US1319002A - Electric heater - Google Patents

Description

P. M. HULBERT.

ELECTRiC HEATER.

APPLICATION FILEDY on. 31, 1910. RENEWED JAN. 15.1919.

Patented Oct. 14,1919.

2 SHEETS-SHEET I.

P. M. HULBERT.

ELECTRIC HEATER.

APPLICATION FILED OCT. 31, 1910. RENEWED JAN Patented Oct. 14, 1919.

PRESCOTT M. HULBEBT, OF DETROIT,

ELECTRIC HEATER,

Specification of Letters Patent.

Patented Oct. 14, 1919.

Application filed October 31, 1910, Serial No. 589,938. Renewed January 15, 1919. Serial No. 271,337.

To all whom it may concern:

Be it known that I, PREsco'rr M. HULBERT, a citizen of the United States of America, residing at Detroit, in the county of Wayne and State of Michigan, have invented certain new, and useful Improvements in Electric Heaters, of which the following is a specification, reference being had therein to transformed commercial electrical current.

Heretofore, various constructions of carployed for developing heat, buthave proven unsatisfactory for various causes among which are first, the combustible nature of the material when heated beyond the tem' perature of ignition, second, the varying resistance under different conditions which render it diihcult to control the heat and current consumption, third the necessity for using a large current volume at low pressure which requires the transformation of the 30V commercial currents available, fourth, the difficulty in fashioning the material into the desired form and spaced dimensions with the requisite mechanical strength and proper electrical resistance. For these and various other reasons carbon heating units are objectionable and unsatisfactory.

It is the object of the present invention,

first, to obtain a method of constructing carbon heating units of any desired form and dimensions; and to impart to each unit an independently selected and predetermined electrical resistance according to the heating effect desired, second, to protect this unit from destruction through combustion and from xcessive heat and. at the same time-to developtherewith high ten'iperatures, third, to place the unit in an accessible position so that the worlo may be conveniently inserted into "and renamed from the zone of high heat, fourth, to provide an effective heat insulation and to guard against loss of heat through com'ccliion when the heating cham; hm' is open. These and other objects are accomplished y the construction as hereinafter describcdyy- I In the drawings,

Figures 1 to 4 are diagrammatic perspective views illustrating the method of constructing the carbon resistance element;

Figs. 5and 6 are similar views showing a modified construction;

Fig. 7 is a verticalcentral section through a protected unit designed for furnace construction;

Figs. 8 and 9 are respectively longitudinal and cross section through a modified form of protected unit;

Fig. 10 is a section through another modification; 7

Figs. '11, 12, and 13 show modifed contructions of resistance elements;

Fig. 14 is a view similar to Fig. 7 of a modified furnace construction,

Fig. 15 is an elevation of the slitted unit having extended dead ends;

Fig. 16 is aperspective View of sectional units designed for a rectangular furnace construction Fig. 17 is a horizontal section showing the connection of the terminals to the resistance; and Fig. 18 is a horizontal section of the resistance after the slitting and'before removing the core.

My improved heating unit is constructed ofsubstantially pure carbon and thus differs from constructions in which mixtures of carbon and inert refractory materials have been employed. Preferably I employ graphitic carbon of that variety which has the electrical current. This slitting may be I performed in various ways, but as shown in .Fig. 3, the tube or cylinder is slitted alternately from opposite ends C, C, the slits being uniformly spaced and the series eX- tending completely around the cylinder, with terminal portions D, D of somewhat greater ection. In slitting, the depth of t :2 cut is less than the thickness of the all of the cylinder and consequently all of the sections between the slits are tied together, and the rigidity of the cylinder is not impaired. The slitted cylinder is then engaged with a suitable chuck or holder lil and is bored in a lathe or other tool. to remove the solid inner shell F, leaving the sections between the slits "tree from each other with the exception of the connection portions at opposite ends. As a result a zig body is termed, the resistance of which is determined by the munber of slits, and the selection of this resistance is not limited by reason of the original size or dimensions of the tubular body, but may be varied. as predetermined.

In place of slitting the body D longitudinally, it may be cut into a spiral form as shown at G Fig. 5, leaving the same uncut inner shell, and subsequently boring through this shell as shown in Fig. (3.

An electrical resistance formed as above described may be practically constructed suitable for use with available con'm'iercial' currents without transformation to reduce the 'oltage. it however, such a resistance were to be heated above the ignition point and exposed to the atmosphere, it would soon be destroyed by combustion and even where protected by embedding in a body of refractory material the same result will follow after a greater length of time. in fact it has been found practically impossible to protect such a resistance by any method heretofore employed. 1 have overcome this difficulty in several alternative ways, first, by protecting the resistance with a use formed of the same material but suitably spaced for insulation, second, by inclosing the resistance with a different material of a refractory nature and in which it is hermetically sealed so as to prevent any access of free oxygen to the carbon while under high heat and at the same time permitting tree transmission of the heat to the work, third, by limiting the tempeinture developed in the resistance to a point below that of ignition.

As shown in Fig. 7, the first of the aboife referred to constructions is employed, that is the inclosingg of the resistance in a case of the same or similar carbonaceous material, the detail construction being' as follows:

The protecting case is formed oft an upper and a lower section ll. ll each being provided with outer and inner annular walls ti? and H. The inner wall. surrounds the chamber in which the work is to be placed while the annular space between the -which separates the ends of the resistance from contact with the base ring H of the case and also preferably attords side supports to hold the upper portion ot the re sistance from contact with the case. The terminal connections for the resistance pass out from the case through an extension thereot which as shown comprises the lateral hollow extension H upon the upper section H and the re'gis'teringdownwardly extending tubular portion H on the section ll. llithin these extensions are arranged the terminal conductors l which are suitably fashioned to be maintained out of contact with the case and to extend from a bcarin; on the resistance 1 to the outlet end of the tube H. The terminals are rigidly attached to the resistance by a mechanical joint and as shown this consists oil a screw 1* of the same material as the terminals and the resistance and clampin the same together. The lower end of each terminal suitably supported in insulating material as indi cated at J. This may be the same as that employed at J, or if desired a less retractor materia as it will not be subjected to as high a degree of heat.

lVith the construction thus jl'ar described the case for the resistance and its cornice tions will. effectually protect the latter from oxidization as it is evident that bctore oxygen from the atmosphere can obtain access to the heated resistance it must pass through the case, and in so doing will become neutralized by union with the -arbon forming the carbon monoxid gas. This gas will have no detrimental ctl'cct upon the resistance whatever tmi'ipcraturc the latter may be h ated to. It is however. necessary to protect the case from destruction and also to provide suitable heat insulation to prevent waste of current. and a means of access "tor the in sertion and removal of the worl: from the heated chamber. This I accomplish by the use of an external gas-tight jacket which is lined with a refractory heat insulating material and is open at the bottom in registration. with the chamber ll" to permit access to the latter. This case will maintain a nonoxidizing atmosphere about the resistance and its protecting case for the reason that the heated gases within the case bcing' under higher vapor tension. will not commingrle by convection with the external atmospheribe ncath. in other words. th tendency is for the gases to rise. and where the cold atmosphere beneath the case is tort-ed upward through the orifice in the bottom by any disturbance, it will be expelled without comminglingby the greater tension of the inner atmosphere.

H is evident from the above description that the outer jacket it gas-tight. above the base, will prevent any exchange ol gases other than that by dillusion, which is too slow to produce a detrimental elicct. Upon lll) the first heating of the resistance the oxygen in the atmosphere Within the jacket will at! tack the carbon of the case H but as soon as the supply is exhausted or neutralized, further oxidation is prevented by the gaseous atmosphere thus developed. Thus the resistance is guarded from injury as long as the protecting case is preserved and the life of the latter depends on the amount of free oxygen or oxidizing gases contained within the jacket each time that it is heated. The amount of gas in an empty jacket would produce but a slight oxidizing effect, but where refractory insulating material is placed within the jacket as a lining this may operate as a holder for'.oxidizing gases, particularly sowwhere there are any carbonates present. I therefore preferably provide a protection for the case H formed of carbonaceous material preferably pulveriz ed charcoal. This may be placed to completely surround the case H without any danger of short ci'rcuiting the electric circuit, and it is evident that any oxidizing gas penetrating this material .will be neutralized before it can reach the carbon case. By the term envelop as employed in the claims is meant. anything that envelops,

whether it be a gas, solid or combination of elements. As shown in detail in Fig. 7, K is a base ring supported on a suitable standard K and apertured at K for accessto the heater. Upon this ring is mounted the case H supported by the tubular extensions H, the supports being held up a sufficient distance to diminish loss of heat in a downward direction to the base. The jacket L is also supported on the ring K and consists of an outer gas-proof wall L preferably formed of metal, and an inner wall L which may be formed of a more refractory material. The inner wall is spaced from the jacket H a sufiicient distance for forming the charcoal containing chamber which preferably connects with a tube L extending upward to the top of the jacket and provided with a detachable gas-tight cap L.

This permits of renewing the supply of charcoal when necessary. Between the walls L and I isplaced a suitable heat insulating material, such as infusorial earth, calcined magnesium oxid or other refractorybodies which are poor heat conductors.

The terminals I are connected with metallic conductors M which are coupled by any suitable means (not shown) with the electric circuits. The work-isinserted and withdrawn from the heating chamber H by suitable means that shown consisting of a re fractory supporting plate N connected/to a vertically extending shank N also of refractory material, and coupled with a slide N upon 'the standard K. The shank N" serves to raise" the support N into the heating chainber,-while the slide N operated by vention but consisting in the integration of the refractory material which is first in a comminuted state, and in which the resistance is embedded. fected by high heat and is carried to such an extent as to form not only a case but a gasproof seal. Thus the surface of the body is either completely fused or is glazed by a more fusible material to form the seal.

Still another modification is shown in Fig. 10 in which the bare resistance I is supported on a refractory insulator base such as H, is surrounded by a jacket L having an inner lining L of a refractory material impervious to the gas and around which the heat insulating material P is placed. I Vith this construction the work is inserted and removed from the jacket as in Fig. 7, and upon heating the resistance is exposed to the oxygen within the heating chamber, but as soon as this is neutralized, will be protected by the lining L from further oxidation. The life of such a resistance is necessarily limited but may be maintained for a sufficient length of time to be of practical service.

Various modifications in the construction of the resistance may be made, as shown in Figs. 11 to 16. Thus in Fig. 11a flat plate Q of graphite is slitted and is provided with terminal connections Q, mechanically engaging the same. In Fig. 12 an arch-shaped construction is formed by a slitted segmental plate R, and in Fig. 13 a slitted dome-shaped construction S is shown. All of these modifications may be employed as elements in any of the protected constructions referred to and illustrated in Figs. 7, 8 and 10. Fig. 14 illustrates another modification which may be employed for a heater of limited length of life and consists of a spiral resistance T surrounding a mutiie or inner case T and itself surrounded by at protecting case formed of alternate layers of carbonaceous material and refractory insulating material T and T The spiral is connected at opposite ends to terminal connections T insulated from-each other by the layers T of insulating material. There is also an outer jackct T with a heat insulating lining T" but not necessarily a gas-tight construction. With this modification the length of'life is limited to the time in which the carbon layers of the outer case remain un- The integration is efconsumed, but during this period the resistance will be protected and a high degree of heat may be developed therein.

My invention is applicable to various uses, but is particularly adapted for the developof metallic resistances generally employed. Thus in the construction shown in Fig. 7 a sufliciently high heat may be developed to fuse platinum silica and other bodies having even a higher fusing point, without any detrimental action upon the furnace itself. In fact there is no limit to the degree of the heat except that at which the carbon vaporizes, as the refractory insulating base may be carried down to a point where it is out of the zone of highest heat. Thus as shown in Fig. 15, the resistance may be formed of a slitted cylinder U having dead ends U extending downward below the poles of the electric current and supported on an insulating base U An intensely high heat may therefore be developed within the portions of the graphite forming the electric circuit, but the temperature of, the lower ends of the bars U will be sufficiently low to avoid destroying of the insulating material.'

lVith the construction as described in use when the current is passed through the slitted resistance, heat will be developed first in the resistance and then by radiation will pass to the carbon case which will rise in temperature at near the same speed as the resistance itself.- The outer wall of the case being in contact with the charcoal body will impart heat to the latter through conduction, and as the ignition point of the char coal is lower than that of the graphite, the former will first be attacked by the oxygen of the atmosphere within the inclosing jacket, this will rapidly convert the free oxygen as well as any carbon dioxid which may, be liberated from the heat insulating material into carbon monoxid, which being fully saturated with carbon will not attack the graphite resistance or its case. Thus the resistance will be protected by the gaseous envelop which together with the carbon walls of the case effectually excludes any free oxygen. During the period that the furnace is under heat, the high vaportension within the heating chamber and the upper portion of the jacket, will preventany exchange of atmosphere by convection, and furthermore, the moisture which is always present in the charcoal and heat insulating material, where the furnace is used intermittently, will cause a constant slow generation of carbon monoxid gas and hy drogen by decomposition of the water vapor in contact with the heated charcoal. This gas will pass out the orifice in the base of the jacket where-it will be burned, and any oxygen carried into the furnace by the introduction or withdrawal of work therefrom,

will be; consumed by uniting with this carbon monoxid gas. \Vhenever it is necessary the cap L may be removed and the supply of charcoal surrounding the graphite case renewed. The charcoal is held from falling ment of high heats above the fusing point out at the base by a retainer wall V of refractory material but at any time when it is desirable to remove the charcoal or any ash accumulating at the bottom of the case, the outer jacket may be lifted off, thereby providing access to all the parts inclosed therein.

lVhile I have shown the resistance with only two terminal connections, it is obvious that intermediate terminals can be extended from the case to permit of varying the resistance for different voltages and to pro duce different heating effects.

What I claim as my invention is:

1. An electrical heating unit, comprising a carbon resistor, a carbon shield for protect ing said resistor from atmospheric convection, and means for rendering the atmosphere reactively neutral to carbon at contact temperature.

2. An electrical heating unit, comprising an integral carbon body slitted to increase the resistance thereof, a carbon case for protecting said resistor from atmospheric convection, an insulator support for said resistor in said case maintained at relatively high temperature, and means for maintaining an atmosphere containing carbon and oxygen reactively neutralto the carbon at contact temperature.

3. An electrical heating unit, comprising an integral carbon resistor body slitted to increase the resistance thereof, a. carbon case for inclosing said resistor spaced therefrom to maintain atmospheric insulation, and a refractory insulator support for said resistor within said case.

4. An electrical heating unit. comprising an integral carbon resistor body slitted to increase the resistance thereof, a carbon case inclosing said resistor and spaced therefrom to maintain atmospheric insulation, a re fractory insulation forsupporting said re sistor within said case. and means external to said case for developing and maintaining an atmosphere reactively neutral to carbon at contact temperature.

5. An electrical heating unit, comprising an integral carbon body vertically slitted to form a series of zigzag sections, a carbon case inclosing said resistor and spaced therefrom to maintain atmospheric insulation. a refractory insulator support for said resistor within saidcase, engaging the ends of said sections, and means external to the carbon case for developing and maintaining an. atmosphere reactively neutral to carbon at the temperature of contact with said resistor.

6. An electrical heating unit comprising a fashioned in contour slitted carbon body,

and a protecting gas-tight case therefor forming a chamber open tothe external atmosphere at a point below the slitted portion of said body.

refractory heat insulating lining. to said jacket, and a carbon body surrounding said slitted body and insulated therefrom forming an oxygen-proof shield therefor.

9. An electrical heating unit comprising a fashioned in contour slitted carbon body, a surrounding gas-proof case therefor, means for developing a non-oxidizing atmosphere within said case enveloping sald body, and a refractory insulating support for said body within said case.

10. An electrical heating unit comprising a fashioned in contour slitted carbon body forming the resistance element, a carbon case surrounding said element and spaced therefrom, a refractory insulator support for said resistance element within said case, terminal connections and an extension of said case from which said terminals pass out of the zone of heat.

11. An electrical heating unit comprising a fashioned'in contour slitted carbon body of annular form, constituting the resistance element, an annular carbon case mcloslng said body, a refractory insulator support for the resistance within said case, and a gasproof jacket surrounding said case forming.

' a chamber opened to the external atm'ospher'e in registration with said chamber within said annular case.

12. An electrical heating. unit comprising a vertically slitted carbon body'constituting the resistance element, and a refractory elec-' trical insulator support for the lower ends of the sections which are between the slits of said body.

13. An electrical heating unit comprising a slitted carbon body, and an insulator support for the ends of the sections of said slitted body.

14. An electrical heating unit comprising ,aslitted carbon body constituting the resistance element, means for maintaining a non-v oxidizing gaseous atmosphere about said element, and a refractory insulator support for said' elementengaging the ends'of the sections thereof.

15. An electrical heating unit comprising a slitted carbon body surrounding a work chamber and constituting the resistance element, 'a gas-proof ja'cket surrounding said resistance element and forming a chamber opened at the bottom in registration with said work chamber, means for maintaining a non-oxidizing gas within said jacket and chamber, anda refractory insulator support for the ends of the slitted sections of said body within said jacket.

16. An electrical heatin unit comprising va verticallyslitted-carbon ody constituting the resistance element, a refractory insu lato-r support for the lower ends of the slitted section, and carbon terminal connections mechanically joined to the ends of said slitted body lead ng outward therefrom.

17. An electrical heating unit, comprising a combustible resistor, a case surrounding said resistor having an opening thereinv for the insertion and withdrawal of work, and means for maintaining a non-oxidizing gas surrounding said resistor and. between the same and said openin in the case.

18. An electrical ,heatlng unit, comprising 'a combustible resistor arranged to form adj aeent thereto a work chamber, a case surrounding said resistor having an opening in its bottom providing access to said work chamber for the introduction and withdrawal of work, thermal insulation interposed between said resistor and case, and means for maintaining a non-oxidizing gas within said work chamber around said resistor, and between the same and the opening in said case. v

In testimony whereof I afl'tix my signature in presence of two witnesses.

PRESCOTT M. HULBERT. Witnesses:

JAMES P. BARRY, 'L. J. WHI'ITEMORE.

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