Process and apparatus for making a welding sleeve
AssigneeGeorge Fischer Ltd.
InventorAlfred Thalmann
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Abstract
A welding sleeve useable for connecting of pipes formed from thermoplastic material, is formed from a tubular body of thermoplastic material and a coil disposed on its inside surface. The coil has a resistance wire encased with thermoplastic material. The windings of the coil (4) are bonded into a compact coil which is inserted into the heated tubular body while it is simultaneously widened. As the result of a partial contraction of the tubular body also of the coil a firm connection develops between the oil and the body. Furthermore, the tubular body has a frozen-in, latent, radial contraction strain as a result of the widening, which during heating during the welding process, eliminates the radial play between coil and the pipes and produces a welding pressure.
Claims11
A process for producing a welding sleeve, comprising the steps of:
- forming a helical coil having a resistance wire in a casing of thermoplastic material with adjacent windings thereof secured together;
- mounting the coil on a mandrel;
- heating a tubular body of thermoplastic material and pushing the body onto the mandrel to widen and stretch the body over the coil while the body is at a temperature between about 20.degree. and about 40.degree. C. below the temperature of the crystallite melting region of the body thermoplastic material such that ends of the body project axially beyond the coil;
- partially cooling and contracting the body about the coil, and shrinking each body end to a conical shape;
- and
- stripping the body off the mandrel with the coil secured on the inside surface thereof and with substantial residual radial contraction strains in the body.
An apparatus for forming a welding sleeve having a tubular body of thermoplastic material with a helical coil of a resistance wire encased in thermoplastic material, comprising:
- a mandrel having means for receiving a coil thereon and having a conical widening surface, said mandrel including first and second portions separable in a plane substantially transverse to its axial direction, said portions having opposed shoulders for axially retaining the coil and being releasably coupled by a first centering means and first locking means;
- at least one pressure member disposed coaxially relative to said mandrel, said mandrel second portion being releasably coupled to said pressure member by a second centering means and a second locking means;
- and means for moving said pressure member in said axial direction toward and away from said mandrel.
Dependencies are inferred from the claim text.