US3031555A - Induction heating - Google Patents

Description

April 1962 N. v. ROSS ET AL 3,031,555

INDUCTION HEATING Filed July 15, 1959 INVENTORS. /V/CHOAAS V. Foss M/ALTEE VANGfL OFF mental.

United States Patent O This invention relates to the continuous heating of strip material such as relatively thin sheet metal by means of inducing electrical current to flow therethrough. More 7 particularly, this invention relates to an inducting device comprising a continuous conductor element which is formed to provide a loop or opening through which the strip material is continuously fed at a predetermined rate. Electrical current at a suitable frequency is provided to the conductor element which induces current in the strip material causing the same to be heated according to well known principles.

In inductors of this type, greater efiiciency can be obtained by offsetting the upper and lower portions of the conductor relative to one another which results in a more effective flux threading area. However, prior devices of this type have the disadvantage that in the heating of strip the induced currents tend to crowd at the strip edges with the result that said edges become overheated as compared with the center of the strip.

This adversely effects the strip by causing it to buckle or warp, and in extreme instances, overheating can cause the edges to melt. When the inductor is used for drying or bonding, the non-uniform heating is extremely detri- A primary object of this invention is to provide an inducting device which will result in more uniform heating across the strip.

Another object of this invention is to provide a device of the above type capable of efiiciently heating very thin strip material at lower frequencies than heretofore thought possible.

A further object of this invention is to provide such a device which is simple in structure, is economical in production, and is highly efiicient in use.

Other objects of the invention and the invention itself will be understood from the following description and the accompanying drawings, in which said drawings:

FIG. 1 is a top plan view of the inductor device of this invention showing strip material passing therethrough;

FIG. 2 is a section view taken along the line 2-2 of FIG. 1;

FIG. 3 is a section view taken along the FIG. 1;

FIG. 4 is a view similar to FIG. 1 showing a modified form of the present invention;

FIG. 5 is a section view taken along the line 55 of FIG. 4; and

FIG. 6 is a diagrammatic plan view of the inductor image showing the current path, induced thereby.

Referring now to the figures of the drawings in all of which like parts are designated by like reference characters, and particularly to the embodiment of FIGS. 1-3, at 10 we show a single turn inductor adapted to pass completely around a longitudinally moving strip 5. The inductor 10 comprises a single, continuous conducting element which forms an uppermost conductor 11 spaced slightly above the strip and a lowermost conductor 12 spaced slightly below said strip. The ends of the conductors 11 and 12 are joined at one end thereof by means of a diagonal connector 13 which is spaced slightly laterally from the edge of the strip and passes downwardly and rearwardly from the upper to the lower conductor. The opposite ends of the conductors 11 and 12 are provided with short diagonal portions 15 and 16 which terminate in the plane of the strip in two laterally line 33 of "ice projecting, parallel terminals 17 and :18. Current for the inductor 10 is provided in any suitable manner such as through a transformer 20 at the desired frequency which would be determined by the thickness of the strip 5.

By referring to FIG. 1, it will be noted that the uppermost conductor 11 is positioned at right angles to or transversely of the edge of the strip 5 at the medial portion 11c thereof and that it is provided at the ends thereof with obliquely directed portions 11a and 11b which are directed laterally and forwardly, the portion 11a connecting with the upper end of the diagonal connector 13 and the portion 11b connecting to the short diagonal portion 15. The conductor 12, which is positioned below the strip 5, is similarly provided with a medial region 12c and with laterally and rearwardly directed oblique portions 12a and 12b connecting with the lowermost and rearwardly directed end of the diagonal connector 13 and with the short diagonal portion 16 respectively. t will be further noted that the upper conductor 11 including the medial region and the oblique portions 11a and 11b lie in a common plane spaced above the strip 5 and that the lowermost conductor 12 including the medial region 12c, and the oblique portion 12a and 12b lie in a common plane spaced slightly below the strip 5. The diagonal connector 13 passes downwardly and rearwardly from the conductor 11 to the conductor 12 at one end of the said conductors and the short diagonal portions 15 and 16 pass downwardly and upwardly respectively and are united with the terminals 17 and 18 at the other end of said conductors.

By referring to FIG. 3, it will be seen that the conductors 11 and 12 are offset relative to each other thereby obtaining a more effective flux threading area than would be otherwise obtained if said conductors were vertically aligned. The oblique portions Ila-11b and -121) prevent the induced current in the strip from flowing outwardly and crowding the edges of the strip whereby said edges would become overheated. The present construction concentrates more of the effective flux toward the center of the strip whereby said center is relatively slightly more heated than the edges.

This is demonstrated in FIG. 6, which shows diagrammatically the current paths which are induced in the strip 5 by the inductor 1G. Said current paths are designated x, y, and z wherein y represents the central and largest path bounded by the conductors 11 and 12. The paths x and z are relatively much smaller than the path y and can be made small enough that the currents cancel out leaving only path y to do the heating. In the diagram as shown, the path y defines the area of greatest heat concentration, and due to the oblique portions 11a-11b and 12a-12b and the manner in which they cross, said path y is confined to the laterally central area of the strip 5 and away from the edges thereof. The induced currents are thereby prevented from crowding at the edges of the strip.

The heating pattern which is effected by the above described device is illustrated in FIG. 1 by means of the heat patterns designated a, b, and c. It will be understood that the strip 5 is moving in the direction indicated by the arrow d. When any given transverse section of the strip passes immediately from under the inductor it the heat pattern will be substantially as illustrated at a wherein the forwardly curved portion of the pattern indicates that more heat is present in the central portion of the strip than is to be found at the edges thereof. As the same section proceeds to the area indicated by the heat pattern b, it will be noted that said pattern begins to flatten out transversely of the strip whereby the edges and the center of said strip attain more uniform temperatures. As said section moves on to the area of the heat pattern indicated at c, the temperature will have 3,0 3 become "equalized whereby it is uniform across the entirewidth of the strip.

It will be readily seen that with the device of the present invention, overheating of the edges is eiiectively pre- "vented and uniform temperature across the width of the strip is attained shortly after the strip passes the inductor 10. The result is an over-all greater efiiciency in heating and makes .possible the efiicient heating of thinner strip at a .lower relative frequency than has been heretofore thought possible.

FIGS. 4 and 5 illustrate amodification of the invention of FIGS. 1-3 wherein a multiple turn inductor 39 is utilized and is formed by a single conducting element which passes around the strip 25 more than once. Each turn of the conductor element around the strip 25 comprises a pattern or form similar to that of FIG. 1, each subsequent turn being spaced slightly from the previous turn and being co-planar therewith. The first turn of the :inductor comprises an upper conductor 31 having obliquely directed portions 31a and 31b and a lowermost conductor 32 having oppositely directed oblique portions 32a and 32b. The conductors 31 and 32 are connected across the plane of the strip and beyond the edge thereof by means of a diagonal connector 33 at one end. The opposite end of the conductor 32 is connected through a diagonal connector 34 to a second, uppermost conductor 35 having obliquely directed portions 35a. and 351; which are parallel with but spaced from the obliquely directed portions 31a and 31b respectively. The upper conductor '35 is connected to a lower conductor 36 having obliquely directed portions 36a and 36b. This latter connection is made by means of a diagonal connector 37 which is positioned parallel with and spaced from the diagonal connector 33. The upper conductor 31 and the lower conductor '36 are provided with laterally directed, straight terminal portions 39 and 40 connected to a suitable source of current such as a transformer 41 as provided in'the first embodiment of our invention.

invention may be made, such as changes in size and dimension, without, however, departing from the spirit thereof or the scope of the appended claims.

What we claim is:

1. An inductor device for heating strip material comprising a single conducting element passing around said strip and spaced therefrom, said conducting element comprising upper and lower transverse conductors positioned respectively above and below said strip, and extending beyond the edges thereof, said conductors being parallel with said strip and horizontally offset along the longitudinal dimension of said strip, portions adjacent the ends of each conductor being obliquely directed in a horizontal plane in the direction of the other conductor and passing across the edges of said strip, a diagonal connector portion connecting said conductors adjacent one edge of said strip, said conductors connected to a source of electrical current adjacent the opposite edge of said strip.

2. An inductor device for heating strip material cornprising a continuous conducting element formed to provide at least one turn around said strip, said conducting element comprising upper and lower conductors spaced respectively above and below said strip in planes parallel to said strip, said conductors having transversely disposed medial portions and obliquely angled end portions lying in a common plane, said end portions of each said conductor being angled in a common longitudinal direction relative to said strip and the end portions of said upper conductor being oppositely directed from that of said lower conductor, said upper and lower conductors so disposed that vertical planes defined by the end portions of said upper conductor intersect vertical planes defined by the end portions of said lower conductor.

3. An inductor device for heating strip material comprising a continuous conducting element having a plurality of turns passing around said strip, said conducting element comprising upper and lower conductors spaced respectively above and below said strip in planes parallel to said strip, said conductors having transversely disposed medial portions andobliquely angled end portions disposed in a common plane, said obliquely angled end portions of each said conductor being angled in a common longitudinal direction relative tosaid strip and the end portions of said upperconductors being oppositely directed from those of said lower conductor, :the upper and lower conductors of each said turn being so disposed that vertical planes defined by the end portions of the upper conductor of said turn intersectivertical planes defined by the end portion of the lower conductor otthe same said turn.

4. An inductor device for heating'strip material comprising a conductor'spaced vertically from said strip and extending outwardly beyond the edges of said strip, the portions of said conductor which pass over the edges'of said strip beingpositioned obliquely relative to said edges disposed in a common plane to amedial portion thereof, and the medial portion of saidconductor being positioned transversely and at rightangles to the edges of said strip.

5. An inductor device for heating strip material comprising a conductor spaced vertically from said strip'and extending outwardly beyond the edges of said strip, the portions of said conductor which pass over the edges of said strip being in a plane parallel to the plane of the strip and directed obliquely relative to said edges, the medial portions of said conductor beingpositioned in the same plane as said obliquely directed portions.

'6. An inductor device for heating stripmaterial comelement comprising portions which extend outwardly beyond the edges of said strip, said outwardly extending References Cited in the fileofthis patent UNITED STATES PATENTS 2,897,328 Alf et a1 July 28, 1959

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