US2365021A - Electric furnace machine - Google Patents

Description

H. A. STRICKLAND, JR

ELECTRIC FURNACE MACHINE I Original Filed March 21, 1941 2 Sheets-Sheet l INVENTOR Horoki ASirLcklcnd, Jr. BY i W ATTORNEY 4b FIG. 10.

Dec. 12, 1944.

H. 'A. STRICKLAND}, JR

ELECTRIC FURNACE MACHINE Original Filed March 21, 1941 2 Sheets-Sheet 2 Patented Dec. 12, 1944 UNITED STATE ELECTRIC FURNACE MACHINE Harold A. Strickland, J12, Detroit, Mich., assignor to Budd Wheel Company, Philadelphia, Pa., a corporation of Pennsylvania Original application March 21, 1941, Serial No.

384,503. Divided and this application September 18, 1941, SerialNo. 411,297

24 Claims.

This application is a division of my copending-application Serial No. 384,503, filed March 21, 1941.

My invention relates to .coils for furnaces for heating by electromagnetic induction, and particularly to those which can be used or are intended for use in the heating of bar or billet stock for forging purposes. In such furnaces, bar or billet stock of either solid or tubular form, and either circular or angularin cross-section, is inserted within a coil adapted to be supplied with power from an alternating current source, usually a high-frequency alternating current source of considerable voltage, and the power being turned on to the coil, heating currents are set up within the mass of the bar or billet to be heated due toothe electromagnetic induction from the coil itself. These currents heat the bar or billetto a forging temperature. Such a bar or billet is commonly called a workpiece. The objects of my invention follow.

Outstandingly I aim to make such a furnace a machine. ThisI achieve through the construction, organization, and automatization of its various component parts, e. g., the heating cil* into which the workpiece is thrust for its heating, and all appurtenant devices. I have aimed to achieve in this machine a quantity production apparatus outstandingly adapted for installation in connection with high-speed production systems and lines common in todays industry.

Reliability, consistency, and continuousness of operation have been important ends which I have had in view. Construction and arrangement of parts, and automatization have also played animportant part in the attainment of these ends. Automatization and coordination of automatization in interlocking of control elements have enabled me to attain these ends to an extent practically eliminating the personal equation of the operator, and likewise eliminating disturbances of these several factors, reliability, consistency,

and continuousness, occasioned by disorders of any kind emanating from whatever source reaching the machine.

One object of this invention is to produce an inducing coil adapted for operation at relatively high voltage so that the time for heating the work with a given current frequency is shortened. One factor contributing to this result is the hermetic encasement of the coil sothat gases and fumes as well as moisture, scale, and dirt of various kinds cannot get in between the coil convolutions. Such sealing is more than mere insulation or mechanical protection.

Another object is to provide .an improved work supporting track' within the heatingtcoil. The

track is water-cooled to aid in conducting excess heat from the surface of the work. A further object is to construct this track so as to reduce the heat developed in it. Yet another object is to provide an improved construction of heating coil and its appurtenant parts.

There is delineated in the drawings that embodiment of my invention now best known to me, but it will be quite apparent that it is subject to yet other embodiments.

Of the drawings:

Figure 1 is a transverse section, transaxial to the heating coil;

Figure 2 is an enlarged horizontal cross-section of the heating coil in a view including the axis of the coil;

Figure 3 is a transaxial section of the heating coil on line 6-6 of Figure 2;

Figure 4 is an enlargement of a portion of such a transaxial cross-section of the coil taken on a line such as |-'l of Figures 2 and 5;

Figure 5 is a correspondingly enlarged portion or a longitudinal section, being a view takenon line 88 of Figure 4 looking in the direction oi,

the applied arrows; 7

Figure 6 is a rear end elevation of a detail of the heating coil showing the detail ofthe mounting of the work-supporting rails which lie Within the coil taken on line 99 of Figure 2;

Figure 'l is a transaxial cross-Section similar to that of Figure 3 applying to a modified form of coil and accompanying workpiece, supports within the coil.

Figur 8 is a perspective view of a bridge-piece connected with a heating coil support clamp;

Figure 9 on the same sheet is a transaxial segmental section showing the bridge-piece of Fi ure 8 in use in connection with a special heating coil;

Figure 10 appearing on the sheet containing Figure 1 is a fragmentary, rear end view of a heating coil showing means for securing workpiece guide rails in connection with the special coil of Figure 9; V

Figure 11 is a diagrammatic illustration of a modified form of the magnetic core.

The heatin coil 40 and the supports for the workpiece within it are of a very special construction which appears'outstandingly in Figures 1 to 6. The coil per se 40 is comprised of hollow conductors 6| generally 01 square shape. Cooling water in sufficient volume to cool the coil 40 is passed through the hollow 62 of this conductor. particularly Figures 2 and 5) are insulated from each other by a spiral of mica 63 or the like,

or else the conductor throughout its length may be wrapped with an insulating tape of an appropriate character, preferably heat-resisting,

Individual turns of the coil (see inside and outs d insulation M. II. s well as insul tion it bet een t e coil s wound on a suitable mandrel (not shown) prep erably a ql fip lb man rel W J', lll l lfll' y there s plac d a a mandre an nn mo t sil inder o hish sre s m -a heets capab e of hi at si tance and impe v ous to ma ture and with a resilient insu ating n 6E9 super m os d-on $1 inn rmost n e at i a N is a ec ndary c linder or mice. 61 which may be com osed o "micanite" r h r omposi e or compound d mice also bonded with varnish. Fi ure 5 is a section of one end of the coil, the right-hand end, as it appears in Figure 3. From this it will be seen that micanite cylinder I! is shorter by a fraction of an inch than the mica cylinder 86, and that the endmost turn ll of the coil 4.. lies axially inwardly of the end of cylinder 6'! a fraction of an inch. thus wordi g a stepp d construction oi the insulating cylinder ends. Coil 48 as insulated at N, ,5 is, wound directly upon cylinder 61. Before the segmented strips are laid on, the coil is wrapped in a single layer of bonded mica. set in varnish. This provides a very important seal against moisture if such should collect in the voids between the outside segments 59. Laid axially upon the exterior of coil 40 are segmental strips I or Micarta, Bakelite, or the like, which together completely en-. case the outer periphery of the coil 40. These longitudinally extending insulating strips 0! are bound in place b overlapped turns ll of in: sulating tape given a water and moistureeproof treatment and baked. The opposite ends 01 the insulating strip 00 are provided with jogs H radially juxtaposed to the stepped ends 01 the insulating cylinders I, I]. A series of mice rings 12 are laid over the end of cylinder I! and against the end turn I! of coil 40, and a unit insulating ring of ldicarta or Bakelite ll is laid over the end or mica cylinder II, these rings o pl ly nilfnc the s ac s between h e dmost turn 6! and the ends oi cylinders I, 6! on the one hand, and ot the stripe I! on the other, They a e s aled in p s tion b coat n and h le ing with a resilient insulating compound. In such fashion the coil 40 is made and hermetically sealed inside, outside, and at each of its ends whereby heat may not crack the insula-. tion, and moisture may not penetrate it.

Heat is prevented from being directly radiated from the red or white hot surfaces of a work.- piece being heated to the mica insulating cylinders 86, 61 by an annular liningof insulating fire brick 1', also shown in Figures 1 and 2. This lin ng of ilrebrick like the insulating outer covering 6 is comprised of longitudinally-laid segments. However, instead of containing the end edges and hermetically sealing together by intervened baked insulating compound, as in the instance 01' the bars I, the individual segments 15 of this lining are spaced from each other by water-cooled work-supporting rails ll intervened between them, and so constructed as to. hold them radially outwardly against the surface of mica cylinder 8!. To this end the opposite side edges or the segments ll of insulating line. ing (preferably comprised or a high-grade ins sulating ilrebrick compound), charntered at 11, e Qhamf e m aatinc a s i t 10a 1'. and the rails 10 are provided with welded-on sheet metal holdl lfl clips 1; of the form hav n a branch x e dins on each s de. or. the r 1' at the angle or the chamber 11 whereby to lie flatly against the chamfer and within the depth of the i9:

The rails Ii are held radially outwardly by three sets 0! supports, one at the middleand one at each end. That in the middle is shown especially in Figures 2 and 3 to comprise an expanding ring 00 of sheet metal. The ring is rmed of the Overlapping wings in or sheet or strip stock welded respectively to opposite sides of the rail 15. and joined in their overlapping portions by a clampingscrew connection I! havin: all 891 993494158 lost-motion connection (not shown) between the overlapp d ends permitting the expansion of the ring I0 to a diameter which moves the rails ll toward or against the inner surface of the mica 6i, and retains them in that position when the devices 82 are tightened' up. Ea'ch'ot thesejoints is insulated by a set of amber mica washers "a. These washers will stand a temperature of 1000 C. If these were not insulated, the ring would act as a shortcircuited turn of a, transformer.

The devices at the opposite ends of coil 40 are diilerent. At the upper or right-hand end of the coil ll as illustrated, there is secured to each rail 16 an outwardly and radially extended sup portin stud l3. These studs are passed respectively through slots or holes, as may be preferred, in the outer ends of metal or insulating material (such as Bakelite or Micarta), rails 84 laid longitudinally over the length of the exterior of coil 40 to project slightly beyond each end. As shown, the rails are of channel crosssection to afiord less generation of eddy currents as well as lightness with strength. At the opposite end (the left-hand, as shown) the projecting ends of work-supporting rails 18 are engaged, Within the loops .5 of screw-hooks 86, thl threaded outer ends of which are carried radially through apertures or slots in the opposite ends of the rails, there being preferably though not necessarily one securing rail 84 for each work-supporting rail 18. When the nuts 81 respectively on the ends of studs 03 and screw-ho0ks 8 are tightened up, they hold the outer ends of the rails I6 toward or against the inner surface of the mica cylinder 8 as does the expanding ring 00. Thus the rails 16 are held in position throughout their length and firmly hold the firebrick lining 15 in place. There may be provided as many expanding rings 80 as are needful to meet the requirements of coil length.

The securing clips 19 are not of an adjacent continuous series. They are separated by wide intervened spaces, In these spaces there are edge-welded in the radial planes of the coil axis A .A to the tubular rails ll, an intervened series of workpiece supports 88 in the form of sheet or strip metal fins whose lengths are axially extending. Their leading edges are chamfered as at 89, to prevent obstruction to the movement of a workpiece being inserted within the coil. They are spaced slightly at each end i'rom the intervened flrebrick securing clips I9. Their radially inner edges 90 are parallel to the axis of the coil Iii though not radially equidistant, and their locus is a cylinder of radius R whose center C is eccentrically above axis A-.A of coil whereby the axis of workpiece of radius W coincides with axis of coil. (See Figures 3, and 4,.) The diameter of the locus cylinder 01 center 0. is slightly greater than the diameter of the heated workpiece to provide tolerance sufllciently great to prevent bindin: due to expansion. Rails I0, clips 19, expanding rings 80, and work-supporting fins 8B areall of high heat-resisting metal, especially fins 88. Water is continuously circulated through the tubular rails 16 in pairs in series, or in series as a group, the connection being generally illustrated by a dotted line connection BI between the two outermost tubes I6 of Figure 2 shown as provided respectively with inlet and outlet openings 92, 93 at the opposite ends ofrails 16. Inlets and outlets are each provided with moisture-discharging lips or flanges 94 which prevent accumulated moisture from running down the rails into the coil.

The entire system of equidistantly spaced polygonal workpiece-supporting rails. 16 and firebrick lining may be bodily removed from the interior of the heating coil 40, by simply removing nuts 81 and the screw-hooks 86, radially removing bars 84, and drawing the ensemble axially outwardly (that is to say, to the right in the instant case). This enables the replacement of worn or broken firebrick segments 15, and repair toany of the rails which may for any reason need repair. To facilitate this the expanding ring 80 need not quite expand the rails I6 and the firebrick segments I into contacts with the inner mica cylinder I56, but provides such tolerance as will enable the ensemble to be slidlongitudinally outwardly without intermediately releasing the clamping screws 82. Ring 80 and the connected rails are readily adjusted to tolerance diameters by fitting to a suitable mandrel and checking by a sizing ring before placing in the coil. However, if need be, a suitable tool will enable the clamping screws 82 to be reached, and one or more of them released. The individual. segments axially separated in the middle by the expanding ring 80 may be individually placed in position or axially withdrawn from the inner or the outer end of the coil, as the case may be, merely by loosening the respective screw-hooks 86 and studs 83 once the expanding ring '80 provides the proper tolerance at their axially inner ends. Thus removals and replacements may be made without removing the ensemble. All of this, of course, is readily achievable when the heating coil and the workpiecesupporting rail ensemble are disassociated from the housing. However, all of these operations may also be achieved while the coil and rail ensemble are in place on the machine, merely by removing hood 41 and front plate 50 and its supported parts as a unit. They together constitute a unit subassembly and may he slid off forwardly.

Heating coil with its workpiece supporting I appurtenances is mounted with its axis coinciding with a general horizontal axis AA of the furnace machine, by supporting it from coil centering c-clamps 98 carried from and forming a part of pedestals erected upon and secured to the cast foundation p ate of the table-portion of the housing. Referring particularly to Figure 1 for the-moment, it will be-seen that the stock-gauge per se comprises a tubular arm I43 lying on the axis A-A of the coil 40, and supported from a plate of the coil casing for reative axial adjustment by a clamping bracket bolted'to the support plate. The tubulararm I43 projects rear wardly through the support plate a considerable distance allowing it to be axially adjusted back and forth, to adjust its forward end with respect to the axially inner end of the coil 40, thereby to engage an inserted workpiece in different axial.

positions within the coil 40. Once adjusted for the proper gauging of the stock, for the proper heating thereof through the properlength. the

gauge arm I43 may be firmly clamped in its supported position.

Mounted on this adjustable arm I43, as shown fixedly although it may be adjustable, is magnetic core 91 comprised of an annular series of radiallyextending, radially-tapering laminations, the details of which are no part of the present invention and are, therefore, not shown. Suiiicient to say, they are bound in place upon the support I43 or equivalent support byany suitable means such, for example, as the commonly known interlocking tongue and groove device I45. This magnetic core is of considerable diameter and axial extent. Therefore, a considerable magnetic mass is shown as of approximately the diameter of the workpiece accommodatable by coil 40. As projected in juxtaposition to the end of a workpiece, it receives the flux flowing external to the coil 40, collects and concentrates it, and conducts it more .or less directly axially inwardly of the inner end of the workpiece. Itsutilization and relative adjustment with respect to the end of the workpiece very considerably improves the reluctance of the magnetic circuit and affords a very flexible control of the distribution of heat in the heating of the axially inner ends of the workpiece. Thus with the proper gauge of the stock in position within the coil 40, plus adjustment of the flux through its axially inner end, irregular or imperfect heating or excessive heating in any portion in the inner end of the bar may be avoided. Thus it combines with such' portion of the stock as may project from the outer end of the furnace to achieve a general reduction in the reluctance of the circuit.

The push-out mechanism comprises a preferably though not necessarily water-cooled pushout rod I46 working axially back and forth within the tubular workpiece stock gauge and support I43.

Devices associated with the feeding-in of the workpieces on the other hand, are mounted in connection with the front plate 50 of the housing of coil 40. Such are the coil mouthpiece and the door and appurtenant instrumentalities. The mouthpiece 98, as has been said, serves to enter the workpieces of bar or rod stock properly upon the axis AA of the coil 40 and the supporting rails I6. By virtue of its susceptibility to removal and replacement from the opening 5|, it may be suited in size to the various sizes of coils and stock. It is suitably bolted inplace (bolts not shown) and mounted with a clearance 96a for radial adjustment to precise position on axis AA. On its inner side it is provided with an annular series of axially and inwardly projecting spaced teeth at I85, the inner side walls of which project radially and axially inwardly toward the coil, and the extremities of which have an extent substantially of the same diameter as those circles on which lie the inner edges of the work-supporting fins ll, while their inner sides meet their inner ends at a relatively sharp angle. All this clearly appears in Figure 2-. Thereby these teeth guide the stock accurately into engagement with the fins ll of the supporting rail I6, preventing impingement upon intermediate transversely-extending walls (this through their inclined inner walls and their extremities), and when the workpiece is pushed out, remove from its foreign matter such as light scale which may have formed (this through the sharp innermost edges). Such foreign matter as is removed falls between the teeth or past their inner extremities and upon the hopper plate v foreign matter drops to which discharges through opening I81 to a. chute I88 projected from the opening I81 exteriorly of the machine. Thus no scale or other the foundation plate 39.

Effective provision is made for water-cooling of all parts whatsoever, such as may be heated in what otherwise would be an undue measure. This includes not only the coil 40 and its work supporting rails 16 and the water-cooled push rod I46 (mention of the hollow conductors for water-cooling of which has already been made), but also the iron core 91. It is pointed out in connection with the rails that through the use thereof a positive coolant is applied throughout the coil and rail length thus tending substantially to reduce the excess heat toward the coil center and to aid in prevention of rail warping. A coil of water-cooling tubing 2H is provided about the magnetic core 91 for the purpose of cooling this mass of laminated transformer iron.

My invention is susceptible of many modifica- ,tions of its various component parts and their coacting inter-relationships and organizations. For example, the heating coil itself may be variously modified. I show in Figure 7 one such modification in which the rails 16 comprise each two tubular devices welded together in the radial plane whereby to give them greater radial depth and stiffness. The retaining clasps I9 and the fins 80 are in turn welded to the radially inner tubular sections. Cooling water is passed through both of the tubular sections. It may be passed down one such tubular section and returned by the other, or it may be passed through them in parallel as may be desired (such connections not being shown). This organization of the work-supporting rails permits a greater depth of heat insulating segments 14 and, of course, connotes a larger diameter of coil relative to the diameter of the workpiece, (the latter shown in Figure 7 generally in dot-anddash-lines).

In connection with the laminated iron utilized in the magnetic circuit in extension of the axis of the workpiece, one form of this core has been described. The best distribution of heat in the end of the workpiece (and it is an aim of this lam nated iron to secure better distribution of heat in the end of the workpiece) I conceive to be had when the diameter of the engaging end of the core is less than the diameter of the workpiece, by substantially about twice the skin depth of current penetration in the workpiece. A diameter of the engaging end of core about two-thirds of the diameter of the workpiece is believed by me to be a good proportion. Thus two important advantages of the inclusion of the core are conjoined, the collecting of the coil flux and in improving the impedance, and uniform heat-distribution in the juxtaposed end of the workpiece.

In Figure 11 I show diagrammatically only another form of the core 91 of transformer iron. It is the same in its general arrangement as that set forth in the principal figures of the drawings, but differs therefrom in having its forward end 91a. reduced in diameter to such an extent that at its extremity it is less in diameter than the diameter of the workpiece W. This reduction, as illustrated, is attained by tapering the laminations radially inwardly, but it may be reduced in other ways. The proportions I have set forth above. While the main body- 51 and coil 2| I may be projected within the open end of the heating coil to meet the workpiece W,

an end 91a of reduced cross-section can all the more readily be so projected as shown.

Throughout the specification I have used the term heating coil to apply to the electromagnetic inducing element to which the workpiece is juxtaposed to receive the electromagnetic induction. This term I wish broadly construed to comprehend electromagnetic inductor devices of all sorts irrespective of the shape and dimensions of the coil and indeed irrespective of whether or not a device has the form of a coil and is but an electrical conductor of some form or other, save as the claims specify otherwise.

Thus it is that I would call attention to the fact that it is my desire that the annexed claims be afforded breadth of interpretation commensurate with the spirit of my invention wherever that spirit is manifest and novel, irrespective of the circumstantial terminology which my present description of the instant embodiment of the invention, may have influenced me to use.

What I claim is:

1. An apparatus for heating a workpiece by electromagnetic induction comprising an inducing coil, and work supporting means within said coil comprising longitudinal passages for'coolant circulation angularly spaced from each other, and projections of high heat resistant material from each such coolant passage, extending inward for cooperation with a workpiece, and longitudinally spaced apart along each coolant passage to reduce the tendency for longitudinal expansion of the heated inner portion of said projections to cause flexure and distortion.

2. An induction heating apparatus comprising a heating coil, and work supporting rails within the coil having heat resistant plates secured edgewise thereto and extending toward the coil center.

3. An induction heating coil having longitudinal work supporting rails within the coil, and segments of thermal insulating material held in place by and between said rails and adjacent the coil.

4. An induction heating coil having associated therewith a plurality of longitudinally and angularly spaced metal supports for cooperation with a workpiece.

5. An induction heating coil having on the inside a plurality of longitudinally and transversely spaced metal supports for cooperation with a workpiece and fluid cooled whereby said supports may conduct heat from the heated surface of a workpiece.

6. An induction heating coil having a plurality of angularly spaced fluid tubes extending longitudinally thereof, and a plurality of longitudinally spaced substantially radial work supports secured along each tube and extending toward the surface of the work to be heated.

'7. An induction heating coil having a plurality of angularly spaced fluid pipes extending longitudinally thereof, and a plurality of longitudinally spaced substantially radial fins secured along each pipe and extending toward the surface of the work to be heated, heat insulating material angularly between thepipes and fins, and securing strips for the insulating material, carried by the pipes and extending transversely of.

the pipes longitudinally between said fins and into engagement with a face of the insulating material that is away from said coil.

8. An apparatus for heating bar stock workpieces by electromagnetic induction comprising a hollow heating coil adapted to receive the work within itself, and a body of magnetic core material for said coil external thereto occupying a position as a substantially axial end extension of the workpiece when in heating position whereby it receives most of the coil flux, said body of magnetic material being substantially adjacent to an end of the workpiec and of a comformation similar to the adjacent coil end but of reduced dimensions.

9, An apparatus for heating a workpiece by electromagnetic induction comprising an inducing coil, a foundation therefor, a work support within the coil, a tapered mouth for directing a workpiece into said coil and work support, a support for said mouth connected to said foundation, said mouth being mounted on its support in a manner to possess limited adjustment in a plane transaxial of the coil whereby said mouth may be substantially axially alined with said coil.

10. An apparatus for heating a workpiece by electromagnetic induction comprising an inducing coil, means for substantially centering the work within said coil, an abutment adjacent at least one end of said coil and against which an end of the work may impinge as astop, said abutment having laminations for juxtaposition to an end of the work whereby said laminations may function as a flux receptive end extension of the work for directing flux axially within said coil and longitudinally beyond said coil and work, said abutment also having a non-laminar projection extending toward the work and longitudinally beyond said laminations for receiving the impact of a workpiece against said projection as a stop.

11. An apparatus for heating a workpiece by electromagnetic induction comprising an inducing coil, a track within said coil and along which the work may be slid, high temperature ceramic segments within said coil extending lengthwise thereof and between portions of said track and means for interconnecting said track and segments.

12. An induction heatin coil having therein a work supporting track, and a mouth having peripherally spaced tapered prongs whereby a workpiece may be directed into the coil, said prongs being connected at a location longitudinally spaced from the adjacent end of said coil whereby the tendency to heating of the prongs by circulation of peripheral currents therein is substantially reduced.

13. An induction heating coil having therein longitudinal metal strips constituting a track on which a workpiece may be slid into and out of the coil, said strips being transversely spaced and supported at longitudinally spaced locations at least one of which is beyond an end of the coil and another of which is intermediate the ends of the coil, said last-mentioned support comprising metallic strips connecting adjacent track portions and being provided with an electrical insulating material in said last-mentioned strips to suppress the peripheral circulation of induced currents therein.

14. An induction heating coil having work supporting rails within the coil, a tapered pronged mouthpiece whereby work may be guided within said coil, said mouthpiece and rails both being eccentric to the coil by an amount substantially such as to bring a cylindrical workpiece generally coaxial with said coil.

15. In apparatus for heating a workpiece by electro-magnetic induction, a tubular heating coil and a workpiece supporting tube within said coil, the axes of said coil and tube being displaced from each other, whereby the axis 01' a cylindrical workpiece placed in said tube, against the side thereof closest to the coil axis, lies in substantial coincidence with the coil axis.

16. The combination with a coil having a hollow workpiece receiving chamber, of an end extension from said coil generally coaxially aligned therewith of material of low magnetic reluctance, said end extension having a diameter less than that of the coil interior.

17. In a machine for heating workpieces by electromagnetic induction, a tubular heating coil, supports in said coil having engaging elements for supporting a workpiece therein, the transverse loci of said engaging elements forming a circle whose center is eccentric to the coil axis. whereby the axis of a workpiece positioned on the support elements nearest the coil axis is substantially coincident with the coil axis.

18. The combination with a coil for heating a workpiece by electromagnetic induction, of a casing for enclosing said coil, a track positioned within and adjacent the inner surface of the coil and along which a workpiece is slidable, said track extending beyond each end of said coil and casing, and track supporting means secured to said track ends and anchored on said casing for holding the tracks in position relative to said coil.

19. In electromagnetic induction apparatus, a heating coil, a releasable external support for the coil, 9. track within the coil along which a workpiece is shiftable, and a support for the track external to said coil, said coil and track forming together an assembly removable as a unit on release of said coil support.

20. The combination of a coil for heating a workpiece by electromagnetic induction, of a track having at least two rails positioned within and adjacent the inner surface of the coil and along which a workpiece is slidable, segments of thermal insulating material between the rails of said track, and track supporting means adapted to force said track and material radially outwardly against said coil.

21. An induction heating apparatus comprising a heating coil, and work supporting rails having plates secured edgewise thereto and extending inwardly toward the coil axis.

22. In electromagnetic induction apparatus, a heating coil having a heating chamber therein, a support for said coil, plural rails forming a grid framework extending axially within said coil, fire resistant material interposed between and secured to said grid rails and forming with said rails a composite tube within said coil, and a releasable support for said rails external to said coil whereby said tube is removable as a unit from said coil.

23. An induction heating apparatus comprising a heating coil and work supporting rails hav-- ing longitudinally discontinuous support members secured thereto and extending toward the surface of the work to be treated.

24. An induction heating apparatus comprising a heating coil, tubular metallic rails inside and adjacent the coil, extending substantially parallel to and along the entire length of the tube axis and angularly displaced substantially completely about the coil periphery to form a tubular work supporting grille, said rails being adapted to receive a coolant. throughout substantially the entire length thereof and to receive the work in direct thermal contact therewith.

HAROLD A. STRICKLAND, Jl.

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