US2840677A - Apparatus for induction heating - Google Patents

Description

June 24, 1958 w. A. EMERSON HAL 2,840,677

APPARATUS FOR INDUCTION HEATING Filed May 15, 1956 United States Patent O APPARATUS FOR INDUCTION HEATING William A. Emerson, William B. Brown, and Clarence A. Kuhne, Baltimore, Md., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 15, 1956, Serial No. 585,040

6 Claims. (Cl. 219-10.67)

This invention relates to induction heating apparatus, and more particularly to an induction furnace for heating tubular articles 'by inducing alternating currents in the walls of the article.

In the industrial arts it has been found desirable to heat large blanks for forging and the like in a time of often less than one minute. High frequency induction heating has been widely used but has been found disadvantageous for the heating of large thick tubular bodies in that high frequency inherently heats the metal at the external surface of the workpiece while that below the surface remains relatively unheated.

In the use of low frequency induction heating diiculty has been encountered in locating a laminated iron core closely adjacent to the workpiece so as to reduce the reluctance of the magnetic path with a consequent reduction in impedance of the coil so as to increase power transfer to the work. Diculties in workpiece positioning with respect to the laminated core have in the past precluded low frequency heating.

It is an object of this invention to provide an improved induction heating apparatus for heating the side walls of tubular metallic articles.

It is another object to provide apparatus for rapid and i eicient mass production induction heating of large work- It is a further object to provide induction heating apparatus for the purposes described in which portions of a magnetic core are adapted to be relatively moved and replaced automatically for insertion of a workpiece therebetween.

It is a still further object to provide induction heating apparatus having an open-core transformer for the purposes described in which power factor and eiliciency are improved and exciting current is reduced by provision of movable flux concentrating means associated with the transformer core.

It is an additional object to provide heating apparatus of the type described for obtaining a controlled predetermined heat pattern in specified areas of a workpiece to be forged or otherwise worked.

A different object of this invention is to provide an automatic induction furnace for heating selected portions of substantially cylindrical tubular workpieces in which a plurality of individual flux concentrating magnetizable members are adapted to be moved into a reluctance decreasing and flux concentrating position simultaneously with movement of workpieces into an inductive relation with the heating coil of a furnace.

A still different object of this invention is to provide automatic apparatus of the type described in which a rst elevator mechanism is reciprocally operative to elevate a workpiece from a delivery position to an induction heating position within a furnace coil and to remove the workpiece when heating is completed, and in which a second elevator mechanism is operative to reciprocally position a plurality of flux concentrating members in a first position and a second position, said first position being Patented June 24, 1958 adjacent to the transformer and adjacent to the positioned of the core structure.

workpiece, said second position being relatively far removed from said transformer and substantially removed from said workpiece whereby said workpiece may be readily conveyed horizontally away from said furnace.

These and further objects will be apparent from the following description taken in accordance with the accompanying drawing, throughout which like reference characters indicate like parts, which drawing forms a part of this application and in which:

Figure l is a partial vertical longitudinal section taken along a diameter of a furnace according to the invention showing diametrically opposed core members in section and further showing the workpiece and flux concentration elevating mechanisms in solid lines in the elevated position and in broken lines in the descended or retracted position; and

Fig. 2 is a transverse horizontal section through one semi-cylindrical half of the furnace, taken along the line II-II of Fig. 1.

For convenience in describing the relative positions of the various parts of the apparatus, it will herein be thought of as standing inan upright position, as in the preferred embodiment, with the furnace inductor coil having its axis vertically aligned as indicated in Fig. l, but it is to be understood that in actual practice the said axis may be positioned horizontally or in an inclined position.

A core structure for the furnace comprises a plurality of elongated vertical inner members 4 disposed within the work path and within the cylindrical workpiece 6. The inner core members 4 are not individually coaxial with the work path but are disposed in spaced relation about that `axis so that the inner core group is coaxial to the work path, workpiece 6 and coil 8.

The outer core structure 10 comprises a plurality of laminated magnetizable core members 12 each having a vertical leg portion disposed closely adjacent the outer periphery of the coils and having upper leg portions 14 and lower leg portions 16 extending radially inward adjacent the top and bottom ends of the coil 8. The upper leg portion 14 extends inwardly a substantial distance beyond the inner diameter of the coil 8 thereby approaching in close proximity to the outward side of the corresponding inner core member 4 to eliminate any appreciable air gap at the upper end of the inner cores. The lower horizontal core leg member 16 is of lesser length, extending only slightly beyond the inner diameter of the coil 8, and terminating short of the work path diameter. A space or air gap is thus provided between the inner end of the lower horizontal leg portion 16 and the inner core member 4 through which the workpiece 6 may be longitudinally inserted and positioned with sidewalls 7 lying adjacent to the inner diameter of coils 8.

The plurality of laminated outer core members 12 together with their respective inner core members 4 provide a plurality of magnetically parallel ilux paths threading axially through the inner core members 4 positioned in the hollow center of the workpiece 7, across an air gap 18 (discussed hereinafter) at the lower end of the core member 4 radially outward through the lower horizontal leg portion 16 and thence vertically upward and radially inward through core members 12. The only substantial discontinuity or high reluctance portion of the magnetic ux path is the air gap 18 between the inner end of the lower leg members 16 and the lower end of core member 4. This gap 18 is necessarily provided in order to allow insertion of the workpiece sidewalls 7 into the space between the inner diameter of the coil 8 and the outer diameter of the inner core assembly.

The separate outer and inner vertical core members 4 and 12, as described, comprise a preferred embodiment It is intended that other suitable configurations of the magnetic core may be satisfactorily employed. For example the core structure may conrprise a plurality of substantially U-shaped core members individually straddling the periphery of the coil 8, with one leg of the U-shaped member extending vertically downward outside the coil and with the other leg portion extending downward inside the 'annular workpiece passageway.

In the form of the invention shown in the drawings the induction coils are of the 6() cycle 460 volt type comprisg ing large diameter separate coil sections. Each coil section 8 is insulated from the next by transite insulator rings Ztl of flat annular configuration having a diameter slightly greater than that of the coil S. Each section of the coil is of the flat spiral wound type comprising a plurality of turns of round or rectangular tubing of conductive metal such as copper or aluminum. Each spiral coil 8 has end leads extending radially and arcuately outward from the coil at one side to an insulating terminal board. By virtue of appropriate connectors provided on the terminal board, various interconnections of the spaced coil sections may be made. To achieve various predetermined heat patterns dilferent coil sections may remain disconnected from any power source as desired, or may be connected in various permutations of series and parallel combinations.

While in the disclosed embodiment the coil is intended for 60 cycle single phase operation, it is evident that the apparatus may be adapted for other frequencies, voltages and numbers of phases in the low frequency power spectrum without departing from the scope of the invention.

Further provided on the terminal board are appropriate connectors for circulating coolant fluid through the separate coil sections. Water (or other coolant) may be supplied to the various coils from a common source through insulating fluid-tight tubing. In addition to fluid cooling, the coils 8 are further protected from the heat of the internally adjacent workpiece 6 by means of a coating 22 of refractory cement such as Sillimanite No. ,lOl (manufactured by Charles Taylor Sons Co., Cincinnati), or the like applied over the horizontal transite rings 20 and the inductor coils 8 on the inside of the coil assembly where the coils face the hot workpiece 6.

The transformer core and coil assembly is located at a convenient elevation from the floor for operation with suitable conventional roller or belt conveyors (not shown) for delivery and removal of workpieces 6. The support structure 25 is provided with a horizontal planar table top 27 having a central opening 29 disposed in spaced relation below the furnace assembly. The support structure 25 for the furnace assembly conveniently comprises four vertical corner posts 31 to the top of which is mounted a substantially planar furnace support plate 33 having a central opening 35 slightly larger than the internal diameter of the heating coil assembly. Circum#Y ferentially spaced around the central opening 35 are vertically and upwardly extending channel members 37 rigidly attached at the lower ends to the furnace support plate 33. The outer core members 12 of the furnace are supported on the channel members 37 by through-bolts or other appropriate fastening means so as to be rigidly located in vertical positions circumferentially spaced around the work path opening in the furnace support plate 37. Y

The respective central openings 29 and 37 in the planar table top 27 and in the furnace support plate 33 are aligned vertically with their central axis being coincident with the central axis of the furnace inductor coil 8 andV Disposed below the table top 2,7 within the rectangularV support structure 25 is an elevating mechanism preferably comprlsing a pneumatic or hydraulically operated cylinder 41, piston and piston rod 43. However, it is understood that other suitable elevating mechanisms may be satisfaci torily employed. Appropriate electrically operated valves, relays, pressure switches, and circuitry are provided for automatic cyclical operation of the fluid operated elevator 39 in synchronism with delivery of workpieces to the work path from an external conveyor. The iiuid operated elevator 39 is preferably disposed in a vertical position in alignment with the axes of the furnace 10 and work path. Rigidly mounted on the upper end of the elevator piston rod 43 is a planar elevator platform 45 of a diameter less than that of the opening 35 in the furnace support plate 33 so that the platform 45 is adapted to substantially close the furnace support plate opening 35 when the elevator is in the raised or heating position.

The primary function or purpose of the elevator platform 45 is to movably support a plurality of preferably laminated magnetizable ilux concentrating core pieces 47. The said core Vpieces 47 are rigidly mounted on the platform 45 in circumferentially spaced positions inwardly adjacent to the periphery of the platform 45. In the central portion of the platform 45 is located a superstructure comprising a workpiece carrier plater49 for supporting a workpiece 6 above the plane of the principal Yele-v vator platform 45. The workpiece support plate 49 is connected for vertical movement relative to the elevator platform 45 by means of a plurality of spaced slide-bolts 51 rigidly attached to the workpiece support plate 49 and verticallyslidable in openings in the elevator platform 45. Enlarged heads 53 are provided at the lower end of the slide bolts 51 Vso that the bolts 51 and the support plate 49 are captively Ebut movably connected to the elevator platform 45. The support plate 49 is thus freely movable for a relatively short distance toward and away 4from the elevator platform 45.

Beneath the tabletop 27 and spaced slightly below the lowermost position of the elevator platform 45 is a planar stop plate 55 adapted to engage the heads`53 of the slide boltsvSl as the elevator platform 45 approaches the retracted position. When the slide bolt heads 53 contact the stop plate 55, further downward motion of the workpiece support plate 49 is prevented while the elevator platform 45 continues to descend. The flux concentrating core members 47 are thus retracted away from the curved side portions 9 of the workpiece 6 and below the tabletop 27 whilethe workpiece support 49 terminates its downward motion when substantially coincident with the table top 27.

At the beginning of the operative cycle a workpiece 6 is conveyed horizontally into approximately the center of the table top 27 by an external conveyor (not shown). A suitable switch is automatically operated by delivery of the workpiece 6 to initiate operation of the iluid operated elevator 39. As the elevator platform 45 begins to ascend, the tapered ends of the flux concentrator core members 47 rise through the annular opening surrounding the workpiece carrier 49. If, as in the usual case, the workpiece 6 is not accurately centered, the tapered ends of core members 47 will joggle the lower end' of the workpiece V6 until reasonably accurate centering is achieved. As the elevator platform 45 continues to rise, annular spacers 57 on the slide lbolts 51 will engage the upper surface of theY platform 45 so that the workpiece carrier 49 will thereafter be supported by and will move together with the platform 45. The platform 45 then continues to ascend until the workpiece 6 is wholly within the peripheral outer core members 12r and the iiux concentrator core pieces 47 are laterally adjacent to the endsso as to reduce the required exciting current, increase the.

power rfactor andV increase overall e'ciency oftheinduc tor furnace. Inone instance of an apparatus havingrnov` .5 able tiux concentrating core pieces of the type described, a 500 kva. furnace was improved as follows:

In addition, it was Ifound that power loss in the transformer coil 8 was reduced by 14% thereby reducing the normally present deleterious heating of the coils and insulation.

In one embodiment for applying the apparatus shown in Fig. 1, a system is provided using two identical furnaces of the type described. Automatic loading devices are provided for delivery' of workpieces from a single gravity roller conveyor to the work paths of both furnaces. Control circuits for the two furnaces are electrically interconnected to provide for alternate energization of the primary induction coils. The operating cycle of the tandem system is as follows.

The first loading device loads a workpiece 6 into the first furnace work path on the workpiece support plate 49. As soon as the workpiece is in position underneath the heating coils 8, the iiuid operated elevating cylinder 39 is energized. Premature energization of the elevating mechanism is prohibited by workpiece actuated switches which determine that the workpiece is properly positioned. Upon energization of the elevator 39 the workpiece 6 ascends into the heating coil 8 of the lirst furnace; a pressure operated switch, responsive to the uid pressure in the cylinder, energizes a conventional timer and a line contactor to apply power to the heating coil for a predetermined interval. Simultaneously with energization of the first heating coil, a loading `device associated with the second furnace is energized and operates to load a workpiece on the workpiece carrier plate 49 of the second furnace. During the heating time interval for the first furnace, the elevator of the second furnace operates to position the workpiece in the coil in position for heating. As soon as the timed heating interval in the lirst furnace is complete, the input power is immediately transferred over to the coil of the second furnace. The tirst furnace elevator automatically descends and the heated workpiece is discharged to an external conveyor. The first loading device is then automatically operated to load a second workpiece on the first furnace carrier plate. When the timed heating interval of the second coil expires the rst furnace elevator is in the ascended position and power is immediately transferred from the second heating coil to the first heating coil and repetition of the tandem working cycle begins.

By virtue of the above described synchronous operation of a pair of heating furnaces, a continuous flow of power from an external system is maintained. Uninterrupted power consumption, as described, is highly advantageous in that variable loading and transient conditions are thereby eliminated from the external power distribution system. Also the continuous power consumption enables the external electrical equipment to be operated at higher average loading with a resultant increase in efficiency and optimum utilization of the external system apparatus.

The apparatus has been described as being in an upright position with the central axis of the furnace being vertically aligned. It is to be understood that in actual use the apparatus may be modified to operate with the work path axis and the induction coil axis in aligned horizontal or inclined positions. It is to be further understood that the form of our invention, as shown and described, is to be taken as a preferred example of the same, and that various other changes and modications '"6 may be resorted to without departing from the spirit and scope of the invention.

We claim as our invention:

l. In an induction furnace having a workpiece pathway for electric heating of hollow metallic workpieces, the combination of an open-core transformer having at least one outer core leg and at least one inner core leg, a coil mounted therebetween, a fluid pressure operated workpiece carrier having a first position and a second position, and a plurality of magnetizable flux concentrating core members mounted for movement with said carrier, said first position being such that said core members are axially spaced from said core legs to allow loading of a workpiece on said carrier between said core legs and said carrier, said second position being such that said workpiece is located concentrically within said coil and said core members are disposed in the workpiece pathway adjacent to said core legs to substantially close the magnetic circuit of said open core transformer.

2. In a furnace for electrical heating of workpieces, the combination of a transformer of the open-core type having a plurality of outer core leg members and a corresponding plurality of inner core leg members with a coil mounted therebetween, a support for said transformer having a substantially planar table top, said transformer being mounted on said support in spaced relation above said table top, a workpiece elevating mechanism mounted on said support below said table top, a workpiece carrier connected to said elevating mechanism for vertical movement relative thereto to a raised position, a plurality of auxiliary core members mounted for movement with said elevating mechanism and normally 1ocated below the plane of said table top, said auxiliary core members being positioned when said workpiece carrier is in said raised position to substantially complete the magnetic circuit of said open-core transformer.

3. In an electric induction furnace having a substantially cylindrical work path and further having an induction coil concentrically surrounding a portion of said work path for inductively heating a workpiece having side walls, the combination of a first plurality of peripherally spaced core members adjacent the outside of said coil having an elongated dimension parallel to the axis of said work path, a second plurality of core members within said work path corresponding individually to and aligned in parallelism with said rst core members, a movable group of auxiliary core pieces mounted one beside another in a plane spaced axially from the end of said coil and circumferentially following the end of said workpiece, said group being mounted for movement from a iirst position to a second position, a reciprocable pusher member for moving a workpiece to be heated axially into said coil with said sidewalls between said rst core members and said second core members, said group of auxiliary core pieces being mounted for movement with said pusher member from said iirst position to said second position, said second position being such that the individual core pieces of said group are effective to substantially decrease the air gap between the ends of corresponding core members of said first plurality and said second plurality.

4. In an induction heating apparatus having a first work station and a second work station and having an induction coil concentrically surrounding the second work station for heating the sidewalls of metallic workpieces, the combination of a plurality of substantially U-shaped magnetizable core members straddling the periphery of said coil with inner legs of each core member projecting downwardly within said coil, a first elevating means for bringing the sidewall of the workpiece to be heated into inductive relation within said coil between said coil and said downwardly projecting core members and are retractably removing it therefrom, a plurality of auxiliary magnetizable core members radially spaced from the axis of said work stations and a second'elevatiug means` supd porting said auxiliary core members for .axial movement to a position substantially adjacent the outer legsfof'said Uv-shaped'members so as Vto decrease the air gap between said outer legs and said innerlegs. y

5. In combination with lan elongated cylindrical inductor coil for heating of hollow cylindrical Workpieces having sidewalls, a plurality of substantially U-shaped core members straddling the inductor coil and spaced around the circumference of the coil each -having an outer leg member adjacent the outside of said coil and anV inner `leg member spaced 'from the inside of said coil, anda plurality of auxiliary core pieces individuallyspaced from the open ends .of said core members iand supported for reciprocal movement axially toward and away from said U-shaped core members, lst elevator means for reciprocally moving Va workpiece axially into said `inductor coil with said'workpiece sidewalls between said inner Yleg members and ,said outer leg members, and second elevator means for moving said auxiliary core pieces to a position `adjacent the ends of said inner and outer leg members, said position being such that each of said core pieces is efective to substantially complete the magnetic circuit between one of said outer leg members and the corresponding inner leg member.

combination of a first plurality of peripherally spaced outer core jleg members positioned adjacent the outside of said coil, a second plurality of inner core leg members spaced fromV the inside Voiisaid'coil and substantially parallel to`said outer core members, anda plurality of auxiliary core pieces movably supported in a firstv position spaced axially from the end of said coil and reciprocally movable to a second position adjacent the ends of ,said outer'core members, said second position being such that said auxiliary core pieces are eiective to decrease the reluctance of the magnetic flux path between the ends of said outer core members and said inner core members.

References Cited in theiilre of kthis patent Y UNITED STATES PATENTS 2,337,258 Limpel ,Dec. 21, 1943 2,359,285 Bennett Oct. 3, 1944 Y2,363,994 Richter NOV. 28, 1944

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