US3320398A

US3320398A - Induction heating coil assembly

Info

Publication number: US3320398A
Application number: US387585A
Authority: US
Inventors: Robert G Armstrong
Original assignee: Ohio Crankshaft Co
Current assignee: Ohio Crankshaft Co
Priority date: 1964-08-05
Filing date: 1964-08-05
Publication date: 1967-05-16
Anticipated expiration: 1984-05-16

Description

y 1967 R. cs. ARMSTRONG 3,320,398

INDUCTION HEATING COIL ASSEMBLY Filed Aug. 5, 1964 2 Sheets-Sheet l INVENTOR.

"I0 ROBERT G. ARMSTRONG BY 1- a? ATTO NEYS May 16, 1967 R. G. ARMSTRONG INDUCTION HEATING COIL ASSEMBLY 2 Sheets-Sheet 2 Filed Aug. 5, 1964 INVENTOR.

ROBERT G. ARMSTRONG ATTORNEYS Patented May 16, 1967 INDUCTION HEATING COIL ASSEMBLY Robert G. Armstrong, Chardon, Ohio, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Filed Aug. 5, 1964, Ser. No. 387,585 4 Claims. (Cl. 219-10.79)

This invention pertains to the art of induction heating and more particularly to an induction heating coil assembly.

The invention is particularly applicable to a coil assembly for heating an elongated workpiece before it enters into a molten metal bath for coating the workpiece and it will be described with particular reference thereto; however, it is to be appreciated that the invention has much broader applications and may be used as an induction heating coil for various other heating operations.

In coating metal onto an elongated workpiece, such as bar stock and wire, it has become somewhat common practice to heat the elongated workpiece to a temperature in the order of the molten temperature of the coating metal and then pull the workpiece through a bath of the molten coating metal. When the workpiece is being heated prior to coating, its surface is susceptible to oxidation; therefore, the heating of the workpiece is generally performed adjacent the molten metal bath and the workpiece is maintained in a reducing or non-oxidizing atmosphere between the heating operation and the time the workpiece is introduced into the molten bath. It has been found that an induction heating coil having a central workpiece receiving passage with an extension protruding into the bath is well adapted for preheating the workpiece. Such a coil can be easily located adjacent the molten metal bath and a reducing atmosphere can be easily formed within the workpiece receiving passage of the coil to prevent oxidation of the workpiece as it is being heated and passed into the molten metal.

The present invention is directed toward an induction heating coil assembly which is well adapted for the purpose of preheating an elongated workpiece prior to introducing the workpiece into a molten bath of coating metal. Heretofore, such a coil assembly included a multi-turn coil potted within a refractory material and held between two spaced support members. The support members were secured to an appropriate mounting frame adjacent the molten metal bath. High permeability iron laminations were mounted around the coil to concentrate the flux lines within the central workpiece receiving passage of the coil. In addition, stainless steel tie rods were positioned around the coil and refractory material and these rods extended between the spaced members for holding the coil in place during the heating operation. Stainless steel is non-magnetic so the tie rods had no appreciable effect on the flux lines created by the coil when the coil was energized with an alternating current.

Although such a coil assembly was generally satisfactory in use, there were certain disadvantages in this assembly. For one, the assembly was relatively expensive and when the coil was energized with a relatively low frequency, the electro-motive forces set up around the coil tended to vibrate the coil until the refractory potting material was destroyed.

These and other disadvantages of the prior induction heating coil assembly are overcome by the present invention which is directed toward an induction heating coil assembly which is relatively inexpensive and durable in use.

In accordance with the present invention, there is provided an improvement in an induction heating coil assembly of the type including spaced support members, a multi-turn coil having input leads adapted to be connected to a source of electrical current, and a plurality of tie rods surrounding the coil and extending between the support members for rigidifying the assembly. The improvement in accordance with the invention includes forming each of the tie rods from high permeability laminations with the laminations extending axially with respect to the coil.

By this construction, the tie rods not only serve the purpose of rigidifying the coil assembly, but they also perform the function of concentrating the flux lines within the central workpiece receiving passage of the multiturn coil. Consequently, there is no need for utilizing separate iron laminations for concentrating the flux lines of the coil assembly.

The primary object of the present invention is the provision of an induction heating coil assembly of the type having spaced support members and a multi-turn coil held therebetween, which coil assembly is relatively economical to manufacture and is durable in use.

Another object of the present invention is the provision of an induction coil assembly of the type having spaced support members and a multi-turn coil held therebetween, which coil assembly eliminates the requirement for both tie rods extending between the support members and iron laminations around the coil to concentrate flux in the workpiece receiving passage of the coil.

Still a further object of the present invention is the provision of an induction heating coil assembly of the type having spaced support members and a multi-turn coil held therebetween, which coil assembly will withstand energization of the coil by a relatively low frequency current.

These and other objects and advantages will become apparent from the following description used to illustrate the preferred embodiment of the invention as read in connection with the accompanying drawings in which:

FIGURE 1 is a somewhat schematic side elevational view illustrating the preferred embodiment of the present invention;

FIGURE 2 is an enlarged cross-sectional view taken generally along line 22 of FIGURE 1; and

FIGURE 3 is a partially cut away, enlarged crosssectional view showing in more detail the structural features of the preferred embodiment a shown in FIG- URES 1 and 2. I

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, the figures show an induction heating coil A adapted to preheat workpiece B which, in the illustrated embodiment, is a wire, as the wire passes into a molten metal bath C held within a holding furnace D. The coil assembly A includes spaced

support members

10, 12 fixedly secured onto

frame members

14, 16, respectively. It is appreciated that the frame members are fixedly secured onto any appropriate structural member so that coil assembly A is held in the proper inclined position with respect to the molten bath C.

Between

frame members

10, 12 there is provided a multi-turn induction heating coil 20 having an internal coolant passage for receiving water or another appropriate cooling medium. The coil 20 includes two

leads

24, 26 which are connected onto bus bars 28, 30 of an oscillator, motor generator set or another appropriate source of alternating current. In accordance with the preferred embodiment of the present invention, the current supplied to the coil by bus bars 28, 30 is in the frequency range of .05-10.() kilocycles, which frequency range is somewhat low in the field of induction heating. It is appreciated that other frequencies could be used as long as the frequencies are approximately 50 cycles per second or greater. The coolant is supplied to passage 22 through

coolant conduits

32, 34 in a manner well known in the art of induction heating.

In accordance with the illustrated embodiment of the present invention, the rnulti-turn coil 20 is potted within a refractory material 40 so that the material insulates the coil from the heat generated within the workpiece B. The refractory material is supported on mounting sleeves 42, 44 extending in opposite directions through the

spaced support members

10, 12, respectively. Within the coil 20 there is provided a non-magnetic, wear resistant sleeve 46 which defines an inner workpiece re ceiving passage 50 for guiding the workpiece B through the induction coil assembly A and into the bath C. An extension 52 supported onto the sleeve 46 and the sleeve 42 extends into the molten metal bath C so that the workpiece receiving passage 50 is opened to atmosphere only at its upper end adjacent sleeve 44. In order to create a reducing or non-oxidizing atmosphere within the passage 50, there is provided, in accordance with the illustrated embodiment of the present invention, an atmosphere inlet 54 connected onto an appropriate source of reducing or non-oxidizing gas, not shown, and adapted to direct the gas through aperture 56 of sleeve 42 and aperture 58 of sleeve 46 so that the atmosphere gas completely fills the passage 50 to exclude any corrosive gases from this passage. The particular atmosphere within the passage 50 does not form a part of the present invention and various atmospheres may be used. Around the sleeves 42, 44 there is provided high temperature seals 60, 62 which allow a certain amount of movement between the

support members

10, 12 and the refractory material 40.

Surrounding the refractory material 40 are a plurality of circumferentially spaced, axially extending tie rods 70 which form a major portion of the present invention. Since each tie rod is substantially identical to the others, only one will be described in detail and this description will apply equally to all the tie rods 70 surrounding the refractory material. The tie rods include a plurality of axially extending laminations 72 having apertures 74 at each end thereof. A yoke bolt 76 is secured onto the laminations by a pin 78 extending through apertures 74. The yoke bolts 76 have shanks 80 which are adapted to extend through appropriately positioned apertures in spaced support members '10, 12 for the purpose of securing the coil 20 and its supporting structure between the

members

10, 12. Nuts 82 are threadedly received on shanks 80 adjacent the support member so that the tie rods are somewhat fixedly secured with respect to this support member. Adjacent support member 12 there is provided a spacer S4 surrounding shank 80 of each yoke bolt and a coil spring 86 sandwiched between

washers

88, 90.

A nut 92 received on shank 80 of the yoke bolts 76 adjacent support member 12 can be tightened on the shank so that the tie rods 70 are placed in a state of tension. This compresses the refractory material 40 and increases its physical strength since the refractory material is known to have higher strength in compression than it does in tension. In essence, the nuts 92 are used to precompress the refractory material so that the strength of the material is substantially increased.

In operation, the tie rods 70 perform a dual function. First, they perform the conventional function or rigidifying the complete coil assembly A. Secondly, the tie rods are formed from soft iron laminations 72 so that they perform the function of concentrating the flux in the passage 50, which flux is created by current fiow through the coil 20. In this manner, the assembly does not require separate flux concentrating laminations with the result that the manufacture of assembly A is substantially simplified. The laminated structure of the tie rods lowers eddy current circulation in the tie rods to reduce the PR heating of the tie rods. It is appreciated that copper shields could be placed at the ends of the tie rods to prevent heating of these ends, especially when higher frequencies are used to energize the coil 20.

The present invention has been described in relation to one physical embodiment; however, various changes may be made in this embodiment without departing from the intended spirit and scope of the invention as defined in the appended claims.

Having thus described my invention, I claim:

1. An induction heating coil assembly including spaced non-magnetic support members, a multi-turned coil having an axially extending workpiece receiving passage and input leads adapted to be connected to a source of high frequency current, a refractory material surrounding said coil, a plurality of tie rods surrounding said coil and extending between said support members, said tie rods being formed from high permeability iron laminations with said laminations extending axially with respect to said coil, each of said rods being secured onto one of said support members and means at the other support member for applying a tension in said tie rods to compress said refractory material and rigidify said assembly.

2. An induction heating coil assembly as defined in claim 1 wherein said high frequency current has a frequency in the range of .05-10 kilocycles.

3. In an induction heating coil assembly including spaced support members, a multi-turn coil having input leads adapted to be connected to a source of electrical current, said coil being secured between said support members and a plurality of tie rods surrounding said coil and extending between said support members for rigidifying said assembly, the improvement comprising: each of said tie rods being formed from high permeability laminations with said laminations extending axially with respect to said coil, said coil being potted in a refractory material and said tie rods being placed under tension to impart a compressive force on said refractory material.

4. In an induction heating coil assembly including spaced support members, a multi-turn coil having input leads adapted to be connected to a source of electrical current, said coil being secured between said support members and a plurality of tie rods surrounding said coil and extending between said support members for rigidifying said assembly, the improvement comprising: each of said tie rods being formed from high permeability laminations with said laminations extending axially with respect to said coil, a spring means for connecting each of said tie rods onto at least one of said support members and means for stressing said spring means to increase the tension on said tie rod and, thus, the compression on said coil.

References Cited by the Examiner UNITED STATES PATENTS 2,759,087 8/1956 Lackner 21910.79 2,888,541 5/1959 Netzer 21910.79 X 3,129,459 4/1964 Kullgren et a1. 21910.79 X 3,133,185 5/1964 Alf 219--10.79 X 3,219,786 11/1965 Wenzel 21910.79 X

RICHARD M. WOOD, Primary Examiner.

L, H. BENDER, Assistant Examiner,