are mounted edgewise in the sidewalls and lie in the bottom and top walls so that one broad side always faces the interior of the furnace. The bands are retained in place by fixed projections 3 on the surrounding bricks, which overlap both edges of the bands. The mountin of the bands in the grooves is then referab y effected by introducing the ban s from one end. In certain cases it is not necessary to arrange such heating elements in all the walls of the furnace. If, for example the bands are only arranged in the vertical walls, they may be mounted as illustrated in Figures 3 and 4. The bricks 1 are here preferably shaped as shown so as to form shelves 6 on the side facing the interior of the furnace, the corrugated resistance bands 2 being placed edgewise on the said shelves. The bands are retained in position partly by projections 4: and partly by brick pieces 5 introduced through holes in the briclnrow above and resting on the bands. The'brickwork behind the bands is given an appropriate section for reflecting the heat radiating towards the brickwork from the band 2, as shown'by the arrow. Figure 5 shows a modification of the groove section shown in Figure 1, in which the said groove is sufficiently wide to permit the introduction of the band sidewise, so that it will not be necessary to do it endwise, as in Figure 1.

I claim as my invention:

1. An electric resistance furnace consisting of refractory walls and resistance elementsin the shape of corrugated bands. arranged along said walls and directly supported by them in such a manner that one broad side of the band is free to radiate to the interior of the furnace.

2. An electric resistance furnace consisting of refractory walls having grooves, corrugated resistance bands loosely mounted in said grooves with one side facing the interior of the furnace, and projections on the sides of said grooves retaining said bands in place.

3. An electric resistance furnace comprising vertical refractory Walls, projecting shelves on said walls, corrugated resistance bands resting edgewise on said shelves, and projections on said shelves outside said bands for retaining them in position.

4. An electric resistance furnace consisting of refractory Walls, substantially open rooves in said Walls, corrugated resistance ands of smaller width than said grooves mounted therein with one broad side facing the interior of said furnace, and means for retaining said bands in place at some distance from the inner extremities of said grooves.

5. An electric resistance furnace comprising refractory walls, resistance elements in the form of corruated bands arranged with their broad sides facing towards the interior of the furnace, and means for supporting said bands solely by contact with the lowermost portions of each band to permit free movement of the upper portions of the bands due to temperature changes.

In testimony whereof I have signed my name to this specification.

u LENNART HGEL.

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