Induction heating device for a metal plate

1. An induction heating apparatus for heating a steel sheet traveling in a longitudinal direction that is in a non-magnetic state at a temperature above the Curie point or non-magnetic metal plate, comprising:

an induction coil for surrounding the steel sheet or the metal plate, said induction coil including an upper induction coil for being located above the steel sheet or the metal plate and a lower induction coil for being located below the steel sheet or the metal plate, said upper induction coil being spaced from said lower coil in the longitudinal direction of the steel sheet or the metal plate, said spacing being a constant longitudinal distance across a transverse direction of the entire width of the steel sheet or of the metal plate,

wherein each of the upper induction coil and the lower induction coil is arranged obliquely at an edge area of the steel sheet or the metal plate so as to form an oblique angle with the transverse direction of the steel sheet or the metal plate.

2. The induction heating apparatus according to claim 1 , wherein the longitudinal distance between a same respective edge of the upper induction coil and the lower induction coil is 0.2 to 6 times the width of a wider of the upper and lower induction coils, projected along the traveling direction of the steel sheet or metal plate, or 0.2 to 6 times the width, projected along the traveling direction of the steel sheet or metal plate, of either coil when the width of the lower induction coil is the same as the width of the upper induction coil.

3. The induction heating apparatus according to claim 2 , wherein the oblique angle ranges from 10 degrees to 60 degrees.

4. The induction heating apparatus according to claim 3 , wherein the distance between the upper induction coil and the lower induction coil is adjustable.

5. The induction heating apparatus according to claim 4 , wherein at least one of the upper induction coil and the lower induction coil is movable in the longitudinal direction of the metal plate.

6. The induction heating apparatus according to claim 4 , wherein at least one of the upper induction coil and the lower induction coil is constructed of a plurality of conductors so that the distance between the upper induction coil and the lower induction coil is adjustable by selecting a specific conductor among the plurality of conductors as the conductor to be energized by alternating current.

7. The induction heating apparatus according to claim 5 , further comprising a guide rail that extends along the metal plate in the longitudinal direction, at least one of the upper induction coil and the lower induction coil being movably mounted on the guide rail.

8. The induction heating apparatus according to claim 3 , wherein a width of at least one of the upper induction coil and the lower induction coil is changeable.

9. The induction heating apparatus according to claim 8 , wherein at least one of the upper induction coil and the lower induction coil is constructed of a plurality of conductors and the width of at least one of the upper induction coil and the lower induction coil is changeable by selecting one or more specific conductors among the plurality of conductors as the conductors to be energized by alternating current.

10. The induction heating apparatus according to claim 1 , said induction coil further comprising an edge induction coil connecting between said upper and lower induction coils, said edge induction coil for being located at an edge of the metal plate.

11. The induction heating apparatus according to claim 1 , wherein the apparatus further comprises:

an AC power supply, wherein said upper induction coil is connected at one end thereof to the AC power supply and said lower induction coil is connected at one end thereof to the AC power supply.

12. The induction heating apparatus according to claim 11 , said induction coil further comprising an edge portion connecting between said upper and lower portions of the induction coil at ends of the upper and lower portions of the induction coil opposite to the AC power source, said edge portion for being located at an edge of the metal plate.

13. The induction heating apparatus according to claim 1 , wherein the apparatus further comprises: an AC power supply, wherein said upper induction coil and said lower induction coil are connected to the AC power supply.