Electrofusing of thermoplastic heating elements and elements made thereby

• US 6,392,208 B1
• Filed: 08/06/1999
• Issued: 05/21/2002
• Est. Priority Date: 08/06/1999
• Status: Expired due to Term

• Current Assignee: Watlow Electric Manufacturing Company
• Original Assignee: Watlow Polymer Technologies
• Inventors: Arx, Theodore Von
• Primary Examiner(s): PAIK, SANG YEOP
• Application Number:
  US09/369,779
• Time in Patent Office: 1,019 Days
• Field of Search: 219/528, 219/535, 219/541, 219/542, 219/543, 219/544, 219/548, 219/552, 219/553, 338/226, 338/231, 338/275, 338/276, 296/101, 296/11
• US Class Current: 219/544
• CPC Class Codes: B29C 65/02 by heating, with or without pressure
• CPC Class Codes: B29C 65/06 using friction, e.g. spin welding non-plastics elements to plastic elements B29C65/645
• CPC Class Codes: B29C 65/08 using ultrasonic vibrations non-plastics element to plastics elements B29C65/645
• CPC Class Codes: B29C 65/342 comprising at least a single wire, e.g. in the form of a winding
• CPC Class Codes: B29C 65/3428 said at least a single wire having a waveform, e.g. a sinusoidal form
• CPC Class Codes: B29C 65/3476 being metallic
• CPC Class Codes: B29C 66/1122 Single lap to lap joints, i.e. overlap joints B29C66/45, B29C66/472, B29C66/52272 take precedence
• CPC Class Codes: B29C 66/342 Preventing air-inclusions
• CPC Class Codes: B29C 66/45 Joining of substantially the whole surface of the articles methods or apparatus for laminating B32B37/00
• CPC Class Codes: B29C 66/71 characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/721 Fibre-reinforced materials B29C66/729 takes precedence
• CPC Class Codes: B29C 66/73921 characterised by the materials of both parts being thermoplastics
• CPC Class Codes: B29C 66/91214 by measuring the electrical resistance of a resistive element belonging to one of the parts to be welded, said element acting, e.g. as a thermistor
• CPC Class Codes: B29C 66/91221 of the parts to be joined
• CPC Class Codes: B29C 66/91411 of the parts to be joined, e.g. the joining process taking the temperature of the parts to be joined into account
• CPC Class Codes: B29C 66/91431 the temperature being kept constant over time
• CPC Class Codes: B29C 66/91655 by controlling or regulating the current intensity
• CPC Class Codes: B29C 70/82 Forcing wires, nets or the like partially or completely into the surface of an article, e.g. by cutting and pressing
• CPC Class Codes: B29K 2023/06 PE, i.e. polyethylene
• CPC Class Codes: B29K 2023/12 PP, i.e. polypropylene
• CPC Class Codes: B29K 2027/12 : containing fluorine
• CPC Class Codes: B29K 2063/00 : Use of EP, i.e. epoxy resins or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2069/00 : Use of PC, i.e. polycarbonates or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2071/00 : Use of polyethers , e.g. PEEK, i.e. polyether-etherketone or PEK, i.e. polyetherketone or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2077/00 : Use of PA, i.e. polyamides, e.g. polyesteramides or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2079/08 : PI, i.e. polyimides or derivatives thereof
• CPC Class Codes: B29K 2079/085 : Thermoplastic polyimides, e.g. polyesterimides, PEI, i.e. polyetherimides, or polyamideimides; Derivatives thereof
• CPC Class Codes: B29K 2081/04 : Polysulfides, e.g. PPS, i.e. polyphenylene sulfide or derivatives thereof
• CPC Class Codes: B29K 2081/06 : PSU, i.e. polysulfones; PES, i.e. polyethersulfones or derivatives thereof
• CPC Class Codes: B29L 2031/779 : Heating equipment
• CPC Class Codes: H05B 2203/003 : using serpentine layout
• CPC Class Codes: H05B 3/286 : the insulating material being an organic material, e.g. plastic
• CPC Class Codes: H05B 3/82 : Fixedly-mounted immersion heaters
• CPC Class Codes: Y10T 29/49083 : Heater type

Abstract

Methods of manufacturing electrical resistance heating elements are provided which include mating a pair of polymeric components around an electrical resistance heating material prior to fusing the polymeric components together, preferably by heat or pressure or both. Methods of stress relieving these polymeric components before, during or after fusing them together, are disclosed. Additionally, thermally conductive, non-electrically conductive additives can be added to improve the service life of the elements. In a further embodiment of this invention, a heating element and method of construction are provided in which first and second polymeric components are joined together with a resistance heating material therebetween. The polymeric components include retention means including a plurality of male connectors located on the first polymeric component, and a plurality of female receiving recesses located on the second polymeric component for mating with the male connectors of the first polymeric component. The polymeric components can optionally be joined together by the fusing techniques of this invention.

Claims

1. A method of manufacturing an electrical resistance heating element, comprising:

a) providing first and second mating polymeric components having first and second facing surfaces thereon respectively, and a resistance heating material disposed between said first and second facing surfaces; and

b) fusing said first and second polymeric components together at least along said first and second facing surfaces, whereby said resistance heating material is captured between said first and second mating polymeric components, wherein said fusing step (b) comprises stress relieving an unmelted portion of the polymer in said first and second polymeric components.

2. The method of claim 1 wherein said providing step (a) provides a gap between said first and second polymeric components.

3. The method of claim 1 wherein said providing step (a) provides said first surface of said first polymeric component with an impression for receiving said resistance heating material.

4. The method of claim 1 wherein said fusing step (b) comprises joining a portion of said first and second polymeric components by one or more of the following processes:

vacuum heat treating, hot isostatic processing, sonic welding, friction welding, compression molding, or electrofusing.

5. The method of claim 4 wherein said fusing step (b) substantially encapsulates said resistance heating material in a fused portion of said polymeric components.

6. The method of claim 1 wherein said providing step (a) comprises providing said first and second polymeric components with the same thermoplastic resin.

7. The method of claim 1 further comprising providing said first and second polymeric components with retention means for retaining said resistance heating material.

8. The method of claim 7 wherein said retention means comprises a plurality of pins located in said first polymeric component and a plurality of pin receiving recesses located in said second polymeric component for mating with said pins of said first thermoplastic component.

9. The method of claim 1 wherein said providing step (a) provides a gap between said first and second polymeric components.

10. The method of claim 1 wherein said joining step (b) further comprises fusing said first and second polymeric components together.

11. The method of claim 1 wherein said male connectors comprise a shape of a circle, triangle or oval.

12. An electrical resistance heating element, comprising:

a first polymeric component having a first surface thereon for receiving a resistance heating material;

a resistance heating material disposed on said first surface, and

a second polymeric component having a second surface for covering over said resistance heating material on said first surface;

a substantial portion of said first and second surfaces being fused together by heat, pressure or both, whereby an unmelted portion of the polymer in said first and second polymeric components is stress relieved.

13. The heating element of claim 12 wherein said resistance heating material comprises a Ni-Cr wire.

14. The method of claim 12 wherein said first and second polymeric components are fused together to substantially eliminate any seam between them visible to the naked eye.

15. The heating element of claim 14 wherein said first and second polymeric components comprised the same thermoplastic resin.

16. The heating element of claim 12 wherein said first polymeric component comprises retention means for retaining said resistance heating material in a pre-determined circuit path.

17. The heating element of claim 16 wherein said retention means comprises a plurality of mating pins and pin receiving recesses located on said first and second surfaces respectively.

18. The heating element of claim 12 wherein said first and second polymeric components are injection molded, creating stress-raising features in said polymeric components.

19. The heating element of claim 12 wherein said resistance heating material is disposed within a gap formed between said first and second surfaces.

20. A method of manufacturing an electrical resistance heating element, comprising:

a) providing first and second molded thermoplastic components containing a plurality of stress-raising features therein, and having first and second facing surfaces thereon, and a resistance heating material;

b) sandwiching said resistance heating material between said first and second thermoplastic components to form a seam; and

c) electrofusing a portion of said first and second surfaces of said first and second thermoplastic components so as to substantially eliminate said seam; and

d) stress-relieving by heating a remaining unmelted portion of said first and second thermoplastic components which contain a portion of said plurality of stress-raising features.

21. The method of claim 20 further comprising applying a pressurized inert gaseous atmosphere or a vacuum to said first and second thermoplastic components and said resistance heating material to minimize air pockets in said heating element during said electrofusing step (c).

22. The method of claim 21 wherein said applying an inert atmosphere or vacuum step occurs immediately before or after said electrofusion step.

23. The method of claim 20 wherein said first and second thermoplastic components are fitted with a vacuum fitting for evacuating said portion of air from said seam.

28. The heating element of claim 22 wherein said non-electrically conductive, thermally conductive additive comprises a ceramic powder.

29. The heating element of claim 22 wherein said thermoplastic components further comprise a plurality of reinforcing fibers.

30. The heating element of claim 28 wherein said reinforcing fibers are disposed at least within a yarn, roving, non-woven or woven fabric.

32. The heating element of claim 30, wherein said ceramic additive is not uniformly dispersed in said fusable polymeric components.

24. An electrical resistance heating element comprising a pair of thermoplastic components having a resistance wire receiving surface therebetween;

a resistance heating wire disposed on said resistance heating wire receiving surface, said thermoplastic components being joined together by fusion to form a fusion bond between said thermoplastic components wherein at least one of said thermoplastic components comprises a non-electrically conductive, thermally conductive additive for improving the thermal conductivity of said element.

25. The heating element of claim 24 wherein said thermoplastic components comprise the same thermoplastic resin.

26. The heating element of claim 24 wherein said resistance heating material comprises a Ni—

Cr wire.

27. The heating element of claim 24 wherein said thermoplastic components are injection molded.

31. A heating element comprising a pair of fusable polymeric components having a resistance heating material disposed therebetween, said fusable polymeric components including a non-electrically conducting, ceramic additive for improving the thermal conductivity of said fusable polymeric components, said fusable polymeric components being fusion bonded together to substantially encapsulate said resistance heating material.

33. A method of manufacturing an electrical resistance heating element, comprising:

a) providing first and second mating polymeric components having first and second facing surfaces thereon respectively, and a resistance heating material disposed between said first and second facing surfaces; and

b) joining said first and second polymeric components together at least along said first and second facing surfaces, whereby said resistance heating material is captured between said first and second mating polymeric components,

i) wherein said first and second polymeric components comprising retention means including a plurality of male connectors located on said first polymeric component, and a plurality of female receiving recesses located on said second polymeric component for mating with the male connectors of the first polymeric component.

34. An electrical resistance heating element, comprising:

a first polymeric component having a first surface thereon for receiving a resistance heating material;

a second polymeric component having a second surface thereon;

a resistance heating material disposed between said first and second surfaces;

said first and second polymeric components comprising retention means including a plurality of male connectors located on said first polymeric component, and a plurality of female receiving recesses located on said second polymeric component for mating with the male connectors of the first polymeric component.

35. The method of claim 34 wherein said first and second polymeric components are fused together.

36. The heating element of claim 34 wherein said first and second polymeric components comprise molded components.