US2404060A - High temperature furnace - Google Patents

Description

July 16, 1946.

R. D. HALL ETAL HIGH TEMPERATURE FURNACE Filed Feb. s, 1944 Patented July 16, 1946 NIT-ED PTEN T 'OLFF l 2,404,060

HIGH TEMPERATURE FURNACE -Roy lI). Hall, fMillington, and -Emlo Romanelli, Bloomfield, N. 'J., assignors to Westinghouse Electr'ic Corporation, East Pittsburgh, Pa., .fa Vacorporat'ion of Pennsylvania Application 'February 3, 1944, Serial No. 520,874

(CLIS- 7 Claims. 1

'This invention relates to furnaces, Aand more particularly, to such adapted *for temperatures high enough 'to sinter andp'therwise heat treat, tungsten and molybdenum.

The principal object of our invention, 'generally considered, isa furnace -adapted'to-eiciently producetemperatures above `1700 C., 'whereby it may beused'for sintering and-/or vheat treating refractory metals such las vtungsten andmolybdehum.

Another object of our inventionis aiiurnace for high tempertures comprising an 'element formed of tungsten or 'molybdenum wire or rods adapted to be heated to incandescence bythe passage of electric current therethrough and arranged to surroundthe material to be' heated, and a series of enclosing reiiecting baffles and associated cover platesv supported on a refractory block, with means for sealingsaid enclosure and admittingprotective atmosphere thereto, `as well vas means vfor conveniently removing the enclosure for the application and `withdrawal of the material being treated.

Other objects and advantagesof the invention, relating to the particular arrangement andconstruction of the various parts, `will become apparent as the description proceeds.

Referring to the drawing:

Fig. 1 is an axial sectional viewpartly.in elevation, of a furnace embodying our'invention and showing an article in place therein, as representative of material which maybe heat treated.

Fig.'2 is a horizontal 'sectional view on the line II-Il of Fig, 1in the direction .of the'arrows.

Fig. 3 is an axial sectional View of the peephole eyepiece assembly.

Furnaces designed for temperature above about 1700o C. cannot contain the usual type of refractories because `the latter are incapable vof withstanding such high temperatures.

Beryllia, Zirconia and .thoria will withstand higher than usual temperatures, lbutthe rst ,is very expensive andzirconia and thoria vare dithcult to use because of vthe lack of shock resistance. Carbon resistor furnaces, .known as Arsem furnaces, are not usable with .hydrogen Yor other protective atmosphere ,required for fabrication of such materialsastungsten and molybdenum.

Tube furnaces involving molybdenum or tungsten tubes may be heated electrically and material such as wire drawn through Vsuch tubes so heated. These are Asatisfactory for small long articles but lcannot be adapted for larger Work. Induction Yfurnaces are diicult to use with protective `atmospheres Vat high temperatures.

rfor t'he furnace.

We have designed a furnace capable oi providingtemperatures up to 2000o C. where molybdenum is used as a heating element, and up to about 2500D C. where tungsten is so used. These furnaces are particularly adapted for treatment of refractory articles, as in -following the invention describedand claimed in the Hall et al. application, Serial No. 511,392, liled November 23, 1943, now replaced by- Serial No. 579,080, nled February-Zl, i945, which refers to the lfurnace which is here claimed.

Theprinciple involved in our furnace is to use the radiant Aheat from wires, bars or Slabs of molybdenum or tungsten disposed around the body 'to be heated. 'Such heating means is, `for insulating purposes, surrounded by reflectors disposed at appropriate distances, the rst reflector being of sheet vmo'lybdenum or tungsten, the former `of which is generally satisfactory, the remaining reflectors being-of molybdenum and/or stainless steel either chromium plated or not, finally ending up with one or more silver plated steel and/or copper reflectors. The last reecting means may be Veither arseparate unit or part of a Water-cooled jacket used as an outer cover The heating element is enclosed in these layers of reflectors and a peep hole is desirably provided at the end of a tube for purposes of temperature measurement. The

vcovering of suchva lpeep'hole-device is preferably korderfto cool them, Iso that refractories such as alumina canbe used for support. Where rods of tungsten :or molybdenum vare used, connectors of drilled cars can be employed. The entire furnace yand shell or jacket is desirably mounted as a unit and designed to be placed on a flat plate of refractory material. IThe shell must be extended kfar enough below'the heated elements to use the furnace -for Aprotective atmospheres such as hydrogen, nitrogen, argon or a mixture of gases, or evacuated and used asa vacuum iurnace. For vacuum purposes the outer contact of this furnace shell and plate can be sealed, as by means of a suitable cement.

The stand carrying the base plate is desirably equipped for exhausting or introducing the atmospheres required and the plate carries on its face a container or stand for supporting the material, article, or articles, to be heat-treated. This stand may be made of molybdenum or tungsten coated with beryllium oxide or thoria, either as discs or powder at the point of contact with the material to be heat-treated to prevent welding. The purpose of this stand is to carry in the optimum heat zone the materials undergoing treatment.

For purposes of loading the furnace, arrangements can be made for either raising the insulating housing or lowering the stand, whichever is more convenient. Furnaces of this type are satisfactory to furnish temperatures sufficiently high to sinter or coalesce tungsten to high density for fabrication purposes if the proper protective and/or reactive atmosphere is used during the treatment.

Referring to the scale drawing in detail, like parts being designated by like reference characters, there is shown one embodiment of our invention comprising a radiation type furnace 42 consisting of a base 43 which may be formed of transita other suitable refractory, or even a metal plate where a vacuum is desired, upon which is supported a preferably circular plate 44 of Alundum, or the like. The plate 44, in turn, holds a hollow cylinder 45 of beryllia or zirconia, carrying a supporting cap 46 of similar material, on which during the sintering operation the treated articles, (or article) such as the refractory metal worm 3|, rests.

The furnace 42 comprises an outer fluid-cooled casing 41, which may consist of hollow copper cylinders 4B and 49 coaxially arranged and connected by annular spacing elements and 52 of brass, or other suitable material, brazed or otherwise suitably connected thereto, forming an annular space through which water may be circulated, as from the inlet pipe 53 to the outlet pipe 54. The inner plate 49 may extend into the annular cavity 55 at the base 43 for support and sealing, as by said cavity holding a sealing liquid, not shown, or if evacuated or holding gas under pressure, by a suitable cement. The inner surface of the water jacket plate 49 is desirably silver plated to minimize the radiation absorbed thereby, and closed at its upper end by a watercooled hollow plate 56 formed of suitable metal, such as copper or steel.

The top plate 56 may be sealed inside of and to 64 and 65 pass, the lower ends of said guides being embedded in the base 43. Alternatively, the studs 51 and 5B may connect directly with one of the elements 5| and 62.

The heating means for the furnace, in theu| present embodiment, comprise a molybdenum or tungsten resistance device, which may be a wire 66 (or if of a large size, rods suitably connected in series) receiving power from leads 61 and 68 passing through the water-cooled plate 56 and suitably insulated therefrom, said device being strung down and up over the annular, desirably Alundum, lower and upper spool members 69 and 1| formed with radial elements 12 and 13 around which the individual loops pass between slots therebetween, said slots being subsequently closed by desirably Alundum retainer rings 14 and 15. The spools and rings are desirably bound together by covering plates 16 and 11, of molybdenum or other suitable material.

The heat developed by the resistance element is conserved by a series of bailies, the inner one 18 desirably comprising sheet molybdenum polished on both sides, or if very high temperatures are desired similarly polished sheet tungsten may be used. The next baffle 19 is desirably formed of stainless steel, chromium plated on both sides or of molybdenum. The remaining three baffles 8|, 82 and 83 are desirably formed of steel sheet, silver plated on both sides, all of the baffles being supported from the upper plate 84 ofthe cylindrical water jacket, also desirably formed of steel, silver plated on both sides, as by means of bolts 85 and 86 and top cover plates 19', 8|' and 82,', desirably respectively formed of material like that of the plates 19, 8| and 82.

In order to allow for inspection of the article, such as that designated 3|, during the heat treat- `ment thereof, the upper plates 19', 8|', B2' and 84, as well as the plate 6D, are all provided with aligned apertures preferably coaxial with the furnace and the vertical section of the inlet pipe 81, to the top of which a valve 88 is shown applied.

The housing 9| of this valve is desirably provided with a horizontal annular web portion 92 terminating at` its outer end in an upstanding threaded iiange portion 93 providing a socket or bezel for the reception of a transparent eyepiece 94, desirably formed of quartz or high-melting-point glass, as shown in Fig. 3. The eyepiece 94 desirably rests on packing means 95 and is secured in place by an annular retainer 96, thereby providing a peep hole device for sighting down axially of the furnace, through the eyepiece 94, the valve 88 when opened, the vertical section of the inlet pipe 81, and the apertures previously referred to in the upper horizontal plates.

From the foregoing disclosure it will be seen that the furnace may be used to heat articles of tungsten or other refractory metal, to the high temperatures necessary to effect the final sintering operation, by radiation from an incandescent refractory resistance element, the heat being conserved by polished ancl/or bright plated baffles, the whole enclosed in a water jacket, and the articles or material during treatment being surrounded by a protective atmosphere, such as wet hydrogen, introduced through the upper pipe 81, and exhausted through the lower pipe B9.

Although a preferred embodiment of our invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

1. A furnace for high temperatures comprising a refractory metal element consisting of a series of sections, to be heated by the passage of electricity therealong, disposed as the elements of a hollow cylindrical surface and arranged to directly radiate heat upon material to be treated, and a series of reflecting hollow cylindrical elements coaxial with said metal element, the inner of said elements being formed of polished molybdenum, intermediate elements consisting of stainless steel, chromium plated on both sides, and outer elements consisting of sheet steel, silver plated on both sides.

2. A furnace for high temperatures comprising a refractory metal device to be heated to incandescence by the passage of electricity therealong, elements thereof being arranged to surround and directly radiate heat upon material to be treated, a base of refractory material formed with a groove, a series of vertically movable reflecting baffles and an outer casing surrounding said heated element, a pair of stiffening rings secured to said outer casing, rods with their lower ends embedded in said base and guidably passing through holes in said rings, and at least one of said baffles extending below the lower edges of the others and telescopingly received in said groove when in normal position.

3. A furnace for high temperatures comprising a refractory metal element consisting of a series of sections, to be heated by the passage of electricity therealong, disposed as the elements of a hollow cylindrical surface and arranged to directly radiate heat upon material to be treated, a series of surrounding reflecting hollow cylindrical elements and an outer casing disposed coaxially therewith, stiffening means secured to said casing, means closing the upper ends of said reflecting elements, a base, rods with their lower ends embedded in said base and guidably passing through holes in said rings, and means for lifting said reflecting elements and associated refractory metal element, with the stiffening means sliding on said rods, in order to allow for the introduction and removal of the material to be treated.

4. A furnace for high temperatures comprising a refractory metal element to be heated to incandescence by the passage of electricity therealong, arranged to surround and directly radiate heat upon material to be treated, a series of reflecting baffles and an outer casing surrounding said refractory metal element, means closing the upper end of said series of baffles, a series of peep holes through said closing means, a pipe alined 6 with said peep holes and passing through said casing, a valve the housing of which is secured to said pipe, said housing having an outer socket, and an eye piece in said socket and through which the material undergoing treatment may be viewed when the valve is open.

5. A furnace for high temperatures comprising a refractory metal element shaped as a series of sections, to be heated by the passage of electricity therealong, and arranged to directly radiate heat upon material to be treated, and a series of reflecting hollow cylindrical elements successively surrounding said metal element, the inner of said elements being formed of molybdenum, intermediate elements consisting of stainless steel, and outer elements consisting of sheet steel.

6. A furnace for high temperatures comprising a refractory metal device, to be heated to incandescence by the passage of electricity therealong, arranged to form elements of a hollow generally cylindrical surface to surround and directly irradiate heat upon material to be treated, a base of refractory material formed with a groove, a series of reflecting baffles surrounding said device, at least one of said baffles extending below the remainder and telescopically receivable in said groove, and means for guiding said baies during raising and lowering thereof with respect to said base.

'7. A furnace for high temperatures comprising a refractory metal device, to be heated to incandescence by the passage of electricity therealong, arranged to form elements of a hollow generally cylindrical surface to surround and directly irradiate heat upon material to be treated, a series of surrounding reflecting hollow cylindrical elements of varying diameters disposed coaxially with respect to said surface, a base for said furnace, means for lifting said reflecting elements and associated refractory metal device with respect to said base, and means to guide said elements during raising and lowering operations.

ROY D. HALL. EMILIO ROMANELLI.

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