Induction heating and melting systems having improved induction coils

• US 4,874,916 A
• Filed: 11/30/1987
• Issued: 10/17/1989
• Est. Priority Date: 01/17/1986
• Status: Expired due to Term

• Current Assignee: Guthrie Canadian Investments Limited 71 Maybrook Drive Scarborough Ontario Canada M1V 2L5
• Original Assignee: Guthrie Canadian Investments Limited
• Inventors: Burke, Patrick E.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US07/127,537
• Time in Patent Office: 687 Days
• Field of Search: 219/10.79, 219/10.43, 219/10.75, 219/10.71, 219/10.491, 219/10.77, 336/60, 336/61, 336/62, 336/82, 336/186, 336/188, 336/205, 336/222, 336/223, 336/224
• US Class Current: 219/671
• CPC Class Codes: H05B 6/02 Induction heating
• CPC Class Codes: H05B 6/22 Furnaces without an endless core H05B6/34 takes precedence
• CPC Class Codes: H05B 6/36 Coil arrangements
• CPC Class Codes: H05B 6/42 Cooling of coils

Abstract

Improved electric induction heating apparatus wherein the coil has two or more windings of special low loss conductor with such windings electrically connected in parallel. The two or more windings can be wound simultaneously one on top of the other and/or disposed radially one outside of the other. The coil windings embedded in a rigid set resinous material thus providing a rigid cylindrical unit. At least one of the coil windings has the low loss conductor around a tube the latter providing a fluid flow path for circulatig cooling fluid therethrough by at least one of current balancing transformers, transposition of the windings, and appropriately choosing the number of turns of each coil layer. A split ring bus can be used at the ends of the coils to connect the windings in parallel and laminated steel yokes can be disposed about the coil. There is also disclosed an improved inductive coil assembly for electric inductive heating apparatus comprising a cylindrical winding embedded in a temperature resistant non-magnetic material such as glass fibre reinforced resin and a heat sink rigid unit removably disposed within such coil unit. The heat sink unit comprises conduit means embedded in a temperature resistant material and providing a fluid flow passage for circulating a cooling fluid therethrough. The heat sink is removably inserted in the inductive coil unit. The helical winding is wound from a liquid cooled low loss conductor.

Claims

1. In electric inductive heating apparatus an improved inductive coil comprising a rigid open ended sleeve-like coil unit that includes two or more co-axial, co-extensive helical coil windings embedded in a temperature resistant, reinforced resin, each of said coil windings comprising a plurality of helical turns of multi-strand insulated conductor, means for connecting said coil windings in parallel and current balancing means operative in response to current flow respective ones of said coil windings thereby automatically forcing said coil windings to maintain a selected predetermined share of current flow including during variations of load and/or frequency.

2. The improvement of defined in claim 1 wherein said coil windings are interleaved such that the helices are one on top of the other forming a single layer coil.

3. The improvement as defined in claim 2 including a plurality of yokes spaced apart from one another circumferentially about said rigid coil unit.

4. The improvement as defined in claim 3 including a split ring surrounding a portion of the rigid coil unit and connecting the coil windings in parallel and further including transformer means balancing the current in the coil windings, said transformer means being connected such that current flowing through one winding of the inductive coil flown through a first winding of the transformer means and current flowing through another winding of the inductive coil flows through a second winding of the transformer means and wherein said first and second windings of the transformer means are inductively coupled in a manner whereby the current flow in the coil windings is automatically balanced by feedback through the transformer means.

5. The improvement as defined in claim 1 wherein said coil windings are formed in coil layers radially one outside of the other forming a multiple layer coil.

6. The improvement defined in claim 5 wherein said coil layers each comprise two or more identical interleaved coil windings.

7. The improvement defined in claim 6 wherein said inductive coil comprises at least two concentric layers internested tightly one upon the other and wherein each layer comprises two or more interleaved coil windings and current transformers connected forcing all windings to carry a predetermined portion of the total current regardless of variations of load and/or frequency.

8. The improvement as defined in claim 7 including a plurality of laminated steel yokes disposed in circumferential spaced relation about the rigid coil unit and outwardly therefrom.

9. The improvement as defined in claim 8 wherein current balancing means and voltage grading within a layer are simultaneously provided by connecting the several interleaved windings in each layer to an outer split ring bus at each end of said rigid coil unit.

10. The improvement as defined in claim 6 wherein current balancing means and voltage grading are provided by a combination of external reactors and current balancing transformers.

11. The improvement as defined in claim 6 including the multi-arm spider at one end of said coil unit and wherein the coil windings are connected to arms of said spider thereby connecting the coil windings in parallel.

12. The improvement as defined in claim 1 wherein said coil windings are disposed tightly one upon the other and embedded in a glass fibre reinforced epoxy resin providing a rigid coil unit and wherein said insulated conductor of at least one of said coil windings comprises a plurality of insulated conductors spiralled around the outside of an elongate tube, said tube providing a fluid flow path through said rigid unit for passing a cooling fluid therethrough.

13. The improvement as defined in claim 1 including means for terminating said coil windings at different circumferential positions around said coil unit.

14. The improvement as defined in claim 13 wherein said means connecting said coil windings in parallel comprises a split ring whose diameter exceeds that of the outer diameter of said coil unit and a plurality of laminated steel yokes disposed in circumferential spaced relation about the rigid coil unit and outwardly therefrom.

15. The improvement as defined in claim 13 wherein said means connecting said coil windings in parallel comprises an electrically conductive multi-arm spider located at one end of said rigid coil unit.

16. The improvement as defined in claim 1 wherein said current balancing means comprises transformer means connected such that current flowing through one winding of the inductive coil flows through a first winding of the transformer means and current flowing through another winding of the inductive coil flows through a second winding of the transformer means, said first and second windings of the transformer means being inductively coupled in a manner effective to automatically balance the current in respective ones of said coil windings.

17. The improvement as defined in claim 1 wherein the insulated conductor of said coil windings comprises a plurality of subconductors spiralled about a common axis, thereby being continuously transposed.

18. The improvement as defined in claim 17 including a heat shield comprising a rigid generally cylindrical sleeve like unit removably inserted in said rigid coil unit.

19. The improvement as defined in claim 18 wherein said heat shield unit is a rigid open ended generally cylindrical unit having an outer surface tapered to facilitate insertion of the heat unit into the rigid coil unit and removal therefrom.

20. An improved inductive coil for electric inductive heating apparatus as defined in claim 1 including a heat shield comprising a rigid, generally cylindrical sleeve-like unit removably inserted in said rigid coil unit.

21. The improvement as defined in claim 20 wherein an inner surface of said rigid coil and an outer surface of said heat shield unit mate with one another and wherein such mating surfaces are tapered facilitating separating one from the other.

22. An improved electric induction heating apparatus coil comprising a tabular coil winding that has a plurality of helical turns of a liquid-cooled insulated conductor, said conductor including an inner cooling tube having predetermined heat transfer properties and predetermined eddy losses taking into account coil geometry, frequency and ampere turns for which the coil has been designed and an outer layer of high conductivity insulated strands disposed spirally about such tube, said strands having a diameter to provide selected eddy losses and of sufficient number to carry a predetermined current through said coil winding and a reinforced resin encapsulating said coil winding to form a strong, rigid and vibration free unit in the form of an open-ended cylinder.

23. The improvement defined in claim 22 wherein said coil winding comprises two or more identical, interleaved windings.

24. The improvement as defined in claim 23 wherein current balancing is provided by current balancing transformers.

25. The improvement as defined in claim 23 including a split ring bus at one end of said coil windings connecting said coil windings in parallel and further including a plurality of laminated steel yokes spaced apart from one another circumferentially about the coil unit and located between said split ring bus and rigid coil unit.

26. The improvement as defined in claim 22 including a heat shield comprising a rigid generally cylindrical sleeve-like unit removably inserted in said rigid coil unit.

27. The improvement as defined in claim 26 wherein an inner surface of said rigid coil and an outer surface of said heat shield unit mate with one another and wherein such mating surfaces are tapered facilitating separating one from the other.

28. The improvement as defined in claim 26 wherein said heat shield comprises a plurality of helical turns of tubing embedded in a rigid resinous material.

29. The improvement as defined in claim 26 comprising two or more closely coupled generally cylindrical coil windings embedded in said resinous material and means connecting said windings in parallel.

30. The improvement as defined in claim 29 including current balancing means comprising transformer means connected such that current flowing through the individual coil windings flows through inductively coupled selected coils of the transformer means thereby automatically forcing the individual coils to carry a predetermined share of the current.

31. The improvement as defined in claim 29 wherein said two or more windings are interleaved providing a single layer coil.

32. The improvement as defined in claim 29 wherein said two or more coil windings are radially one outside of the other providing a multiple layer coil.

33. The improvement as defined in claim 32 wherein each coil layer comprises two or more interleaved windings.

34. The improvement as defined in claim 33 including current balancing means comprising transformer means connected such that current flowing through the individual coil windings flows through inductively coupled selected coils of the transformer means thereby automatically forcing the individual coils to carry a predetermined share of the current.

35. The improvement as defined in claim 34 including a plurality of laminated steel yokes disposed in circumferential spaced apart relation about the rigid coil unit.

36. The improvement as defined in claim 35 including a split ring bus at one end of the coil windings and connected to such windings thereby connecting the coil windings in parallel.

37. An induction apparatus comprising two or more cylindrical, closely coupled, multiple turn, co-axial co-extensive coil windings embedded in a rigid resinous material and providing a rigid open-ended generally cylindrical coil unit, means connecting said coil windings in parallel and current balancing means comprising transformers connected to said coil windings such as to provide feed back from one winding to another and thereby automatically forcing all windings to share a predetermined portion of the total current.

38. In electrical induction heating apparatus an improved induction coil comprising a rigid open-ended generally cylindrical unit having at least one sleeve-like coil winding embedded in a rigid set resin material, said sleeve-like coil winding comprising a plurality of helical turns of conductor said conductor consisting of a plurality of insulated multi-strand cabled conductors spirally disposed about the outer surface of a tube.

39. In an electric induction heating apparatus, an induction coil assembly comprising a first rigid open-ended sleeve-like coil unit of at least two coil windings embedded in a glass fibre reinforced resin material, each said coil winding comprising multiple helical turns of conductor comprising a central cooling tube selected to have predetermined heat transfer properties and predetermined eddy losses at the coil geometry chosen and for the frequency and ampere turns for which the coil is designed and an outer layer of high conductivity insulated strands spirally disposed about said cooling tube, the diameter of said strands and the number being so chosen as to provide selected eddy current loss characteristics for a chosen design current and a rigid open-ended sleeve-like heat shield unit removably inserted in said coil unit, said heat shield unit comprising tubular passage means through a rigid heat resistant resinous material for circulating a cooling fluid therethrough.

40. An assembly as defined in claim 39 wherein said tubular passage means comprises a tube helically wound into the form of a cylinder and embedded in a fibre reinforced resin.

41. An assembly as defined in claim 39 wherein mating surfaces of the first and second cylindrical units are tapered to facilitate removal of one from the other.

42. Improvements in induction heating apparatus comprising a rigid generally cylindrical induction coil unit having a helical coil winding of water-cooled conductor encapsulated in glass fibre reinforced resin to form a strong, rigid and vibration free unit;

a helically wound heat-shield winding encapsulated in a glass fibre reinforced resin forming a second strong rigid sleeve like unit removably disposed within and concentric with said induction coil unit for facilitating replacement in case of damage, said water-cooled conductor, from which the induction coil is wound, comprising an inner cooling tube around which is spirally disposed an outer layer of high conductivity insulated strands which carry the main induction current of the heating coil, the material of the inner cooling tube having adequate heat transfer properties to remove the heat generated by the current through the outer layer while at the same time having an electrical resistivity which is sufficiently small that the eddy losses induced in the cooling tube will be very small compared to the losses in the main conducting portion of the water-cooled conductor, the diameter of the strands comprising the outer conducting layer providing selected eddy loss characteristics, which depend on the frequency and the field strength required in the coil while predetermined number of strands are provided to carry the current for which the induction coil is designed, said strands being transposed so that each will carry its proper share of the total current, said heat sink winding comprising a tube helically wound into the form of an open ended cylinder and embedded in a fibre reinforced resin.

43. The improvement as defined in claim 42 wherein said coil unit comprises two or more coil windings connected in parallel.

44. The improvement as defined in claim 43 including transformer means connected to said windings forcing each winding to carry a predetermined proportion of the current.

45. The improvement as defined in claim 44 including a plurality of laminated steel yokes disposed in circumferential spaced apart relation about the rigid coil unit.

46. The improvement as defined in calim 45 wherein said means connecting said windings in parallel comprises a split ring bus at one end of said coil windings.