US1271760A - Electric furnace. - Google Patents

Description

C. A. PFANSTIEHL.

ELECTRIC FURNACE.

APPLICATION mu) ocr. 30. ms

Patented July 9, 1918.

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C. A. PFANSTIEHL.

ELECTRIC FURNACE.

APPLICATION man OCT. so. me.

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CARL A. PFANSTIEHL, 0E HIGHLAND PARK, ILLINOI$, ASSIGNOR '10 PFANSTIEHL COMPANY, INC., OF NORTH CHICAGO, ILLINGIEL A CORPORATION'OF NEW YORK.

IEIlliEC'lRIC FURNACE.

Specification of Letters Patent.

Patented J ulyf), 191 8.

Application filed October 30, 1916. Serial No. 128,399.

To all whom it may concern.

Be it-known that I, CARL A. PFANs'riniiL, a citizen of the United States, residing at Highland Park, in the county of Lake and State of Illinois, have invented a certain new and useful Improvement in Electric Furnaces, of which the following-is a full,

clear, concise, and exact description, reference being had to the accompanying drawings, formingza part of this specification.

=My invention relates to electrically heated furnaces for reducing the oxids of metals to their metallic forms, and is particularly designed for andusefulfor the reduction of tungstentrioxid W 0 to metallic tungsten powder.

-.It has been found that tungsten metal made :from fine and regularly. grained or "POWdQI'Gd'lLHHgStEHlS superior as to its malleability ito tungsten made from coarse grained powder. ltyhas also been found that the process which the powder -must undergo to change it from its powdered state into the state of solid metal is more readily and more satisfactorily carried out if the powdered metal is very fine and regular. It has also been found that very line and regular tungstenpowder may be compressed into ingots or other articles having sufficient strength that they may be readily handled, oreven'worked, whereas llrlS impossible to compress more coarsely -.grained tungsten into such solid and workable ingots or articles.

One oflthe elements which aids in the production of finely grained tungsten powder .is the reducing furnace in which the caused by the union of the hydrogen with the liberated oxygen before this water has an opportunity toreunite with the tungsten. It has been found advisable to maintain a speed of movement of from eight to twelve feet persecond in the hydrogen .gas as it passes OVQr'the tungsten trioxid. This gas must be previously heated to the temperature atwhich reduction takesplace and one Jof the objects ofthis invention, therefore, is the .lprovision of a suitable and etlicient preheating element for bringing thehydrogen gas up to the reduction temperature.

Experience has shown that in the reduction of tungsten powder some sub-oxid of tungsten is formed which slowly attacks all known forms of insulation which will withstand the heat necessary for a furnace lining. It has been found, however, that the metal nickel is not attacked by this suboxid of tungsten and one of the objects of this invention, therefore, is the protection of the silica tube, about which and in which this furnace is constructed, by means of a thin nickel lining.

Still further objects of the invention are the provision of suitable water cooled ingress and egress members and suitable detachable stoppers therefor which provide ready means for charging and emptying the furnace.

My invention is illustrated in the accompanying drawings in which,

Figure 1 is an elevation;

Fig. 2 is a section on lines 2-2 of Fig. 1,

Fig. 3 is a section on lines 33 o Fig. i; and

Figs. 4 and 4 are lefthand and righthand longitudinal sectional views of the furnace.

Similar characters of reference refer to similar parts throughout the several views.

This furnace comprises a silica tube 6 about five feet in length and about three inches in diameter centrally supported by means of a metal box 7 containing a packing 8 of magnesium oxid. The box 7 is supported upon metal brackets 10, or in any other suitable manner. The ends of the tube 6 extend into metal water jacketed members 11 and 12, each of which is likewise supported upon suitable brackets 11 and 12 Projecting from the leftliand or ingress member 11 and insulatedly supported thereon is a rod 13, preferably of nickel. This rod extends centrally through the bore of the furnace and is covered by means of a sheath or tube 14 of silica. The inner end of the rod 13 has attached to it the inner end of a ribbon 15 of nichrome metal. This ribbon is formed by winding it upon a flat mandrel, the natural spring of the nichrome metal serving to cause the ribbon to uncoil to a certain extent upon the withdrawal of the mandrel whereby the ribbon assumes the shape illus trated in Fig. 3and thus presents its radiating surfaces to substantially all paths which the gas may take in passing through the furnace. The outer end of this nichrome ribbon is attached to the post 16 which is likewise supported in the water cooled end member 11.

The central portion of the main tube 6 is surrounded by a second nichrome heating element 18, this element being entirely embedded, except at its terminals, within the magnesium oXid packing. It has been found that if this heating element which actually surrounds the tungsten trioXid which is to be reduced is so placed that the sub-oxids of tungsten can reach it that it, as well as the silica tube, becomes attacked by the gases. By means of my invention,

however, the hydrogen gas is so highly preheated that sufficient heat to maintain the reducing action is conducted from the heating element 18 through the silica tube and through the nickel lining 20 within the silica tube. This nickel lining is made of a thin sheet of pure nickel which, although rolled into the form of a tube, has suflicient spring to cause it to be forcibly pressed throughout its length against the inner surfaces of the silica tube 6. In this manner the silica tube is protected from the injurious sub-oxids or basic oXids of tungsten and the life of the furnace is increased many fold over the life of a similar furnace which is not provided with the protecting nickel lining.

The tungsten trioxid to be reduced is placed in a small nickel boat 21 having three compartments formed by its base and the two shelves arranged within the boat. This boat, after being filled with the oxid, is slid into the furnace through the opening created by the removal of the plug 23 which is supported in the water cooled end member 12. The boat is preferably provided with a nickel wire 24: which is permitted to lie within the furnace during the reducing operation and by means of which the boat is withdrawn from the furnace after reduction. 7 It is unnecessary that the silica wall of the furnace be protected throughout the entire length thereof since experience has shown that the suboXid of tungsten which attacks the furnace wall does so only at points where the temperature of the silica is maintained very high.

It has been found advantageous to circulate the hydrogen gas through the reducing furnace under a considerable pressure, that is, under a pressure somewhat greater than that of the atmosphere. A suitable cement for sealing between the water cooled terminal and the silica tube is made by wetting plaster of Paris with a solution of one part gum arabic and ten parts water. The gum arabic seals the pores of the plaster of Paris so that it becomes gas tight. Cements which have to be heated to soften them originally so that they will adhere both to the metal terminals and the silica tube invariably cause the shrinkage of the copper terminal to break the silica tube, since both the silica tube and the copper terminal must be heated at the time the parts are cemented together. Silica tube, however, does not materially contract as it cools, whereas the metal terminal contracts considerably and creates such a pressure on the tube as to break it. With the plaster of'Paris compound, however, the cement may be applied cold and no breakage therefore occurs. Such a seal is illustrated at 25.; I have also found it to be advantageous to paint the parts of this seal which are exposed to atmosphere with bakelite which effectually prevents the absorption of moisture by the sealing material.

Just beyond the inner end of the hydrogen ingress tube 27 is a disk 28 supported in such manner as to spray the incoming hydrogen gas and thus prevent it from passing through the first few turns of'the heating element 15 in the form of a column whereby the gas would be ineflectually heated and whereby pockets would be formed which would become overheated and would permit the heating element 15 to become too hot at points within these pockets' Suitable pyrometers 29 are provided for reading the temperature of the furnace at various points.

Although some of the details of this invention may be modified it is to be understood that the invention contemplates and embraces such modifications andthat it is not intended that it shall be unduly limited to the specific disclosure. i

Having thus described my invention what I claim as new and desire to secure by United States Letters Patent is 1. In a furnace for reducing tungsten trioXid to metallic tungsten the combination with a tube of refractory material, of a heat. ing element surrounding the tube, a nickel protecting lining covering the inner wall of the tube within and insulated from said heating element, and means for supporting the tungsten trioXid to be reduced within said metal lining.

2. In a furnace for reducing tungsten tri-' oxid to metallic tungsten, the combination with a silica tube of a nickel lining therefor, means for supporting the tungsten trioXid to be reduced within said nickel lining, and means outside the silica tube for heating the contents of the furnace to bring about the reduction of the tungsten trioXid to metallic tungsten.

3. In a furnace for reducing tungsten trioXid to metallic tungsten the combination with a tube of refractory material, of a heating element near the ingress end of said tube, said heating element comprising a ribbon of conducting material loosely wound upon a central support, each convolution of said conducting material being formed so as to engage said central support, and also being formed so as to extend away from the central support substantially to the inner Wall of the furnace tube.

4c. A furnace for the reduction of tungsten trioXicl to metallic tungsten having a heating element, and a nickel lining insulated 10 from the heating element for protecting the Walls of the furnace from the sub-oxids of tungsten.

In Witness whereof, I hereunto subscribe my name this 23d day of October, A. D. 1916.

CARL A. PFANSTIEHL.

Witnesses:

WM. OSCAR BELL, MARGARET GROBBEN.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C.

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