Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-04-23
2001-02-27
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S294000, C156S309600, C219S633000, C219S643000, C285S021200, C285S319000, C285S921000
Reexamination Certificate
active
06193834
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for fusion joining a pipe with respect to a fitting, and more particularly to an improved apparatus and method wherein a novel heating element is insertably positioned between a fitting and a portion of the pipe.
2. Description of Prior Art
Various conventional apparatus and methods exist for fusion joining polyethylene pipes, such as those that employ heat fusion, electrofusion or induction fusion techniques. Electrofusion uses a conventional resistive heating method wherein a wire spiral coil is typically internally moulded within the thermoplastic fitting. An electrical current is applied directly to the wire coil via terminals on the fitting which results in the coil heating the thermoplastic material to a temperature which softens the thermoplastic material enough to fuse the pipe to the fitting.
In GB1149716 there is described an electrical resistance heating coil for use as a welding sleeve for joining plastics pipes to fittings wherein the pipe and fitting describe an annulus within which the welding sleeve is mounted. The coil comprises an electrical resistance wire embedded in a sheath of plastics material of precisely defined dimensions in order, it is said, to provide adequate welding efficiency. The proposed design complicates manufacture and it is difficult to connectorise the coil to an external power source. In addition, the existing wires provide potential leak paths from the joint region.
In a conventional induction fusion method for joining a pipe and a fitting, a heating element is moulded within the thermoplastic fitting. Current flow is induced through the heating element by a primary induction coil that is positioned around the portion of the fitting that contains the heating element. The temperature of the heating element is raised enough to soften or melt the fitting material and the pipe material, thereby resulting in fusion between the fitting and the pipe. Examples of induction fusion methods and apparatus are described in DE-A-2136656, EP-A-026191 and EP-A-513391. Such apparatus require a fitting with a moulded-in heating element. Thus, such methods cannot be used with existing conventional plastics fittings that do not contain a moulded-in heating element.
GB 2272663 describes a plastics pipe having an enlarged diameter portion at one end, which is provided at its inner surface or in the vicinity of its inner surface with a heating unit. A second plastics pipe to be joined is inserted into the enlarged portion and the heating unit energised. In manufacturing the pipe having the enlarged diameter portion, an end of the pipe is heated and softened, the enlarged socket formed, and the heating generating unit incorporated, in one embodiment, by pressure-inserting the heat generating unit on a core mould into the socket. The heat generating unit can be an electrofusion coil embedded in a plastics material, or a bare induction fusion element.
The electrofusion heat generating unit of GB2272663 is inconvenient, due to the necessity of providing a large flange to accommodate the terminals of the coil, difficult to overmould and expensive to manufacture. The bare induction fusion element, even when pressure inserted into the socket, is not completely surrounded by plastics material and is liable to overheat and be subject to thermal runaway. Once thermal runaway has started in one part of the element, its resistance changes dramatically and that area of the element draws in current (voltage, power) such that the rest of the element will not heat. The overheated region of the element can also cause local degradation of the thermoplastic material. In such cases usually the melt region cannot be contained, and thus a good fusion joint cannot be made.
The entire disclosures of all the above mentioned patents are incorporated herein by reference for all purposes.
It is apparent that there is a need for an apparatus and method that can be used to fuse a fitting with respect to a pipe, using induction techniques and a conventional fitting that does not contain a moulded-in heating element.
SUMMARY OF THE INVENTION
It is one object of this invention to provide an electrofusion joining apparatus and method that can be used with conventional fittings to join a pipe either directly to or with respect to a fitting or another pipe.
It is another object of this invention to provide a novel induction heating element which can be quickly and easily field-installed within a conventional thermoplastic fitting or within an electrofusion fitting from which the moulded-in heating element has been omitted.
The above and other objects of this invention are accomplished with an apparatus that employs a novel induction heating element which is insertable within a socket or mountable on a flange of a fitting.
In a first aspect, the invention provides an apparatus for fusion joining a pipe with respect to a fitting, the apparatus comprising:
an induction heating element, the element being wholly encased or coated with a fusible thermoplastic polymeric material,
a fitting provided with a socket and/or a flange, the induction heating element being wholly insertable within said socket or mountable on said flange, such that the fitting and the element together define a throughbore,
a portion of the pipe being insertable within the throughbore or mountable on said flange whereby the induction fusion element can, when energised, provide a fusion joint between the fitting and the said portion of the pipe.
In a second aspect, the invention provides a method for fusion joining a pipe with respect to a fitting, the method including the steps of:
providing an induction heating element, the element being wholly encased or coated with a fusible thermoplastic polymeric material,
inserting the induction heating element wholly within a socket of the fitting, or mounting the induction heating element on a flange of the fitting, such that the fitting and the element together define a throughbore,
inserting a portion of the pipe into the throughbore, or mounting a portion of the pipe on said flange, and
energising the induction fusion element to provide a fusion joint between the fitting and the said portion of the pipe.
In a third aspect, the invention provides certain novel induction heating elements as more particularly described herein.
The induction heating element of this invention is provided with a casing or coating of a fusible thermoplastic polymeric material, which can, for example, be a polyolefin, such as polyethylene. The polymer encased or polymer coated induction heating element can be easily inserted within a socket or mounted on a flange of a conventional fitting, such as a coupling, a standard tee, a hot-tap tee, a tapping tee, another pipe, a valve or the like, such that the fitting and the element together define a throughbore. Preferably the fitting and the element each wholly surround the throughbore such that the throughbore passes through an aperture, opening a hole in each of them. A portion of the pipe to be joined can then be inserted within the throughbore or mounted on the flange. In the fusion step, the induced alternating current flowing through the conductive material of the induction heating element increases the temperature of the polymeric material to near, at or above the melting temperature, which results in fusion of the end or adjacent portion of the pipe either directly to or with respect to the fitting.
According to the invention, it is not necessary to use a conventional heat fusion fitting that has an insert-moulded heating element. In the apparatus and method of this invention, the fitting does not require a two-step method for manufacturing the fitting and the electrofusion method of this invention can be accomplished with standard, off-the-shelf thermoplastic fittings or with electrofusion fittings from which the moulded-in electrofusion element has been omitted. Because of the simplified manufacturing process associated with standard, off-the-shelf th
Ball Michael W.
Fish & Richardson PC
Tolin Michael A
Uponor Aldyl Company
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