US2787457A - High temperature furnace - Google Patents

Description

April 2, 1957 D. A. BOGDAN HIGH TEMPERATURE FURNACE 2 Sheets-Sheet 1 Filed May 14, 1954 I INVENTOR. 17. ,4. 506129.

HIGH TEMPERATURE FURNACE David A. Bogdan, West Orange, N. L, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 14, 1954, Serial No. 429,930

4 Claims. (Cl. 263-41) The present invention relates to furnaces and, more particularly, to a high temperature hydrogen furnace for treating projection lamp filaments.

the manufacture of projection lamp filaments the sectional coil is first Wound on a steel mandrel on a conventional automatic coil Winding machine. The wound coil is then degreased and annealed in a hydrogen atmosphere at 1300 C. for about one half hour. The coil is then cut to length, as on a rubber wheel. After dissolving the steel mandrel in alternate solutions of hydrochloric acid and caustic and rinsing in hot and cold water the coils are dried and inspected.

Zrior to bending the coil into a plurality of aligned sections to form a projection lamp filament, the coil may be mounted on a tungsten mandrel and pro-fired at a temperature desirably about 1800 C. in a hydrogen atmosphere. However, owing to the defects of the conventional high temperature (about 2000 C.) hydrogen furnaces (where it would be desirable to bake the coils) they are annealed instead on the aforementioned mandrels for 5 minutes. After bending the sectional coils into the plurality of sections desired, on an automatic bending machine, the coils are again baked at about l650 C. for approximately /2 hour to set the bent coil. The baked bent coil is removed from the refractory metal mandrel and the now formed filament is then trimmed and prepared for mounting on a filament mount stem. At present these coils must be reset by hand at a subsequent flashing operation to obtain optimum spacing. This last operation would be eliminated, if the coils were rigidly set as would be accomplished by the subject invention.

The best coil condition for bending is the soft state. The bending operation tends to Work harden and increase the rigidity of the coil. Further, it has been found that the prefiring operation at 1800 C. and the hydrogen bake after bending at about 1650 C. for at least /2 hour in the heat zone can be eliminated. Instead the bent coils may be baked at 2200 C. for about minutes in hydrogen.

Conventional 2200 C. hydrogen furnaces are limited in size to about 2. Vs" inside diameter and a 14" length of heating tube or mufile. This size is unsatisfactory for the handling of a large scale production of projection lamp filaments. In considering a 2200 C. hydrogen furnace of larger capacity it is impossible to fabricate a one piece mufile long enough to be practical and heavy enough to be sturdy. The maximum volume of tungsten capable of being worked is limited. by present known n'tEil'lOClS of manufacture.

in addition conventional 2200 C. hydrogen furnaces must be rebuilt about fifteen times. a year due to erosion of the tungsten tube, poor electrical contact and sa ging. it has been felt that even the best of refractories or high temperature insulators, for example zirconia, tends to attack the tungsten tube in the region of about 2000" C. Refractories have been defined as materials Patented Apr. 2, 19.57

2 of construction whose major purpose is the confinement of heat. The life of refractories in furnaces is affected by one or more of the following: mechanical abrasion, shrinkage expansion, deposition of solids in the pores by gases, chemical combination with gases, and other materials. Conventional furnaces, in which the tungsten tube is in contact with the high temperature insulation, zicronia, would be limited as to maximum temperature. Again, it is a known fact that all high temperature insulation becomes electrically conductive at very high temperatures. Thus, the electrical losses of high temperature insulation themselves, for example at 2200 C. result in diversion of energy from the work in the mufile and at the same time reduce the insulating value thereof.

The conventional high temperature hydrogen furnaces also suffer from a linear expansion of the mufie. At temperatures in the neighborhood of 2200 C. this linear expansion of the muffie may amount to about bi change in muffie length per 36" of muffle length.

Hence, it has been found advantageous according to the present invention to provide a 2200 C. hydrogen furnace of suificient capacity to handle large lots, for example, of projection lamp filaments, and which will overcome the defects of prior art high temperature hydrogen furnaces.

The non-sag mufile or the heating element of the furnace of the invention comprises a plurality of longitudinal refractory metal strips or slabs fabricated in the form generally of an open ended cage and clamped to terminal plates of the furnace by means of dogs. In addition, the terminal end plates are water cooled thus keeping the electrical connections at a substantially constant temperature and providing little change in clamping pressure. The thicker tungsten slabs employed in the muffle will prevent erosion of the heating mufile and will eliminate poor electrical contact.

To overcome the electrical conductivity of high tern; perature insulators, the lower slabs of the heating mufile are mounted on a plurality of bridges, the feet of which are relatively cool enough to safely be in contact with the high temperature insulation. In addition, the insulation is further protected by separating the tungsten mufile slabs from the insulation by molybdenum reflectors. Linear expansion of the heating muffle is compensated for by the employment of corrugated end portions affixed to the terminal cover plates of the furnace.

. To reduce any additional throal losses at the unloading end of the furnace an insulated throat portion is'disposed between the terminal plates and the water cooled end portion of the cooling charnbcn In addition, asled type baffie may beprovided at each end of the furnace to prevent excessiveend losses therefrom.

In its general aspect the present invention has as its objective a high temperature hydrogen furnace which prevents failure of the high temperature insulation and compensates for linear expansion of the refractory metal u l A specific object of the invention is an improved heat rnuflle for a high temperature furnace of increased capacity and of restricted sagging.

Another object is a flexible terminal cover plate for a high temperature hydrogen furnace for providing constant temperature electrical contact and permitting the linear expansion of theheat mutlle.

An additional object is a novel mufile bridge to protect the insulation from high temperature and to reduce electrical conductivity of said insulators.

Other objects of the present invention will become apparent to those skilled in the-art to which it appertain's as the description thereof pr0cecds...both by. direct-reel 'tation thereof, andby implication of thecontexts:

rt /ems? a o Referring now to the drawing in which like numerals of reference indicate similar parts throughout the several views:

Fig. l is a vertical sectional view of the high temperature hydrogen furnace of the invention.

Fig. 2 is a vertical sectional view of the high temperature hydrogen furnace of Fig. 1 along the line IIII of Fig. l in the direction of the arrows and showing the means for mounting the refractory metal slabs of a heat muflle of the furnace of Fig. 1 to a flexible water cooled terminal cover plate.

Fig. 3 is a vertical sectional view of the furnace along the line liI-JII of Fig. l in the direction of the arrows, and showing details of the heat muffle, the heat muffle mounting bridge and the refractory metal reflectors.

Fig. 4 is a perspective view of the novel heat muflle mounting bridge of the invention.

Fig. 5 is a view similar to Fig. 3 but showing an alternative embodiment of the furnace structure employing a sectional cylindrical heat mufile capable of heating by radio frequency or high frequency current.

Referring now to the drawings in detail the reference numeral designates a high temperature hydrogen furnacc. The furnace it), particularly Fig. 1, has a generally open ended box-like refractory metal shell 12 fabricated, for example, from a suitable moderate temperature iron, such as black iron, and secured for example to a frame l4. A row of a plurality of upstanding refractory bricks l6 may rest on a bottom portion of the shell 12. These bricks 16, may for example, be suitably 2000 F. (1048 C.) brick. A layer of horizontal refractory bricks 18 suitably 3000 F. (1660 C.) brick maybe juxtaposed between the bricks 16 and a refractory metal floor 20, suitably molybdenum plate. It will be understood that a plurality, for example 2 in the present showing of Fig. l, of heat muffle bridges 22 rest on the floor and support, as hereinafter explained, a heat or heat container muffle 24.

The heat muflle 24 is surrounded by a plurality of refractory metal reflectors 26, suitably molybdenum, for example, 3 above and 2 below the heat mutfle 24- in the present showing of Figs. 1 and 3. The lower reflectors 26 (Fig. l) are broken or interrupted to permit the passage therethrough of the heat mufiie bridges 22. Below the lower refractory metal reflectors 26 a double layer of horizontally positioned zirconia bricks 28, capable of withstanding 2400" C., may be positioned on a plural layer of horizontally positioned high temperature bricks 39, capable of withstanding about 1800" C. As shown in Fig. l the end portions of the refractory metal reflectors 26 are insulated by vertical upstanding zirconia bricks 2S and are separated from a pair of resiliently mounted terminal plates 32 thereby.

It will be understood that above the upper refractory metal reflectors 26 (Fig. l) a similar layer of zirconia bricks 28 followed by successive layers of bricks I8 and 16 is provided. Vertical upstanding zirconia brick 28 is likewise provided to shield the end portions of the refractory metal reflectors 26 and to separate them from the terminal plates 32. As shown in Fig. l the furnace 10 is provided with a loading chamber or tube 34 on the left hand end of the furnace 10 and an unloading or cooling chamber 36 on the right hand end of the furnace 1-3 when viewed in Fig. 1.

As shown in Fig. 1, sled type baflles or heat retainers 38 may be provided in the loading tube 34 and the cooling chamber 36 to minimize end losses therefrom during the loading and unloading operations. Further, the portions of the loading tube 34 and the unloading tube or cooling chamber 36 adjacent to the terminal plates 32 may be suitably insulated, for example with fused alumina grains, capable of withstanding a temperature of 1800" C. The alumina is packed about the tubes 34 and 36 between the tubes themselves and their outer shells 40.

It will be understood that the outer shells 40 of the tubes 34 and 36 project inwardly and are secured by their peripheral flanges and bolts 37 to the terminal plates 32 to further minimize end losses therebetween.

Terminal plates Each of the terminal plates 32 (Figs. 1 and 2) has a fenestrated casting or body 44, of for example bronze, provided with a hollow spiral water cooling inner portion 46 for maintaining the body 44 and electrical connection: 4-? (Fig. l) at a constant temperature. A generally rcc tangular resilient end mounting plate 59 provided with annular corrugations 52 is secured to the inner face of the ends of the body 44, as by bolts 54 (Fig. 2), to permit expansion of the refractory metal heat muffle 24 during the high temperature operation of the furnace 1G in the neighborhood of 2200 C. The outer edges of the plate 50 are connected to the shell 12 of the furnace at; by bolts 56 extending through insulators 58 carried by the shell 12. The high temperature insulators prevents a short circuit from one end of the furnace 7.9 to the other.

The heat muffle 24 having an internal volume of, for example 4" x 4 x 36" comprises a plurality of 10 in the showing of Figs. 1 and 3, refractory metal slabs :56 arranged in the form of an open ended cage. Each of these slabs 63 extends beyond the shell 12 and is provided with L-shaped end portions 62 which are secured against the outer faces of the terminal plates 32 by suitable dogs 6-4 and bolts 66 which are threadable into the body 4 of the end plates 32. It will be understood that two dog-- 6dare provided, one at each end of the furnace i for each of the slabs 60. Each of the dogs 64 is prov st. with a suitable longitudinal adjustment slot (Fig. 2) for the proper positioning of the respective slabs 69 thereby.

Molybdenum reflectors As shown particularly in Fig. 3 the molybdenum rcflectors 26 have a plurality of, for example, 3 arch-like members 68 which surround the cage-like heat muflie 24 in spaced nesting relation by means of spacers 59. The outer arch-like member 68 is independent of the self supporting zirconia brick 23. Underneath the heat muffle 24 a plurality of layers, for example 2 in the showing of Fig. 3, of inverted refractory metal channels 7d are pro vided to form the bottom reflectors 26. It will be understood that the bottom layer of the channels 76 rests on a flat reflector plate 71 of the furnace.

Bridges Each of the refractory metal heat muffle bridges 22, for example tungsten (shown in Figs. 1 and 4) may comprise an inverted V-like arch 80 provided with a plurality, for example 4, bridge retaining member locking slots 82. The slots 82 may be aligned in pairs in a vertical plane suitably perpendicular to the longitudinal axis of the arch S0 and for the securement therein of transverse brick retaining members 84 by interlocking complementary registering inclined vertical slots 86 in the members 84 with the slots 82. It will be understood that each of the bridges 22 may be assembled without riveting or welding thus preventing the collapsing of the arch 80 during the high temperature operation of the furnace 10 in the neighborhood of 2200 C.

Each of the sled type baflles 38 (Fig. l) is an A-like refractory metal member, suitably molybdenum. The baflies 38 have one inclined side resting on the bottom of the loading tube 34 (on the cooling chamber 36) with its cross piece 90 disposed outwardly respectively toward the loading and unloading end of the furnace 10. By this positioning of the baflles 38, a hook may be inserted within either the loading chamber 34 or the unloading chamber 36 to Withdraw the bafile 38 and to permit respectively either the loading or unloading operation. It will be understood that each of the baflles 38 is of sufiicient size to substantially till the end portions of the tubes 34 and 36 and thus prevent end losses therefrom.

Alternative embodiment In the showing of the alternative embodiment of Fig. 5 a sectional refractory metal heat baffle 24a comprising a plurality of small cylinders 100 may be employed. Each of these refractory metal cylinders 100 may be hydraulically pressed from powdered tungsten with about 3" outside diameter, a 2 /2" length and A" wall thickness. To approximate the length of the heat muffle 24 of Figs. 1 and 3 it would be necessary to employ 14 of the cylinders 100.

The cylinders 100 of the heat mufiie 24a are supported by a pair of refractory metal (handily tungsten) longitudinal supports 102 of generally inverted V-like cross section. The supports 102 in turn may rest on a plate of zirconia insulation 107. Refractory metal plates 106, for example of molybdenum, are disposed between the zirconia plates 107 and successive layers of high tem perature insulation 18a and 16a respectively. The heat muftle 24a, as in the prior case, is surrounded by the arch like members 68 of the molybdenum reflectors 26 separated one from the other at their upper portions by refractory metal spacers 69 of molybdenum. The bottom portions of the members 68 are separated and insulated, one from the other by high temperature insulation, such as zirconia bricks 28a. An R. F. coil 110, suitably copper tubing is disposed about the refractory metal reflectors 26 and the lower insulation 28a, 18a, and 16a. The coil 110 rests in transverse grooves 112 in a longitudinal asbestos spacer 113 resting on the outer member 68 and suitable transverse grooves 114 provided in a pair of bottom guides 116, of suitable high temperature insulation material, such as the bricks 16a.

Operation After the slabs 60 of the heat mufile 24 (Figs. 1-3) have been heated by electrical power through the connectors 48 and the terminal plates 32 to the required high temperature operation in the neighborhood of 2200 C. and the desired hydrogen atmosphere within the furnace has been produced, a hatch, not shown, on the outer end of the loading tube 34 is opened and the sled baflle 38 is withdrawn to permit the loading of a large number of work pieces through the loading tube 34 and into the heat muffie 24. The sled baffle 38 is then returned to its prior position within the loading tube 34 adjacent to the heat muffie 24, thus minimizing end losses from the heat muffie 24.

After the desired treatment at 2200 C. in the hydrogen atmosphere within the heat muffie 24, a hatch (not shown) on the outer end of the cooling chamber 36 is opened and the cooling chamber sled bafile 38 is withdrawn from the cooling chamber 36, as by means of a hook. The treated work pieces are then withdrawn from the heat muffle 24 into the cooling chamber 36 and allowed to cool for any predetermined length of time with the hatch (not shown) on the cooling chamber closed. At the end of the cooling period the hatch (not shown) of the cooling chamber 36 is again opened and the now treated cooled work pieces are withdrawn from the cooling chamber 36. The sled type heat baffle 38 is inserted into the cooling chamber 36 adjacent to the heat muflle 24 to again minimize end losses therefrom and the cycle is then repeated.

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

1 claim:

l. A high temperature furnace comprising a shell, a resiliently mounted terminal plate about each end of said shell, high temperature insulation within said shell and said terminal plates, a refractory metal floor plate embedded within said insulation, a plurality of refractory metal br dges on and in contact solely with said floor plate, a refractory metal heat muffle on said bridges comprising a plurality of longitudinal slab-like members ar ranged in an open cage-like configuration and a plurality of refractory metal reflectors upstanding from said insulation in spaced nesting relation about said heat mufile.

2. A high temperature furnace comprising a shell, a resiliently mounted terminal plate about each end of said shell, high temperature insulation within said shell and said terminal plates, a refractory metal floor plate embedded within said insulation, a plurality of refractory metal bridges on and in contact solely with said floor plate, each of said bridges comprising an inverted V-like arch provided with bridge retaining member locking slots and a plurality of bridge retaining members in said slots.

3. A high temperature furnace comprising a shell, a resiliently mounted terminal plate about each end of said shell, each of said terminal plates having a body provided Lth means for water cooling and a resilient end mounting plate about said terminal plate and provided with annular corrugations thereon, high temperature insulation within said shell and said terminal plates, a refractory metal floor plate embedded within said insulation, a plurality of refractory metal bridges on and in contact solely with said floor member, a refractory metal heat muille on said bridges comprising a plurality of longitudinal slablike members arranged in an open cage-like configuration and a plurality of refractory metal reflectors upstanding from said insulation in spaced nesting relation about said heat muffle.

4. A high temperature furnace comprising a shell, a resiliently mounted terminal plate about each end of said shell, high temperature insulation within said shell and said terminal plates, a refractory metal floor plate embedded within said insulation, a plurality of refractory metal bridges on and in contact solely with said floor member, a refractory metal heat mutfie on said bridges comprising a plurality of longitudinal slab-like members arranged in an open cage-like configuration, each of said slabs being mounted by means of adjustable dogs to said terminal plates, and a plurality of refractory metal reflectors upstanding from said insulation in spaced nesting relation about said heat mufile.

References Cited in the tile of this patent UNITED STATES PATENTS 1,520,408 Ebeling Dec. 23, 1924 2,099,967 Spencer et a1 Nov. 23, 1937 2,277,595 Levy et al. Mar. 24, 1942 2,457,846 Strickland Jan. 4, 1949 2,468,456 Ness Apr. 26, 1949 2,548,485 Lubbock Apr. 10, 1951 FOREIGN PATENTS 637,923 Germany Nov. 6, 1936

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