US1947793A

US1947793A - Electric furnace

Info

Publication number: US1947793A
Application number: US400327A
Authority: US
Inventors: Fred E O'neil; Joseph F Callahan
Original assignee: ACHESON GRAPHITE Co
Current assignee: ACHESON GRAPHITE Co
Priority date: 1929-10-17
Filing date: 1929-10-17
Publication date: 1934-02-20
Anticipated expiration: 1951-02-20

Description

Feb. 20, 1934.

F. E. O' NEIL ET AL ELECTRIC FUHNACE Filed oct. 17, 1929 2 Sheets-Sheet l v BY , ATTORNEYS.

Feb. 20, 1934. F. E. oNEn.. r-:r AL 1,947,793

ELECTRIC FURNCE Filed oct. 17, 192`9 2 sheets-shan 2 fy, C 7 INVENToRs/ BY y ATTORNEYS.

Patented Feb. 20, 1934 UNITED STATES PATENT OFFICE sistors of carbon,

I 1,941,793 ELECTRIC FURNACE l Fred E. ONeil and Joseph F.` Callahan, Niagara Falls, N. Y., assignors to Acheson Graphite Company, a corporation of New Jersey l Application October 17, 1929. Serial No. 400,327

` l 14 Claims. (Cl. 20L-75) This invention relates' to electric furnaces and in particular to electric furnaces including regraphite or the like, and to means for protecting such resistors.

Resistors of carbon or graphite when used-for high temperature work are subject to rapid deterioration because of the effect of the oxygen in the atmosphere surrounding the resistors. Many attempts have been made to render satisfactory 10 the operation of such resistors at fairly high temperatures and to extend the field of use of such resistors by providing some means for preventing oxidation of been proposed to coat refractory material.

the resistor. For example, it has These attempts have not been satisfactory and probably for the reason that it is difficult to provide such a refractory coating having the same coeflicient of expansion as the resistor proper. Furthermore, even where this difficulty has been obviated to some extent the resistors admitted through any tective coating causes at this point.

are short-lived because the oxygen minute opening in the prodeterioration of the resistor Such local action is cumulative in as it commences, the resistor heats up rapidly at this particular point and the oxidation then The formation of such hot spots in the rate.

proceeds at a more rapid resistor is very objectionable and is one of the problems with which the users of electric furnaces have been confronted at all times.

It has also been proposed to enclose a resistance element within a sleeve, only enough clearance being provided so as to permit removal and replacement of the resistance element. Here again local oxidation due to minute openings in the protecting sleeve materially shortens the life of the resistor.

According to the present invention resistors of carbon, graphite or the like are protected from oxidation, and the danger of hotspots resulting from local oxidation is entirely eliminated. This is accomplished without restorting to the considerable expense and labor involved in coating a resistor with an inert refractory substance. The

means which I employ for. protecting the resistor has the following advantages over the previous means used.

The resistor may be made in any it may be made in sectogether in end to end contact. The temperature of the resistor may be controlled at desired points throughout its length by'varying the cross-sectional area of the resistor sections.

In general,

/ according to our invention the heatthe resistors with an inertl ing element for our electric furnace comprises a resistor arranged within a protective casing of a non-metallic refractory material. .The resistor comprises one or more graphitic or non-graphitic carbon resistance elements. The resistor is held in spaced relation to the walls of the casing and means are provided at the ends of the casing for sealing the space between the resistor and the casing. Thus a considerable free space is provided within the refractory casing and, while it might be supposed that oxygenin this free space would attack the resistorl and that the resistor would rapidly deteriorate, yet it haslbeen discovered that the life of the resistor is extraordinary -as compared with that of an unprotected resistance element of the same material. For example, a resistor which would not last more than a day or two when unprotected has been found to have a life in excess of three Weeks and even then the deterioration was not such as to materiallyaffect the efciency of the unit. A resistor operating Within a refractory casing having a relatively large free space surrounding it is notsubject to local oxidation, perhaps for the reason that any oxygen gaining access to the interior of the protective casing does not take effect at a single point on the surface of the resistor but becomes uniformly distributed throughout the entire free space and attacks the resistor throughout its entire surface. It has been found that such oxidation proceeds very slowly and without the formation of 'any hot spots in the resistor. The oxidation that does occur results in the formation of reducing gases within the free space surrounding the resistor and these gases tend to prevent further entrance of oxygen and if any oxygen should enter, its action on the resistor Will be very slow and will be distributed along it.

The protecting tube or casing forming a part of this invention, may consist of such non-metallic refractory materials as carborundum, silica, fire clay or other inert material, the selection of any particular material for this purpose depending in large measures upon the temperatures to be employed and the conditions of furnace operation in general., It has been found however, that a carborundum protective casing is of particular value because of its stability at very high temperatures and because of the fact that within the carborunvdum tube the atmosphere is made reducing by the We `prefer to employ means within the protective tube or casing for supporting the resistor out of contact with the wall of the protecting tube. Such supporting means may be more or less permanently associated with the protective tube but we prefer to employ supporting means in the form of annular blocks fitting securely around the rewhere the resistor comprises several resistance elements the annular members may also serve the purpose of connecting one element with another in end to end contact.

Graphite blocks provide an excellent means for supporting and electrically connecting the ends of the adjacent sections of the resistor. 'I'he lubricating action of the graphite allows the blocks and the resistors to be readily slipped through the protective tube. The movement of the graphite blocks in the tube is also facilitated by beveling the edges of the blocks. Due to the relatively low electrical resistance of graphite as compared to other forms of carbon, the resistance of the joint can be kept relatively low, and can thus be prevented from becoming excessively hot and causing the block to stick to the resistors or to the protective tube. 'I'he resistance and temperature of the joint may also be kept relatively low by making the cross-sectional area of the block relatively large.

Our invention contemplates the provision of an electric furnace including a furnace wall having an opening therein through which the resistor may extend into the furnace chamber, and from which the resistor may be removed, when necessary, without disturbing the protective tube.

Our invention also includes the use of a scavenging material, such as lamp black or other readily oxidizable material, which may be placed within the free space inside the protective tube. This readily oxidizable material will combine with any oxygen present within the tube before the resistor has attained a temperature high enough to cause oxidation of the resistor.

The various objects and advantages of our invention will be more apparent upon considering the following detailed description which is to be taken in conjunction with the accompanying drawings in which,

Fig. l is a horizontal sectional view of an electric furnace embodying one form of our invention;

Fig. 2 is a cross-sectional view of a resistor terminal and a portion of our resistor and the protectivek tube.

Figs. 3 and 4 are cross-sectional views of modified forms of portions of our resistor and protective tube.

effect an exchange of heat between the two lines of cars. This makes it necessary to have an extended furnace chamber and it is not desirable to have it heated throughout the entire length.

According to one embodiment of our invention the furnace is heated by means of resistors locat ed in a recess along the sides of the central portion of the furnace. They are encased in a protective casing or refractory tube shown at 6 and 7. 'Ihe tubes comprise a plurality of sections 8 of refractory material such as carborundum, silica or iire clay and these sections are interconned by means of collars prefer to support the resistance spaced relation to the tube by means of supporting blocks l1. 'Ihe supporting blocks t loosely in the tube and are provided with beveled edges 12 to facilitate the movement of the block within the sheath. The blocks 1l may be used only for supporting the resistor elements by projecting the elements therethrough as shown inFig. 3.

In Fig. 2 the resistor elements are connected to the supporting block 11 by a screw threaded packing is held in place by a refractory ring 16 which is urged inwardly against the packing by bars 17 having a nut and bolt 18 cooperating `therewith. The outer end of the leading in rod extends outside of the furnace wall. A fluidcooled electrical connector 19 is secured to the end of the rod to supply the current to the resistor. The connector is supplied with cooling fluid through a conduit 20 and with electricity through a conductor 21.

In Fig. 3 we have shown a modified form of a means for supporting and connecting the resistor elements 10 within which may be positioned along the resistor wherever desired. The elcments are connected by a screw member 22 preferably made of graphite. 'I'he member 22 is screwed into a bore in the adjacent ends of the resistor elements to hold them together.

In Fig. 4 we have shown a modified form of supporting and connector block 1l for the resistor elements 10. In this form a. push socket is formed in the center of the block into which may be readily removed from the tubes when necessary, but when the bores of the tubes are out of alignment, the more or less flexible coupling shown in Fig. 4 greatly facilitates the removal of the resistors.

We prefer to use carborundum tubing for the4 protective sheath because of the fact that it will stand high temperatures and also because of the fact that the decomposition products form a reducing atmosphere within the tube which helps to protect the resistance elements from oxidation. Silica, lire clay or other refractory material may be employed, but these materials are not as suitable for the high temperatures as the carborundum.

The resistor may consistl of graphite, carbon or the like, the graphite being preferable because of its temperature resistance characteristics. The resistance of the graphite `resistor is more constant throughout a wide range than is the case with a carbon resistor. f.

n We have shown within the protective tube small quantities of readily oxidizable material 23 such as lamp black which may be inserted into the protecting sheath for the purpose of combining with the oxygen which may be present in the space surrounding the resistor. 'The oxygen will unite with this carbon to form a neutral or reducing gas a't temperatures lower than that necessary for oxidation of the resistor.

The refractory protecting sheath during operation of the furnace becomes because of its relatively large surface it radiates heat elciently while at the same time it protects the enclosed resistance elements from oxidation. The resistance elements may be easily replacedv without in any way interfering with the protecting tube, and resistors of great length may be employed because a great many sections of the resistance material may be connected end to end within the protecting tube.

It is to be understood that our invention is not limited to the particular embodiments illustrated and described but includes such modifications thereof as fall within the scope of the appended claims.

We claim:

1. A heating element for an electric furnace v comprising a sealed tube of non-metallic refractory material adapted to be opened at its end, a replaceable resistance element suspended in a gaseous atmosphere within said tube, and a nonfusible support within said tube for supporting said resistance element in spaced relation to the Wall of the tube and to provide a gas space between said resistance element and said tube.

2. A heating element for an electric' furnace comprising a sealed tube of non-metallic refractory material, said tube being adapted to be opened at its end, a replaceable resistance element suspended in a gaseous atmosphere within said tube, said resistance element comprising a plurality of sections, means for electrically connecting said sections, and a non-fusible support within said tube for supporting said resistance element in spaced relation to the wall of the tube and to provide a gas space between said resistance element and said tube.

3. A heating element for an electric furnace comprising a sealed tube of non-metallic refractory material adapted to be opened at its end, a replaceable resistance element suspended in a gaseous atmosphere within said tube, and a nonfusible support surrounding said resistance element and fitting loosely within said tube for supporting said resistance element in spaced relation to the wall of the tube and to provide a gas space between said resistance element and said tube.

4. A heating element for an electric furnace comprising a sealed tube of non-metallic refractory material adapted to be opened at its end, a

highly heated and replaceable resistance element within said tube and means within said tube for supporting and suspending said resistance element in a gaseous atmosphere Within said tube, said means cornprising an annular non-fusible member secured to said resistance element andfltting loosely in said tube.-

5. A heating element for an electric furnace comprising a sealed tube of non-metallic refractory material, a resistance .element within said tube, and means within said tube'for supporting said-resistance element in spaced relation to the wall of the tube, comprising an annular member secured to said resistance element and fitting loosely within said tube, the outer edges of said member being beveled to facilitate'movement of said member through said tube. 6. A heating element for an electric furnace comprising a sealed tory material, a carbon resistor enclosed in said tube, said resistor comprising a plurality of sections arranged in longitudinal alignment with each other, a conductive support resting on the inner'wall of said tube and interposed between the .ends of said sections for electrically connecting them together and supporting them in spaced relation to the inner walls of said tube.

'7. A heating element for an electric furnace comprising a plurality of sections of non-metallic refractory tubing, means for connecting said sections end to end, a resistance element sealed within said refractory tubing, and means within .said tubing for supporting said resistance elesaid means ment in spaced relation to the tubing, comprising an annular member secured to said resistance .element and fitting loosely within said tubing, the outer edges of said member being beveled to facilitate movement of said member through said tubing.

8. A heating element for an electric furnace comprising a sealed tube of non-metallic refractory material, a carbon rod resistance element Within said tube, and means within said tube for supporting'and suspending said resistance element in a gaseous atmosphere Within said tube, said means comprising an annular graphite memtube of non-metallic refracber secured to said resistance element and fitting loosely within said tube.

9.v A heating element for an electric furnace comprising a plurality of sections of non-metallic refractory tubing, means for connecting said sections end to end, a resistance element sealed within said refractory tubing, and means within said tubing for supporting said resistance element in spaced relation to the tubing, said means comprising an annular graphite member secured to said resistance element andfitting loosely within said tubing, the outer edges of said member vbeing beveled to facilitate movement of said member through said tubing.

l0. A heating element for an electric furnace comprising a sealed carborundum tube, a graphite resistor suspended in a gaseous atmosphere within said tube and an annular graphite support for said resistor secured to said resistor and fitting loosely within said tube.

ll. A heating element for an electric furnace comprising a sealed carborundum tube, a graphite resistor suspended in a gaseous atmosphere within said tube and an annular graphite' support for said resistor secured to said resistor and fitting loosely within `said tube, and a material more readily oxidizable than said resistor inserted in the space between said resistor and said tube.

12. A heating element for an electric furnace comprising a sealed tube of non-metallic refractory material, a carbon resistor enclosed in said tube, said resistor comprising a plurality of sections arranged in longitudinal alignment with each other, a conductive support resting on the inner wall of said tube and interposed between the ends of said sections for electrically connecting them together and supporting them in spaced relation to the inner walls of said tube, and a material more readily oxidizable than said resistor partially filling the space between s'aid resistor and said tube 13. A heating element for an electric furnace comprising a sealed tube of non-metallic refractory material, a carbon resistance element suspended in a gaseous atmosphere within said tube in spaced relation to the walls thereof` for free circulation o! rgases about the resistance element and a material more readily oxidizable than the resistance element llin'g a small portion of the space between said resistance element and the wall o! said tube.

14. A heating element for an electric `furnace comprising a sealed tube o! non-metallic refractory material, a carbon resistance element sus pended in a reducing atmosphere within said tube in spaced relation to the walls thereof for free circulation of gases about the resistance element and finely divided lamp black lling a small portion of the Space between said resistanoevelement and said tube.

FRED E. ONEIL. JOSEPH F. CALLAHAN.