US2814707A - Induction heating device - Google Patents

Description

INDUCTION HEATING DEVICE John C. Turnbull and Lester W. Morgan, Lancaster, Pa.,

assignors to Radio Corporation of America, a corporation of Delaware Application November 12, 1954, Serial No. 468,268

4 Claims. (Cl. 219-1053) This invention relates to high frequency heating transformers, and more particularly to an improved heating transformer for heating small metal parts.

Induction heating is Widely used in many industries. Such heating generally involves a source of high frequency electrical signals in the radio frequency range. The high frequency signals are applied across a coupling coil or a primary of a transformer and a voltage is induced into a pickup unit or secondary of the transformer. An object to be heated is generally placed in close proximity to the pickup unit. High frequency currents are induced in the metal part thereby heating the part. The transformer utilized may be in various forms.

In many industries, it is desirable to use induction heating for heating small metal parts. Induction heating is very often utilized during the manufacturing of many electron tubes. In the manufacture of electron tubes, for example, it is often desirable to heat small metal parts during the process of sealing metal parts to glass. Very often, it is inconvenient to directly contact the surfaces of the metal parts to be heated during various processes of manufacture. For example, during tube manufacturing the surface of the metal part to be heated is located within a glass envelope or inside a container into which it is often impractical to insert an induction heating transformer. In such cases, it is desirable to have a pickup unit, which may be considered as the secondary of the transformer on one side of the glass surface and a high frequency coupling coil, which may be considered as the primary of the transformer, on the other side of the glass surface, or other object.

In utilizing induction heating to heat small metal parts, water cooling is often required in the heating device or transformer. This Water cooling involves additional equipment and expense as well as being inconvenient.

In some manufacturing processes using induction heating, it is desirable to provide a convenient means for varying the amount of current flowing in the secondary of the transformer Without varying the current in the primary. In such cases, a convenient means for varying the coupling between the primary and secondary of the transformer is desirable.

It is an object of this invention to provide an improved high frequency heating device wherein the high frequency coil and the pickup unit may be disposed on different sides of a surface.

It is a further object of this invention to provide an improved high frequency heating device which does not require cooling during the heating operation.

It is still a further object of this invention to provide an improved induction heating transformer in which the coupling between the primary and secondary of the transformer may be conveniently varied.

It is still a further object in this invention to provide an improved induction heating transformer for electron tube manufacturing in which a small metal part, such as a prong, may be sealed to glass.

In accordance with the present invention, a high frenited States Patent 9 quency induction device for heating a small metal part is provided. The unit includes a metallic disc or pickup unit having an aperture adapted to receive the metal part. A slit extends from the aperture to the edge of the metallic disc. The metallic disc, in this case, acts as a secondary of an induction heating transformer. A coupling coil, adapted to be connected to a source of high frequency electrical currents, acts as the primary of the transformer and provides means for applying high frequency currents to the metallic disc. The high frequency current induced in the metal disc flows around the circumference of the disc, over the surface of the slit and around the inside surface of the aperture surrounding the metal part thereby inducing high frequency currents in the metal part. The metal part, which is in close proximity to the disc, is thereby heated. The coil and the disc are free to move relative to each other so that the coupling therebetween may be varied. The distance between the disc and the coil may be made fairly large, if desired. This induction heating device is applicable to processes for sealing a metal pin or prong to glass during electron tube manufacturing, as well as other manufacturing processes.

Other objects and advantages of the present invention will become apparent and suggest themselves to those skilled in the art to which the invention is related, from a reading of the following specification in connection with the accompanying drawing, in which:

Figure 1 shows a high frequency induction device, in accordance with the present invention;

Figure 2 is a top view of the high frequency induction device shown in Figure l, and

Figures 3 and 4 show a high frequency induction device similar to the device of Figure 1 employed to seat a support.

Referring to the drawing, a metallic disc or plate 10 is provided with an aperture 12. A slit 14 connects the aperture 12 to the outer edge to the disc 10. The disc 19 may comprise a copper blank and, in effect, acts as a secondary of a high frequency induction heating transformer. The aperture 12 is dimensioned and adapted to receive a small metal part 16. For example, this metal part may be a pin or prong to be sealed to an electron discharge device.

A relatively large coupling coil 18 acts as a primary of the induction heating transformer. The coil, which may be, for example, a single turn of wire, may be connected to a high frequency generator (not shown). The generator provides a source of high frequency electrical currents to be used in the heating device.

The present invention is described in connection with a process of sealing glass to a metal part during a tube manufacturing step or steps. It is understood, however, that the invention will find applicability in numerous other manufacturing processes.

A glass element 20, which may, for example, be a. glass envelope of an electron tube device, is inserted between the coil 18 and the metallic disc 10. The glass is provided with an opening 19.

The small metal part 16 is inserted into the aperture 12 of the metallic disc 10. The metal part 16 extends through the opening 19 of the glass element 20. it is seen that the metallic disc 10 and the coil 13 are disposed on opposite sides of the glass element 20. In electron tube manufacturing it is often desirable to apply heat to a surface of a small metal part within the tube envelope. The arrangement shown, embodying the present invention, provides ideal means for doing this. The invention also provides convenient means for applying heat to the surface of a metal object in a container, within which it is difficult to insert a heating transformer.

In considering the operation of the device shown, high frequency currents are applied to the coil 18, which may be considered as a transformer primary. Current is then induced in the metallic disc 12, and the induced current path is around the circumference of the disc. At the point where the slit 14 meets the circumference, this induced current is interrupted, and a radio frequency voltage is thereby induced across the slit 14. Since the current path down the slit 14 and around the aperture 12 has a relatively small impedance, this induced voltage will produce a heavy radio frequency current in this circuit. The current in the aperture 12 will in turn induce a large heating current in the metal part 16.

The opening 19 of the glass 20 is sufficiently small so that the metal part 16 is relatively close to the glass. The metal part may be held in position by any convenient means or may be self supported by the glass when the opening 19 is small enough to contact the part. The glass receives heat from the small metal part when the metal part is heated. When the temperature of the glass reaches a certain point, the glass will begin to melt. While the glass is in a plastic state, it contacts the metal part to thereby form an intimate bond or contact therewith. The heating process is then stopped. In tube manufacturing, the glass is then generally placed in an annealing oven to remove any strain produced in the glass during the heating process.

In the arrangement shown, it is seen that the coupling between the coil and the metallic disc may be easily varied by changing the relative positions thereof. The distance between the coil and the metallic disc may be made relatively large, if desired.

The metallic disc 10 may be of relatively large mass and surface area. Consequently, the disc does not require water cooling, as would a very small coil made to fit closely around the metal part 16.

The hole in the metallic disc 10 may be rectangular, triangular and any desired shape, dependent upon the shape of the metal part to be heated. It may also be located anywhere within the disc but preferably not too close to its outer edge.

Referring to Figures 3 and 4, there is illustrated another form of the invention. The heating device is similar to the one illustrated in Figures 1 and 2 and, consequently, are assigned the same reference numbers. In this form a glass element 22 is disposed between pickup unit 10 and the coupling coil 18. The metal part 16 is inserted within the aperture 12 of the pickup disc. It is to be noted that the glass is not apertured in this arrangement of the parts in accordance with the invention. The metal part 16 is in close contact with the glass 22. When the metal part 16 is heated, the resulting heat causes the glass to melt thereby causing the metal part 16 to sink into the glass. After the metal part has reached a desired position within the glass, the heating process is terminated. The seated position of the metal part 16 with relation to the glass 22 after heating may be that shown in Figure 4.

This form of the invention provides a convenient means for embedding a metal stud within glass. This stud may be employed as a convenient electrical connecting point within a glass envelope or another container.

The heating unit described herein, embodying the present invention, may be used in many manufacturing processes where it is desired to heat metal parts within a container or envelope. It is particularly applicable to cases where it is desired to seal a metal part to a glass surface and it is desirable to have the pickup unit and the coupling coil on opposite sides of the glass.

What is claimed is:

1. A high frequency induction heating unit for sealing a small metal part to another part constituted of nonconductive, fusible material comprising a metallic disc having an aperture adapted to receive said metal part, said metallic disc having a slit extending from said aperture to the edge thereof, means for applying high frequency currents to said metallic disc being disposed on the side of said other part opposite from said metal part, said means being freely movable with respect to said metallic disc whereby said fusible material may be placed between said metallic disc and said means during the operation of said heating unit.

2. A high frequency induction heating unit for sealing a metal prong to a glass body having an opening therein and associated with an electron discharge device comprising a metallic disc having an aperture adapted to receive said metal prong, said metal prong being adapted to extend through said opening in said glass body, said metallic disc being associated with said metal prong on one side of said glass body, said metallic disc having a slit extending from said aperture to the edge thereof, and a coil for applying high frequency currents to said metallic disc, said coil being disposed on the side of said glass body opposite to said metallic disc, said coil being freely movable with respect to said metallic disc whereby the coupling between said metallic disc and said coil may be varied.

3. A high frequency induction heating device for sealing a metal prong to the glass envelope of an electronic discharge device comprising a disc of conductive material having an aperture adapted to receive said metal prong, said disc having a slit extending from said aperture to the edge thereof, a coil for applying high frequency currents to said disc, said coil being a single turn of wire, said coil being freely movable with respect to said disc whereby said glass envelope may be disposed between said disc and said coil during the operation of said heating device.

4. A high frequency induction heating unit for heating a small metal part in a glass member comprising a metallic disc having an aperture adapted to receive and closely surround said metal part, said metallic disc having a slit extending from said aperture to the edge thereof, means for inducing a voltage in said metallic disc whereby high frequency currents are induced in said metal part, said high frequency currents heating said metal part and said glass member whereby said glass melts and forms a close bond with said metal part, and said voltage inducing means being freely movable with respect to said metallic disc whereby said glass member may be placed between said metallic disc and said voltage inducing means during operation of said heating unit.

References Cited in the file of this patent UNITED STATES PATENTS 2,359,500 White Oct. 3, 1944 2,432,491 Thomas Dec. 9, 1947 2,484,650 Ross Oct. 11, 1949 2,522,949 Jarman Sept. 19, 1950 2,756,313 Cater July 24, 1956 FOREIGN PATENTS 1,083,042 France Jan. 4, 1955

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