US2945756A - Electric arc resistance furnace and method of melting refractory materials - Google Patents

Description

July 19, 1960 Filed Alfil 2o, 1959 J. s. BALLANTINE 2,945,756 ELECTRIC ARc RESISTANCE RURNACE, AND METHOD oE MEETING REERACTQRY MATERIALS 4 Sheets-Sheet 1 July 19, 1960 J s. BALLANTINE 2,945,756

ELECTRIC ARC .RESISTANCE FURNCE, AND METHOD OF' MELTING REFRACTORY MATERIALS Filed April 20. 1959 4 Sheets-Sheet 2 July 19, 1960 vFiled April- 20, 1959 .l s. BALLANTINE 2,945,756

ELECTRIC ARC ESISTANCE FURNACE. AND METHOD OF MELTING REFRACTCRY MATERIALS 4 Sheets-Sheet 3 4 Sheets-Sheet 4 l 0 ivf..

.\ RRS/f3 July 19, 1960 .1.s. BALLANTINE ELECTRIC ARC RESISTANCE FURNACE. AND METHOD 0E MEETING REERACTCRY MATERIALS Filed April 20, 1959 United States Patent ELECTRIC ARC RESISTANCE FURNACE METHOD F MELTING REFRCTORY `MA TERrALs James S. Ballantine, 121 North Shore Road,

Absecon, NJ.

Filed Apr. 20,1959, Ser. No. 807,673 7 claims. (cl. ls- 10) The present invention relates to electric rarc resistor furnaces of the type which are particularly useful for melting highly refractory metals and similar materials.

A purpose of the invention is to regulate the' pressure on a stack of arc-resistor rings to assure most elective aiming, maintaining an axial pressure in the range of between I() and 150 p.s.i. and preferably in the range b etween 50 and 125 p.s.i. and most desirably between 75 and o psi.

A further purpose is to apply a high pressure on the stack initially so as to maintain resistance heating-conditions for preheat `and elhnina-IOn of gases, desirablyusing initial pressure in excess of 200` vpsi. and suitably in the range between 200 and 400 psi., and then .to adjust the pressure Vinto the arcing pressure range, and permissibly increase the voltage to promote arcing.

A further purpose is to concentrate the heat of anv electric arc-resistor furnace more effectively in the charge and obtain a higher temperature.

A further purpose is to divide vthe load of an electric resistor furnace more evenly between different parts of an electric circuit, especially different phases.

A further purpose is to employ tubular refractory terminals for the `stacks and` desirably clamp the terminals by terminal clamps.

A further purpose is to make the tubular refractory terminals resilient by slitting them near the ends remote from the stack. Y p

lA further purpose is to transmit clampiugjpressure from the terminals of the outer stack to the terminals of the linner stack for the purpose of supporting the outer Stad Further purposes appear. in the specification and in the claims.

In the drawings I have chosen to illustrate a few only of the numerous embodiments in which my invention may' appear, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Figure l is a diagrammatic fragmentary central verti- V cal section of the furnace of the invention.

Figure 2 isa section of Figure 1 on the line M thereof.

Figure 3 is an enlarged fragmentary section of Figure 2 on the line 3-3.

Figure 4 is a circuit diagram showing one circuit arrangement which maybe used.

'Figure 5 is an enlarged plan section through concentric 1 rings of an inner and outer stack, the section being taken yFigari-.si 7 `and 8v are viewsccrresponding te-Fi'giues und 6 respectively but illustrating a variation in which vand Figure 8 is fa 'section on the lines-4s of .Figure 7.

vof loose granules.

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Figure 9 is an axial section similar to Figure 6 showing a variation in which the interlocks are of 'U-shape rather than V-shaped.

Figure l0 isa circuit diagram showing the adjustment of the pressure in accordance with the invention.

YDescribing in illustration but not in limitation and referring to the drawings:

In -the prior art there has been great diiculty in melting and superheating highly refractory materials and especially metals, and accomplishing Ialloying'aud purifyingv of melts of such material. The .present invention makes possible the melting, superheating, alloying and refining of highly refractory materials such as elemental zirconium, tungsten, hafnium, titanium, boron, molybdenum, cobalt, and mixtures of the same in any proportions, `and radioactive isotopes of the same. The invention may also be applied to metals of the platinum group, including platinum, palladium and iridium alone o1' in mixtures. The invention may also be applied to the melting of any of Ithe above elements in combination with other'metals, such as copper, iron, nickel, zinc, vanadium, manganese and the like. The invention is also applicable to the Amelting of refractory compounds of the elements, especially those mentioned above, and particularly carhides.

In accordance with the invention, melting is accomplished by an arc-resistor furnace in which the arcing distance is small and is the distance of contact between successive arc-resistor rings in stacks which suitably surround the charge. In accordance with the invention preferably two or more concentric resistor stacks surround vthe charge, so that heat losses of the inner stack are prevented or compensated for by heat developed in the outer stack.

In the preferred embodiment of the invention, arcing is assured by controlling the pressure on the stack so that the stack will be maintained under a pressure within favorable arcing limits.

In the preferred embodiment of the invention a stack of interlocked resistor rings is arranged endwise to form each resistor path, the interlocks being preferably of V or U formation in axial sectionat the ends.

The arc electrodes are simple to replace and repair as they can readily be assembled and disassembled. Each different phase dcsirably has substantially the same resistance, and this can be adjusted by providing the same cross sect-ion in inner and outer resistor rings, for example where there is the same number of rings in the stacks.

'lubular refractory terminals endwise of the stacks `transmit current to the resistor rings, and in at least some cases the clamping pressure of the outer terminals is transmitted from an outer stack toi an inner stack through spacer segments.

For high temperature work the arcing electrode rings and terminals consist of carbon. In making them up it is desirable to include Ia small percentage, preferably not more than about 2 percent, of silicon as a binder. In

operation, the silicon distills off leaving substantially only carbon as the resistor. The carbon used will preferably be of the'character employed for electric arc furnace electrodes. For low temperature work the rings and the terminals may be of silicon carbide.

The refractory to contain the charge will in many cases -be carbon in the form of va Crucible or in the form In other cases the oxide or other refractory compound of the material being melted will form the refractory lining. It has been found to be desirable to employ an inert gas around and in the furnace during operation. The preferred inert gas is helium, although anotherinert gas such as argon, neon, xenon or `rent, however, can be used.

krypton may be used. Nitrogen is generally not recommended because of the danger of forming cyanogen.

Alternating current is preferred, preferably of commercial frequency asit-causes a stirring effect which is desirable to eliminate gas from the charge. Direct cur- If the melt is allowed to solidify while alternating current is still passing through 'the resistor (the current being cut down to allow solidi- `cation) it has been found that large crystals are obtained with -better crystal orientation.

It will be understood, however, that the invention is useful even though this feature is not employed.

It will be understood that the currents employed in accordance with the invention will be relatively large, preferably of the order of several thousand amperes at relatively low voltages, suitably in the range of from to 60 volts on the secondary.

It has been found experimentally that the stack of electrode rings actually develops a high temperature in the charge with a lower current consumption when arcing than a corresponding continuous refractory resistor, the

reason levidently being that heat is more effectively concentrated in-the charge and less heat is dissipated in the case of arcing rings than with Ia continuous resistor. The localized arcing from ring to ring greatly increases the Vtemperature in the rings and heats the charge up more 4quickly since the point of arcing becomes incandescent almost immediately. It has also been found that much more accurate regulation of heating can `be obtained Vusing the elect-rode rings of the invention.

In the forms shown in the drawings the furnace of the invention comprises an over-all furnace casing of suitable refractory which forms an envelope and supports the internalstructure. In the interior of the furnace a charge -21 to be melted, suitably one of the elements mentioned yabove or a' mixture, is contained in any suitable container,

here a carbon crucible 22 covered by a relatively loose tting cover 23 which permits the escape of contained gas. The Crucible rests'on a vertical support 24 extending to the bottom of the furnace casing and suitably consisting of carbon. Surrounding the crucible, desirably .in slightly spaced relation, is a stack 25 of inner refractory resistor rings 26, which have at the top 'and bottom 'interlocks 27, suitably consisting of cooperating male and female V-shaped grooves and ridges. If desired, however, the interlocks may be of U cross section as shown at 27 in Figure 9.

The 'number of refractory rings in the stack will vary although in many cases three rings are suitable for small l furnaces, and four to ve arcing rings are believed to be adequate for most installations.

Aterminals 30 are air-cooled through passages not shown.

Surrounding stack 25, and in spaced relation from it, is a second stack 25 of refractory resistor rings 26. These have similar interlocks 27 or 27 at the two ends and form a continuous end-to-end engaging stack. The

outer stack 25 connects at its upper end with an an-A nular refractory terminal 28' of the same diameter as the stack 25 and likewise `at the bottom connects to an yannular refractory terminal 29 surrounding the refractory terminal 29.

Inside the terminals 28 and 29 at the respective upper Aand lowerA endsnare placed refractory spacer segments 55144 which is provided with a bridge 45 pivotally vconhave the same arcing resistance is suitable. .shows a construction having inner electrode rings 262 4 v 32 (Figure 2) which occupy most of the space between the terminals 28' and 28 and 29' and 29. Each of the outer terminals 28' or 29 at its outer end is longitudinally slit at 33 suitably at diametrally opposite positions, and the slit 33 is desirably lined up with the space 34 between the respective spacer segments 32. 'Conductive clamping terminals 34 surround the remote ends of the tubular refractory terminals 28 and 29' and are clamped together by bolts 36. v

The terminals 35 extend out through the casing in the furnace as shown in Figure 1 and are water-cooled by means not shown.

The refractory resistor rings 26 are desirably of carbon like the rings 26 and the terminals 28 and 29 are likewise desirably of carbon while the clamps 30 and 35 are desirably of a metal such as copper.

In the forms shown in the drawings, there are only two concentric stacks of refractory electrode rings but it will p be understood that additional stacks can be placed around the outer stack 25', each stack being of successively larger diameter and spaced from the stack inside 'and the stack outside.

The respective stacks are desirably connected in dif- 4ferent phases of the electric circuit as shown in Figure 4 which provides an open delta circuit with the stack 26 in one phase, the stack 26 in another phase and the third phase containing no resistor. However, `as later explained, single phase operation is also quite practical.

It is desirable to balance the elect-rode stacks of the ,different phases as there is danger that if this is not done the arcing surfaces will later change due to a tendency t'o equalize the arcing resistance of the different stacks.

Any suitable arrangement .in which the different stacks Figure 7 which are of small diameter but respectively thicker cross ,section and outer electrode rings 263 which are of large Vdiameter and relatively less thickness, the overall cross lsections transverse to the axis of the rings 262 and 2163 being substantially the same, and in this case the number of rings in each stack being the same. l

In order to obtain effective operation of the arcing electrodes, it is quite important to control the pressure von the stack.

.described and having an outer set of arcing rings 25', with suitable electrical terminals 30 and 30 for the .inner stack and 35 and 35 for the outer stack.

I illustrate in Figure 10 a furnace 37 having an inner stack of arcing rings 25 as previously In this case a single phase is used placing the stacks electrically in series with secondary 38 of power transformer 40. f

The stacks suitably rest upon an insulating support 41 and -a base 42. At the top an insulating ring 43 applies pressure to both of the stacks from a pressure ring necting at 46 to a link 47 which pivotally connects L at 48 to a lever 50 which is on fixed pivot 51. The

primary 5 2 of transformer 40 is in series with solenoid 60,53 whose core or armature 54 is connected to pull rod 55 which is adjustably threaded at 56 into a nut 57 which is pivoted at 58 to the end of the lever 50 remote I from the lever fixed pivot. Also in series with the sole- ,noid 53 is a variable resistor 60, the solenoid, the primary and the resistor being across the power lines.

In operation of the device of Figure 10, a suitable joining the nut 57, so `as to place the arcing rings of the stack under a pressure in excess of 200 p.s.i. and

701 preferably between 200 and 400 p.s.i., a preferred pres- Asure being ofthe order of 250 p.s.i.

f-sistor is then adjusted lto provide a voltage across the The variable resecondary of the transformer of approximately 10 volts.

' The stacks heat up and in the course of about one hours preheating `achieve atemperature of 2000 After uniform preheating has been achieved the weight is removed from the end of the lever 50, and the resistor 60 is readjusted to apply a secondary voltage which is suitably in the range of 40 to 60 volts. The pressure then applied by the solenoid 53 to the stack is in the range of to 150 p.s.i. and suitably about 75 p.s.i. Under these conditions of relatively 10W pressure, arcing occurs and a temperature is built up in excess of 5000 F., and in some cases as high as 10,000 F. under a current of 1500 to 2500 amperes. In the particular installation being described, a cross section of each of the rings was of the order of 1.25 square inches, and the interior diameter of the smaller ring was of the order of 1.8 inches.

It will be evident that it is important that there be some pressure maintained, as otherwise the mechanical force would be sucient to separate the arcs, and also as the carbon becomes consumed the arc spacing increases and the device would cease to operate.

It will be understood that the pressure regulation can be accomplished by other means than that shown.

The present application is a continuation-in-part of my application Serial No. 389,373, filed Oct. 30, 1953, for Electric Arc Resistance Furnace, now abandoned.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or pant of the benefits of my invention, without copying the process and apparatus shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. An electric arc resistance furnace, comprising a plurality of refractory combined arcing and resistor rings arranged in contact end to end in a stack, terminals connected at each end to the stack of rings, a source of electric current connected to the terminals across through the stack, and means for maintaining pressure on the stack in the range between 10 and 150 p.s.i.

2. A furnace of claim 1, in combination with automatic means responsive to the input current to maintain a predetermined pressure level on the rings.

3. 'I'he method of developing high temperature, using a stack of arc-resistor rings, which comprises passing an electric current through the stack of arc-resistor rings, and maintaining a pressure axially of the stack which is in the range between 10 and 150 p.s.i. to promote arcing.

4. The method of maintaining a high temperature, using a stack of arc-resistor rings, which comprises compressing the stack axially under a pressure exceeding 150 p.s.i., passing an electric current through the stack to preheat the stack, the rings acting as resistors, then reducing the pressure axially of the stack to a pressure between 10 and 150 p.s.i. and increasing the voltage to promote the arcing.

5. In an electric arc resistance furnace, an inner stack of concentric refractory resistor rings engaging one another end to end and constructed and arranged to surround the charge, an outer stack of refractory resistor rings engaging ione another end to end, surrounding the inner stack in spaced relation and concentric therewith, tubular refractory terminals engaging the ends of the inner stack and extending in prolongation thereof, tubular refractory terminals engaging the ends of the outer stack in prolongation thereof, terminal clamps engaging the outsidesA of the terminals for the outer st-ack and pressure spacers interposed between the terminal of the outer stack at each end and transmitting pressure from the terminal clamps of the outer stack to the terminals of the inner stack.

6. In an electric arc resistance furnace, an inner stack of concentric refractory resistor rings engaging one another end to end and constructed and arranged to surround the charge, an outer stack of refractory resistor rings engaging one another end to end, surrounding the inner stack in spaced relation and concentric therewith, tubular refractory terminals engaging the ends of the inner stack -and extending in prolongation thereof, tubular refractory terminals engaging the ends of the outer stack in prolongation thereof, the terminals of the outer stack being slit longitudinally at the ends remote from the stack, refractory pressure segments interposed between the slit portions of the terminals `for the outer stack and the terminals for the inner stack, and terminal clamps surrounding the slit portions of the terminals for the outer stack and engaging the same.

7. The method of obtaining a preferred crystal orientation in refractory materials using a stack of refractory arc-resistor rings which comprises melting a charge cornprising a refractory material by pas-sing alternating current of the order of several thousand amperes through a stack of refractory arc-resistor rings surrounding the charge while maintaining electric arcs from ring to ring, thus rendering the refractory material highly fluid, stirring the iluid refractory material vigorously by induction from the aroing current, and then reducing the alternating current and allowing the charge to solidify, while passing through the rings alternating current insuflicient to hold the charge molten.

References Cited in the file of this patent UNITED STATES PATENTS 984,119 Wood Feb. 14, 1911 1,023,309 Helberger Apr. 16, 1912 1,177,680 Brown Apr. 4, 1916 1,663,810 Morse Mar. 27, 1928 2,402,582 Scaff June 25, 1946 2,657,247 Bretschneider Oct. 27, 1953 FOREIGN PATENTS 169,756 Great Britain Oct. 3, 1921 915,619 France Nov. 13, 1946

Claims (1)

1. AN ELECTRIC ARE RESISTANCE FURNACE, COMPRISING A PLURALITY OF REFRACTORY COMBINED ARCING AND RESISTOR RINGS ARRANGED IN CONTACT END TO END IN A STACK, TERMINALS CONNECTED AT EACH END TO THE STACK OF RINGS, A SOURCE OF ELECTRIC CURRENT CONNECTED TO THE TERMINALS ACROSS THROUGH THE STACK, AND MEANS FOR MAINTAINING PRESSURE ON THE STACK IN THE RANGE BETWEEN 10 AND 150 P.S.I.

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