US3691339A - Multi-phase induction heating device - Google Patents

Abstract

An induction heating device comprising a frame generally defining a loading receiving chamber and at least three overlapping, electrically insulated, induction heating coils adapted to be magnetically coupled with a load within the chamber. Each of the induction heating coils has a series of repeating loops comprising two spaced, generally parallel legs, with the plane defined by the parallel legs of each loop and between these legs being generally exterior of the chamber.

Description

O United States Patent [151 3,691,339 Cachat [451 Sept. 12, 1972 MULTI-PHASE INDUCTION HEATING 2,678,371 5/1954 Andrew ..336/181 X DEVICE 2,471,777 5/1949 Reinartz ..336/ 181 X R24,698 9/1959 Logan et al ..2l9/l0.79 X

72 I t F. l 1 Cleveland Ohm 2,849,584 8/1958 Tudbury ..219/10.7s Asslgnw Park-Ohio Industries, I Cleve- 3,379,962 4/1968 Kasper ..l3/26 x land, Ohio [22] Filed: May 7, 1971 Primary Examiner-J. V. Truhe Assistant Exammer-B. A. Reynolds PP N04 141,676 Attorney--Meyer, Tilberry and Body 521 US. Cl. ..219/1o.s7, 219/1035, 219/1019 ABSTRACT [51] Illt. Cl. ..ll05b 9/02 An induction heating device comprising a frame [.58] new krch'zlgl 10-57; generally defining a loading receiving chamber and at 27; 336/171 181; 310/184 207; least three overlapping, electrically insulated, induc- 318/131 tion heating coils adapted to be magnetically coupled R f ed with a load within the chamber. Each of the induction 1 e heating coils has a series of repeating loops comprising UNITED STATES PATENTS two spaced, generally parallel legs, with the plane defined by the parallel legs of each loop and between 1,920,325 8/1933 Schmidt ..l3/26 these legs being generally exterior f h h 509,705 11/1893 Threlfall ..318/131 X 2,005,901 6/1935 Long ..l3/26 X 1 Claim, 4 Drawing Figures l 3 A 2 4 3 A B A B I @(S LWQ/( j C /20 ll'" -2 u- 6 l J 3 Q B lo PATENTEDSEP 12 I972 I I I I f ql I I I I I I I I 1 I I I I I I ll:

I l I l INVENTOR. JOHN F. CACHAT ATTORNEYS BY Mew, 744 8 Body MULTI-PIIASE INDUCTION HEATING DEVICE This invention relates to the art of induction heating and more particularly toa multi-phase induction heating device.

The invention is particularly applicable for inductively heating large loads such as heavy billets or ingots and it will be described with particular reference thereto; however, it should be appreciated that the invention has much broader applications and may be used in other induction heating installations, especially melting metal and holding molten metal.

In rolling mill operations, it is necessary to heat large ingots or billets to a temperature sufficiently high for subsequent rolling. A variety of systems have been employed for this heating operation. For instance, it is somewhat common to place the ingots within a gasfired soaking furnace. After several hours, the ingot is through heated sufficiently for rolling. This process is relatively slow and results in an excessive amount of scale on the outer surface of the ingot. Such scale can detrimentally affect the ultimate rolled product. To overcome these difficulties, it has been suggested to heat inductively the ingot by placing the ingot within a multi-turn induction heating coil. When the coil is energized, the magnetic coupling between. the ingot and the coil causes current flow within the ingot which creates R heating. This induction heating process results in less scale and decreases the heating time necessary for bringing the ingot up to rolling temperature. However, the induction heating coil includes a plurality of turns surrounding the workpiece and the reactance within the coil is substantially high. When a single coil is placed around the ingot, it is connected onto one phase of an incoming polyphase power source, and the balance of the polyphase system is detrimentally affected. This problem is substantially increased when the power required is high, such as experienced in ingot heating. Consequently, there has been considerable effort devoted to devices for balancing the polyphase or three phase power source when induction heating is used for raising the temperature of an ingot. In some cases, dummy loads are employed. In other instances, three separate, axially spaced coils are placed around the ingot with each coil being in one phase of the polyphase source. These arrangements have resulted in a better balance of the three phase source; however, they do have certain disadvantages. Dummy loads create losses. The use of three separate axially spaced coils-provides different heating along the length of the billet. Also, if the permeability along the billet changes, imbalance can be created from one coil to the other.

All of these disadvantages and others have been overcome by the present invention wherein an induction heating installation utilizes three or more overlapped coils each of which is connected toone phase of a polyphase source and are wound around the load in a configuration generally matching the winding of an electric motor stator.

In accordance with the present invention, there is provided an induction heating device comprising a frame defining a load receiving chamber and at least three overlapping, electrically insulated, induction heating coils adapted to be magnetically coupled with a load in the chamber. Each of the induction heating coils has a series of repeating loops comprising two spaced, generally parallel legs, with the plane defined by the parallel legs of each loop and between these legs being generally within the frame and exterior of the chamber. Means are provided for connecting one phase of a polyphase source to each of these induction heating coils.

By constructing an induction heating device in accordance with the above description, the several loops of the overlapped coils include parallel legs which are not on opposite sides of the load. The load is within a chamber surrounded by the series of loops similar to the loops found within the stator of an electric motor. In this manner, each of the phases is accurately balanced because all corresponding portions of each coil within the loop are generally exposed to the same portionof the load being heated. This construction allows a large number of coils which will create a relatively small driving force on the load itself during the heating operation.

In accordance with another aspect of the invention, successive loops in a given induction heating coil can have opposite hand winding so that any motive force created by one loop is cancelled by an adjacent loop. When such an induction heating device is employed for melting or holding molten metal, the spaced legs of each loop create a substantially reduced stirring action even though cycle current is used.

The primary object of the present invention is the provision of an induction heating device using at least three overlapped coils, which device results in a balanced load for a polyphase source connected thereto.

Another object of the present invention is the provision of an induction heating device using at least three overlapped coils, which device results in uniform heating ofa load within the device.

Yet another object of the present invention is the provision of an induction heating device using at least three overlapped coils, which device reduces stirring action when used for metal melting or holding molten metal.

These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings in which:

FIG. 1 is a wiring diagram showing the application of the present invention;

FIG. 2 is a top cross sectional view showing the preferred embodiment of the present invention;

FIG. 3 is a side elevational view taken generally along line 3-3 of FIG. 2; and,

FIG. 4 is a schematically represented layout of the coils used in the preferred embodiment of the present invention.

Referring now to the drawings wherein the showings are for the purpose of illustrating, schematically, the preferred embodiment of the present invention and not for the purpose of limiting same, FIG. 1 illustrates a three phase power supply having input leads L L and L and Y-connected coils l0, 12, 14 defining phases A, B, and C, respectively. In accordance with the present invention, the coils 10, I2, 14 are all used to heat inductively a workpiece B in the form of a slab or ingot. This workpiece, or load, could also be metal for melting or molten metal to be held in the molten state.

In accordance with the present invention, the induction heating coils 10, 12, and 14 have a particular configuration which is illustrated in FIGS. 2-4. A frame 20 formed from a high permeability material includes a plurality of elongated slots 22 defined between elongated ribs 24. These ribs have outer pole surfaces 26 facing an inner workpiece receiving chamber 30 into which the workpiece or load B is placed. Within the slots there are provided a plurality of parallel conductors A B C A B C etc. These parallel legs are formed by winding an induction heating conductor in a pattern which creates a series of repeating loops each of which has two of the parallel spaced legs. FIG.'4 illustrates a preferred type of winding pattern wherein the coil is shown in solid line, the coil 12 is shown in dashed line, and the coil 14 is shown in dotted line. It is noted that the individual coils, as shown in H6. 4, include alternate left and right hand loops as they extend around the workpiece receiving chamber 30. This par ticular type of alternate hand winding configuration is useful to reduce the magnetomotive force erierted on the load during heating. One loop tends to drive the load in one direction and an adjacent loop cancels that tendency. However, itis within the contemplation of the present invention to wind the coils l0, l2, and 14 around the frame in the same hand, since the magnetomotive force exerted on the load will generally be somewhat low and can be counteracted by the weight of the load.

By constructing the coils 10, 12 and 14 in accordance with the present invention, the coils do not contain loops which circle the workpiece as is standard practice in the induction heating art. Since corresponding legs, i.e. A 13,, C etc., of the three coils 10, 12, and 14 are adjacent each other, the corresponding legs are subjected to substantially the same impedance during the heating operation. This provides an efficient manner for balancing the load in all three phases of the system, as shown in FIG. 1. By using a plurality of legs in this manner, there is a reduction in the stirring action caused during melting of molten metal because adjacent flux fields are out of phase. There is no accumulation of flux field phases which can impart a large stirring action upon the molten metal when low frequency is used.

In accordance with the invention, sufficient number of loops are formed in the coils l0, l2, and 14 to provide at least about 24 pole surfaces between adjacent loops. This number of pole faces creates a uniform heating of the workpiece. The coils are formed from hollow conductors to allow passage of coolant therethrough.

Having thus defined my invention, I claim:

1. An induction heating device comprising a frame defining a load receiving chamber; three overlapping, electrically insulated, induction heating coils adapted to be magnetically coupled witha load in said chamber, each of said induction heating coils having a series of repeating loops comprising two spaced, generally parallel legs with the plane defined by said parallel legs of each loop and between said legs being generally within said frame and exterior of said chamber; means for connecting one phase of a three phase source to each of said induction heating coils; and, said series of loops of each of said-coils including a plurality of alternate right hand arid le ft h and wo und loops.

Claims (1)

1. An induction heating device comprising a frame defining a load receiving chamber; three overlapping, electrically insulated, induction heating coils adapted to be magnetically coupled with a load in said chamber, each of said induction heating coils having a series of repeating loops comprising two spaced, generally parallel legs with the plane defined by said parallel legs of each loop and between said legs being generally within said frame and exterior of said chamber; means for connecting one phase of a three phase source to each of said induction heating coils; and, said series of loops of each of said coils including a plurality of alternate right hand and left hand wound loops.

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