US1915747A - Electric furnace and resistance element therefor - Google Patents

Description

W, E. MOORE June 27, 1933.

ELECTRIC FURNACE AND RESISTANCE ELEMENT THEREFOR Filed Oct. 19, l93l 2 Sheets-Sheet 1 June 27, 1933. 'W M ORE 1,915,747

ELECTRIC FURNACE AND RESISTANCE ELEMENT THEREFOR Filed Oct. 19, 1931 2 Sheets-Sheet 2 fig .5

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Patented June 27, 1933 PATENT OFFICE MOORE, OF PITTBBUM'H, PENNSYLVANIA, ASSIGNOB T PITTSBURGH RESEARCH CORPORATION, OF PITTSBURGH, PMSYLVANIL nnncmc rumucnann RESISTANCE We 'rnnanron Application flledoctober 1B, 1931. Serial No. 589,798.

My invention relates to improvements in electric furnaces, and more particularly to a furnace for heat treatment of metals, although not necessarily restricted to this use.

Heretofore in the operation of furnaces of this character, repairing of the furnace or of the resistance elements therein necessitate a considerable loss oftime due to the fact that the furnace must cool down before workmen can enter it to make repairs. I

propose to overcome this difficulty by providing a resistance element which may be removed with the roof'of the furnace, thereby effecting a saving in the time required for repairing the furnace and resistance elements.

Another object of my invention is to provide a novel resistance element and-novel supporting means therefor.

-2'0 Otherobjects and advantages of my invention will be apparent during the course of the following descri tion.

In the accompanying rawin swhich form a part of this specification an wherein like characters of reference denote like parts throughout the same, v Figure 1 is a vertical transverse sectional view through a furnace embodyinginy invention.

" Figure -2 is a longitudinal sectional viewtherethrough, Figure 3 is a fragmentary horizontal se tional View. showing one form of'resistance element,

Figure 4 is a similar 'view showing another form of resistance element, I

, Figure 5 is a detail elevation of a furtherform of resistance element,

Figure 6 is a similar view of still another form of resistance element, and,

Figure 7 is a detail of a still further form I preferably arranged in the same plane, and

of resistance element.

In the drawings, wherein for the purpose of illustration is shown a preferred embodiment of my invention, the numeral 10 designates a heat treating furnace hood arranged over the stationary base 11. The hood 10 is provided with a removable roof 12, and

the entire hood is lifted. on and off the base by meansof the usual shop crane. The usual are arranged exteriorly of the roof and exfurnace hood is provided with an interior shoulder or shelf adjacent its lower end which extends towards the furnace base. This shoulder collects scale, dust and dirt, and therefore must be cleaned at regular intervals. In order to obviate this difficulty I have provided the shelf 13 with-a substantial slope towards its inner edge as seen in Figures 1 and 2. ,With this arrangement debris will slide off the shelf when'the hood is raised, thereby rendering the shelf self clean mg. In the usual furnace of this type the electric heating elements are supported onand secured to the side walls of the furnace hood. In my invention the electric heating elements are supported entirely by the removable roof 12; and are removed therewith when the roof is lifted from the hood 10. A

A series of heat resistant metal rods 14 70 carry stirrups 15 at their lower-ends, and project upwardly through bushed openings in the brickwork of the roof arch, pass through bearing plates 16 and are held in the bearing plates by nuts 17 enga%ug the screw threaded ends of the rods. ach of the stirrups 15 carries an insulating, resistor supporting spool 18. Theresistor comprises a strip orribbon '19 which asses over the spools 18,and.depends there m in a series of loops which are spaced from the walls of the hood 10 and extend to a point adjacent the shelf 13. The ends of the resistor elements are connected to terminals 20 which tend through the same. Various distributions of the resistor may be effected b lengthening some of the rods 14 and there y shortening the corresponding. resistor loop, as seen in Figure 2. Y Y I The lower ends of the resistor loops are a difierent vertical distribution of the resistor loops is desired, it is only necessary to change some of the rods 14 in contrast to the old method which required tearing down the walls of the furnace to'replace the resistor supports. I Z

Due to the fact that the rods 14 are in tension; they may have a small cross section, and the heat conductivity from the interior of the furnace through the roof'arch will conse-' quently be reduced to a minimum. When the roof with its resistor loops is lowered onto the furnace hood, the loops are guided into position b the T-headed bolts 21.

While t e usual flat ribbon resistor may be used, I prefer to use a resistor strip or ribbon which has been passed throu h a cor rugating roll or the like and has a ished or channeled cross section, as seen in Figure 3. This shape of heater element has reater 4 strength than a flat ribbon due to the ateral stiffness im arted by the dishing feature, and at a very s lght increase in cost. Where the dished ribbon passes over the spools it has a tendency to flatten out.

. In place of the dished form shownin Figure 3, the resistor element may be passed ive through corrugating rolls which will -shaped cross section, as shown in igit an ure 4. Y

In Figure 5 I have shown another modification of the resistance' element in which it is twisted into an auger shape to form a resistor which will equally expose its surface to the furnace interior. I

In Figure 6 the flat resistance element is I wound into a helix of a relatively small diameter to increase the effective heating surface of the resistor.

In Figure 7 the resistor 19 is bent into alternate loops 22 v longitudinally and transversely of t e resistor strip to strengthen the resistor and to increase the exposed heating surface by its doubled corrugated efiect.

While I have shown and described the preferred embodiment of my invention it isto be understood that various changes in the size, shape and arrangement of parts may be resorted to without departing from the spirit of my invention or the scope of the subjomed claims.

Having thus described my invention, what I claim and desire to protect by Letters Patcut is:

1. In a heat treating furnace, a base, a removable hood adapted to be placed over said base, electric heating elements arranged in proximit to the wallsof said hood, and a sloping s elf arranged about the interior of the hood beneath the heating elements.

2. In a heat treating furnace, a furnace hood, a removable roof therefor, a resistance elementv supported by said roof and adapted to extend a substantial distance down into said furnace hood, and guide members secured to said furnace hood for said resistance element, whereby the resistance element may be removed from the hood with said roof.

3. In a heat treatin furnace, a furnace hood, a removable roo therefor, an electric resistance element supported bysaid roof and extendingjdown' into said furnace hood in' proximity to the walls thereof, and guide supports for said resistance element arranged on the walls of the furnace hood, whereby said resistance element is removable with said roo Y 4. In a heat treating furnace, a furnace body, a removable roof therefor, resistance supports secured to said roof, an electric resistance element carried by said suplpgrts and extending down into said furnace dy, and guide members for said resistance element secured to the walls of the furnace body.

5; In a heat treating furnace, a' furnace, body, a removable roof therefor, a resistance ribbon for said furnace, and means carried by said roof to support said ribbon in loops of different lengths which extend down into said furnace b0 6. In a heat treating furnace, a furnace furnace, a furnace 9 y, a removable roo therefor, a plurality of resistance supporting members depending from said roof, said members being of vary ing length, means .at the ends of said members for supporting a resistance element which extends down into the furnace, and

means on the walls of the furnace body for guiding the lower end of the resistance element.

9'. In a heat treating furnace, a furnace hood, a removable roof therefor, a plurality 11 v of resistance supporting elements depending from said-roof insulatin spools carried by the ends of said supporting elements, a resistance stri su ported by said spools and depending t ere rom in spaced loops which .120

extend. down into the furnace hood, means in said furnacehood for guiding the loops of resistance, and terminal members in said roof for the resistance strip.

10. In a heat treat hood, a removable roo therefor, a plurality of supporting elements .of varying lengths 'depending'from said roof, insulating furnace, a furnace s ools carried b the ends of said su portin of y ted on said 1 0 ements, ,a resistance strip supper tric resistance element comprising a strip of resistance material twisted into an auger shape and arran ed in a series of spaced loops in the furnace, t e overall Width of the auger shaped element being substantially equal to the width of the strip from which it is formed.

In testimony whereof I affix my signature.

WILLIAM E. MOORE.

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