Heat fusion fitting

Details Heat fusion fitting Heat fusion fitting

2000-03-31

2003-07-01

Nolan, Sandra M. (Department: 1772)

Plastic and nonmetallic article shaping or treating: processes

Utilizing heat releasable stress to reshape solid workpiece

C428S035800, C428S036910

Reexamination Certificate

active

06585924

ABSTRACT:

This application claims the benefit under 35 USC 371 of PCT/GB98/01368, filed May 21, 1998, which claims priority under 35 USC 119 from United Kingdom application GB 9710487.1, filed May 22, 1997.
This invention relates to heat fusion fittings, and more particularly to an improved method for the manufacture of heat fusion fittings and to new heat fusion fittings and pipe joints produced thereby.
Heat fusion fittings comprising in-line couplings, T-joints, bends, saddle fittings, patches and similar devices have been known for many years. In a typical heat fusion fitting, an electrical resistance heater element is embedded in the inner surface of a sleeve a thermoplastic polymeric material, the sleeve being adapted to fit over a plastic pipe or pipes to be connected. Such fittings are conventionally termed electrofusion fittings.
In an in-line coupling the pipes are inserted into the sleeve into abutment with one another, or into abutment with a stop member, and the heater elements are then energised. Upon heating of the heater elements, the adjacent regions of the sleeve are softened to the point of fusion, whereby the polymeric materials of the pipes and sleeve are fused together.
Essentially the same approach is employed for saddles and patches except that conventional means are employed to hold the elements in intimate contact prior to completion of the fusion process.
U.S. Pat. No. 2,739,829 takes a slightly different approach using induction heating as opposed to resistance heating. Strips of metallic material are placed between a sleeve and pipes to be joined at two locations spaced from the abutment region of the two pipes. A coil connected to an AC source is employed to heat the metallic strips to produce fusion of the polymeric material of the sleeve with the polymeric material of the pipes. Other patents disclosing the use of induction heating in heat fusion fittings include, for example, WO80/02124, EP-A 0572546, EP-A-0513391, and U.S. Pat. No. 4,256,945. The entire disclosures of each and every one of the abovementioned patents are incorporated herein by reference for all purposes.
Heat fusion fittings are conventionally manufactured by injection moulding the entire plastics body of the fitting over the metallic heating element. This is because of the need to locate the heating element or elements accurately within the fitting in order to leave so-called “cold zones” or unheated areas at the ends of the fitting, and adjacent the abutment region of the pipes, in the case of an in-line coupling, to prevent escape of fused polymeric material from the melt fusion regions.
Various efforts have been made to find a more cost effective method for the manufacture of heat fusion fittings, for example, by extruding a tubular polymeric sleeve, heating the sleeve, inserting the electrical resistance heating element into the sleeve on a mandrel which simultaneously expands the sleeve, removing the mandrel and allowing the sleeve to contract around the heating element. Various methods of this type are described in Swiss Patent No 544906, DE-A-2302458, GB-A-2036518 and in U.S. Pat. No. 4,362,684, the entire disclosures of which are incorporated herein by reference for all purposes. In U.S. Pat. No. 4,362,684 it is stated that the simultaneous widening and sliding of the tubular sleeve body onto the heating coil create radial contraction strains in the tubular body which produce welding pressure and facilitate bonding of the pipes. However, in practice, it is found that any such effects are minimal, since the radial contraction strains in the sleeve are dissipated after a very short time, and the fusion process produces only a relatively localised heating such that the main body of the sleeve remains relatively cold and could not possibly contract to produce a welding pressure as suggested in U.S. Pat. No. 4,362,684. Further difficulties also arise in connectorising electrical resistance heating elements inserted into a tubular sleeve body in this way.
For whatever reason, to the best of the Applicants' knowledge, none of the abovementioned methods have been put into practice commercially, and the method of choice for the manufacture of heat fusion fittings remains injection moulding.
In U.S. Pat. No. 5,189,271 there is disclosed a connector comprising a heat shrinkable sleeve heated by a ferromagnetic member which in turn is heated by a varying magnetic field, the ferromagnetic member having a Curie temperature above the shrink temperature of the sleeve.
In a further and separate development, for plastics pipes having improved temperature and pressure resistance, it has been proposed, for example, in U.S. Pat. No. 4,927,184, to use a pipe wall comprising at least a layer of a cross-linked polyolefin material. Pipelines including such pipes also require higher strength fittings, and U.S. Pat. No. 4,927,184 also suggests that the fitting can comprise an outer layer of a cross-linked polyolefin material. It is suggested that if the cross-linked outer layer of the fitting is heated, it will be subject to a contraction, exerting a pressure on the pipes, but this would appear very unlikely, as the cross-linked outer layer is not expanded, and in the heat fusion process it would remain relatively cold. It is also suggested that the fitting can be extruded, but no information is given as to how this production method could be put into practice. The entire disclosure of U.S. Pat. No. 4,927,184 is incorporated herein by reference for all purposes.
According to the present invention, there is provided a heat fusion fitting comprising a body comprising at least an outer layer of cross-linked polymeric material and an induction heating element in contact with the body.
In a first aspect, the invention provides a method for the manufacture of a heat fusion fitting, which comprises:
(i) forming a body comprising at least a first layer of a first cross-linked polymeric material,
(ii) embedding or partly embedding a ferromagnetic heating element in a second polymeric material to form an insert, the ferromagnetic heating element having a Curie temperature equal to or greater than the crystalline melting point or softening point of the second polymeric material, and
(iii) assembling the body and the insert to form the fitting.
In another aspect, the invention provides a heat fusion fitting comprising a body comprising at least a first layer of a first cross-linked polymeric material, a second layer of a second polymeric material, and a ferromagnetic heating element, the ferromagnetic heating element being embedded or partly embedded in the second layer and having a Curie temperature equal to or greater than the crystalline melting point or softening point of the second polymeric material.
In a further aspect, the invention provides a kit of parts for a heat fusion fitting, the kit of parts comprising a body and an insert, the insert comprising a ferromagnetic heating element embedded or partly embedded in a fusible polymeric material, the ferromagnetic heating element having a Curie temperature equal to or greater than the crystalline melting point or softening point of the polymeric material, and the body being adapted to receive the insert and comprising at least a first layer of a first cross-linked polymeric material.
In the majority of applications, the fitting will, in use, be positioned over a pipe end or spigot to be connected and the invention will henceforth be more particularly described with respect to such an external fitting. In such cases, the first layer of a first cross-linked polymeric material will be an outer layer of the body and the second layer of a second polymeric material will be an inner layer, with the insert being positioned internally of the body. It will be appreciated, however, that the fitting could also be an internal coupler, whereupon the first layer would become the inner layer of the body and the second layer would become the outer layer of the body, the insert then being positioned externally of the body, and that such fittings are also included within th

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