US2417029A - Electric induction heating apparatus for continuously heating a plurality of metal strips - Google Patents

Description

March 4, 1947. G p w soN 2,417,029

7 ELECTRIC INDUCTION HEATING APPARATUS FOR CONTINUOUSLY HEATING A PLURALITY OF METAL STRIPS Filed May 22, 1944 IN V EN TOR. GOIderB Wilson BY W E.

AI'IURNEY Patented Mar. 4, 1 947 ELECTRIC INDUCTION HEATING APPARA- TUS FOR CON TINU OUSLY HEATING A PLU- RALITY OF METAL STRIPS Golder P. Wilson, dustries, Inc, a

Alton, Ill., assignor to Olin Incorporation of Delaware Application May 22, 1944, Serial No. 536,751

6 Claims.

This invention relates to the electric induction heating of metal strip,

The transformer principle, in electric heating, is well known, in which a primary coil is supplied with an alternating electric current and the metal to be heated, when placed in inductive relation ship with the primary coil, is heated by its resistance to the induced electric or magnetic current.

Various means have been proposed heretofore for continuously bringing the metal to be heated into inductive relationship with the primary coil but all such prior means have been attended by one or more serious disadvantages. For instance, according to one method, the strip was continuously passed in an axial direction through a pri mary coil, the metal being heated by the locally induced magnetic and electric eddy currents. This method has the disadvantage that with high conductivity non-magnetic strip it is diflicult to induce electrical eddy currents of sufiicient magnitude to heat the strip to an eilective treating temperature. According to another method, two wires were continuously passed in parallel paths on opposite sides of a primary coil. A complete electric circuit about the primary coil through the wires was provided by means of metal bars having rollers on their ends in electrical contact with the moving wires. Such a method has the disadvantage that a portion of the induced current is consumed in overcoming the resistance oiTered by bearings, brushes and the like, and, in some instances the contact parts are subject to wear requiring frequent replacements.

It is an object of this invention therefore to provide means of heating metal in strip form overcomin such disadvantages.

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

Another object is to provide improved means for effecting the continuous heat treatment of metal strip having either high or low electrical conductivity.

Still another object of the invention is to provide an improved electric furnace suitable for the heat treatment of non-magnetic metal such as copper or its alloys in the form of strip.

Other objects and advantages will become apparent from the description and accompanying drawing, in which the figure is a diagrammatic perspective view of a metal strip heating apparatus illustrating one embodiment of this invention.

The above objects and advantages are accomplished in accordance with this invention by providing a novel apparatus in which at least two spaced metal contact rolls are employed to electrically connect at least two metal strips, with at least one of the strips between the rolls passing through an alternatin electromagnetic field. Thus a complete electric secondary circuit free of bearings, brushes and the like is provided by the electrical loop formed by the moving strips and contact rolls, the strips being heated by their resistance to the induced electric current.

Referring to the drawing, in the embodiment illustrated in the figure, the metal strip I is passed around metal contact roll 3 over support roll 9, through laminated iron core 4 with primary coil 5 having leads 6 and I, over support roll 8, and around metal contact roll I8. The metal strip 2 is passed around the other end of metal contact roll I8, over support roll Ill and support roll I I, and around the other end of metal contact roll 3. A complete electric secondary circuit is thus provided for the primary induction means 5 by the metal strips I and 2 which are electrically connected by the contact rolls 3 and 18. If desired, the primary induction means 5 may loo-supplemented by laminated iron core !2 with primary induction coil I3 having leads It and I5 through which metal strip 2 may be passed.

A spray system such as illustrated at I 6 may be employed to spray a. cleaning or pre-heating fluid, such as live steam onto metal strips I and 2. A spray system, such as illustrated at I7, may be employed to spray a fluid onto strips 5 and 2 after they have passed through the respective electromagnetic fields applied to them. For instance, metal strip I can be cooled by means of spray system I? prior to contact with contact roll I8 and metal strip 2 can be cooled by means of spray system I7 prior to contact with contact roll 3. In operation, the portions of the strips in contact with the metal contact rolls are preferably all kept at the same temperature to avoid any tendency of the loop to continuously increase in size.

1Any suitable means may be employed for advancing the strips I and 2 through the furnace, and it should be noted that in the specific embodiment illustrated in the figure, strips I and 2 travel in opposite directions. Thus strip I enters the furnace over contact roll 3 and leaves the furnace from contact roll I 8, whereas strip 2 enters the furnace over contact roll i8 and leaves the furnace over contact roll 3. If desired, the strips l and 2 may be so arranged that they pass over contact rolls 3 and i3 and through the furnace in the same direction.

In the operation of the heating apparatus illustrated in the figure, a source of alternating electric current is supplied to the leads 5 and l of primary coil 5 which then sets up an alternating electromagnetic held through which strip l passes, and an electric current is thereby induced in the electrical loop formed by the moving strip i, contact rolls 3 and i3, and moving strip 2. Additional electric current can be induced in the electrical loop by applying an alterhating electric current to the leads it and of the primary coil it which then sets up an electromagnetic held through which strip 2 passes. Live steam may be sprayed on strips l and 2 from spray system it to preheat and clean the metal strips. Wet steam or water may be sprayed from spray system ll to cool the strips down to the desired temperature, which is preferably that of the strip entering the furnace.

The strips '5 and 2 are bent around a substantial portion of the surface of the metal contact rolls 3 and it so that a large surface of contact is provided with good electrical connection and low amperage per square inch between the strips i i3 and the metal rolls 3 and it to prevent arcing and burning of the strips.

The alternating electric current applied to the primary leads l5 and l and i l and it may be of either high or low frequency or, for instance, any of the available standard commercial frequencies. The temperature to which the metal strips l and 2 are heated can be regulated either by varying the speed at which the strips travel through the furnace or by varying the power applied to the primary coils 5 and it. The cores Q and i2 may be mounted on any suitable supports and the rollers 3, 5i, 8, l8, id and ll may likewise be mounted on any suitable support. Care must be taken, however, to avoid providing any electrical connection between such rollers through their support, since the induced current might then how through the supports instead of being confined to the strips l and 2. Such short circuiting can be avoided with metal rolls in any or the well known ways, for instance, by supplying the rolls with bearings made of an insulator or by providing separate supports, or supports made of an insulator. It is preferred, however, to form the support rolls 3, 9, iii and it themselves from an insulator.

Any other suitable means may be employed for supplying the alternating electromagnetic held through which the metal strip passes. For instance, the primary induction means may consist of primary coil wound about a leg of the core inside the loop formed by the metal strip, or for instance, may consist of a coreless primary coil disposed within the loop formed by the strip.

In accordance with this invention magnetic or nonmagnetic metal of either high or low electrical conductivity may be continuously heated in the form of flat strip having any desired width. Likewise, the heating may be accomplished by applying current to the primary coil of any desired frequency within practical limits.

The furnace of this invention may be employed to anneal brass or other metal strip, or may be employed for such operations as normalizing, quenching, and drawing, for instance as is carried out on steel strips, or for the reflowing of tin or other metal coatings on metal strip, or for making copper clad steel sheet,

or other laminated sheet, and the like. The temperature to which the metal sheet is heated will depend upon the time of passage and current density of the electric current induced in the loop formed by the metal strip and contact rolls, which as stated above can be controlled by either or both the input to the primary coils or by the speed or travel of the strips through the furnace.

This invention accordingly provides means for the economical continuous heating of metal in strip form and has a wide field of utility without being subject to all the disadvantages obtained with prior processes and apparatus. The current induced in the metal strip is not required to pass through any brushes, bearings, or the like of high resistance. The contact rollers, for instance made of aluminum or copper or its alloys, which close the electrical secondary loop have a very low resistance, so that highly efficient heating is accomplished. It is to be understood that the embodiment of the present invention as shown and described is only illustrative and that the scope of the invention is not to be limited thereby except in so far as defined in the following claims.

Having thus described the claimed and desired to secure l. A furnace for continuously heating metal strip by means of electric current induced in the strip comprising means for advancing a plurality of spaced metal strips through said furnace, means for establishing an alternating electromagnetic field, a plurality of spaced metal contact rolls each in contact with each of said strips, and means for guiding at least one of said strips between said contact rolls through and in inductive relation to said alternating electromagnetic field.

2. In an electric induction furnace, for heating metal strip the combination which comprises means for advancing a plurality of spaced metal strips through said furnace, means for establishing an alternating electromagnetic field for each of said strips, a plurality of spaced metal contact rolls each in contact with each of said strips, means for advancing each of said strips between said contact rolls through and in inductive relation to its said alternating electromagnetic field, and means for cooling each of said strips after it has passed through its said electromagnetic field.

3. In an electric induction furnace for heating metal strip, the combination which comprises means for establishing an alternating electromagnetic held, two spaced parallel metal contact rolls, means for advancing two spaced metal strips in contact with each or said rolls, and means for guiding th portion or" at least one of said moving strips between said rolls through and in inductive relation to said alternating electrow magnetic held.

4. A furnace for continuously heating metal strip by means of an electric current induced in the strip comprising means for establishing an alternating electromagnetic field, spaced metal rolls, means for simultaneously advancing a plurality of spaced metal strips in spaced contact with each of said rolls, and means for guiding portion between said rolls of at least one of strips through in inductive relation to said field.

5. A furnace for continuously heating metal strip by means of an electric current induced in invention what is by Letters Patent the strip comprising means for advancing a plurality of spaced metal strips through said furnace, means for maintaining said strips spaced in said furnace, means for establishing an alternating electromagnetic field, means for guiding at least one of said strips through and in inductive relation to said field, a metal r011 electrically connecting said spaced strips at the ingress of said strip into said field, and another metal roll electrically connecting said strips at the egress of said strip from said field.

6. A furnace for continuously heating metal strip by means of an electric current comprising means for establishing an alternating electromagnetic field, spaced metal contact rolls, means for simultaneously advancing a plurality of spaced metal strips in spaced contact with each of said rolls, means for guiding the portion be- 6 tween said rolls of at least one of said strips through said field, and means for maintaining a substantially uniform temperature in those portions of the strips in contact with each of said rolls.

GOLDER P. WILSON.

REFERENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS

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