Process and apparatus for making a welding sleeve
First Claim
1. 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°
and about 40°
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.
1 Assignment
0 Petitions
Accused Products
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.
41 Citations
11 Claims
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1. A process for producing a welding sleeve, comprising the steps of:
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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°
and about 40°
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. - View Dependent Claims (2, 3, 4)
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5. 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:
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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. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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Specification