Induction heating system for 360.degree. curing of can body coatings

• US 5,821,504 A
• Filed: 04/07/1997
• Issued: 10/13/1998
• Est. Priority Date: 06/04/1990
• Status: Expired due to Term

• Current Assignee: Nordson Corporation
• Original Assignee: Nordson Corporation
• Inventors: Gacka, Mark, Sprenger, deceased, Robert A., Sprenger, Barbara
• Primary Examiner(s): HOANG, TU BA
• Application Number:
  US08/838,408
• Time in Patent Office: 554 Days
• Field of Search: 219/604, 219/609, 219/635, 219/645, 219/647, 219/650, 219/653, 219/672, 34/247
• US Class Current: 219/635
• CPC Class Codes: F26B 15/18 the objects or batches of materials being carried by endless belts
• CPC Class Codes: F26B 3/347 Electromagnetic heating, e.g. induction heating or heating using microwave energy
• CPC Class Codes: H05B 6/103 multiple metal pieces successively being moved close to the inductor

Abstract

A method and apparatus for 360° induction heating of a can body to cure or partially cure a protective coating applied thereto. The can bodies are inductively heated by placing them in a medium frequency, oscillating magnetic field generated by a multiple turn induction coil helically wound around the transport path of the can body. By using a medium-frequency field and by centering the can bodies with respect to the induction coil, the can bodies may be evenly and uniformly heated around 360° of their circumference.

Claims

1. A method of at least partially curing a coating onto an electrically conductive cylindrical workpiece by induction heating comprising the steps of:

(a) generating a magnetic field oscillating at a frequency of approximately 500 Hz to 50 kHz along a heating path;

(b) transporting the workpiece through the magnetic field generated in said step (a) along the heating path;

(c) at least partially curing the coating onto the workpiece around a 360°

circumference of the workpiece during said step (b) of transporting the workpiece through the magnetic field.

2. A method of at least partially curing a conductive an electrically conductive cylindrical workpiece by induction heating as recited in claim 1 further comprising the step of centering the circumference of the workpiece with respect to the magnetic field during said step (b).

3. A method of at least partially curing a coating onto an electrically conductive cylindrical workpiece by induction heating as recited in claim 2, wherein said step of centering the circumference of the workpiece with respect to the magnetic field comprises the step of physically limiting movement of the workpiece on all sides of the circumference of the workpiece during said step (b).

4. A method of at least partially curing a coating onto an electrically conductive cylindrical workpiece by induction heating as recited in claim 1, said step (a) of generating an oscillating magnetic field comprising the steps of:

(a) providing an induction coil helically along and around the heating path; and

(b) generating a current within the induction coil oscillating at a frequency of approximately 500 Hz to 50 kHz.

5. A method of at least partially curing a coating onto an electrically conductive cylindrical workpiece by induction heating as recited in claim 4, further comprising a step (c) of centering the circumference of the workpiece with respect to the magnetic field by supporting the workpiece to be substantially concentric with the induction coil.

6. A method of at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece by induction heating as recited in claim 1, further comprising the step of sensing for a discontinuity in a rate of transfer of the workpiece along the heating path.

7. A method of at least partially curing a coating onto an electrically conductive cylindrical workpiece by induction heating as recited in claim 1, further comprising the step of sensing a temperature of the workpiece as the workpiece is transported along the heating path.

8. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece by induction heating comprising:

a path of travel within the apparatus;

an induction coil circumjacent about said path of travel for heating the workpiece around a 360°

circumference of the workpiece;

a current source for generating a current within said induction coil oscillating at a frequency of approximately 500 Hz to 50 kHz so as to generate an oscillating magnetic field within said path of travel;

a conveyor for transporting the workpiece along said path of travel; and

a controller for controlling said current source.

9. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 8, said controller shutting off said current source if a temperature of the workpiece exceeds a predetermined value while the workpiece is transported along said path of travel.

10. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 8, further comprising circulation means for circulating air around said induction coil to prevent said induction coil from overheating.

11. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 8, wherein said conveyor comprises an endless belt on which the workpiece rests, said endless belt capable of moving along said path of travel.

12. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 11, wherein said belt is comprised of stainless steel.

13. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 11, further comprising a channel mounted along said path of travel, said endless belt being located within said channel.

14. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 8, wherein said induction coil is wound around said path of travel so as to create a magnetic field that is uniform along said path of travel.

15. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 8, wherein said induction coil is wound around said path of travel so as to create a magnetic field that varies along said path of travel.

16. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 8, further comprising a cylindrical tube, said conveyor transporting the workpiece along said path of travel through said tube.

17. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 16, wherein said inner diameter of said tube is approximately 0.5 inches greater than said outer diameter of the workpiece.

18. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 16, further including means for allowing said tube and said induction coil to be removed and replaced by a second tube and a second induction coil having diameters different than said tube and said induction coil to accommodate workpieces of different diameters.

19. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 16, wherein said induction coil is helically wound around said tube.

20. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece as recited in claim 19, further including means for allowing said tube and said non-liquid cooled induction coil to be removed and replaced by a second tube and a second non-liquid cooled induction coil having diameters different than said tube and said non-liquid cooled induction coil to accommodate workpieces of different diameters.

21. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece by induction heating comprising;

a path of travel within the apparatus;

a non-liquid cooled induction coil circumjacent about said path of travel;

a current source for generating a current within said non-liquid cooled induction coil so as to generate an oscillating magnetic field along said path of travel;

a conveyor for transporting the work piece along said path of travel; and

a controller for controlling said current source.

22. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 21, further comprising a rate change sensor for sensing a discontinuity in the rate of transfer of the workpiece along said path of travel.

23. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 22, wherein said rate change sensor comprises an optical sensor mounted at either end of said path of travel, said optical sensor having a transmitter transmitting an optical signal to a receiver, said optical sensor indicating a discontinuity in the rate of transfer of the workpiece along said path of travel during operation of the apparatus when a predetermined period of time passes during which no signal, or a constant signal, is received in said receiver.

24. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 21, wherein said conveyor comprises an endless belt on which the workpiece rests, said endless belt moving along said path of travel.

25. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 21, wherein said induction coil is wound around said path of travel so as to create a magnetic field that is uniform along said path of travel.

26. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 21, wherein said induction coil is wound around said path of travel so as to create a magnetic field that varies along said path of travel.

27. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 21, further comprising a cylindrical tube, said conveyor transporting the workpiece along said path of travel through said tube.

28. An apparatus for at least partially curing a coating onto an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece as recited in claim 27, wherein said induction coil is helically wound around said tube.

29. An apparatus for heating a coating on an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece by induction heating comprising;

a housing;

an electrically non-conductive tube supported within said housing and having a first end and a second end;

an induction coil within said housing provided around said tube;

a conveyor for conveying the workpiece through said tube; and

a controller operatively connected to said induction coil for controlling operation of said apparatus.

30. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 29, wherein an interior of said tube is sealed off from an interior of said housing.

31. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 29, wherein said conveyor comprises a chain for supporting the workpiece, said chain being an endless chain circulating through said tube.

32. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 31, further comprising a channel provided along a length of said tube for preventing contact between said chain and said tube.

33. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 32, wherein said channel is electrically non-conductive.

34. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 29, wherein said conveyor comprises:

an endless chain circulating through said tube;

a plurality of wheels for supporting and advancing said chain, two wheels of said plurality of wheels defining a surface of said chain on which the workpiece is supported, said surface lying in a plane intersecting said tube; and

guides provided on either side of said chain along at least a portion of said surface to maintain the workpiece on said chain.

35. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 34, further comprising a plurality of hooks provided in said chain and spaced apart a distance greater than a lengthwise dimension of the workpiece, a hook of said plurality of hooks capable of engaging the workpiece to prevent relative movement between the workpiece and said chain.

36. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 34, further comprising a tension wheel engaging said chain to maintain tension in said chain.

37. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 29, further comprising means for circulating air through said housing.

38. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 29, further comprising means for circulating air through said tube.

39. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 29, wherein a spacing between turns of said induction coil ranges from approximately 0 to 0.25 inches.

40. An apparatus for heating a coating on an electrically conductive cylindrical workpiece around a 360°

circumference of the workpiece by induction heating comprising;

a housing;

a tube supported within said housing and having a first end and a second end;

an induction coil within said housing wound around said tube;

a conveyor for conveying the workpiece through said tube;

a sensor for monitoring the workpiece as it is conveyed through said tube; and

a controller for controlling a supply of current to said induction coil in response to preset parameters and in response to feedback signals from said sensor.

41. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 40, wherein said sensor comprises a rate change sensor for sensing a discontinuity in the rate of transfer of the workpiece through said tube.

42. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 41, said controller capable of shutting off supply of current to said induction coil when a feed back signal from said rate change sensor indicates a discontinuity in the rate of transfer of the workpiece through said tube.

43. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 40, wherein said sensor comprises a temperature sensor for sensing a temperature of the workpiece.

44. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 43, said controller capable of shutting off supply of current to said induction coil when a feed back signal from said temperature sensor indicates that a temperature of the workpiece exceeds a predetermined temperature.

45. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 40, further comprising:

first means for circulating air within said housing; and

second means for circulating air within said tube;

said controller further controlling said first and second air circulating means.

46. An apparatus for heating a coating on an electrically conductive cylindrical workpiece as recited in claim 40, wherein a spacing between turns of said induction coil ranges from approximately 0 to 0.25 inches.