US2427485A - Electric induction furnace for continuously heating metal strip - Google Patents

Description

- p -'16, 1947. G. P. WILSON 2,427,485

ELECTRIC INDUCTION FURNACE FOR CONTINUOUSLY HEATING METAL STRIP Filed Aug. 21, 1943 I N VEN TOR.

Golder T Vz'lson BY 2s ATTORNEY Patented Sept. 16, 1947 ELECTRIC INDUCTION FURNACE FOR CON- TINUOUSLY HEATING METAL STRIP Golder P. Wilson, Alton, Ill., assignor to Olin Industries, Inc., a corporation of Delaware Application August 21, 1943, Serial No. 499,527

Claims. 1

This invention relates to the continuous heating of metal strip and particularly to the heating of metal strip by means of electric induction.

It has heretofore been well known that heating of metal can be accomplished by electric induction by employing the transformer principal in which a primary coil is supplied with alternating electric current, and the metal to be heated, when placed in inductive relationship with the primary coil, is heated by its resistance to the induced electric or magnetic current.

Methods and apparatus having various means for bringing the metal into inductive relationship with the primary coil have been described heretofore. For instance in one method of heating metal strip, the strip was continuously passed in an axial direction through a primary coil, the metal being heated by the locally induced magnetic and electric eddy currents. Such methods and apparatus have the disadvantage however, that with high conductivity non-magnetic strip it is difiicult to induce electrical eddy currents of sufficient magnitude to bring the strip to an effective treating temperature.

According to other methods, the metal in the form of wire, or coiled rod, was fed in the path of a helix around or through a primary coil, but such methods and apparatus have among others the disadvantage of not being suitable for use with wide strip, due to the difiiculty involved in forming such strip into a helix.

According to still another method described for heating metal in the form or wire or strip, two such wires were continuousl passed in parallel paths on opposite sides of a primary coil. A complete electrical secondary circuit about the primary coil through the wires was provided by means of contact bars having rollers on their ends in electrical contact with the moving wires. Such methods and apparatus, in which contact bars, brushes and the like are employed, have the disadvantage in some instances that contact parts are subject to excessive wear requiring frequent replacement and that an appreciable portion of the induced current is consumed by the contacting means.

All such prior methods and apparatus for the electric induction heating of metal have been attended by one or more serious disadvantages and it is an object of this invention to provide an im proved apparatus overcoming all such objections.

Another object of this invention is to provide an improved apparatus for the efiicient and economical heating of metal strip by electric induction.

Another object of the invention is to provide an efficient electric induction furnace for economically effecting the continuous heat treatment of metal strip.

Still another object of the invention is to provide an electric induction furnace suitable for the heating of magnetic or non-magnetic metal strip of either high or low electrical conductivity.

Other object and advantages will become apparent from the description and accompanying drawing, in which Figure 1 is a diagrammatic view of an electric induction furnace illustrating one embodiment of this invention,

Figure 2 is a diagrammatic view of an electric induction furnace illustrating another embodiment of this invention, and

Figure 3 is a sectional view of a contact roll illustrating an embodiment of this invention,

The above objects and advantages are accomplished in accordance with this invention by providing a novel process and apparatus in which the metal to be heated in strip form is passed over metal contacts which in turn are electrically connected by means of a liquid conductor, and an electric current is induced in the electrical loop formed by the moving strip, contacts and liquid conductor. It has been found that very eiiective and efficient heating can be accomplished in this manner since currents of high amperage and relatively low voltage can be induced in the strip with practicall no loss of power due to the contacting and connecting means.

Referring to the drawing, Figure 1, in one embodiment of the invention, the metal strip I, advanced by any suitable means, is passed over a metal contact roll 2, up over rolls 3 around the primary coil 4, and over contact roll 5 on the discharge end of the furnace. The primary coil 4 is provided with leads 6 and laminated iron core I. Contact roll 2 having an axle 8 is provided at its ends with metal projections 9 and H! and contact roll 5 having axle H is provided at its ends with metal projections 12 and 13. The projections 9 and I2 are at least partially submerged in the conducting liquid I l held in container l5 and the projections i0 and I3 are at least partially submerged in the conducting liquid (4 held in container IS. The contact rolls 2 and 5 are thus electrically connected by the liquid conductor M at both ends of the contact rolls, and a complete secondary electric circuit is provided around the primary coil t in the loop formed by the moving strip, contact rolls and liquid conductor. The strip l is bent around a substantial portion of the surfaces of contact rolls 2 and 5 by passing it over rolls 24 and so that a large area of contact is provided between the strip and contact rolls with good electrical connection and low amperage per square inch of contact surface to prevent arcing and consequent burning of the strip,

An alternating current, which may be of either high or low frequency or, for instance any of the available standard commercial frequencies, is applied to the primary leads 6 and the strip i is heated by the current induced in the loop. The contact rolls, liquid conductor, and rolls contacting the strip in the loop are insulated from any supporting metal frame-Work in order that all the induced current will flow through the moving strip instead of being short-circuited through such frame-work.

The temperature of the strip can be regulated either by varying the speed at which the strip travels or by varying the power supplied to the primary coil 4. For instance, employing an in duction furnace designed as described above, yellow brass strip about 5.663 inches wide and 0.012 inch thick may be passed through the furnace at the rate of about 17.3 feet per minute with a power input to the primary coil 4 of about 18.4 kilowatts per hour to yield about 233 pounds of brass strip heated to a temperature of about 700 C. per hour.

In another embodiment, illustrated in Figure 2, the strip 1 is advanced over a contact roll El, down thtrough pinch rolls 18, around the pri-- mary core 23 which carries the primary coil H), with leads 22 up through pinch rolls 2i} and finally over contact roll 2|. Contact rolls l7 and 2| are electrically connected by means of a liquid conductor, for instance held in container 3 l. The pinch rolls l8 and 213 may be operated, for instance, in conjunction with the strip advancing means to provide the desired tension on the strip as it passes over contact rolls H and 2! while maintaining the strip substantially without tension between the pinch rolls l8 and 2t as it passes through the electromagnetic field set up by primary IQ. In this embodiment of the invention, with heavy metal strip, however, a good contact electrical contact between the strip and contact rolls is ordinarily obtained due to the weight of the metal and no auxiliary means such as the pinch rolls l8 and 20 are essential in order to obtain the necessary contact with the contact rolls. It is desirable, however, to provide a relatively large surface of contact between the strip and contact rolls, for instance b passing the strip over rolls 2% and 21,

Any suitable means may be employed for inducing a current in the secondary loop, provided that the current is of suflicient magnitude to heat the strip to the desired temperature. For instance, the primary coil may be wound on a leg of the core outside the loop, Figure 2, or on the leg of the core inside the loop, as illustrated in Figure 1, or the core may be omitted and the primary coil disposed within the loop.

The contact rolls such as indicated at 2 and 5 of Figure l and at I"! and 21 of Figure 2, may have any suitable form, but in the preferred em bodiment illustrated in Figure 3, they have a contact portion 233 and a spaced cup-like flange or projection 29 at one or both ends of the roll, the contact portion and flange being carried by any suitable axle 3B. The flange 29 is at least partially submerged in the liquid conductor and hus provides a connection of low resistance between the liquid conductor and strip through the contact portion 28 of the contact rolls. With such construction it is possibl to avoid any contact or wetting of the strip itself with the liquid conductor. The 1iquid conductor may be applied in any suitable manner to provide the electrical connection between the contact rolls, for instance the liquid conductor may be employed at only one end of the contact rolls instead of at both ends.

The liquid conductor employed may be any suitable molten metal or liquid such as mercury, Woods metal, or any suitable electrolyte or other suitable fluid. In operation it is ordinarily dcsirable to confine such liquid conductor M in the containers such as l5, l6 and 3|, and close-fitting covers may be provided for this purpose.

The induction furnace of this invention may be employed to heat metal strip of either high or low electrical conductivity for instance in an annealing operation or in any other operation in which it is desired to continuously or semicontinuously heat metal in strip form. The hot strip may be cooled in any suitable manner depending upon the speed of cooling necessary to give the desired physical properties of the metal and, if it is desired to pickle the strip after it is heated, such pickling may be accomplished for instance by passing the strip through a suitable pickling bath as it leaves the furnace.

The heating of more than one strand of metal may be readily accomplished in accordance with this invention, for instance by providing contact rolls for each of such strands and so connecting the liquid conductors accompanying the contact rolls that the moving strands are electrically connected in series, or parallel as desired, with respect to the primary induction means. Similarly more than one strand of the metal may be heated by simultaneously passing a plurality of strands over contact rolls, either with one on top the other, for example in forming laminated sheet or the like or, for instance with narrow strands, side by sid in parallel paths. The word strip, therefore, is used in describing the invention herein and in the claims in a sense inclusive of one or more strands of the metal to be heated.

This invention accordingly provides means for the continuous heating of magnetic or non-magnetic metal strip of either high or low electrical conductivity in the form of flat strip having any desired width, wire, or the like and has a wide held of utility without being subject to all the disadvantages and limitations attending prior processes and apparatus.

It is to be understood that the embodiments of the invention as shown and described herein are only illustrative, and that many changes may be made therein without departing from the spirit and scope of the invention as set forth in the following claims.

Having thus described the invention, what is claimed and desired to secure by Letters Patent 1. In an electric furnace for heating metal strip, the combination comprising a liquid electrical conductor, spaced metal rolls having stripcontacting portions and separate portions carried in and electrically connected by said liquid conductor, means for advancing said strip in contact with said rolls, means for establishing an alternating electromagnetic field, and means for guiding the portion of the strip between said rolls through and in inductive relation to said field.

In an electric furnace for heating metal strip, the combination comprising a liquid electrical conductor, spaced metal rolls having stripcontacting portions and separate portions carried in and electrically connected by said liquid conductor, means for advancing said strip in contact with said spaced rolls, means for holding said moving strip in contact with a substantial portion of the contact surface of said spaced rolls, means for establishing an alternating electromagnetic field, and means for guiding the portion of the strip between said rolls through and in inductive relation to said field.

3.111 an electric furnace for heating metal strip, the combination comprising a mercury bath, spaced metal rolls having strip-contactin portions and separate portions carried in and electrically connected by said mercury bath, means for advancing said strip in contact with said rolls, means for establishing an alternating electromagnetic field, and means for guiding the portion of the strip between said rolls through and in inductive relation to said field.

4. In an electric furnace for heating metal strip, the combination comprising a liquid electrical conductor, spaced metal rolls having stripcontacting portions and separate portions in and electrically connected by said liquid conductor, means for advancing said strip in contact with said rolls, means for establishing an alternating electromagnetic field, means for guiding the portion of the strip between said rolls through and in inductive relation to said field, and driven. pinch rolls between and adjacent to each of said spaced metal rolls for maintaining the hot portion of said strip substantially without tension.

5. In. an electric furnace for heating metal strip, the combination comprising a liquid electrical conductor, a metal roll on the charge end and a metal roll on the discharge end of said furnace for contacting said strip, said rolls having end portions carried in and electrically connected by said liquid conductor, means for advancing said strip in contact with said rolls, means for establishing an alternating electromagnetic field, and means for guiding the portion of the strip between said rolls through and in inductive relation to said field.

GOLDER P. WILSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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