US1734536A - Electric furnace - Google Patents

Description

N0V- 5, 1929. v. soRREL Er A1.

ELECTRIC FURNACE Filed Aug. 4, 1928 Patented Nov. 5, 1929 IUNITED STATES `PATENT OFFICE -vICTOB SORREL LOUII'IS lANDR LFONT, 0F GRENOBLE, FRANCE, ASSIGNORS T0 UGINE-INFBA, v0F GRENOBLE, FRANCE ELECTRIC Application led August 4, 1928, Serial No.

l Our invention relates tol electric furnaces of the resistance type suitable for thermic treatment of metals and other substances and the objects of the inventionare; first, to provide a device of the character. described with improved means for detecting variations in temperature and fqr automatically regulating the temperature'at the value to which the members to be treated must be subjected; second, to provide improved means `for assuring protection of the heating resistances by automatic diminution of the intensity of the current flowing throu hthem when the desired temperature has een attained; and, third, to provide a furnace in which the consumption of electric energyis very small, and which, moreover, is characterized by a notable equality in temperature in all parts of the. furnace and an unlimited mechanical resistance to shocks to which the heating body j may become subjected, such as the falling of heavy metallic pieces j thereon.

Briefly outlined our furnace comprises essentially a metallic heating chamber, heated'l by means of electrical resistances and prefera ly protected by suitable insulation, in combination with a temperature change detecting arrangement and an automatic temperature regulator consisting of a balance whose equilibrium is controlled by variations (as a function of the temperature) in magnetism of a magnetic body suspended on the said balance and extending into the interior of the heating chamber, the said magnetic body being subjected to the attraction of an electro-magnet or other magnetic field produced by suitable means.

The beam of the balance is provided with a suitable device for regulating the quantity of electrical energy drawn by the resistances of ,the furnace supplying heat thereto. n

The equilibrium of the balance having been destroyed by reason of the magnetic attraction developed in the magnetic body, as soon .'FURNACE 297,474and in France September 29, 1927.

corresponding to a certain regulation of electrical energy (maximum heating point for example) to a position corresponding to another regulation (minimum heating point for example). f

If, at this second position ofthe bala-nce, the temperature of the furnace tendsto descend below the temperature corresponding to the critical transformation point of the ,magnetic body, the strong magnetism thereof becomes reestablished, the "equilibrium of the balance is broken anew and hence the mean temperature of the furnace remains subst-antiallyconstant and equal to the said transformation point. Otherwise, the strong magnetism of the magnetic body can no longer reestablish itself and the temperature of the furnace continues to rise slowly.

The invention will now be described more in detail with reference to the accompanying drawing forming part of this specification and in which- Fig. 1 is an axial section through the furnace;

Fig. 2 isv a corresponding plan view with parts removed; and

Fig. 3 is an electrical detail of the furnace partly in section.

Referring to `the drawing, the apparatus comprises a vertical metallic cylinder y-b having a circular, elliptical or other shape base according to the shape of the objects to be treated said cylinder beingclosed at its lower extremity by a bottom b of the same metal.

In accordance with the range of temperatures to be attained said cylinder is composed of a slightly magnetic metal or one in which strong magnetism disappears at a temperature well below the operating temperature of the furnace, which is practically inoxidizable under the conditions in which it is used and which exercises no chemical 1ction on the objects to be treated. Thus according tothe scale of temperatures to be attained we use, for example, different copper bronzes or aluminum, German silver, nickeline, ferro-nickel, nickel, chrome-nickel or their equivalents, whereas for the higher temperatures or special chemical treatment,

wire from the metallic wall may be brought about by any of the Well-known means in the art such as by means of beads of refractory material threaded jointly end for end over the entire length of the wire.

At the lower extremity of cylinder b, beneath the bottom thereof, is disposed a powerful electro-magnet at" which, may be of any of the well-known types in the art such as, horseshoe, bipolar, multipolar, or circular of the iron-clad type and is adapted to be excited by either direct or alternating current.

The whole is enclosed in a sheet metal casing e and the space between said cylinder b and said casing is filled with a suitable heat insulating substance f.

The upper extremity of the furnace is closed by means of a cover g of refractory material divided into two equal sectors suitably hinged at L-t and balanced to open in the direction of the arrows of Fig. 1. Said cover fits in a ring z', also of refractory material for assuring the closing of the annular space containing the heat insulating substance.

On the upper part of the casingl e exterior thereto is fitted a vertical supporting tube j in which is held a rigid rod k supporting a balance Z on its upper extremity. @ne end of the balance arm' carries a wire rod of metal im,v penetrating the furnace through a `small orifice provided for that purpose furnished in the Center of the cover g'. Within the furnace. suspended on the said wire rod is a magnetic body m and the balance is placed in equilibrium with the furnace out of circuit.

The balance arm supporting the wire m carries a contact at n, controlling directly or throughthe medium of a relay the magnitude of the current circulating in the heating element o. A

Fig. ,3 shows diagrammatically4 a control arrangement for direct opening and closing of the electric circuit which is particularlysimple and dependable. lIn* said ligure, the contact n is constituted by a sort of fork 1,

mounted on the balance arm by means ofV an insulating support 2 and the branches of which are each adapted to be plunged in a cup 3 partially filled with mercury 4I and connected iny series, for example, with the circuit to be opened and closed.

Variation in electric energy supplied to -the heating ,element c may be brought about by any of the well-known means in the art such as, connecting in series 4or parallel different sections of the heating coil, coupling ina-1,536

the sections bythrees connected in star or delta, when three-phase current is used; more Preferably the heat control device is ary ranged in such a manner that maximum heating is attained in the furnace when the beam of the balance is inclined toward the bottom of the furnace (attraction of the magnetic body m. by the electro-magnet a?) and minimum heating at the moment the beam returns to its position of equilibrium (strong magnetism of body m disappears).

rllhe operation of the arrangement is as follows:

rl`he balance Z, which term as used in this specification is intended to include any apparatus for obtaining the value of the vertical component and capable of gravity and magnetic attraction by the mass of the magnetic body m suspended from the balanceA beam suoli as a steelyard, spring and lever combinations and their equivalents, being equilibrated beforehand with the magnetic body m which it supports, if the electron'agnet d is excited, the magnetic attraction developed by the body m destroys the equilibrium and the balance beam inclines toward the bottom, placing the furnace at a working temperature of maximum heating. This attraction is observed whether'the electro-magnet is fed by alternating current or direct current.

The heating coil c being connected to the terminals of a source of direct or alternating electric current of the desired frequency, the temperature of the' furnace gradually rises and when the critical temperature at which strong magnetism disap ears (Curie point) is reached in the mass otPthe magnetic member m', the strong magnetism thereof disappears and the beam of the balance again rises to its position of equilibrium placing the furnace at a working temperature of minimum heating.

The disposition and arrangement of the parts permits obtaining, by varying the nature of the magnetic body or alloy sus pended on the beam of the balance (such as nickel, iron, steel, cobalt and the like), automatically either a constant temperature in the furnace equal to the transformation temperature strength of magnetism of the metallurgical vmetals or alloys. Such metals or .alloys are temperature tends to decrease below that corresponding `to the critical point of transformation. Strong magnetism is then `reestablished, the equilibrium of the balance is broken anew and brings the furnace back to the high working temperature desired.`

In the second case, the intensity of minimum heating is adjusted in such wise`that the 'equilibrating temperature of the furnace subjected to this region will be slightly higher than the critical temperature of transformation of the magnetic body m connected to the balance.' v Strong magnetism in said body can no longe!` be reestablished therefore and the temperature of the furnace continues to rise slowly.

The device and its method of operation above described are particularly suitable for attaining rapid and y.dependable tempering of steelsl" In such a case it is merely necessary to suspend the4 pieces to be treated from the balance beam and equilibrate the. masses thereof in vsuch a manner that the beam normally comes back to a horizontal position. The electro-magnet d being thenexcited, the balance beam becomes inclined and automaticallyv establishes heating in the furnace in the neighborhood of maximum. 'When the transformation temperature of the heated pieces is attained (critical temperature where strong magnetism disappears the balance returns to `lts position of equi ibrium, thus reestabl'ishing mild heating, minimum heating being provided, as hereinbefore described in connection with the second case, in such wise that the temperature of the furnace continues to rise very slowly. The. tempering of the members in question will of course take place at different temperatures according to the composition of the steels in question, but always in the neighborhood and above the tempera-ture of the critical point thereof. Once this point is obtained it is sufficient from then on, tofollow the indications given by a thermo-couple placed in the immediate neighborhood of the pieces being treated,-for determining the precise instant at which it would 'be suitable to effect the tempering operation.

Our process is also perfectly adapted to Operationsr for placed "in the furnace and a magnetic core whose critical point corresponds to-a temperature in the neighborhood of the annealing temperature is suspended from the balance beam. Such an arrangement being establislred, thetransformation temperature, with maximum heating is certain not to be passed.. Observation of a galvanorneter fed by a thermo-'couple will enable the operator to stop t-he annealing operation at the desiredtemperature. y

'Having described our invention what we annealing vclaim as new and desire to secure by Letters Patent is- V 1. An electric furnace of the type descrlbed comprising, in combinationa heat insulated metallic chamber composed of a metal which 2. An electric furnace of the type described comprising, in combination, a heat insulatedl metallic chamber, an electrical resistance for heating said chamber, a balance on said furnace, a rod 'suspended on one arm of said balance extending into said heating chamber, a

magnetic body on the extremity of said rod,

means for creating a magnetic field for said body and a switch for said electrical resistance adapted to be 4opened and closed by the oscillations of said balance whereby the temp erature of said furnace is automaticallyregula'ted.

3. An electric furnace of the type described comprising, in combination, a heat insulated metallic chamber', an electrical resistance for heating saidchamber, a balance on said furnace, a rod suspended on one arm of said balance extending into said heating chamber, a magnetic body on the extremity of said rod, means for creating a magnetic field for'said body said means including an electro-magnet f andv a switch for said electrical resistance adapted tobe opened and closed by the oscillations of said balance whereby the temperature of said furnace is automatically regulated.

4. An electric furnace of the type described comprising, in combination, a heat insulated metallic cylinder composed of metal which is non-magnetic at tlie working temperatureY of said furnace, a coil of resistance wire wound on said cylinder, means for controlling the electrical energy supplied to said resistance coil and electro-magnetic heat responsive means adapted to automatically operate said first means for regulating the temperature of said furnace.

5. An electric furnace of the type described comprising, in combination, a heat insulated -metallic cylinder, al coil of resistance wire wound on said cylinder, a balance on said furnace, a rod suspended on one arm of said baly ance extending into said heating chamber, a magnetic body on the extremity of said' rod. means for creating a magnetic field for said body and a switch for said resistance coil adapted to be opend and closed by the oscillations of said balance whereby the temperature of said furnace is automatically regulated.

6. A n electric furnace comprising in co1n` Alf 1,754,536

loiiiation a heat insulatefl metallic cylinder compose of metal which is non-magnetic at the Working temperature of said furnace, a resist-ance heating. coil surrounding saiol cylinder, a magnetic body suspended Within said cylinder from a movable support outside said uinace9 means for creating an elect-r0magnetic. ield for said looy, and a switch contiolling the supply of urrent to said heating 3G coil and itself controlled by the movement of Said movable supporto ln testimony whereof We have axecl our signatures.,

VCTQR SiRREL. Louis ANDR :ummm

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