US1660191A - Current-regulating means for electric induction furnaces - Google Patents

Description

my 21, aym m C. B. FOLEY CURRENT REGULATING MEANS FOR ELECTRIC INDUCTION FURNACES Oriainal Filed March 25, 1922 lllllll Uimrias B ui Ze 17,

- M (a 5M Patented Feb. 21, 1928.

, UNITED STATES PATENT OFFICE.-

CHARLES B. FOLEY, OF FORT WAYNE, INDIANA, ASSIGNOR TO CHARLES B. FOLEY, INO., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

OURRENT-REGULATING MEANS FOR ELECTRIC INDUCTION FURNACES.

Application filed March 23, 1922, Serial No. 545,985. Renewed J'u'ly 14, 1926.

This invention relates to electric furnaces and particularly to those furnaces of the I induction type in which a loop or channel of molten. metal forms the secondary of the transformer which supplies energy to the furnace.

One object of this invention is to provide a simple current regulating means for a furnace of this type. Another object is to increase the operatin efliciency of the furnace. Still another 0 ject is to increase the power factor of the furnace and still another object is to provide means for easil adjustingl the furnace to melt metals of di ferent c aracteristic's, for example, metals having different electrical resistance.

These objects are accomplished by providing an additional coil for the transformer which is so disposed that the leakage flux is 10 very materially reduced and by roviding means for varying the number 0 effective turns of this coil.

In' electric furnaces of the type contemplated by this invention, the primary coil 55 ofthe t ansformer is placedwvithin the bore of a re ractory tube which, together with the furnace walls, forms the channel for the molten transformer secondary. A laminated iron core is passed through the primary coil 80 and is closed upon itself outside of the refractory tube to form a closed magnetic circuit for the transformer.

In any transformer the current in the primary coil'produces magnetic flux in the 85 iron core in one direction and the current in the secondary coil produces magnetic flux which is opposed to that produced by'the primary and this condition always produces a certain amount of stray or leakage flux,

40 that is, flux which does not stay within the iron core but completes its magnetic circuit without threading or interlinking both the primary and secondary coils. This leakage flux generally finds a path through the space between the primary and secondary coils.

In the ordinary ower transmitting transformer it ispossible to construct the iron core and the primary and secondary coils in such manner that the space between these coils is very small and the leakage flux consequently negligible. However, in the construction of the electric furnace, while it is possible to place the primary coil very close turns to the coil that produced it without I threading both the primary and secondary.

Placing the primary coil within the refractory tube, as described above, locates it as close to the secondary as possible but even with this construction the leakage flux is very high, sometimes reaching as much as 50% of -the flux produced by the primary coil. This loss of flux causes a serious drop in the voltage generated in the secondary coil and reduces the secondary current Which in turn reduces the amount of heat imparted to the metal.

It is well known that two primary coils when placed on the same core and connected in multiple will, with the secondary open circuited, each produce its proportional share of the required total magnetic. flux. I have discovered that by placing one of these coils .on the outside leg of the transformer core of a furnace of the above mentioned type such coil not only still tends to supply 1ts share of flux but at the same time tends to greatly reduce the amount of stray or leakage fiux; in other words, the flux produced by the primary coil, instead of finding its way back through the space between the primary and secondary coils, remains in the iron core and threads both of these coils.

This increase in the total flux threading both rimary and secondary, as would be expecte causes the secondary voltage to approach the normal calculated value, increases the heating current in the molten secondary and improves the power factor of the furnace.

By providing suitable switching contacts the number of turns of this coil may be readily varied and a convenient control of the furnace current secured thereby.

It very frequently happens that at one time an electric furnace will be called upon to melt a metal of very low electrical resistance such as brass, while at another time it may be desired to melt a metal of very much higher electrical resistance such as German silver. Also where a furnace has been in continuous operation for several weeks, the wear on thewalls of the channel increases the cross section of the seconda and causes the primary to become overloa ed. A control to take care of such conditions as these must possess a considerable range, and in order to increase the range of control, the coil which is provided on the outside leg. of the transformer may be made use of as an auto-transformer in which the secondary may be connected by asuitable switch mechanism to either buck or boost the voltage applied to the main primary coil of the trans former located within the refractory tube.

In the accompanying drawings- Fig.1 is a view in central vertical section of an induction furnace of the crucible type such as is described in my copending application, Serial No. 545,984, filed March 23, 1922. It will be understood, however, that the invention is equally applicable to induction furnaces of other types.

Fig. 2 is a diagrammatic view illustrating the current regulating means .employed in accordance with this invention; and

Fig. 3 is a diagrammatic view of a modification of the circuit arrangement shown in Fig. 2.

The furnace shown in Fig. 1 consists of an upper section 1 cemented to a lower section 2, the two sections being firmly held together by tie-rods 3. Numeral 4 designates the tapping nozzle of the furnace and 5, the valve through which the flow of metal from the,

nozzle iscontrolled. The valve is operated a ainst the tension of a coil spring by means of the lever 6. The furnace as fully described in my copending application above identified has fixed in its lower section arefractory tube 7 located in registry with coaxial windows 8 cut through the sides of said lower section, the tube forming in conjunction with the bottom and sides of the lower section a plurality of loop-shaped channels 9 whereby the metal contained: in the furnace is brought into inductive relation with current inducing means constituted by a primary winding 11 and a laminated magnetic core 10.

Referring to Fig.2, in addition to the pri mary winding 11, which is located within the refractory tube 7, there is provided a second winding or coil 12, which is energized in parallel with the primary 11 and connected to assist it, that is, so as to produce magnetic flux in the same direction as the primary winding. This second winding is provided with taps 14 and a switch mechanismindicated generally at 13 for the purpose of varying the number of efi'ective turns of this second winding.

Each of the figures of the drawing indicates clearly the large area for flux leakage that exists in an electric induction furnace between the primary winding 11 and the secwearer ondary winding which is comprised by the single turn 9 of molten metal. As described above, the magnetic flux produced by the primary winding 11 is in one direction and that produced by the secondary winding 9 is in the opposite direction, and when these fluxes attempt to neutralize one another a portion of the primary flux is diverted from its path in the iron core and sentthrough the space between the primary and secondary so that it does not intcrlink the primary coil with the secondary coil. The presence of the second coil 12, however, which is connected so as to assist the coil 11, causes the majority of the primary flux to stay within the iron core and magnetically interlink both the primary and secondary.

Referring to Fig. 3, it will be seen that the second coil 12 is provided at one end with a predetermined number of turns of increased cross section and suitable taps forming the secondary of an auto-transformer of which the whole coil 12 is the primary. Appropriate switching mecha nism 19 connects the primary Winding 11 with the secondary of this auto-transformer and by placing the switch 19 on the various taps 16, 17 and 18, the secondary of this auto-transformer can be made to either add to or subtract from the voltage applied to the primary 11. By this means the current taken by the furnace can be adjusted within very considerable limits to compensate for the wear of the secondary channel caused by the molten metal or for materials of different electrical conductivity which it may be desired to melt in the furnace.

This invention not only provides an effective means of current control but the use of the secondary primary coil 12 as a means for improving power factor is very advantageous as it placesthe user of the electric furnace in a much better position in contracting for power. It also permits the use of a smaller amount of copper in the main primary winding and reduces the heat loss due to electrical resistance in this winding.

I claim:

1. In an electric induction furnace having a loop-shaped channel and a magnetic core linked therewith, a primary winding on said core located within the loop of said channel, and a second winding located on said core outside of said loop, both said windings being adapted to be so connected to an external source of current as to be thereby energized in parallel.

2. In an electric induction furnace having a loop-shaped channel and a magnetic core linked therewith, a primary winding on said core located within the loop of said channel, a second winding located on said core outside of said loop and means for varying the number of turns in the second winding.

3. In an electric induction furnace having a loop-shaped channel and a magnetic core linked therewith, a primary winding on the core, a part of said winding being located within the loop of the channel and a part outside of said loop, and means for varying the efiective currents of that part of the winding located outside of said loop.

4. In an electric induction furnace having a loop-shaped channel and a magnetic core linked therewith, a primary winding on said core embraced by the loop of said channel, a winding on said core located outside said loop, and means for varying the number of effective turns of the latter winding,

5. In an electric induction furnace having a loop-shaped channel and a magnetic core linked therewith, a primary winding on the core located within the loop of the channel, a'second winding located on the core outside of said loop, and means for connecting the primary winding in series with a portion of the second winding.

In testimony whereof I hereunto atlix my signature.

CHARLES B. FOLEY.

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