US1201224A - Electric furnace. - Google Patents

Description

H. W. GILLETT` & J. 'M.'LOH'R. ELECTRIC FU'R'NACE. APPLICATION FILEDr NOV. 5.*1915. 1 ,201 ,224. Patented Oct. 10, 1916.

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Patented Oct. 1Q, 1916.

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UNTTED, STATES PATENT OFFICE'.

HORACE W. GYILLETT AND JAMES M. LOHR, 0F ITHACA, NEW YORK.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Oct. 10, 1916.

Application ledvNovember 5, 1915. Serial No. 59,868.

To @ZZ -urtom it may concern Be it known that we, HORA-cn W. GILLETT and JAMES M. Lona, citizens of the United States, and residents of the city of Ithaca, county of Tompkins, and State of New York, have invented certain new and useful Improvements .in Electric Furnaces, of which the following is a specification.

This invention relates to electric furnaces and more particularly to electric furnaces adapted to be revolved or rocked while running, of the indirect arcl type, in which an arc is or arcs are struck between or among two or more electrodes, the arc or ares being over the charge to be heated, but not struck between' electrode and charge.

One object of our invention is to provide a furnace of the known advantages of this type and so constructed as to be operable in melting volatilizable metals or alloys containing them without excessive loss of the volatile metals.

More iarticularly, it relates to furnaces for meltmg alloys containing Zinc, such as the various brasses and German silver, or containing manganese, such as ferro manganese.

Another purpose of our invention is to provide a furnace suitable for the melting and refining of steel and other ferrous and non-ferrous alloys, even when not conta1n' ing volatile constituents, the lining of which will have a long life before repair or renewal Vis necessary. l

Other objects will appear from the following description.

It has been found by experiment that when yellow brass or other alloys high in zinc content are melted and brought to the required pouring temperature in an electric furnace of the indirect are vtype in which the charge is not stirred in some manner so as to be very thoroughly mixed, especially during the latter part of the heat, when the metal is hottest, the surface of the metal becomes heated hotter than the bulk or body of the metal. When the furnace is opened, as in pouring, the zinc volatilizes suddenly and violently from this surface layer and the-zinc losses in such a furnace are high. It is well known that yellow brass of the compositions used for making brass sheet and tubing, must be cast at a temperature considerably above the melting point of the alloy, to obtain sound castings which will work well in the rolling or drawing operations. For example, a brass containing GTS/f, copper, 33% zinc, must be cast at about 1100o centigrade. At this temperature the vapor pressure of the zinc in the alloy is nearly that of the atmosphere, while at 1150O or thereabout, this vapor pressure is that of the atmosphere, z'. e. the alloy actually boils. .lt is well understood, according to the laws of physical chemistry that in a closed furnace, .the pressure of zinc vapor may be more than one atmosphere and that therefore the charge or the upper portion of it which received the direct radiation from the arc, mayv become superheated, t'. e. above its boiling point at atmosheric pressure. On opening the furnace and relieving the pressure, the superheated layer will suddenly' release zinc4 vapor in sufficient amount to reduce the Zinc content of that layer to such a point that its vapor pressure is that of the atmosphere at the temperature of that layer. Since the hotter metal tends to remain on the surface on account of. its lower specific gravity, there is little or no tendency for the temperature of the metal to be equalized by convection currents in this type of furnace.

In order to equalize the temperature throughout the molten charge and avoid local overheating at the surface, some method' of stirring or mixing the charge must be resorted to. Y

Whether the explanation given above of the high loss of zinc in melting yellowbrass in an indirect are furnace kept motionless or practically so during melting, is Correct or not, experiments have shown that by a sufficiently rapid agitation of the charge, as by rocking or rotating a furnace, suitably designed for such purpose, the violent shooting out of zinc vapor no longer occurs -on opening the furnace to charge or to pour.

and the zinc losses are materially reduced.4

The necessary agitation and mixing of the molten charge might be obtained in a furnace of the indirect arc type, kept sta 'tionary during melting, by some form of mechanical stirrer introduced into the bathJ The construction and operation of such a device offers difficulties however that are obviated in `a furnace designed to be moved in such a manner and rapidly enough to produce a sufficient agitation of the charge.

lVe are aware that indirect arc electric furnaces have been designed in which the furnace as a whole is oscillated by rotating about a slightly inclined vertical axis, in order to produce some agitation-of the bath. Such a furnacel is described in the United States Patent 1,105,859, to Ernesto vtassano. It is very doubtful if the agitation securable in a furnace of this form would be suiiicient to effectually prevent local overheating in such alloys as yellow brass. Moreover this form of indirect arc furnace does not allow the washing of the furnace walls or roof b v the molten charge, thus preventing them from overheating and from comparatively rapid failure, asis shown by the necessity of frequent repairs or renewals of thereof .of this type of furnace in commercial operation. iVe are also aware that a furnace has been designed and is described in United States Patent 949,511 to Charles A. VeekS, in which the furnace is built in the form of a horizontal cylinder, so mounted as to be revoluble by suitable gearing about its horizontal axis.` The electrodes are mounted, in the case of a single pair of electrodes, in the horizontal axis of the cylinder or in the case of two pairs, horizontally in the place of the horizontal axis and symmetrically 'placed in reference to it.

In either case, the electrodes are mounted so as to have no circumferential motion when the furnace shell is rotated, but instead the furnace shell rotates about the hubs or trunnions within which the electrodes are stationary, save for such adjustment as isrequired to maintain the arc. lin order to ,allow this rotation, without appreciable clearance between the outside of the trunnion and the inside of the ring-shaped opening in the end of the furnace, a packing is provided to make the opening gas-tight. Water is run through them to cool the electrodes. v l

Now, it has been found, in experiments described by C. A. Hansen in an article The electric melting of copper and brass, in volume (3, 1912, page 110, and particularly on page 126, of the Transactions of the American Institute of filet/als that when the Weeks furnace was operated in zinc melting so that there was an atmosphere of zinc va por Within the furnace, the zinc vapor con- .densedto metallic zinc in the clearance between the electrode and the walls of thev hole through which the electrode was intro' duced, and in the clearance between trunnion and furnace shell, so that the electrode was soldered in place by zinc to the.

Walls of the electrode hole and thefurnace vrocking of the furnace.

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shell to the trunnion sothat the electrodes could not lvv adjusted nor the furnace Shell rotated.

Since in melting yellow brass or other alloys containing zinc, there is also an atr mosphere of zinc vapor which will condense in these clearances, it is obvious that the furnace as' designed by feeks is not fitted to be rotated during the melting of alloys high in zinc.

We are aware also that an indirect arc electric furnace has been designed and is described in United States Patent 1,076,518 to Ivar Rennerfelt in which a two-phase three-electrode arc is struck over lthe charge contained within a furnace shell having the general form of a horizontal cylinder, in which the furnace is revolubly mounted on rollers and in which a projection is provided in the refractory lining 'which is intended'to stir or mix the charge by rotating the furnace one way or the other. This furnace cannot be rotated so as to wash the Whole or nearly all of the furnace Wall with molten metal, because the -third or neutral electrode of the two-phase arc is introduced at a point in the circumference of the cylinder. Hence, even were the charging door and pouring spout located as'close as possible to the third or neutal electrode, there would still be a large portion of the lining that could not be washed and cooled by the charge without bringing the charge into contact with the third or neutral electrode and into the hole through which it passes. No gearing is provided for the continuous rotation or The projection in the'hearth interferes with clean pouring of the chargeand scraping out of slag. Moreover, the form of the arcs struck among the three electrodes of this furnace is such that the arc is not exactly central, but is thrown down near or actually onto the charge when the neutral electrode is in a vertical posi- This will make it more difficult to avoid local overheating than in a furnace with the arc central and at an unvarying distance from the surface of the molten charge at all points in the arc of rotation.

yOur invention, then, provides a revoluble indirect arc furnace in which the above mentioned drawbacks of existing furnaces are obviated,in which the circumference of the lining may be wholly or almost wholly washed by the molten charge, sufficient agitation of the charge maybe obtained without the use of projections in the lining, and in which the electrodes rotate with the furnace shell, requiring no joint in which zinc, for example, may condense. It provides, besides a mea-ns of melting volatile metals or alloys containing them without high losses of metal, one in which the furnace walls have a long life because of the Washing of them by the charge so that they Varenever heated fora long time to temperatures Y higher than the charge is heated to, and in `nace is largely absorbed by the charge as it is brought periodically'in contact with' thesel parts of the lining.l

In the accompanying drawings, Figure 1 is a vertical section 'and Fig. 2 a sectional view of the furnace in Fig. 1 on the line VV-W of a simple.form of our furnace, in which the current is led from the bus bars 1 through flexible copper or aluminum cables 2 to the electrode holders 3, of bronze,

Vfor example, which'clamp the carbon or graphite electrodes 4.

The electrodes areadjusted by an automatic regulator, or by hand, for. example,

by` means of a handle 5 controlling-a spiral gear 6, which moves the electrode in and out as desired to start or regulate the arc. The shaft of this gear is held by the insulating sheet 7 which is of some such insulating material as heavy asbestos mill board, and serves to 'insulate the electrodes, which pass through a hole in it, from the furnace shell. Each insulating sheet is fastened to the shell b several braces, 8, only two of which are siiown. Also fastened to this insulating sheet is a jacket 9 of copper or other material of high. heat conductivity, provided with fins for air-cooling of the electrode. These may be re laced by water-cooling cylinders or boxes 1f desired, but the watercooling should not be suiiicient to allow the electrodes. to run so cool that metallic zinc is condensed in them in suicient quantity to solder the electrode in place when melting alloys containing zinc.

The furnace shell 10, of iron, steel or bronze, Aof cylindrical, spherical, or ovoid shape, is lined rst with a layer 11 of circular tile or suitable 'shapes' of brick. Red

building. brick is suitable for this layer, or a checkered construction may be used, using alternate red brick and kieselguhr brick. In cases where the furnace is1 not so lar e that the crushinv strength of kieselgu r brick is too low, all kieselguhr brick may be used. TheJ next layer 12 consists of circular tile or suitable shapes of a grade of heat-inlsulating brick having lower refractoriness and less heat conductivity than fire brick. As such brick is usually of an acid nature, a thin layer 13 of chromite, carborundum, or other neutral refractory may be used to separate it from the inner layer 14,if that is to be of a basic nature. This inner la er 1 4. is built of circular tile or suitable s apesnof brick. Magnesite brick may be used, but for a brass-melting furnace, 1fthe walls are cooled by washing with metal, a good grade $5 of fire brick, especially the kinds higher in alumina than the ordinary grades, is pref erable. This lining of highest refractoriness is brought out about the electrodes and spout as shown. By using such a composite lining, with refractories of lower melting point but which are better heat insulators for temperatures which they will with` stand, outside of layers of higher. meltlng point but poorer heat insulators, a

better heat insulation can be secured than by a single refractory of high enough meltlng point to stand up at the temperature of the furnace chamber. If desired, however, a

single refractory may be used.` A combined l charging door and pouring spout 15 is provided, to be4 closed by the door 16, which! may be luted in gas-tight by iireclay, for example. The electrodes used are of such diameter as to t as snugly as possible in the holes in the y,end walls of the furnace without fitting so tightly as to prevent their adjustment. The shell has circular holes in the ends, denoted by X, of such size as will prevent short-circuiting through the shell or larcing from electrode or jacket to shell.

The furnace is supported on four or more rollers 17, or by other suitable means, and is rotated by two gears 18 encircling the furnace which mesh with other gears 19. These are driven at will by some source of power (not shown), an electric motor being convenient, so arranged as to rotate-the furnace from a point where the level of the molten charge has the position Y-Y in Fig. 2, in one direction, to a point where luted up to retain the molten metal, and.y

held in by some suitable locking device, asl by a bar 2O held in suitable ears attached to the shell. The flexiblev cables must then be replaced by a sliding contact, like a commutator, between bus bars or other leads and suitable electrode holders.

Various changes in details of construction and arrangement of parts maybe made by one skilled in the art without departing from the spirit and scope of theinvention we set forth in the following claims.

We claim:

1. An electric arc furnace comprisinga shell inclpsing a refractory retaining hearth of` circular cross section, mechanically revoluble on its horizontal axis, adjustable electrodes between which the arc is formed introduced through the ends and revolving with the body of the furnace, an opening into the body of the furnace for a combined charging door and pouring spout, and provision for tightly closing this.

2. An electric furnace comprising a shell inclosing a refractory retaining hearth of circular cross section, built up of layers in which the heat insulating power of each layer is greater than that of the layer next inside it, mechanically revoluble on its horizontal axis, means for revolving said shell and hearth in one direction to a hired point and then revolving in the reverse direction to another fixed point, electrodes introduced through the ends of the furnace, and revolving with the body of the furnace, means for lateral adjustment of these electrodes, means for air-cooling these electrodes and supports for the 4rneans of adjustment and air-cooling by which they are electrically insulated from the shell, an opening into the bodyof the furnace for a combined charging door and pouring spout and, provision for tightly closing this.

3. An electric arc furnace comprising a substantially cylindrical refractory hearth having its aXis substantially horizontal, said hearth being mountedl to turn about said axis, adjustable arc electrodes passing through the ends of said hearth and turning therewith.

fl. An electric arc furnace comprising a substantially cylindrical refractory hearth having its axis substantially horizontal, said hearth being mounted to oscillate about said axis, adjustable arc electrodes passing through the ends of said hearth and oscillating therewith and means to oscillate said hearth.

HORACE W. GlLLlET'll. JAMES M. LfEtt,

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