US1671451A - Electric vacuum furnace - Google Patents

Description

- May 29, 928.

1,671,451 M. D. sARBEY ELECTRIC VACUUM FURNACE Filed Dec. l. 1325 1N ENToR: Zfma l 6ATTORNEYS.

u that can be at the same time shall afford a simple means.

`Planned May 29; 192s.

UNITED STATES MAURICE D. SARBEY, OF CLEVELAND, OHIO, ASSIGNOB T0 TH'E XEIET LABORA- TORIES CO. ING., A CORPORATION 0F NEW YORK.

ELECTRIC VACUUM rumucn Application filed December chamber havealso required separate gaskets.

and compressing means therefor, which demand constant attention to prevent leakage at these points. Furthermore, the furnace walls have been opaque, with merel a small window providing a view of the inside of the chamber from only one `point.

One of thc principal objects of this invention is to provide a furnace which has a simple seal for retaining the highest vacua roduced over mercury, which of access to lthe parts inside the furnace, and shall also provide a convenient means for. leading into the furnace the required size and type of electrical conductors to supply heating current to a resistor within the furnace, if the latter is to be so heated.

Other important objects of this invention are: to provide a heating resistor whichl shall very rapidly reach the desired high temperature and with which the heating can be carried on in the absence of carbon or other vapors which mightaffect the charge;

to provide expansion and contraction compensa-ting means in the electrical circuit that includes the resistor so that the latter may expand under heat without distortion; and to provide a 'transparent furnace wall through which the operation in the chamber may be watched from various points.

The above and other objects and the novel features of this invention will be apparent from the following description taken with the accompanying drawings, in which Fig. 1 schematically illustrates a vertical section of an electric vacuum furnace embodying this invention; and

Figs. 2 and 3 are detail sectional views l, 1925. Serial No. 72,550.

on the lines II-II and III-III of Fig. 1.

Referring to the drawings, the furnace comprises a vacuum chamber V that has a Wall 1V desirably in the form of a hollow transparent glass globe having a hollow stem W at least 30 inches long. The tubular stein W', while preferably of transparent glass integral with the globe, may be of metal, bakelite or other suitable material cemented tothe globe, and is disposed in a substantially vertical position. The wall W, W may be of any size and shape suited to the operation for which -it is to be used and to the material of which it is made. The furnace wall may be movably supported, as by suspending it in a shackle S that may be raised and lowered.

Normally the chamber V is liquid sealed, preferably by means of mercur The lower open end of the tube W is disposed below the levelof a body of mercury M in a reservoir R; while inside the hollow stem W', but spaced from and desirabl concentric with it, isa tube D, made of' suitable insulating material such as glass or hakelite, which extends through a mercury tight joint in the bottom of the revervoir R and has its -lower end projecting below the level of a body of mercury M in a reservoir R. These two reservoirs constitute a stationary base for supporting the conductor and resistor assembly to be described, communicate with the atmosphere, and are of suitable size to hold the quantities of mercury required for the mercury columns built u when high degrees' of vacuum are create in` the furnace chamber.

Air or other gases may be withdrawn from the chamber V to carry on operations under vacuum, and hydrogen, nitrogen, argon or other desired gases may be introduced into the same through a pipe H which, as shown, extends through a mercury tight seal in the bottom of the reservoir R and through the mercury M and tube D into the chamber V, but may of course extend through either body of mercury and terminate at a suitable height inthe chamber V. To withdraw gas, the outer end of this pipe is connected to a suitable vacuum pump or other evacuating means.

The char e in the chamber V is desirably electrically cated by means of a resistor T which is connected in series circuit with electrical conductors C and K, which may bewire rods or tubes of metal or any material suited to the currents and temperatures to be used. If the resistor is to be operated at a temperature above the melting point of the conductor material, the conductors may be made as double or return tubes through which water or other cooling medium may be circulated. As shown, the conductor C may be in the form of an inverted U-shaped copper tube, the le s of which extend into opposite sides lof t e reservoir R through suitable mercury tight joints, thence up throu hvthe mercury M and the annular s ace tween the walls W and D, and into te chamber V, where they are connected by the bend VC. Similarly, the conductor K may be an inverted U-shaped copper tube, in a plane perpendicular to the conductor C, extending throu h mercury tight Joints in thebottom of t ereservoir R, thence up through'the mercury M and tube D into the chamber V, the bend K at-its upper end bein disposed a distance below the bend C. As s own, the conductors C and K, and the respective barometric columns of mercury through which they pass, are insulated from one 'another by the tube D. If desired, the lower ends of the conductors C and K may be bent under the lower edges of the stem lV -and tube D, respectively, e

and brought up throu h the surfaces of' mercury seals M, M. 'urthermore, by suitably insulating the conductors C and K, the tube D as well as the mercury M and reservoir R may be dispensed with and all ipes and conductors brought out through t e mercury seal M. Other supports ma be used to carry the resistor assembly an hold the several parts in position, and wood or -metal space bloc-ks may be placed inboth the tube D and the stem W to reduce the quantity of mercury required for the columns. Positive and negative current supply cables 10 and 11 may be secured to the conductors C and K, respectively, by clamps 12 and 13; and suitable rubber hose. vor other means may also be coupled thereto for circulating cooling fluid therethrough.

The resistor T is adapted to carry -the furnace charge and preferably consists of a refractory metal, such as tungsten, molybdenum or the like, and is desirably in the form of a container or cylinder formed by unitin two elongated curved sheets of tungsten, or exam le. The upper open end of the vertical tu ular resistor is rigidly held and electrically connected to the condutor C by a copper casting B which may be split vertically into two similar sections vand clamped to the legs of 'that conductor by bolts B'. The castlng sections clamp the resistor against a thin steel ring N concentric with a hole L formed by opposed recesses in the casting sections, thereby providing good electrical and mechanical connection between the resistor and the conductor C. The charge to be heated is placed inside the cylinder, access to which is obtained through thephole L. The bend C is curved so as not to obstruct a View through the Wall lV eudwise into the upper end of resistor to watch the charge. Since the interior of the heatlng element or resistor is practically completely enclosed, and is visible through the Wall'W, it can be sighted with an optical pyrometer, thereby obtaining true bla-ck body telnperatures without correction.

A round steel block E fits into and closes the lower end of the resistor cylinder T, and the latter is clamped to the block E by the halves of a split steel ring F which are secured together by bolts F. The resistor is thus in good electrical contact with the bottom bloc-k'E, which carries two spaced copper switch blades J on its ylower side to receive and make good sliding contact with a stationary copper block Gr that is electrically and mechanically secured to the top bend of the conductor K. As the resistor T heats up it expands considerably, which expansion and subsequent contraction are compensated for b the sliding connection between the blades and the block G, thus avoiding damage to the resistor and other parts of t-he furnace. The casting B and ring N are kept cool b the circulation .of cooling water -throug the conductor C; While the block G,

blades J, ring F and block E are similarly cooled by the circulation of coo-ling water through the conductor K. With this cooling system, the furnace can be operated at any temperature up to .the melting point of the tungsten or similar resistor, for such comparatively short lengths of time asit is usually desired to operate such a furnace, without damaging the terminals carrying the resistor and without distorting the latter. l

To heat a charge to a high tempera-ture under vacuum or sub-atmospheric pressure, the operation of .the furnace is briefly as follows: Assuming that the exhaust pipe H is open to the outer air, the wall W, W may be freely lifted oli' by the shackle S, exposing the resistor T. The material to be heated is then placed inside the resistor, and

the wall W, W is so replaced as to submerge the lower end of the stem W in lthe mercury M, thereby sealing the chamber V since the tube D is already sealed by the mercury M. The pipe H is then connected to .the vacuum pumps to commence evacuating the chamber V. As the air is pumped out, the mercury rises in each of the .tubes W and D to the same height above their respective mercury reservoirs. As the air remaining in the furnace chamber appreaches zero, Ithe mercury in the two con# centric tubes W', D approaches barometric hei ht, but since these tubes are over 30 inc es long the mercury does not rise into the furnace chamber but remains approximately at a predetermined level, even with the most nearly perfect vacua. The degree of-vacuum can be readily estimated by the height of the mercury column in the stem W', for exam le, but of course it may b e more'accurate y determined by the use of gauges.

When the desired degree of vacuum has been reached, suitable electric currentis supplied by closing a switch in circuit with cables 10, 11. The path of the current is as follows: cable 10, conductor C, clamp B, re-

-sistor T, clamp E, block F, blades J, block G, conductor K and cable 11. At the end of the heating period, the current is shut olf, atmospheric pressure is restored in the chamber V and, when the concentric columns of `mercury have dropped to their levels in the -res`ervoirs, the globe or wall W, W' may be lifted olf, giving quick and free access to the resistor and the charge therein.

f The mercury makes an -absolute seal aroundrthe opening of the furnace, as well as around theelectrical conductors, exhaust pipe and other structural parts, and 'preserves without loss the vacuum or other de- .sired` pressure in the furnace chamber.

l .Vacua can therefore be produced and held up tothe capacity of the best vacuum pumplng equipment,I without the use ofv anyv troublesome joints, packings or ground glass surfaces. By using water-cooled terminals for the resistor and providing expansion compensating means, operation of the improved furnace becomes very reliable and economical. By using a suitable resistor, such as tungsten or molybdenum, very high temperatures can be very quickly attained, so that successive operations can` follow each other very rapidly. Such temperatures are limited only by the melting point of the resistor, which in the case of tungsten is over 3000 C. The heating may be carried on in the absence of carbon or other vapors which might affect the charge, the temperatures reached being independent of the use of any refractories since the furnace chamber is entirely free of these.

Any class of material may be heated in the furnace, irrespective of its electrical conductivity or the conductivity of a special container for it. The seal described may be used with any means of heating which can be used in a vacuum and is not limited to the -use of the resistor'and heating means described. The resistor described is not limited to use in a vacuum but may be used in any type of furnaceand in other suitable atmospheres. Various other. changes may be made in the construction shown without departing from the principles of this invention or sacrificing any of its advantages.

I claim:

1. A furnace adapted for operations under high vacua comprising a. furnace chamber having means therein for sup orting a charge and means removable to a ordaccess to such charge-supporting means, a barometric liquid seal cooperating withsuch removable means to seal said chamber, and a conduit opening into said chamber. 2. An'electrical furnace comprisin a furnace chamber having therein means i101' supporting a charge, a conductor extending into saidchamber to supply electric current to heat said charge, said chamber having a wall removable to afford access to such supporting means and charge; and mercury means cooperating with said Wall and said conductor to seal said chamber.

3. A furnace comprising a furnace chamber, barometric mercury sealing means for said chamber, means for heating a charge in said chamber, and meanswhereby gas may be withdrawn from or introduced into said chamber.

4. A furnace as claimed in claim 3, wherein said sealing means comprises concentric barometric columns of mercury.

. 5. An electric furnace comprising a furnace chamber, liquid sealing means for said chamber, electrical means for heating a charge 1n said chamber, and mea-ns for con ducting electric current through said liquid 7. An electric furnace comprising a furnace chamber, mercury sealing means therefor, electrical heating means within said chamber, means for conducting electric current through said sealing means to said heating means, and means whereby gas may be withdrawn from or introduced into said chamber. v

8.' An electric furnace as claimed in claim 7, wherein such conducting means comprises liquid sealing means to said heating means comprising means whereby such conducting I and sealing means are adapted to be cooled.

13. An electric furnace comprising a furnace chamber, barometric columns of mer-- cury sealing said chamber, a resistor in said chamber, electrical conductors extending through such mercury columns into said chamber and connected in circuit with said resistor, and a gas conduit extending through one of said mercury columns into said chamber.

v 14. An electric furnace comprising a furnace chamber, electrical heating means entirely therein, electric' current conducting means in circuit with said heating means, including relativelyslidable contacts adapted to compensate for the expansion and con.- traction of such heating means, and barometric sealing means cooperating with said chamber and conductor to seal the furnace chamber. i

15. A -vacuum furnace comprising the combination of a base, a wall cooperating with said base to provide a furnace chamber, liquid scaling means between said base and said wall, heating means disposed in saidy chamber at a greater height than the level of said sealing means when the gas is completely .exhausted from said chamber, and means whereby gas may bey exhausted from said chamber.

16. In an electric resistance furnace, the combination rof a conductor and resistor assembly, supporting means for vthe same, a wall cooperating with said supportlng means to provideal chamber enclosing said assembly, said wall being removable lfrom said' supporting means to afford access to said assembly, and a barometric seallng means cooperating with said wall and said contherein adjacent said closed end, a body of mercurycooperating with said open end to provide a-barometric seal for said chamber, a resistor in said chamber, conductors electrically connectedto yopposite ends of said resistor and means whereby one end of said resistor isfree to expand .relatively to the conductorconnected thereto.

19. An electric furnace comprising a tubular wall of substantially uniform diameter and of sufficient lengthpto provide the height required for a barometric seal, said wall enclosing a. furnace chamber, a resistor in said chamber, and. mercury sealing means cooperating with said wall to seal said chamber.

In testimony whereof, I affix my signature.

MAURICE n. SARBEY.

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