US1801791A

US1801791A - Induction-furnace protective circuits

Info

Publication number: US1801791A
Application number: US433292A
Authority: US
Inventors: John V Breisky; Thomas H Long
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1930-03-05
Filing date: 1930-03-05
Publication date: 1931-04-21
Anticipated expiration: 1948-04-21

Description

April 2l,A 1931. J. BREISKY ET AL l 1,801,791

INDUCTIN FURNACE PROTECTIVE CIRCUITS Filed March 5, 1950 `unimore M Breisy ThogYzas H. Long 2p 26 ATTORNEY rammed Apr. 21, 1931 UNITED STATES PATENT OFFICE JOHN V. BREISKY, OF PITTSIBURGH, AND THOMAS E. LONG, F IRWIN, PENNSYLVANIA,

ASSIGNORS T0 WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A COB- PORATION OF PENNSYLVANIA' INDUCTION-FUBNACE PROTECTIVE CIRCUITS Application filed March 5,

Our invention relates to electric furnaces and more particularly to electric induction furnaces. Y l

'An object 'of our invention is to provide a means for and a method of protecting the inductor coil against engagement by material lescaping from a crucible located within it.

Another object of our invention'is to provide a control system cooperating with the inductor coil that shall preclude energization thereof in case a dangerous breakdown occurs in the insulation in the furnace structure.

In practicing our invention, we provide a two-part shield, preferably made of nonmagnetic but electric-conducting material, located in the space between a crucible and a surroundin inductor coil, the two parts of the shield ge each other as well as from the coil and the crucible. We provide, also, a source of electric energy for the two-part shield and means operatively associated with the inductor coil and the circuit connected to the two-part shield for interrupting the supply of electric energy to the coil in case of the existence of an electric circuit between the two parts of the shield.

In the single sheet of drawings:

Figure 1 is a view, in horizontal section,

3Q of a part of an induction-furnace structure embodying our invention, taken on the line I-I of Fig. 2.

Fig. 2 is a view, in vertical section, through a furnace structure embodying our invention,

certain portions being broken away to show the internal assembly thereof. Fig. 3 is a schematic top plan View of a modified form of two-part shleld, and;

Fig'. 4 is a View, in vertical section, taken on the line IV--IV of Fig. 3.

We have found, in the operation of induction furnaces, particularly when melting certain metals or alloys that there is a possibility ofthe crucible cracking in places. The

cracks or openings are so small as to be more ing electrically insulated from 1930. Serial N0. 433,292.

properly called hair cracks but areof suffi-- v engagement with the inductor coil, it might cause a serious accident in case an operator were to attempt to stir the molten material with a metal stirrer, and damage to the inductor coil might also result by reason of a short-circuit if two or more turns of the coil were engaged by the molten metal.

Referring to Figs. 1 and 2 of the drawings, a furnace structure 11 includes an outer casing 12 which may be. of metal and is shown as of substantially pot shape, the particular furnace which we illustrate being one of the smaller sizes of such furnaces.

A Crucible 13 of any suitable refractory material is located within the outer casing 12 and is spaced therefrom and supported therein by granular electric-insulating material 14, such as some form of zirconium sand'or its equivalent, as usually employed in this art.

An annular plate 16 may be provided to cover the granular material 14 at the top of the casing 12 where it is not covered by a pouring spout 17 constituting a part of the Crucible 13.

It is to be understood that any suitable or Idesired means may be supplied to permit of tilting the furnace to pour' the molten metal and that a cover for the furnace may be provided, but, as these details form no part of our present invention, we have not illustrated them.

An inductor coil 18 is located between the Crucible 13 and the casing 12. The conductor constituting the plurality of turns of electric conducting material may be of any suitable or desired shape and is here shown as being substantially rectangular in lateral section, this being shown for purposes of illustration but it is to'be understood thatany suitable or'desired shape of conductor,

method of support and insulation between adjacent turns, may be employed.

A two-part protecting shield is located be tween the coil and the crucible and, in the modification shown in Figs. l and 2, this shield includes a divided or laminated inner cage 21 and a substantially similar laminated outer cage 22, each of substantially cylindrical shape and so divided or slotted as to provide no closed electric circuit or circuits therein which might be of such area or section as to cause thegeneration of excessive amounts of heat therein by inductive ellects.

The two parts of the shield are insulated from each other by a tubular member 23 which may be of mica, and the outer part 22 is located closely adjacent to and within the inductor coil 18 and is spaced and insulated therefrom by a tubular member 24 which may also be of mica.'

The inductor coil is energized from a suitable source of electric energy indicated by inductors L1 and L2. A source of electric energy, including supply-

circuit conductors

25 and 26, is connected to the two parts of the shield hereinbefore described, and a circuit controlling device 27, such as an electromagnetic circuit breaker` is provided in the circuit of inductor coil 18 and controlled by the owof current from the supply-

circuit conductors

25 and 26 and between the two parts of the shield.l For this purpose, stationary cooperating contact members 28, oi' the usual kind, may be connected in circuit with conductor L1, and an actuating coil 29' may be connected in circuitwith supply-circuit conductor 25 to, actuate a contact-bridging member-31 so that, in case a current of a predetermined value traverses supply-

cir cuit conductors

25 and 26 and coil 29, the supply of energy to inductor coil 18 is interrupted.

The circuit breaker may be provided with means for controlling an alarm, including an auxiliary contact-bridging member 32 cooperating with stationary contact members 33 to control the energization oan alarm de-l vice 34, which may be visual or audible, from a source of electric energy 36.

Referring more particularly to Figs. 3 and i of the drawings, we have 'there 'illustrated a modied form of shield. v The main difierence is that, instead of the two parts of the shield being located in coaxial' but radially displaced relation relatively to each other, as shown in Figs. 1 and 2, the two parts are in the same circular plane, but alternate so that strips or bars 37 ofone part of the shield will alternate in peripheral position with strips or bars 38 of the other part of the shield.

Suitable electrical connections are pro-- suitable mechanical means for holding they asomar er-actuating coil 29 is connected in this cir- V cuit to be effective for the same purpose as that hereinbefore described.

.In Figs'. 1 and 2, we have shown a ground connection 43 as being provided for the inner part ofthe shield and it may be desirable to use this ground although this is not absolutely necessary when using a two-part shield energized from a separate source of electric energy. y

As was hereinbefore stated, hair cracks may occur in the wall of a crucible, and molten material may escape through themI and into the granular electric insulating material 14 and thus cause caking of the same, and it is obvious that it is not always possible tov visually observe such leakage of material in case of a completely enclosed furnace structure. Hence, it may happen, if no protective device is provided, that either the full potential of the circuit connected to the inductor coil may be effective at the molten material or at the Crucible of electric-conductive ma- If molten material does escape through the l wall of the furnace and engages only a portion of the inner part of the shield, it will i,

eventually destroy the insulation between the two parts of the shield and electrically connect them. rlhis permits a current to flow between the two

parts

21 and 22 of the shield and, if the effective current value is large enough, it will eect deenergization of the inductor coil 18, thereby not only calling attention, in an unmistakable manner, to the dangerous condition of certain parts of the furnace, but also removing the danger to an operator.

The device embodying our invention thus provides relatively simple means for electing interruption of the supply of energy to the inductor coil in case of breakdown of the insulation between the two-parts of the shields, as well as means for preventing energization of thecoil in case of the breakdown parts. The device embodying our invention thus provides also means for indicating the electrical.v condition oit the furnace structure and, more specifically, of a predeterinined thereof, as well as simultaneensly indiill cating the mechanical condition of the crucible.

Various modications may be made in the device and system embodying our invention without departing from the spirit and scope thereof, and we desire, therefore, that only such limitations shall be placed thereon as,

are imposed by the prior art or are set forth in the appended claims.

1We claim as our invention:

l. In an induction furnace having a crucible and an inductoi coil surrounding it, a two-part shield located between the coil and the Crucible, electric-insulatingmaterial between the two parts of the shield, a source of electric energy lconnected to the two parts of the shield, .and electric means actuated by the breakdown of the electric-insulating material between the two parts 'of the shield for eifecting interruption of the energizing circuit of the coil.

2. Iii an induction furnace having a crucible, an inductor coil surrounding it, a twopart shield located between the coil and the crucible, electric-insulating material between the crucible, the parts of the shield and the coil, and electric means for preventing energization of the coil in case of electrical connection of the two parts of the shield.

3. In an induction furnace having a crucible, an inductor coil surrounding it, a source of electric energy connected to said coil, a circuit breaker in the circuit of said coil, a two-part grounded shield between the coil and the crucible and electric-insulating material between the coil and 'the crucible and between the two parts of the shield, electric in'eans operatively associated with the grounded shield for controlling'the energiza-r tion of the coil through said circuit breaker in accordance' with 'the electrical 4condition of the insulating material between the two parts of the shield.

4.-. In an induction furnace having a crucilile, an inductor coil surrounding it, a twopart shield between the coil and the crucible and electric-insulating material between the o -1 l' r coil, the Crucible and the two parts or the shield, electric means operatively associated i with the shield and the coil to control the en 6. In an induction furnace having a crucible, an energizing coil surrounding it, two- -partshield between the coil and the Crucible,

electric-insulating material between the coil, the crucible and the two parts of the shield, a source of electric'energy connected to the two parts of the shield, and electric means in the circuit of the two-part vshield for controlling tlie energization of the energizing coil in accordance with the amount of current flowing between the two parts of the shield.

7. In an induction furnace having a crucible, an energizing coil surrounding it, a twopart shield between the coil and the crucible and electric-insulating material betweenfthe coil, the Crucible and the two parts of the shield, electric means operatively associated with the shield and the coil to control the energizatioii of the coil in accordance with the condition of the electric-insulatin material between the two parts of the s ield,

engagement of the two parts of the shield ,i

by molten metal from the Crucible.,

9., In an induction furnace having a crucible, an energized inductor coil surrounding it a two-ioart electric-conductin shield be.

'tween-the coil and the crucible and a source of electric energy connected to the two parts u of the shield, means electrically connected to the two-part shield and the inductor coil to effect deeiiergization of the coil when elec tric current of a predetermined value iowa from one part of the shield to the other part thereof.,

l0, in

an electric heating device having a heating coil in operative relation inatef,

rial to be heated, a multipart shield between the heating coil and the material being heated and sources of electric energy' connected to the heating coil and to the parts of the shield to energize the same, means electrically conf l 'to the heating coil and to the shield.

deenergizatioii of the heating coil w of an electric current of predetervalue between the n l l an electric heating neomei insulating material normally insulating the heating coil, the material being heated and the parts of the shield from one another, electric means connected, in circuit with the mul- 5 ti-part shield and the heatin coil for controlling the energization' of t e heating coil in accordance with the condition of the insulating material between parts of the shield.

In testimony whereof, We have hereunto 10 subscribed our names this 26th day of February, 1930.

JOHN V. BREISKY. THOMAS H. LONG