Inductor For Heating An Elongated Workpiece Having A Varied Profile

Abstract

An induction heating inductor for heating an elongated workpiece having a varied profile which inductor includes two generally parallel conductors extending the portion of the workpiece to be heated and generally U-shaped flux concentrators around these conductors with spaced legs facing the workpiece and wherein the length of the legs are varied to form substantially a mirror image of the workpiece profile.

Description

The invention relates to the art of induction heating and primarily to an inductor for heating an elongated workpiece having a varied profile.

The invention is particularly applicable for inductively heating a shaft-like workpiece having a tapered profile, 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 for inductively heating a variety of elongated workpieces having varied profiles along their lengths.

In hardening elongated, shaft-like workpieces it has become somewhat common to use a single turn inductor having two parallel conductors extending the length of the workpiece. The workpiece is rotated adjacent the energized parallel conductors to heat inductively the portion of the elongated workpiece adjacent the conductors. Thereafter, appropriate means is used to quench harden the heated portion of the workpiece. The present invention relates to an improvement in an inductor of the type including two generally parallel conductors formed into a single loop and energized by an alternating frequency power source. Heretofore, when the profile of the elongated workpiece was varied to include axial tapers or stepped portions along the length of the workpiece, the heating effect along the parallel conductors was not varied. This resulted in un-uniform surface heating of the workpiece as it was rotated. To overcome this difficulty, it has been suggested to modify the parallel conductors extending along the length of the workpiece to correspond with the profile of the workpiece. As is obvious, this solution substantially increased the difficulty experienced in forming the inductor and added to its expense. Also, it was difficult to modify such an inductor to compensate for engineering variables or to change the inductor for use in different workpieces.

All of these difficulties have been overcome by the present invention which relates to a single turn inductor for use in heating an elongated workpiece, which inductor is modified to change the heating effect along its parallel conductors in accordance with the profile of the workpiece to be heated.

In accordance with the present invention, there is provided an improvement in an induction heating inductor for heating an elongated workpiece having a given length to be heated, a central axis and an outer surface with a generally preselected axially extending profile, which inductor includes at least one generally straight conductor extending axially along the surface of the workpiece and carrying a generally U-shaped flux concentrator with two spaced legs facing the workpiece surface. The improvement, in accordance with the invention, includes varying the length of the legs of the concentrator to form a profile for these legs, which profile approximates the mirror image of the surface profile of the workpiece. In this manner, the heating effect along the length of the workpiece is substantially uniform without requiring modification of the parallel conductors.

The primary object of the present invention is the provision of a single turn inductor for heating an elongated workpiece having a varied profile, which inductor includes flux concentrator means for varying the heating effect along the conductor in accordance with the profile of the workpiece.

In accordance with another object of the present invention there is provided a single turn inductor for heating an elongated workpiece having a varied profile, which inductor includes a flux concentrator extending along the length of the parallel conductors and having a varied profile that is the mirror image of the workpiece profile.

These and other objects and advantages will become apparent from the following description used in conjunction with the accompanying drawings, in which:

FIG. 1 is a pictorial view showing, somewhat schematically, the preferred embodiment of the present invention;

FIG. 2 is an enlarged cross-sectional view taken generally along line 2--2 of FIG. 3;

FIG. 3 is an enlarged plan view taken generally along line 3--3 of FIG. 2;

FIG. 4 is an enlarged cross-sectional view taken generally along line 4--4 of FIG. 3;

FIG. 5 is an enlarged cross-sectional view taken generally along line 5--5 of FIG. 3; and,

FIG. 6 is a top elevational view showing, somewhat schematically, a modification of the present invention.

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, FIGS. 1-5 show an induction heating apparatus A for inductively heating an elongated workpiece B having an outer surface profile 10 including a cylindrical portion 12 and a tapered portion 14. The workpiece has spaced ends 16, 18 and a length L to be heated between these ends. Centers 20, 22 locate the workpiece on its axis a for rotation by an appropriate means, schematically indicated as driven motor 24. An inductor C is used for inductively heating the workpiece. This inductor includes two parallel spaced conductors 30, 32, a first cross-over conductor 34 at end 18 and a second cross-over conductor 36 at end 16. These conductors form a single turn loop having a well known construction. To energize this loop, there is a discontinuity portion 40 dividing cross-over conductor 36 into two sections, 36a, 36b. This discontinuity portion could be located at various positions within the loop formed by the conductors of the inductor. Leads 50, 52 connect the sections 36a, 36b with a power supply, schematically represented as generator 54, having a power factor correcting capacitor 56. The structure so far described is essentially the same as now being used for inductively heating shaft-like workpieces.

In accordance with normal practice, there are provided two flux concentrators 60, 62 having U-shaped legs 60a, 60b and 62a, 62b, respectively which legs face toward the workpiece B. The U-shaped concentrators could be formed by a plurality of adjacent soft iron laminations or other high permeability material, such as ferrites. In accordance with the present invention, the legs of the flux concentrators are modified to provide profiles 70, 72 for concentrators 60, 62, respectively. These profiles are substantially mirror images of the profile 10 formed by the outer surface of workpiece B. Of course, in the illustrated embodiment the profiles 70, 72 could be formed by a plurality of steps or by gradual changing of the lengths for the legs of the concentrators. The term "mirror image" is used to indicate that the profiles 70, 72 have essentially the reverse shape of the workpiece profile 10, but not that this shape is identical from a dimensional standpoint. It could vary to provide basically the function described later.

Referring now to FIGS. 4 and 5, the effect of the varied contour for the flux concentrator legs is schematically illustrated. As shown in FIG. 4, if the legs 60a, 60b, 62a, 62b have their longest lengths, the flux fields x are concentrated to provide a heating pattern generally shown by the dashed lines within the portion 12 of workpiece B. With these flux concentrator legs retracted, as shown in FIG. 5, the flux density of each field y is reduced so that, in the smaller portion 14, of the workpiece B the heating depth is somewhat reduced beyond that which would have been caused hy the leg being at the length shown in FIG. 4. This causes the heating pattern shown by the dashed lines which is substantially the same as the heating pattern in the larger cylindrical portion 12. In this manner, there is a modification of the flux fields emanating from the parallel conductors 30, 32 which variation attempts to compensate for the variations in the cross-section of the workpiece B along the length L. After the workpiece B is heated, is is then quench hardened according to known practices.

Referring now to FIG. 6 a modification of the invention is illustrated. The same parts as shown in the preferred embodiment bear like numbers. The workpiece B' includes stepped portions 80, 82 and 84. The inductor C' includes flux concentrators 90, 92 on conductor 30 and concentrators 94, 96 on conductor 32. These flux conductors are formed into U-shaped configurations, as were concentrators 60, 62, and are positioned opposite the enlarged portions 80, 84 of workpiece B'. The intermediate openings 100, 102 are adjacent the reduced portion 82 of workpiece B'. These openings could be filled by flux concentrators having shorter legs, as is apparent from the description of the preferred embodiment of the present invention. The operating characteristics of this modification are substantially identical to the operating characteristics as explained in connection with the preferred embodiment of the invention as shown in FIGS. 1-5.

Claims

Having thus described our invention, we claim:

1. An induction heating inductor for heating an elongated workpiece having a given length to be heated, a central axis and an outer surface with a preselected axially extending profile whereby some portions are more close to said axis than other portions of said surface, said inductor comprising at least one generally straight conductor extending axially along said surface for said given length and a generally U-shaped flux concentrator over said conductor with two legs spaced facing said workpiece surface, the improvement comprising: said legs of said concentrator having varied lengths and forming a profile approximately the mirror image of said surface profile.

2. The improvement as defined in claim 1 wherein said concentrator is formed at least in part from a plurality of generally U-shaped iron laminations.

3. The improvement as defined in claim 1 wherein said concentrator included interrupted portions along its profile.