Apparatus and method for heating annular workpiece, and heating coil

1. A heating apparatus for an annular workpiece having a first rim, a second rim and a bottom portion between the first rim and the second rim that are provided continuously in a circumferential direction, the heating apparatus comprising heating coils to be opposed to a portion of the annular workpiece, the heating coils and the annular workpiece being movable relative to each other in the circumferential direction to heat a recessed surface of the annular workpiece by induction heating, the recessed surface being formed by the first rim, the second rim and the bottom portion,

wherein the heating coils comprise:

a first heating coil comprising a first corner conductor portion opposed to a first corner portion between the first rim and the bottom portion, and a first bottom conductor portion connected to the first corner conductor portion so as to be opposed to the bottom portion; and

a second heating coil comprising a second corner conductor portion opposed to a second corner portion between the second rim and the bottom portion, and a second bottom conductor portion connected to the second corner conductor portion to be opposed to the bottom portion,

wherein the first bottom conductor portion comprises a first bottom longitudinal conductor portion extending in the circumferential direction, the first corner conductor portion being longer than the first bottom longitudinal conductor portion, and

the second bottom conductor portion comprises a second bottom longitudinal conductor portion extending in the circumferential direction, the second corner conductor portion being longer than the second bottom longitudinal conductor portion.

2. The heating apparatus according to claim 1 , further comprising a first position adjusting portion supporting the first heating coil such that the first heating coil is displaceable with respect to the recessed surface of the annular workpiece; and a second position adjusting portion supporting the second heating coil such that the second heating coil is displaceable with respect to the recessed surface.

3. The heating apparatus according to claim 1 , wherein the heating coils comprise a plurality of sets of the first and second heating coils, and the plurality of sets of the first and second heating coils are arranged so as to be distributed in the circumferential direction, and the annular workpiece is rotated to heat the recessed surface of the annular workpiece by induction heating.

4. The heating apparatus according to claim 1 wherein the first bottom conductor portion and the second bottom conductor portion are opposed to different regions of the bottom portion of the annular workpiece in a width direction of the bottom portion.

5. The heating apparatus according to claim 1 , wherein the first corner conductor portion and the first bottom conductor portion of the first heating coil are disposed along a plane to be opposed to the first rim and the bottom portion of the annular workpiece, the first rim and the bottom portion having a curved surface shape.

6. The heating apparatus according to claim 5 , wherein the second corner conductor portion and the second bottom conductor portion of the second heating coil are disposed along a plane to be opposed to the second rim and the bottom portion of the annular workpiece, the second rim and the bottom portion having a curved surface shape.

7. A heating method for an annular workpiece having a first rim, a second rim and a bottom portion between the first rim and the second rim that are provided continuously in a circumferential direction, wherein heating coils are opposed to a portion of the annular workpiece, and the heating coils and the annular workpiece are moved relative to each other in the circumferential direction to heat a recessed surface of the annular workpiece by induction heating, the recessed surface being formed by the first rim, the second rim and the bottom portion, and the heating coils including a first heating coil and a second heating coil, the heating method comprising:

arranging a first corner conductor portion of the first heating coil to be opposed to a first corner portion between the first rim and the bottom portion and a first bottom conductor portion of the first heating coil to be opposed to the bottom portion;

arranging a second corner conductor portion of the second heating coil to be opposed to a second corner portion between the second rim and the bottom portion and a second bottom conductor portion of the second heating coil to be opposed to the bottom portion; and

heating the recessed surface such that the first heating coil is disposed at a position corresponding to a deformation of the recessed surface on a side of the first rim and such that the second heating coil is disposed at a position corresponding to a deformation of the recessed surface on a side of the second rim,

wherein the first bottom conductor portion comprises a first bottom longitudinal conductor portion extending in the circumferential direction, the first corner conductor portion being longer than the first bottom longitudinal conductor portion, and

the second bottom conductor portion comprises a second bottom longitudinal conductor portion extending in the circumferential direction, the second corner conductor portion being longer than the second bottom longitudinal conductor portion.

8. A heating coil configured to be opposed to a portion of a workpiece having a rim and a bottom portion that are provided continuously in a longitudinal direction and to be moved relative to the workpiece in the longitudinal direction to heat a recessed surface of the workpiece, the recessed surface being formed by the rim and the bottom portion, the heating coil comprising:

a corner conductor portion extending in the longitudinal direction so as to be opposed to a corner portion between the rim and the bottom portion; and

a bottom conductor portion connected to the corner conductor portion in series to be opposed to the bottom portion,

wherein the bottom conductor portion comprises a bottom longitudinal conductor portion extending in the longitudinal direction; and

the corner conductor portion is longer than the bottom longitudinal conductor portion.

9. The heating coil according to claim 8 , comprising a plurality of the bottom longitudinal conductor portions connected to each another in series, wherein the plurality of the bottom longitudinal conductor portions are located at different positions in the longitudinal direction of the workpiece and at different distances from the corner conductor portion.

10. The heating coil according to claim 8 , wherein the corner conductor portion comprises a rim opposing surface opposed to the rim of the workpiece, the rim opposing surface being separated from the rim more on a side of a top of the rim than on a side of the bottom portion of the workpiece.

11. The heating apparatus according to claim 1 , wherein the first corner conductor portion and the first bottom conductor portion are disposed along one plane.

12. The heating apparatus according to claim 2 , wherein the first position adjusting portion and the second position adjusting portion are configured such that a gap between the recessed surface and the first heating coil and a gap between the recessed surface and the second heating coil are individually adjustable.

13. The heating method according to claim 7 , wherein the first corner conductor portion and the first bottom conductor portion are disposed along one plane.

14. The heating method according to claim 7 , further comprising individually adjusting a gap between the recessed surface and the first heating coil and a gap between the recessed surface and the second heating coil.

15. The heating coil according to claim 8 , wherein the corner conductor portion and the bottom conductor portion are disposed along one plane.