Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1996-03-12
1998-10-20
Ball, Michael W.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156294, 1563042, 1563046, 285 212, 219535, B32B 3120, F16L 4702
Patent
active
058241795
DESCRIPTION:
BRIEF SUMMARY
The invention relates to methods of joining reinforced thermoplastic pipes.
The invention particularly, though not exclusively, relates to joining of pipes which have their pressure rating enhanced by each having a layer or layers of fibre reinforcement. The fibres, for example, can be wound directly over an inner pipe of thermoplastic material or can be preformed into tapes before winding. In another example, the fibres or tapes extend purely longitudinally down the inner pipe. An external layer of thermoplastic material, not necessarily of the same type or grade as the inner pipe, is added over the reinforcement to completely cover the latter for protection. The fibres or tapes may be fused to each other and to the inner pipe and the external layer or, if preferred, the fibres or tapes may be loose. The inner pipe together, with the surrounding layer or layers of reinforcement and with the added external layer, forms a pipe having a pipe wall between the inside surface of the inner pipe and the outside surface of the external layer and the layer or each of the layers of reinforcement lies at the centre of the pipe wall or lies between the centre and the outside surface of the external layer.
It is known to join thermoplastic reinforced pipes using a mechanical fitting which is clamped onto the pipe, for example, or which compresses the thermoplastic material between an inner metal supporting tube and external metal collar. Such fittings are designed to create a fluid seal and to have substantial resistance to "pull out" of the pipe from the fitting.
Such fittings, which are largely of metal, are subject to corrosion. Moreover, the internal fluid may affect the properties of the thermoplastic so that it softens, with the result that the clamping forces, and hence the seal and "pull out" characteristics, are lost over a period of time.
It is the aim of the invention to avoid the use of such fittings.
According to the invention, a method of joining two reinforced thermoplastic pipes by a butt fused welded joint is provided, each pipe having an inside and an outside surface and a pipe wall extending between the inside and the outside surface and one or more layers of reinforcement fibres lying within the outer half of the pipe wall, the end portions of the pipes being heated by being forced against a heater plate interposed between them so that thermoplastic material from the end portions of the pipes becomes molten and then following removal of the heater plate the end surfaces are forced together and molten material from the end portions is upset involving inward and outward flow of thermoplastic material to form internal and external beads, after which the pipes are allowed to cool while being constrained against axial separating movement, and the or each reinforcement layer is wholly or primarily displaced outwardly by said outward flow during upsetting from its original position so that, at the welded joint, there is a layer of thermoplastic material between the layer or layers of reinforcement fibres and the common inside surface which layer is free from reinforcement fibres.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:
FIGS. 1 to 4 show various stages of joining two thermoplastic pipes together;
FIG. 5 shows on a larger scale the zone of the joint shown in FIG. 2; and
FIG. 6 shows a second embodiment.
FIG. 1 shows two pipes 10, 12 which are to be joined by a butt fused welded joint. One pipe 12 has an electrofusion coupler 14 encircling the pipe 12. The coupler 14 is a loose fit upon the pipe 12, a diametral clearance 16 being shown. The coupler 14 carries a heating element which is embedded in the thermoplastic wall of the coupler and comprising two groups 18, 20 of windings surrounding the pipe 12. The heating coil is connected to terminals (not shown) within shrouds 22, 24 integral with the coupler 14.
Each pipe 10, 12 comprises an inner pipe 30 of thermoplastic material having an inside surface 32; a layer or layers of
REFERENCES:
patent: 3919034 (1975-11-01), Carini
patent: 4357962 (1982-11-01), Shaw et al.
patent: 4492063 (1985-01-01), Schock et al.
patent: 4530521 (1985-07-01), Nyffeler et al.
patent: 5328541 (1994-07-01), Usui et al.
Patent Abstracts of Japan, No. JP2060730, Jan. 03, 1990.
Patent Abstracts of Japan, No. 5-272690, Oct. 19, 1993, vol. 18, No. 51 p. 74.
Patent Abstracts of Japan, vol. 18, No. 51, p. 74, JP-272690.
Ball Michael W.
British Gas plc
Tolin Michael A.
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