US2640861A

US2640861A - Resistance furnace

Info

Publication number: US2640861A
Application number: US197684A
Authority: US
Inventors: Harry C Kremers
Original assignee: Harshaw Chemical Co
Current assignee: Harshaw Chemical Co
Priority date: 1950-11-27
Filing date: 1950-11-27
Publication date: 1953-06-02
Anticipated expiration: 1970-06-02

Description

June 2, 1953 H. c. KREMERS 2,640,861

RESISTANCE FURNACE Filed Nov. 27, 1950 INVENTOR;

H.C. KREMERS ATTY.

FIG. 3

Patented June 2, 1 953 REsIsT'ANcE FURNACE Application November 27, 1950, Serial NO.19,7;6 84

(Cl. r'13---.25-)

GlCIaims.

This invention relates to a furnace suitable fOIa use in roducing macrocrystals, especially those which are produced-athigh temperatures. More specifically the invention relates to a portionofsueh a iurnace which may be referred to as a. top heater.

In the production of macrocrystals, the material from which the crystal is to be produced is melted in a cruciblaand the crucible containing is moved from'a' compartment which is at atemperatureahove the melting pc the material slowly into. a compartment which is maintained at a temperature somewhat below--themelting point of the material. By adjusting the speed at which the crucible moves to the rateat-Whi h thecrystalgrows; the liquidsolid boundary can 'be maintainedatthejunction of thetwo compartments mentioned. Prior to the presentinvention it has been'proposed to use graphite heating-elements furnaces of this kind, both generally cylindrical elements. for. heating the vertical: Walls of the cylindrical. crucible and fiat, circular elements for heating. the top of thecrucible. Accordingly, I do: not

claim Nbroadly thegeneral arrangement. of. the.

heatingelements, but-only the specific'construo-H tion as set forthin the appended claims The present invention hasreference .to provements in the .tonheater. and. to its relation.

to-other elements inthe furnace, having as its:-

principal object the rovision. of. a. novel top heater which will present to thetop. surface-of; theunaterial in the crucible. a substantiallynniformly heated. surface covering.substantially the entire area Witl'iinthe cross section. of. theside: heater.- Aiurther ohjectis to.provide..-a shield. surrounding the. top: heater and tending/ to. smoo hout any slight irregularities not removed. by heating element design; whereby to. main: tain -With'in the heated. compartments as. .much. as possible of the heat generated Within thefurnace. Other objects .will become apparent. as the description proceeds.

In theaccompanyingdrawings, Figs. 1 and:2 are top plan views of. the two complementary. heatin elements making up. the .top heater; Fig 3 is averticalfragmentary sectional. View through.

furnace embodying theinvention, and. {l is; a fragmentary view corresponding approx-imately I to the line 4-- l ofFig: 3, omittingeverythingex ceptthe two .heatingelements .andthesupporting ring for jthetonshield.

Inthemlrawings, the numeral i ll indicates generally a. turnaoesh'ell which: may beicomposed of: steeband providedswitht a Jacket I I iorthe -cir+ culation of cooling.- 'fini'd',-suitably water: Within source of electric current. maybe maintained ama temperature approximatin-g that of *the innersurfaceof the-shell 10,

preferably a little higher, by-adjusting its cross section: to avoid any great heating dueto-passage of current, or by water coolihg by :meansofinternal passages, or bybeing ccmposedof 1 material of-'goodsheat conductingproperties. Secured to the upper-ends of the conductorsHare-surrporting lihks l3 .which may be attached to -theconductors l2 by means of studs Hi.

other: ends, thec-linl zs 1 l3 serve tosupport-and energize a pair orto -neater: elements I tend ll These mayhespaced apart by means ofblocks ll; andfthe elementsJ3," is, it, andl'i may all be: secured-together hy means of bolts l All these elements; i 2 Ate-l filinclusive, rnay be com poseduof -carbon, preferably graphite;-

Byc:reference...to Figs. 1 and 2, it will be seenthat the-.heatin elements. i5 and were con-- verted .by'..means-.of saw-cuts into substantial-1y ribbon;form theevarious reaches ofwhichare of approidmatelyithe same widthand cross section- With. the .exceptionthatat the turns the Width -is r not uniform. It will be seen that the saw outs inthe elementdifi eX-tend atfan' angle 7 to those: in the element IB'L-Whereby' When they are superposed,

the saw-cutsxwill intersect-at substantial angles These angles are :not critical, it -being. important only that'the saw -cuts in the upper-and lower heaters I5 land. ISintersect-at a-subs-tantial angle.

In: no case can the-ang1e-exceed 9O since if the woplateswere superposedand rotated, as soon as...the angle of. intersectionwould reachthere would: :be uponnfurther rotation, an intersection: atlanangle.of lessthan 90. A small opening 9 in the: center of each or the elements It .andmlfii is.:usefulsfor receiving a probe, notshown; which: may .be: employed for determining the; height. of i the. solid-liquid boundary in the materialb'ein'g treated; and; also results in-asaw-gout following an arcuate path wherebythe outside-ireaches 2 G :are '..of .isuhstantially uniform- Widthh Itf will. be sseenvthat when the elements. lfikandxlt are superposed, thecol'cl corners 2 I willl not lie zone .abovelthelntherabut willl be positioned m spaced.angularsrelaticnz to each: vowelmas-- much as the outer-most edges of the

elements

15 and 16 project beyond the side-heater, which is generally indicated by the numeral 22, the irregularities of heating surface not compensated for by the angularity of the saw-cuts in elements l and IE will be located at points far enough from the center that such irregularities will be unimportant in the general combination illustrated.

The side heater 22, which, per se, forms no part of the present invention, may also consist of carbon, preferably graphite, sawed to ribbon form, suitably connected to a source of current, not shown. Outside the side-heater 22 is a carbon shield 23 suitably supported and on the top of which rests a ring 24, having formed therein notches 34 through which the arms 35 of the heaters l5 and may pass without contacting the shield or the ring 24 and which supports a top shield 25, preferably also composed of carbon. superposed upon the top shield 25, which rests on the ring 26, being supported in spaced relation thereto by lugs 26, is a molybdenum sheet 21. superposed on the sheet 2! is another disc of carbon 28 upon which rests another sheet of molybdenum 29. The flange 36 of the shield carries inner and outer molybdenum sheets 3| and 32. The molybdenum sheets may be relatively much thinner than shown and are provided with bright surfaces whereby to reflect the radiant heat instead of transmitting it.

Within the side heater 22 is an elevator 33 which is movable u and down therein, and which is adapted to support a crucible containing the material to be heated.

The structure illustrated and described has been designed with primary reference to use in a vacuum type furnace and the structure other than the top heater and related structure has been shown in a diagrammatic fashion. For example, the shell IU would actually be, in practice, provided with means at the top to facilitate handling by means of hoisting equipment and the supports 12 might be provided with passages for cooling fluid which have not been shown. Again, the cylindrical shield 23 may be covered with molybdenum sheet or a pair of spaced molybdenum sheets covering the entire cylindrical surface thereof.

The principal feature of the invention is to be seen in Figs. 1 and 2, it being understood that the element I6 is superposed on the element IS, the right hand projection as seen in Fig. 1 being superposed on the right hand projection as seen in Fig. 2, and the left hand projection as seen in Fig. 1 being superposed on the left hand projection as seen in Fig. 2 whereby the saw-cuts which divide the circular portion of these elements will intersect each other at fairly sharp angles, leaving only the smallest possible area which is not covered by a highly heated portion of one of the elements, 15 or l6. Such slight irregularities as result from small uncovered portions at the intersections of the saw-cuts and the central opening l9 will be smoothed out by the shield 25 and the

molybdenum sheets

21 and 29.

Another feature of the structure disclosed is that the cross section of the links I3 is less than the combined cross sections of the projections 35 so that the links [3 will be relatively highly heated by the passage of the curent so as to supply heat to the cooled conductors [2 without pulling such heat from the heating elements I5 and I6. Thus, the cooling of the conductors l2 will maintain them at a temperature sumciently 4 near the temperature of the inner surface of the shell ID to avoid irregular heating of the material in the crucible without interfering with the function of the top heater elements l5 and 16.

Having thus described my invention, what I claim is:

l. A heater comprising a pair of spaced, approximately parallel, carbon plates of approximately the same size, each plate having deep, narrow slits formed therein and spaced to form therebetween a ribbon, the slits in one of said plates extending at a substantial angle not exceeding to the slits in said other plate at all points at which said slits overlie each other, the active heating areas of said plates together substantially completely covering an approximately circular area and substantially only such circular area, and means electrically connecting said plates to a source of current.

2. A heater comprising a pair of spaced, approximately parallel, carbon plates of approximately the same size, each plate having deep, narrow slits formed therein and spaced to form therebetween a ribbon, the slits in one of said plates extending at a substantial angle not exceeding 90 to the slits in said other plate at all points at which said slits overlie each other, the active heating areas of said plates together substantially completely covering an approximately circular area and substantially only such circular area, and means electrically connecting said plates, in parallel circuit, to a source of current.

3. A furnace comprising a generally cylindrical side heater, 2. top heater covering the upper end of said side heater and comprisin a pair of spaced, approximately parallel, carbon plates of approximately the same size, each plate having deep, narrow slits formed therein and spaced to form therebetween a ribbon, the slits in one of said plates extending at a substantial angle not exceeding 90 to the slits in said other plate at all points at which said slits overlie each other, the active heating areas of said plates together substantially completely covering an approximately circular area of approximately the size of but not of less diameter than the upper end of said side heater, means for supporting a receptacle containing material to be heated within said side heater and below said top heater, and means electrically connecting said plates to a source of current.

4. A heater comprising a pair of spaced, approximately parallel, carbon plates of approximately the same size, each plate having deep, narrow slits formed therein and spaced to form therebetween a ribbon of a width not less than about ten per cent of the diameter of said plate, the slits in one of said plates extending at a substantial angle not exceeding 90 to the slits in said other plate at all points at which said slits overlie each other, and means electrically connectin said plates to a source of current.

5. The invention as defined in claim 1 wherein further a heat reflecting shield is provided in spaced relation to one of the plates and covering the circular portion thereof for reducing loss of heat in one direction, said shield being provided with at least one heat reflecting surface covering the circular portion of said plate.

6. A heater comprising a pair of carbon plates of similar dimensions superposed one upon the other but spaced apart, each of said plates having an approximately circular portion and oppositely extending projections, said circular portion having deep, narrov-r, approximately equidistantly spaced slits formed therein and extending transversely thereof and making an angle With an axis passing through said projections and the center of said circular portion of from 85 to 20 degrees of are, being approximately parallel to each other and alternate said slits communicating with opposite edges and each terminating short of the edge opposite that with which it communicates a distance approximating the distance between said slits, thereby dividing said circular portion into a grid continuous with said projections offering approximately uniform heating characteristics over the whole heater area except at the two return bends nearest each said projection, one of said plates being a mirror image of the other as viewed from the top whereby said slits in the respective plates intersect at substantial angles and said return bends of nonuniform characteristics are oppositely located. HARRY C. KREMERS.

References Cited in the file of this patent UNITED STATES PATENTS