US1755350A - Electric-furnace resistor - Google Patents

Description

April 22, 1930. F. A. FAHRENWALD ELECTRIC FURNAGE RESISTOR Filed May 19. 1924 JNI/ENTOR zumkA. rezzwda w E Patented Apr; 22, 1930 UNITED STATES PATE-NT ori-*ICE` ELECTRIC-FURNACE RESISTOR Application filed May 19,

This invention relates to electric furnaces and has for its object the provision of a cast resistance-heating unit which shall be cheaply and readily made, easily installed and re- 'placed, and having high radiating efficiency combined with a high degree of uniformity in physical structure; the provision of a new and improved mode of supporting such resistance elements while permitting expansion and contraction between the same and the furnace Walls; while further objects and advantages of the invention will become apparent as the description proceeds.

In the drawings accompanying and forming a part of my application, I have ilflustrated certain typical forms in which my invention may be embodied, but without intent to limit myself thereto. Fig. 1 illus-v trates a portion of a furnace showing two resisting elements on adjacent walls thereof, one in elevation and the other in section; Fig. 2 is a cross sectionalv view of one of the elements corresponding to the line 2-2 of Fig. l; Figs. 3,4, and 5 illustrate modified cross sectional forms; and Figs. 6, 7, and 8 illustrate modified supporting eXpedients. Fig. 9 shows the method of connecting two sections of the resistor.

The essence of my invention consists in forming the resisting elements of such cross section as to enable a homogeneous article, of uniform electric resistance at all points, to be made by casting and this object is accomplished by making the same of such shape that the contraction area shall existat the surface 0f the article ,and I further form the article with a large proportion of emissive area as compared with its cross sectional area.

A device of this character as provided for electric furnace use is necessarily made of some oxidation-resisting alloy of comparatively high melting-point and while I do not restrict myself to any one composition or alloy, experience shows that practically all substances having these essential qualities have the further property of contracting at the instantof solidification-which therefore prevents their filling the mold completely and necessitates a shrinkage area at some point. If it be attempted to cast a resistor 1924. Serial No. 714,289.

of square or rectangular or circular or oval section, the surface port-ions first become cooled in a substantially uniform manner so that the necessary shrinkage is produced by an internal disintegration. This means f that the crystalline structure of the metal is disrupted internally at different points, with the :result that the resistance varies from point to point so that it is impossible to em-v ploy a long element of this nature as a heating element in a furnace since some parts will burn out before others reach the working temperature.

` I have discovered, however, that by making the parts 0f certain asymmetrical'cross sec- 65 forwardly projecting ribs or fianges 2. This concentrates the heat of the metal at or near the junction points and causes these to cool more slowly with the result that the point of contraction occurs at 3 opposite each rib or 80 flange while the body of the casting retains a homogeneous structure.

-Such a device may made in the form of a long, straight strip if desired, but my preference is to form it in sinuous shape as shown in Fig. l having a plurality of spaced limbs (which are generally more or less straight and parallel) connected at alternate ends by curved loops and to hang it on the wall of the furnace in a substantially vertical position 9 by means of hooks 5--5 registering with the .tops of the loops. At the exterior of each 'depending loop I have shown an integral finger 6 loosely received in the aperture of a suitable eye-bolt 7 in order to prevent swing- 95 ing or displacement while at the same time permitting necessary expansion and contraction of the parts. The terminal 8 consists of a massive bar of metal projecting through the wall of he furnace ,and welded to t e 10 y fastened to thisterminal by any suitable ments wherein .the energy concentration is` expansion.

clamp' 10. However, I do not restrict myself to this Inode of mounting since it is equally permissible to employ fingers 6-6 at each loop, both sets of fingers being received in suitable eye-bolts 7-7 as'shown inFig. 6; or to emplov T-shaped members 12 at the top -co0perating with suitable' hooks 155-13,

while the lower ends may be prevented from swaying by any suitable means such as the downturne'd hook 14. In Fig. 8 I have further shown the velement as supported by two upwardly facing hooks 5-5', the lower hook being spaced sutiiciently to permit the desired Other expedients may also be used.

The rib 2 may run from end to end if desired, as shown in Figs. 6 and 7 or it may be discontinued for a short distance at the upper loops as shown at l5 in F i'gs.,1, 8, and 9, the base portion 1 being thickened at that point to increase the physical strength and electrical conductivity to prevent overheatingr adjacent supports. This local .thickening also facilitates gating and pouring. In case the resistor is too long to cast in one piece the sections are preferably terminatedwith- 'in the limits of this portion 15 as shown in Fig. 9, the gap being filled in by welding.

It will be understood that the employment of varying thicknesses of metal at different parts of the same cross section, as exemplified for instance in the use of one or more longitudinal ribs, exhibits advantages not wholly confined to heating elements made by casting, since the provision of an increased emissive surface available for the radiation of heat as compared with the cross-sectional" area available for the conduction of the electricity which generates that heat is a valuable feature in all massive-type heating elehigh. -I do not, therefore, limit myself further than is required by the prior art.

Having thus described my invention vv hat I claim is:

1. A resistance heating unit made of a cast alloy which shrinks on setting and comprising a flat section having one or more ribs projecting from the plane of said flatsection.

2. A resistance heating unit made of a cast alloy which shrinks on solidification` and comprising a` base section and a longitudinal rib projecting from one'side thereof.

3. A resistance heating unit made of a cast made of a heat resisting alloy which shrinks on solidiiication.

6. A cast resistor heating element of serpentine shape, having straight legs of T section and loops of flat section, the loops having a larger cross-sectional area than the egs. 7. A cast metal electric resistance heating grid formed of a bar of substantially T-shaped, cross sectional shape looped upon itself to provide a plurality of vertical parallel portions connected at alternate ends by curved portions.

8. A cast metal resistor for electric furnaces consisting of a sinuous grid having straight legs of ribbed section connected at alternate ends by integral loops.

9. A cast metal resistor for electric fur- In testimony whereof, I hereunto affix my` signature.

FRANK A. FAHRENWALD.

alloy which shrinks on solidification and com- I prising a base section having a longitudinal rib projectin from one side thereof and spaced from oth marginal edges.

4. A resistance heating unit made of cast metal in serpentine shape, the body of the same comprising a base section and a longitudinal rib projecting from one side thereof.

5.A A cast resistor having a T section andl

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