Thermoplastics welding method

• US 4,090,899 A
• Filed: 12/03/1975
• Issued: 05/23/1978
• Est. Priority Date: 12/06/1974
• Status: Expired due to Term

• Current Assignee: Georg Fischer AG
• Original Assignee: Georg Fischer AG
• Inventors: Reich, Fritz
• Primary Examiner(s): Simmons, David A.
• Application Number:
  US05/637,118
• Time in Patent Office: 902 Days
• Field of Search: 156/293-295, 156/304, 156/77-79, 156/272, 156/275, 156/83, 264/45.6, 264/46.5, 264/46.6, 264/46.9, 264/54, 285/41, 285/284, 285/286, 285/288, 285/292, 285/295, 285/423
• US Class Current: 156/79
• CPC Class Codes: B29C 65/02 by heating, with or without pressure
• CPC Class Codes: B29C 65/0672 Spin welding
• CPC Class Codes: B29C 65/342 comprising at least a single wire, e.g. in the form of a winding
• CPC Class Codes: B29C 65/3432 comprising several wires, e.g. in the form of several independent windings B29C65/3436, B29C65/344 take precedence
• CPC Class Codes: B29C 65/3468 characterised by the means for supplying heat to said heated elements which remain in the join, e.g. special electrical connectors of windings B29C65/3668 takes precedence
• CPC Class Codes: B29C 65/3476 being metallic
• CPC Class Codes: B29C 65/3612 comprising fillers
• CPC Class Codes: B29C 65/368 with a polymer coating
• CPC Class Codes: B29C 65/4815 Hot melt adhesives, e.g. thermoplastic adhesives
• CPC Class Codes: B29C 65/4875 being spherical, e.g. particles or powders
• CPC Class Codes: B29C 65/5007 characterised by the structure of said adhesive tape, threads or the like
• CPC Class Codes: B29C 65/5057 positioned between the surfaces to be joined B29C65/5035 takes precedence
• CPC Class Codes: B29C 65/52 characterised by the way of applying the adhesive B29C65/50 takes precedence; apparatus for applying liquids in general B05C; processes for applying liquids in general B05D
• CPC Class Codes: B29C 65/82 Testing the joint
• CPC Class Codes: B29C 65/8246 Pressure tests, e.g. hydrostatic pressure tests
• CPC Class Codes: B29C 66/112 Single lapped joints
• 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 66/1142 Single butt to butt joints
• CPC Class Codes: B29C 66/116 Single bevelled joints, i.e. one of the parts to be joined being bevelled in the joint area
• CPC Class Codes: B29C 66/1222 comprising at least a lapped joint-segment
• CPC Class Codes: B29C 66/1224 : comprising at least a butt joint-segment
• CPC Class Codes: B29C 66/1282 : comprising at least one overlap joint-segment
• CPC Class Codes: B29C 66/12841 : comprising at least two butt joint-segments
• CPC Class Codes: B29C 66/14 : the joint having the same thickness as the thickness of the parts to be joined B29C66/1142 takes precedence
• CPC Class Codes: B29C 66/341 : Measures for intermixing the material of the joint interlayer
• CPC Class Codes: B29C 66/5221 : for forming coaxial connections, i.e. the tubular articles to be joined forming a zero angle relative to each other
• CPC Class Codes: B29C 66/52241 : with two right angles, e.g. for making T-shaped pieces
• CPC Class Codes: B29C 66/5229 : involving the use of a socket
• CPC Class Codes: B29C 66/52293 : said stop being external
• 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 66/73921 : characterised by the materials of both parts being thermoplastics
• CPC Class Codes: B29C 66/8262 : using "pressure means" which are associated with at least one of the parts to be joined and remain in or on it
• CPC Class Codes: B29C 66/8264 : using the thermal expansion of the parts to be joined
• CPC Class Codes: B29K 2023/00 : Use of polyalkenes or derivatives thereof as moulding material
• CPC Class Codes: B29K 2023/06 : PE, i.e. polyethylene
• CPC Class Codes: B29K 2023/0633 : LDPE, i.e. low density polyethylene
• CPC Class Codes: B29K 2023/065 : HDPE, i.e. high density polyethylene
• CPC Class Codes: B29K 2023/12 : PP, i.e. polypropylene
• CPC Class Codes: B29K 2025/06 : PS, i.e. polystyrene
• CPC Class Codes: B29K 2027/06 : PVC, i.e. polyvinylchloride
• CPC Class Codes: B29K 2027/16 : PVDF, i.e. polyvinylidene fluoride
• CPC Class Codes: B29K 2059/00 : Use of polyacetals , e.g. POM, i.e. polyoxymethylene or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2067/00 : Use of polyesters 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: F16L 47/02 : Welded joints; Adhesive joints
• CPC Class Codes: F16L 47/03 : Welded joints with an electrical resistance incorporated in the joint

Abstract

A welding method for joining self-supporting structures made of thermoplastics by assembling said structures to form an area of mutual overlap, generating heat in said area to produce a welding zone having an elevated temperature and containing said thermoplastics in an at least plastic state for mutual coalescence of said structures in said area; an expanding agent is provided in the welding zone to generate a gas pressure therein for promoting coalescence of the weld. The invention is particularly suitable for welding tubes and other pipeline elements, such as fittings or sleeves, of thermoplastics and produces a tumescent weld which fills any macroscopic voids while including a plurality of minute closed cell voids.

Claims

1. A method of welding mutually overlapping portions of self-supporting objects made of weldable thermoplastic material, said self-supporting objects being capable of withstanding or supporting gas pressure produced in a welding zone without a significant deformation thereof, said welding being effected substantially without an external pressure which acts vertically to the welding zone, by heating to form a welding zone containing said thermoplastic material in an at least plastic state in an area between said mutually overlapping portions, said method comprising the step of providing an expanding agent in said welding zone, said agent producing at the temperature of said welding zone a gas pressure effective in said welding zone.

2. The method of claim 1 wherein said expanding agent is a normally solid chemical substance capable of producing a gaseous decomposition product when heated to the temperature of said welding zone.

3. The method of claim 1 wherein said expanding agent is included in a thermoplastics material that is present in said welding zone.

4. The method of claim 1 wherein said heating is effected by an electrical conductor for resistance heating of said welding zone.

5. The method of claim 4 wherein said electrical conductor is a heating coil provided in said welding zone.

6. The method of claim 5 wherein said expanding agent is provided in a layer adjacent to said heating coil.

7. The method of claim 1 wherein said heating is effected by inductive high frequency heating.

8. The method of claim 2 wherein said expanding agent is provided in said welding zone as a mixture comprising said agent and a thermoplastics material, said mixture being applied onto a surface of one of said objects in said area between said mutually overlapping portions.

9. The method of claim 1 wherein said heating is effected by friction and said expanding agent is present in the friction zone.

10. A method of weldingly connecting interpenetrating self-supporting elements made of a weldable thermoplastic material, said elements being capable of withstanding or supporting gas pressure produced in a welding zone without significant deformation thereof, by assembling said elements so as to form at least one area of mutual overlap of said elements substantially without an external pressure which acts vertically to said area, heating said thermoplastic material to an elevated temperature for fusion and coalescence in said area of overlap and in the presence of an expanding agent capable of forming a gas at said elevated temperature for promoting said coalescence;

and allowing said coalescence to solidify at a temperature below said elevated temperature.

11. The method of claim 10 wherein said elements include an insert comprising a thermoplastics material and a metallic conductor for electrically heating said insert.

12. The method of claim 11 wherein said expanding agent is provided in said thermoplastics material of said insert.

13. The method of claim 12 wherein said metallic conductor is arranged in said area of overlap to be encompassed by said coalescence.

14. The method of claim 10 wherein said heating is effected by frictional engagement of at least two of said piping elements.

16. The welding element of claim 10 in the form of a welding insert having a generally circular cross-section.

17. The welding element of claim 10 in the form of a mat.

18. The welding element of claim 16 in the form of a welding sleeve.

15. A self-supporting welding element for welding structures made of a thermoplastic material substantially without an external pressure which acts vertically to the welding zone, said element comprising a thermoplastic portion capable of being weldingly connected with said structures, a metallic conductor for electrical heating embedded in said thermoplastic portion, and an expanding agent capable of forming a gas upon heating to a temperature where said thermoplastic material of said structures and said thermoplastic portion are in at least plastic state.

19. The welding element of claim 15 in the form of a friction ring suitable for friction welding and having a wedge-shaped profile for welding to a friction welding socket.