US1751408A - Electric furnace - Google Patents

Description

March 18, 1930. c. IPSEN 1,751,408

ELECTRIC FURNACE Filed Oct. 23, 1924 Fig. I.

f lnvnfior Carl L. Ipsen,

b His Attor nes.

Patented Mar. 18, 1930 cant L. IPSEN, or scnmmctrsnv, NEW YORK, ASSIGNOB.

- rm, acon.ronarron or NEW zro GENERAL ELEcrBrcooM- YORK Enterit s summon 'Application filed October 23, 1924. Serial in. 745,511.

My invention relates to electric furnaces,

more particularly to electric resistance furnaces, and has for its'object provision ofimproved means for supporting the heating resistor. v f

More specifically my'invention-has reference to electric resistor'furnaces which operate at comparativelyhigh temperatures, such' that the margin of temperature difi'erence is very. small between the normal operating tem perature of the furnace and the temperature at which oxidation of the heatin resistor takes place, With a resistor made 0 a nickel-. chromium alloy this. maximum operating temperature is approximately 1000 to 1100 p 0., due to the limitations imposed by the resistor. Such furnaces are used in the heat treating annealing, etc. of metals. i i

In or er to obtain the highest possible safe operating temperature without injury to the heating resistor, the temperature -difference between the heating resistor and the interior.

of the furnace chamber is made as small as possible. A reduction of this temperature difl'erence'makes a corresponding increase in the safe operating temperature of the furnace. A- low tem erature difference is most readily obtained mounting, the resistor directly in the heating chamber so that heat so is radiated freel from the resistor to the charge. Such a urnace is sometimes termed a direct heat furnace to distinguish 'it'from a muflle type furnace in which the resistor is placed behind mufiles through which the heat must be conducted to the furnace chamber. With the direct heat, furnace the char e is heated evenly by radiation and once the eek ing-up period is over there is but little temperature difier'ence between the resistor and 43 the furnace chamber.

One method of supporting the resistor in the direct heat furnace is to hang the resistor on suitable insulators which are secured to the furnace wall.

' porting insulators constitute extensions on the bricks forming a partof the furnace wall. In shape, the resistor has taken theform of a series of depending loops which are hung on the supporting insulators along the side walls of the furnace. The depending loops somedirect contact withthe insu v manner brought indirect contact with the in no 'oxi ation. It is thus safe operating temperature of the-furnace is invention these metallic the form of ring like metallic members which- In some cases thesesup; bar secured to the.

times hang free and sometimes pass around i and under another set of insulators. 3

When the resistor is hun on insulators in sulators, Ihave found that. theresis'tor operates at higher temperatures .atthepoints of contact with the insulators; This'is' due to the fact that radiation and conduction of heat 'from the resistor is obstructed at these points by the insulators which are verypoo'rfheat conductors. The resistor insome" instances has failed at these-points. of, support-or engagement with the insulators due tooverheating andexcessive oxidation, while the atorsor is'inany' remaining portions of the resistor forming a preponderance of its length showed little or very materially reduced by thehigher operating temperature ofithe resist'onat these apparent that the points. Furthermore, when the loops depend' I or hang entirely free there atendency for them to become distorted upon repeated heat-. ing and cooling so that they ma engage each other, causing short-circuits'. oreover, the use of supporting insulators built into the wall or permanently secured to the wall-makes it diflicult or impossible to change the spacing ofthe loops for the the amount of heat part of the furnace chamber.

In carrying out my invention I su purpose of varying pport the resistor directly on members having good heat conductivity and also having a very small area of contact with the resistor. This generated in a particular.

form of supportofi'ers the least possible imr pediment to the radiation and conduction ofv heat from the resistor at the points of support. Theresistor is therefore maintained at a uniform temperature. In one form of my The' spacing of the convolti supports may take of the. resistor may be varied ing theresistor to freely expand and contract as awhole in heating'and cooling.

For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 is a sectional elevation view of an electric furnace embodying my invention; Fig. 2 is an enlarged fragmentary/view in perspective showing the su ports for the resistor; Fig. 3 is an view showing casing 16. The endwalls of the furnace are also constructed of heat refractory material,.

one about being remoi'able to afford access to the heating chamber.-

The furnace chamber is heated by means of resistors hungalong its' walls, two. resistors 17 and 18 hung adjacent the side walls being shown. These resistors are preferably formed from a ribbon of nickel-chromium alloy or other suitable resistance heating material, which ribbon is bent in zig-zag conformation nto a serles of convolutions comprising "a lurality of "vertically extending straight ength 19 joined by upper bends 20 I and lower bends 21., Obviously, however, the

resistor may be cast-to'liave the desired conformation. Each resistor is secured to a bar 22 made of a suitable heat refractory electrically insulating material, such as aluminum oxide. This bar is secured to the wall of the furnaces near the top of the wall, and the resistor is secured to the bar, so as to hang therefrom, by means of metallic ring shaped members or loops 23; forming supports for the resistor, passing around the bar and under the upper bends 20 of the resistor.

24 are provided in the upperedge and sides' These loops are made from a suitable heat resisting material having good heat conductivity which may be the'same as the material of the resistor. To facilitate assembly the loops may be formed from U-shaped lengths of wire the ends of which are joined over the upper edge of the.bar by twisting them together, as indicated at 23. Suitable grooves of the bar in which the supporting loops23 are seated and by means of which the loops are secured in proper spaced relation on the bar,

and the convolutionsof the resistorthereby properly spaced. Preferably these grooves,

24 are rovided-on the bar at relatively short .interva s, so that the spacing of the convoluc3 tions ofthe resistor maybe varied at any time by adjusting the supporting loops 23 on the bar. In making this adjustment the loops may be loosened by untwisting the ends. The loops may also be made large enough to be lifted out ofthe grooves and slipped along the bar as desired. 7

The bar 22 is secured to the wall of the furnace by-lneans of metallic pins 25 which aresecured inspecially constructed bricl-zs 26 forminga part of thefurnace wall. For the purpose of securing or anchoring the pi ll. 25 in the bricks 26, the inner ends of the pins may be bent at right angles and seated in suitable recesses in the bricks. For example, a groove 27 is formed in the top of each brick '26 together with a recess 28 at the inner end of the groove. When the bricks 26 are laid into the wall, the pins 25 are slipped in place 7 in the groove and recess and secured therein by the next tier'of bricks. The pins 25 are made of a suitable heat resisting material which may be the same as the material of'the resistor. Suitable spacing electrical insulators 29, prefe'rablywasher shaped, are placedon the p1ns-25 between the bar 22 and the wall whereby thebar is spaced away from the wall, and the resistor consequently hung in spaced relation to the wall. The object in hanging the resistor in spaced relation to the wall is to prevent obstruction by the wall of the free radiation of heat from the resistor. Apertures .may be provided in the bar through which the pins 25 extend when thev bar is placed thereon. The bar may be secured on'the pins, for example, by means of cotter pins 30 in the ends of the pins.

; If desirable the bar 22 may be substantially equal in length to the length of the heating chamber, ora plurality of short bars may be provided and secured to the furnace wall in end to end relation.- This latter construction has certain advantages since each short bar may be supported by a single brick 26, for example, by means of two pins 25 secured to the briclo With this construction the spacing of the "pins can be more-easily made to correspond with the spacing of the holes in the bar.

The lower ends of the convolutions of each resistor are attached to a second insulating bar 31 which is similar in construction to the bar 22/ It is, however, turned so'thatthe grooves 32 are on its sides and lower edge. Metallic loops 33 sim ilar to loops '23 pass around the bar andover the lower bends 21 of the resistor, i. e.', through'the convoluti'ons, whereby.-- the bar-33 is hung from the convolutions of the resistor. This lower bar 31 is not secured in any" way to the furnace wall and therefore the resistor is free to expand and contract as a whole upon changes in temperature. The lower ends of the C011:- volutions of the resistor,'however, are spaced apart by thebar 31 and are thus prevented from twisting and curling and thereby formits entire lengt ing short-circuits around sections of the resistor. Also, the weight of the lower bar 31 keeps the lengths'19 of theresistor straight.

The loops 33 may be adjusted along the length of the bar 31 to vary the spacing of the lower ends of the convolutions of the resistor in the manner described with reference to loops 23.

I have found that during use a marked permanent growthor increase in length of the resistor occurs whichiis'much greater than thenormatincrease in length'when the resistor isheated. [The lower bar 31 is'therefore spaced above thefflo or of the furnace .a

distance greater than the normal increase in lengthof the resistor .due to heating to reventthe bar from coming to rest on the ottom of the furnace'fwhenjthis growth of the resistor takes place. To give the lower bar greater freedom, the twisted ends of the loops v 33 may be arranged on the side of the bar as shown in Fig. 2;- p -By means of this construction theresistor is supported in a spaced relation with respect to all heatand electrically insulating parts. The only parts actually'in engagement with the resistor are the-supporting oops 23 and the-lower loops '33whicjhare made-of a material havinggood heat conductivity. Consequently any appreciable rise in temperaturedue to obstruction of heat radiation is prevented at the points of engagement be tween-the'loops andthe resistor. .Moreover, by means of this'construction the area of contact between the resistor. and the parts in engagement with it is made'very small and thereforethe actual obstruction of heat radiation from the resistor is'reduced to a-mimmum. The result. is a resistorwhich is supported with the smallest possible contact with other parts of thefurnace and which has heat conducted, rapidly away from these small points of contact. The resistor therefore op erates at a uniform temperature throughout It will be observed that wn ue the resistor as a whole hangs free and can expand and contract independently of its supports, the va rious convolutions forming the resistor do not de end or hang free. I

Whi e I have described my invention as embodied in concrete-form and as operating in a specific manner in -ac cordance with the provisionsof the patent statutes, it should ben nderstood that 1 do not limit my invention thereto, since various modifications thereofcuring said member to said wall in spaced relation therewith at intervals along the length of said member, a sinuous heating resistor in said chamber, and members having good heat conductivity engaging'and supporting said resistor and attached to said elongated member so that said resistor is hung therefrom in spaced relation to said elongated member and said wall so as to provide for free radiation of heat from said resistor whereby hot spots are prevented when operating. close to temperatures producing oxidation of the resistor material.

2. An electric furnace comprising a heat refractory wall forming a' heating chamber, a heat refractory bar, a plurality of supports for securing said bar to said refractory wall in spaced relation therewith at intervals along the length of saidbar, a heating resisf tor formed of'a plurality of vertically arranged loops, a second heat refractory bar substantially parallel with said first bar, 'me tallic members securing the upper ends of said loops to said first bar so that said resistor is hung therefrom and metallicmembers securing said second bar to the lower endsof said loops so as to suspend said second bar, said metallic members providing for free radiation of heat from said resistor whereby hot spots are prevented when operating close to temperatures producing oxidation of the resistor material. v

3. An electric furnace comprising a heat refractory wall forming a heating chamber,

an elongated membermade'of electrically insulating material secured to said wall in spaced relation thereto, a-resistor shaped ina plurality of substantially straightlengths joinedat their adjacent ends by bends to form a continuous conductor. and metallic mem- ,bers connecting said bends to said elongated members so as to suspend said resistor in spaced relation with saidelongated member and said furnace wall to provide for free radiation of heat from said resistor whereby hot spots are prevented when operating close to the temperatures producing oxidation of the resistor material.

4, An electric furnace comprising .a heat refractorywall forming a heating chamber, an elongated member made of electrically insulating material structurally independent of said wall secured to said wall inspaced relation thereto, a metallic resistor comprising a series of convolutions joined by bends, and metallic memberscooperating with said-bends forming mechanical connections between said resistor and said memberwherehy said resistor is hungfrom said member in spaced relat-ion to said member and said wall, 'so as to provide for free radiation of heat from said resistor said metallic members being adj ustable so that the spacing of said convolutions may be varied, and means for adjusttiOnSi secured to said wall in spaced relation thereto, a resistor constituting a series of spaced convolutions, and members carried by said bar for securing said resistorthereto, said members being adjustable-on said bar to vary the spacin" of said convolutions.

6. An e ectric furnace comprising a heatrefractory wall forming a heating chamber, a

bar made of electrically insulating material secured to said wall in spaced relation thereto, a resistor'constituting a series of spaced convolutions, and metallic ring shaped members encircling said bar for securing said resistor thereto said members being adjustable longitudmally of said bar to vary the spacing of said convolutions.

.7. An electric furnace comprising a heat refractor wall forming a heating chamber,

a pair 0 elongated members made of electrically insulating material in said chamber structurally independent of said wall, a heating resistor comprising a series of convolu' tions, connecting members made of a material having a high heat conductivity securing the convolutions'of said resistor to said members to provide for free radiation of heat from said resistor wherebyhot spots are prevented when operating close to the temperatures, producing oxidation .of the resistor mate;

rial, and a mechanical connectionbetween one of said members and said wall'whereby said resistor and said other memberare hung therefrom.

8. An electric furnace comprisin aheat refractory wall forming a heatingohamber,

a bar made of electrically insulating material in said chamber secured horizontally to said 7 wall in spaced relation thereto, a resistor,

comprising a plurality of vertically extending lengths joined at their 'adjacents ends to form a continuous conductor, supporting connections between said bar and said resistor comprising metallic members connecting said resistor to said bar at the junctions between the upper ends of said lengths so as to suspend said resistor in spaced relation with said bar and said furnace wall to provide for free radiation of heat from said resistor whereby hot spots are prevented, a second bar made of electrically insulating material and metal lic connecting members securing said second bar to said resistor at the junctlons between the lower ends of said lengths to provide for free radiation of heat from said resistor, said resistor and said second bar being hung from said first bar.

9. An electric furnace comprising a heat refractory wall forming a heating chamber, a bar made of electricallyinsulating material extending longitudinally of said cham- ,heat conductivity connecting said second bar to the lower ends of the said convolutions at the junctions thereof.

10. An electric furnace comprising a heat refractory wall forming a heating chamber, I

upper and lower bars made of electrically insulating material in said chamber, a heat- 7 ing resistor in said chamber comprising a plurality of vertically extending lengths joined by bends, metallic supporting members connecting said resistor to said upper bar at the upper bends of said resistor, metallic members connecting said lower bar to the lower bends of said resistor so that said lower bar is supported by said resistor both sets of said metallic members being longitudinally adjustable on said bars, and a plurality of spaced metallic pins'forming a mechanical connection between said upper bar and said wall whereby said resistor and said lower 'bar are hung from said upper bar.

11. An electric furnace comprisin a heat refractory wall forming a heating 0 amber, a bar made of electrically insulating material secured to said wall in spaced relation thereto,

a resistor constituting a series of spaced convolutions, metallic memberssccuring the con-. volutions of said resistor to said bar so that said resistor is hung from said bar, a second bar made of electrically insulating material, and metallic members securing said second bar to said convolutions so that said bar is hung from said resistor, said metallic mem bers being adjustable on said bars to vary the spacing of said convolutions.

12. An electric furnace comprising a heat refractory wall forming a heating chamber, a bar made of electricallyinsulating material secured to said wall in spaced relation thereto, a resistor constituting a series of spaced convolutions, metallic ring shaped members encircling said bar for securing the convolutions of said resistor thereto, a second bar made of electrically insulating material, and metallic ring shaped members encircling said second bar and interlinking said convolutions whereby said second bar is hung on said resistor, said ring shaped members being adjustable on said bars to vary the spacing ofsaid convolutions. ;;1-9

13. An electric furnace comprising a'heat refractory wall forming a heating chamber,

metallic pins secured in said wall projecting my handthis 22nd day into said chamber, a bar made of electrically insulating material carried by said ins in spaced relation to said wall, a resistor ormed into a series of convolutions, and metallic members made of a material similar to said resistor securing said resistor to said bar so that said resistor is hung from said bar in spaced relation to said bar and said wall.

In witness-whereof, I have hereunto set of October, 1924. CARL L. IPS EN.

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