US1377574A - Method of and apparatus for anneaxing sheets of metal - Google Patents

Description

F. C. FRARY.

METHOD OF AND APPARATUS FOR ANNEALING SHEETS 0F METAL.

APPLICATION FILED DEC-8.1919.

1,377,574. Hmnented May .10, 1921.

L I f, 7 7

I WIIINESSIES l2, 7 f 6 INVENTOR the magnetic field and the-number. of oscil- U D S A ES,

OFFICE? V FRANCIS o'jrnAnY, or oAKMoN'r, PENNSYLV NIA,

rANY or AMERICA, A conronA'rron orrnNNsYLvANIA.

mnrnon or Ann APPARATULS ronANNEA Lnve snnnirs or METAL.

To all whom it may concewt:

Be it known that I, FRANCIS a resident of Oakmont. in. the county of Allegheny and State of Pennsylvania, have invented a new-and useful Improvementin Methods of and Apparatus for Annealing Sheets of Metal, of which the following is a specification. I i

This invention relates to gmethod of and apparatus for annealing sheets of metal, such as alumi num,-copper, or other metal.

Its object is. to'provid'e a method and apparatus whereby such sheets may be .profgressively and continuously anneal ed at a predetermined temperature and much more rapidly .and uniformly than by existing methods.

. Generally stated, the invention comprises ,a method-by which the sheet of metal to be annealed is'movedthrough an alternating magnetic field ofcontrolled strength, and

in which the field and sheet arerpreferably so positioned, relative to each otherthat the magnetic lines of force-are approximately perpendicular to thesurface of the sheet,

whereby powerful eddy currents are "set-up .in the sheet and develop heat" uniformly throughout the body-of the metal (2', 6., be-

tween its twosurfaces) in that portion of the sheet through which the magnetic field passes. Thus by movingr the sheet in its own plane across such magnetic field all portions of it are subjected to the same heating efi'ect andfor the same period of time,

and since theradiation losses areconstan't for a givenset of conditions, 'allparts of the sheet can be quickly broughtto; the] same temperature, Furthermore this tem-- perature can be controlled for a given thickneSS of sheet by varying the strength of lation per second. I

It is known thatif the metal a a sheet can all be brought to the proper temperature, the annealing action is extremely rapid, if not instantaneous. The long time re- ,quired forflannealing the metal in ordinary types of annealingv furnaces isdue to the diificulty of heating all of the metaltolthe desiredtemperature without danger; of overheating and. the resultant ury to some of it 'unles the temperature of a furnace is kept very close to the; annealing tempera Specification of Letters Patent. I Patented pla 10 1921 Application filed December 8, 1919. Serial No. 343,240., i

of the presentmethod all partsof the metal injuriously affecting any part of the sheet. In the accompanying drawing Figure 1 1 a diagrammatic view illustrating the principle of theinvention; Fig. 2 is a longitufdinal sectional view of one form of, appa-' ratus suitable for carrying out the method; and Fig. 3 1s a plan view of'the lower transformer member of Fig. 2. y

j The principle of my invention is illustrated in'simple form in; Fig. 1 in which there is illustrated a transformer consist .ing of an iron magnetic circuit 1, and .an exclting c0112 connected to a suitable source of alternating current 3, and in which 1 the magnetic circuit is provided with an air "gapi through. which a sheet or strip of metal Q5 such as aluminum .foil or sheet) is moved by means of any suitable mechanism, such for instanceas feed rollers (not shown). Themovement of thissheet or strip, as will be understood, is in a direction perpendicular to theplane of the paper, so that such sheet or. strip is caused to continuously pass through the field at the gap 4, and at such av ratethatthe eddy currents produced in any given portion of the sheet or strip dur- I ing it passage through this field are just sufiicient to heatit to the desired temperayture. After-s 1ch heating is attained the sheet or strip cools toroom temperature and tion can be raised in this manner is dependent upon (.1) thetimethat a given portion :of it remains inthe magnetic field, (2) the strengthof the field, (3) the number of alternations of the exciting current per second, and. (4) the rate of loss of heat from the surface ,of the sheet "or strip byradiafield and the number of alternations on the exciting current per" second, as well as the'other conditions named, can be read: ily varied and controlled, any given sheet or strip of metal can be quickly raised to the y desired annealing temperature, without danger of, overheatingjany portion thereof.

Assre'non 'ro ALUMINUM cominto the" piles of metal, Since by the use i is ready .for the next operation which it may be desired to perform upon it. The maximum temperature to which a sheet 'or strip of given metal of a given cross sec- .tion. Inasmuch" as the strength of the This principle can obviously be applied in many ifierent ways and by various forms of-apparatus. Figs. 2 and 3 show a suitable form of apparatus for the continuous annealing or aluminum sheet or foil. These views illustrate a structure 1 of transformer steel (laminated) which is built up to form a magnetic field having poles 6 and spaces or slots 7 for holding the exciting coils 2 through which the magnetizing current flows. The coils may be arranged around alternate poles only, as shown in the drawings, or they may be wound around each pole ifv desired; but in either case it is preferred to so arrange the windings that, as

- indicatedin Fig. 3, at anygiven instant alternate poles will have the same magnetic character and adjacent poles will be of opposite character. a

A laminated pole-piece 8 is supported in any suitable way a short distance above the magnet described, leaving a suitable gap between the two for the passage of the strip or foil 5. In order to minimize radiation from the strip or sheet to the magnetic circuit, suitable sheets 10 of an electrically conducting but non-magnetic material (such as.

nickel sheets) are placed parallel to and immediately above or below the sheet being annealed,between it and the two halves of the steel magnetic circuit,and the spaces between each of these sheets and the mag netic circuit are filled with some refractory heat insulating substance 11 such as infusorial earth. When the magnet is excited by alternating currents from a suitable source, these nickel sheets will be heated by eddy currents set up within them, and will radiate heat toward each other, and also tend to radiate heat toward the steel magnetic circuit, but the latter radiation is to a large extent prevented by the-heat insulation 11. Eddy currents will'also, of course, be set up in the strip or sheet 5 of metal passing between the nickel sheets. By properly choosing the thickness and electrical re sista-nce of the nickel sheets a condition can be secured such that the power consumed 11. them is just sufficient to maintain them'at approximately the desired annealing temperature, thus enabling substantiallyall the heat which is produced by the eddy currents in the material being treated to be utilized for the purpose of raising the temperature ofthe material being treated to the desired point, and by preventing radiation losses to bring the surface of the moving sheet to the same temperature as the interior thereof. Th1s is particularly easy whenthemetal to be treated is one having a' good electrical conductivity, such as aluminum or copper. The nickel sheets 10 tend to expand on being heated and therefore suitablesprings 12, or equivalent devices are provided to maintain them in a state of tension and thus prevent buckling. 13 indicates suitable feed rolls for progressively moving the sheet or strip through the magnetic field.

This apparatus described permits the maximum temperature which is to be attained by the material being treated to be closely controlled and also permits this temperature to be attained through the whole mass of each successive sheet, it enables the conditions to be so chosen that the metal being treated may be only partially annealed, that is. softened to a predetermined extent, instead of being completely annealed, or made dead soft. This feature is of particular advantage with metal, such as aluminum foil, where complete annealing of the material would make it too weak for certain subsequent operations, for instance, too weak to stand the necessary tension involved in subsequent passages through reducing rolls.

The arrangement shown-in the drawings is illustrative merely of the principal fea- V tures of suitable apparatus. 'Actual commercial apparatus may difier considerably in detail from that illustrated, as will be apparent to a person "skilled in the art.

I claim: I

1; The method ofcontinuously annealing sheet-metal, consisting in passing it through an alternating magnetic field whose lines of force out transversely through the sheet, and thereby inducing in the metal eddy currents of sufiicient intensity to cause the metal to be uniformly heated to an annealtemperature by varying oneor moreof the factors-rate of movement of the metal, strength of the magnetic field, and frequency of the exciting'curre'nt.

w 8. The method of continuously'annealing sheet metal consisting in passing the same between stationary metallic sheets disposed on both sides of the sheet to be annealed and located in an alternating field whose lines of force cut said stationary sheets, the electrical resistance and thickness of the stationary sheets being such that they become heated to the desired temperature by eddy currents induced therein.

1. The method of continuously annealing sheet metal, consisting in passing it through an alternating magnetic field whose lines of force cut the plane of the sheet, thereby inducing in the'metal eddy currents of sufiied to an annealing temperature during its passage through said field, and reducing the amount of heat radiated from the moving sheet during its passage .through'the magnetic field by inducing eddy currents in stationary metallic sheets disposed in said magnetic field on both sides of the moving sheet.

5. The method of partially annealing strength and moving the sheet at such rate that all parts of the metal are heated to the same temperature terval of time. I

6. An apparatus for the continuous anand for the sameinnealing of sheet metal, comprising a magmy hand. 7

netic circuit having oppositely disposed I poleswith a gap between them, means for exciting said circuit with an alternating current, and means for passing a sheet of metal through the gap between the poles whereby the lines'of force passing from pole to pole cut transversely through the plate.

7. Apparatus for the continuous annealing of sheets or strips, comprising an open magnetic circuit, an alternating current source for exciting said magnetic circuit and thereby producing a magnetic field, a pair of electrically conducting'sheets located in said field and spaced apart, and means for passing the sheets or strip to be annealed between said electrically conducting sheets and through said magnetic field.

In testimony whereof, I have hereunto set a FRANCIS c. FRARY.

Witness:

' a G; G.'TRILL.

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