US2448012A - Induced heating of continuously moving metal strip with pulsating magnetic flux - Google Patents

Description

Aug. 31, 1948. R M- BAKER 2,448,012

INDUGED HEATING oF coNTINUoUsLT MOVING METAL STRIP WITHv PuLsATING MAGNETIC FLUX Filed sept. 9, 1944 wlTNEsEs:

ATTORNEY Patented Aug. 31, 1948 2,448,012 INDUCED HEATING F CONTINUOUSLY MOVING MET AL STRIP WITH PULSAT- ING MAGNETIC FLUX Robert M.

Westinghous burgh, Pa., a corp Balzer,` Pittsburgh, Pa.,

e Electric Corporation,

oration'of Pennsylvania Application September 9,

16 Claims. (C1. 21913) My invention relate quency heating; but is erally, to high-fremore particularly directed to refinements in induction-heating of elongated traveling non-magnetic material, such as strips, sheets, plates, and the like, for the'pu'rpose of controlling the quality or manner or the heating, or for maintaining the position of the material with respect to the field-establishing means, or both.

This invention is in the nature of a continuation-in-part oi my ccpending patent-application, Serial No. 521,229, iiled February 5, 1944, and of an improvement on the full disclosure thereof. It is also related to my copending patent-application, Serial No. 513,260, iiled December '7, 1943.

My invention is herein described in connection -with a preferred form in which elongated coilable metallic strip is passed longitudinally, or in the direction of its length, thro or alternating magnetic field for heat-treatment, the magnetic flux lines passing transversely through the faces oi the strip and inducing electrical currents therein which heat' the strip, a form oi induction-heating generally designated as transverse-flux induction-heating. In the embodiment herein described, flux lines may be considered to pass through one face of the strip, through the strip, and then out of the 'other face.

A difficulty of heating non-magnetic strip-like material by means `of a substantially uniform transverse iiux resides in the tendency of its lengthwise portions along and near the edges or thin side-surfaces of the strip to become hotter than its intermediate central portions. For the sake of brevity, I hereinafter call such portion, which includes the edge and inner contiguous material oi the strip for an extent short of the longitudinal center, as a border-portion. My associated application, Serial No. 521,229, shows and claims embodiments for counteracting or nullifying this tendency in a manner to cause the temperature distribution across the strip, from edge to edge, to be more uniform. One of the embodiments therein disclosed does this by providing weaker heat-inducing fields at the border-portions of the material. Speciilcally, this is done by displacing opposite cooperating magnetic-eld-producing field-structures so that they are laterally out of line. Another embodiment utilizes a fleld-aecting means, in the form of a shield or screen, along the longitudinal borders of the magnetic eld, which, in a sense, absorbs the current-inducing effect of the `iield along the border-portions of the traveling strip. The aforesaid patent-application, Serial No.

s, gen

ugh a pulsating y assgnor to East Pitts- 19454, Serial No. 553,381

521,229, places emphasis on and claims the former embodiment. The instant patent-application is more concerned with embodiments using fieldscreening means for not only preventing excess heating of the border-portions of the strip, but for the additional purpose of centering the strip between the field-producing field-structures.

Non-magnetic strip, such as aluminum or brass, for example, is for the most part self-centering when passed through a transverse-ux induction-heating furnace, such as disclosed or reierred to in my aforesaid patent-application, Serial No. 521,229. However, there may be a tendency for strip passing between the eldstructures oi such a furnace to rub against a pole-face, thereby scratching or otherwise marring the strip. I reason that an electrical force is created along the edges of the strip by the currents induced therein, which tends to drive such edges towar a field-structure. The current induce be considered to flow in oblong paths lying in the plane of the strip, These oblong paths have curved ends or turns in the strip border-portions, with components substantially paralleling the adjacent edge, and have straight connecting-parts extending across the width of the strip, between the end-turns, as more particularly shown in Fig. 4 of my patent-application, Serial No. 521,229. The current-now along the straight connecting parts of the oblong path cooperates with leakage flux in the core-slots of the field-structures to provide a centering effect on moving non-magnetic strip in the air-gap, which tends to -center the non-magnetic strip between the field-structures, but the current-flow in the end-turns'oi the oblong path reacts with the heat-inducing magnetic field thereat, giving rise to forces which tend to move the strip toward a field-structure. In any event, the strip may tend to bow crosswise in the work-passage. By the use of fieldaiecting means, or field-screening means, eX- tending over the edges of the strip along the lengthwise borders of the air-gap, or work-passage, not only is overheating of the strip borderportions reduced but the tendency for the strip to migrate toward a core is practically eliminated so that the strip passes centrally through the induction-heating furnace.

An object of my invention resides in providing an induction-heating furnace for controllably electrically heating traveling elongated strip-like material.

Another object o viding an electrical furnace i my invention resides in prowhich produces a inducing means.

Still another object of myinventionv is to" provide an induction-heating furnace having laterally adjustable held-structures to one or both of currents in these portions.

-Other objects, features and innovations of my invention will be discernible from the following the accompanying generally schematic yand simplied drawing, in which:

Yliigure 1 is a diagrammatic Fig. 6 is an enlarged sectional view, substantially on the line VI-VI of'Fig. v5, more clearly showing the cross-section of a preferred' screening-means; and

Fig. 7 is an elevational view'of a plate, secured to a field-structure, for supporting the screening means.

In Figures 1 and 2, a transverse-'flux inductionheating furnace is shown in a simplified form.

structures i and 2 having parallel ilatpole-'faces 3 and ll, respectivelyVspace'd kapart to form a shallow air-gap or work-passage 5. vThe eldcan be considered to pass from one pole-face to The strip passes downwardly .together by :a v.cross-member l l tion, is a 'tromagnetic nerd-structures I passage while the border-portions have a tendency to be forced to a field-structure and also to overheat. For substantially reducing both ber 8 along each longitudinal border of the workpassage 5, having plate-like legs 9 and i0 on opposite sides of the associated border-portion of the strip.

Each member 8 comprises a U-shaped member comprising the plate-like legs 9 and l0 joined Each leg has a free edge |.2.in the work-passage, so that the Us'of themembers 8 face each other. Secured kto thecross-member I i, in heat-exchanging relahollow member I3 cooling Iiuid may be passed for removing heat introduced in the legs 9 and and 2 are energized to provide the heat-inducing transverse ilux in the work-passage. Each of the legs 9 and have its free edge l2 serrated, as more strip'G and the field-structures l and 2.

Figs. 3 and 4 show an induction-heatingfurnace having automatic means for changing `the lateral .positions of the held-structures for controlling the relative positions of lafield-structure and an adjacentstrip-edge, as more described and claimed in my aforesaidpatentapplication, Serial No. ally-movable eld-structures i9 and'20 provide awork-passage 2| through which non-magnetic strip 22, having edges 23, moves downwardly after `passing around an upper roller `lll! which,

passage. Strip-moving means, represented by a pull-unit 26, pulls `the strip through the induction-heating furnace.

yEach of the vfield-structures I9 and 20 comprises vcomb-shaped laminations formed into a magnetic core 27 having like poles or teeth 28 and like slots .29, alternating with each other. "Windings or coils 3U are iiXed in the slots 29 and are so energized by any suitable alternatingcurrent source, connected to the.v coi1s.30, that a pole on oneeld-structure will have apolarity opposite to that of the directly opposite pole on the other 'Held-structure, .as indicated `by the ldesignations in Fig. 4. `field-structure is provided with a separate ning-means`3i which the topA of .the...associatecl eld-structure forv providing a light beam cutbya .strip-edge. -..A control rmeans v32, f associated Witheach. scanning .means 3l, is ,electrically connected thereto land respondsin accordance .with vthe extent, to which a strip border-portion interruptsk the light beam. The response. correspondingly `controls .the ,en-

ergization of a reversi-ble .motor 33 fortheassooiated'field-structure. Energization oa motor from the closest edgeof the strip.

Y In `the embodiment of Figs. 1 and 2, 'the screening-means are separate. from the eldstructures so that they can be'independently adjusted, but the screening-means can be xed or adjustably secured to the field-structures, as shown in Figs. 3, 4 and 5. In this last embodiment a screening-means 34 is secured to each field-structure for movement therewith. It comprises an elongated U-shaped member for controlling the effect of the transverse magnetic field on the border-portions of the strip 22, and for separating or screening this transverse magnetic eld from the field produced by the parts of the induced currents flowing in the portion of the strip, which lies within the screening-means 34.

Fig. indicates, in a limited way, a practical form of a field-structure having a screeningmeans thereon. The field-structure comprises a frame which includes top and bottom channelbars 35 and equally spaced frame-members 36. Lamlnations of a general form shown in Fig. 4 are clamped, in any suitable manner, between the frame-members 36 so as to provide the core 21. The core has an outer planar pole-face consisting of the extremities of the teeth 28. A fieldstructure of this sort is described in greater detail and claimed in the R. M. Baker et al. patentapplication, Serial No. 542,380, filed June 27, 1944.

A small plate 31 is secured to the upper channel-bar 35 and a small plate 38 is secured to the lower channel-bar, the plates being along the side of the pole-face which is maintained relatively inside of a strip-edge. The plates 31 and 39 adjustably support the screening-means 34 which comprises a relatively near plate-like member 39 and a relatively far plate-like member 40, considered with respect to the field-structure with which they are associated. The members 39 and 40 are of the same width with each having a straight free edge 4I at a longitudinal side of the screening means, which lies inside the magnetic field between the field-structures. The far member 40 is as long as the field-structure, but the near member 39 is longer, having ends protruding beyond the ends of the member 40, so that a screening-means can be secured to the plates 31 and 38 in a manner permitting its free edges to be adjustably positioned parallel to or at a slant to the direction of movement of the strip 22. To this end, the plate 31 has an elongated hole 42 for receiving anywhere therein a. fastening bolt of a bolt and nut means 43. The bolt passes somewhat loosely through a round hole 44 in the upper protruding end of the near member 39 which can swing thereon. The lower protruding end of the member 39 comprises a curved slot 45, centered on hole 44. Any part of the slot 45 can receive a bolt of a bolt and nut means 46. This last bolt passes through a somewhat enlarged hole 41 in the plate 38. By the use of suitable spacers and nuts for the boltY and nut means 43 and 46, the edges 4| ofthe screening-means 34 can be placed in various different positions with respect to the associate fieldstructure, in an obvious manner. The dashed line 4|' in Fig. 5 indicates an adjustment of the screening-means which places its edge obliquely in the work-passage, with the screening-means inserted further into the work-passage at the exit end. Preferably, the members 39 and 49 are equally spaced from the parallel median plane of the work-passage therebetween so that the members 39 and 49 for each screening-means 34 lie on opposite sides of a border-portion of the strip 22. The members 39 and 49 are abuttingly welded, or otherwise secured in good thermal relation, to' a relatively heavy metal end-bar 48' of the same length as the member 39. Welded or soldered to the outer surface of the bar 48 are a pair of hollow metal tubes having a U-bend 49 joining their bottom ends so as to provide a continuous passage for a cooling fluid which can be admitted and withdrawn from the other ends of the tubes.

The plate- like members 39 and 40 and also the bar 48 of the screening-means are preferably, but not necessarily, of a metal having a resistivity vlower than that of the strip being heat-treated. The members 39 and 40 should have a thickness equal to at least that of the "depth of current penetration in centimeters. This depth of penetration is usually considered equal to P 5030\/f where P'is the resistivity of the material of the members 39 and 49, in ohm-centimeters, and f is the frequency in cycles-per-second at which the transverse magnetic field alternates or pulsates. The thicknesses of the members 39 and 40 can be, and preferably are, greater than the depth of penetration. If they are made less, the transverse magnetic field between the fieldstructures, in effect, penetrates the screeningmeans 34, so that some of the flux gets through for heating the edge-portions of the strip and reacting with the current-flow therealong.

By means of tests an indication can be obtained of the manner in which a strip is heattreated when the screening-means occupies different positions. A hardness traverse across the width of the strip is preferred for obtaining the temperature distribution therealong. By variously adjusting the screening-means, skill coming with experience, an adjustment can be found for a given material which will provide a heattreatment across the width of the strip of utilizable uniformity, within a variation in temperature which, from actual tests, l'. approximate at 5% for aluminum. I can not state exactly how far a screening-means should overlap the strip. About one-third to one-half of a pole pitch seems to be the average overlap for aluminum sheet with the extending portions of the screenmembers 3'9 and 49 extending laterally beyond the end-bar 48 a width of about two-thirds of the pole pitch of the field-structures. If the overlap or the width of the extending portion is insufficient the screening of the magnetic field may not be so thorough. If too great, more heat may be lost in the screening-means than is necessary. It is also desirable t0 skew the screening-means, so that the straight edges 4| are oblique to the parallel frame-members 355 and the length-direction of the teeth 23. This makes the effect of the screening-means more gradual as the strip passes into and through the induction-heating means.

The spacing between the members 39 and 40 Should be sufficient to receive, with satisfactory working clearance, the thickest Istrip expected to be treated, but I prefer to make the spacing; greater so that the members can be faced with an, insulating lining 5! without decreasing the clear,` ance. Preferably, the lining is of some soft insulating material, such as absestos board, and at least as long as the far member 4i) so that sparking between the metal of the screening-means and the strip is minimized, and so that any occasional rubbing or contact of the strip on the inner sides. of the screening-means will not seriously mar or 7 Scratch the Lsurfaces of y,strip :having Ysurface nishes which must be protected during Aheattreatment. The extreme .edge of` the strip `should also clear the `screen-bar 48 suincient tominimize theepossibility of contact or vsparking therebetween.

While I havedescribed my invention in a manner understandable to those skilled in the art, an-d in forms which I now prefer, it is .apparent that renements and improvements-.and other embodiments may be made, utilizing the teachings and principles of my invention hereinv described.

I claim as my invention:

1. Transverse-flux heating-apparatus having a relatively shallow and Wide work-passage for receiving elongated strip-like material for-heattreatment, said heating-apparatus comprising. in combination, means for establishing a pulsating magnetic eld across the shallow part of the work-passage, for introducing heat vinto the material, and means comprising a screen along a border of the work-passage, extending only partially across a wide side of the work-passage,'for screening both faces of a longitudinal edge-portion of the material from decrease the tendency for electromagnetic lreaction between said material edge-portionand said eld to aiect the heating across the width of the material.

2. The combination with a transverse-flux induction-heating means including a work-passage, and means for moving strip-like material in a certain direction through said work-passage, said induction-heating means comprising linx-producing means having a distinct field-structure on i each side of said work-passage, for-providingfan alternating magnetic field in said Work-passage; ofa metallic screening-means alonga borderof the work-passage, for providing a field-screen betweensaid field-structures, on the one hand, and a longitudinal portion alongan edgeof the material, on the other hand, said metallic screening-means comprising an elongated ynon-magnetic metallic member having an edge inside the field, extending in said direction.

3. The invention of claim 2, characterized by said metallic screening-means having passages for cooling fluid along a portion thereof which is opposite to its said edge.

4. The combination with a transverse-flux-induction-heating means including a Work-passage, and means for moving strip-like-material ina, certain direction through said Work-passage, ysaid induction-heating means comprising flux-producing means having a distinct field-structure on each side of said work-passage, for providing an alternating magnetic rleld in-said work-passage; of a metallic screening-means along a border of the work-passage, extending in said" direction, for screening a portion ofthe material from theel'd, said metallic screening-means comprising a nonmagnetic metallic memberfhaving an edgeinside the eld, extending in said direction, r.and

member to a field-structure. l5. The combination with a transverse-'Ilumineachy side of said work-passage, for providingan alternating magnetic iield in said work-passage;

along -each border said field, wherebyv to .f

member being between one of said field-struc'- tureswand :a medial partof the .work-passage, wherebyto retain: the material centrally in vsaid work-passage.

i6..The invention of claim 5, ycharacterized by said members having an :edge in said neld, and means for --removing heat :introduced `into said 7. In combination.; a transverse-ilux inductionheating means including a work-passage through which strip-like ymaterial -can `bemoved longitudinally, said induction-heating means comprising flux-.producingmeans having a'eld-structureon eachside ofsaid work-passage, for providing an `alternating magnetic neld in ,said work-passage, means for moving'one of said eld-structures-wth respect to the other for changing theux 4distribution of saidiield in said work-passage.; and a screening-means along a longitudinal edgeof one of said ield-structures'for screeni-ng aportionof the .material from. said field, said member .being attached to one of said field-structures.

8. In combination, a transverse-linx inductionheating means yincluding-a work-passage through which strip-like material can be moved longitudinally, said induction-heatingmeans` comprising ilux-.producing `means having *a distinct fieldstructure oneach side 'of said Work-passage, `for providing anal-ternating magneticeld in said work-passage, meansy for laterally moving one of said-field-structureswith respect tothe other, and metallic screening-means longitudinally along bothvsides of the work-passagef-for screenyin gboth longitudinal portions of the material which are near and along an edge thereof-from the field, yeach of saidmetallic screening-means comprising two non-magnetic metallic members the `Iield, each of said screening-means ,being-secured to a diierent ,one of. said field-structures.

,9. The invention of` claim 8, vcharacterized by each of Isaid, screening-means having an edgein said eld `oblique tothe `direction -of travel for saidmaterial.

10. In combination, a transverse-flux induction-heating means including a Work-passage through which `strip-,like material can be moved longitudinally, said induction-heating means comprising linx-producing means having .a distinct eld-structureon leach side of-.said VWork- `passage, for providing a pulsating magnetic eld in said work-passage, means for laterally Vmoving one of. said field-structures with respect t0 the other,.and metallic screening-means along each longitudinal border of the work-passage, for screening :both longitudinal portions of the fmateriaLalong. its edges from the eld, each of 4said screening-means being generally U -shaped in cross-section and provided. with passages vfor cooling uid in.y the,.crossmember `of the U.

11. In combination, a,transverse-iiux induction-heating. means including a work-passage through whicnstrip-like.material ca-n be moved longitudinally, said. induation-heating `means comprising fluxfproducingmeans having a eldstructure on each `side of saidwork-passage, for providing a4 pulsating magnetic eld in said Workpassage, supportingA means for supporting one of saideld-structures for movement laterally of said work-passageso `that; it canifollow'an edge of the moving strip-like material, and a screening-means longitudinally along the-Work-passage for screening a border portion ofthe materialso that thel eld isscreened therefrom, said screening-means being attached to said movable eldstructure for movement therewith.

12. An electromagnetic structure of a type described, comprising a core having a .plurality of alternating poles and slots, the pole-faces lying in a generally flat surface, metallic field-screening means, and means attaching said metallic held-screening means to said core in front of said surface, said metallic screening-means being narrower than said core.

13. The invention of claim 12, characterized by said poles and slots being elongated and generally parallel, and said metallic screening-means comprising a non-magnetic metallic member spanning a plurality of poles and slots.

14. An invention including that of claim 13 but characterized further by said non-magnetic metallic member having an edge-portion obliquely passing across the face of a plurality of said poles and slots.

15. The invention of claim 12, characterized by said .poles and slot being elongated and generally parallel, and said metallic screening-means being elongated in a direction transverse to the length of said poles and along an edge of said core.

ROBERT M. BAKER.

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

UNITED STATES PATENTS Number Name Date Frary May 10, 1921 Northrup May 30, 1933 Adams Nov. 3, 1936 Ronci Aug. 2, 1938 Sessions July 30, 1940 Stansel Dec. 3, 1940 Sherman et al Oct. 27, 1942

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