Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-10-23
2001-07-10
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S195000, C138S144000
Reexamination Certificate
active
06258197
ABSTRACT:
FIELD OF INVENTION
The invention relates to a method for manufacturing a pipe fitting, said method comprising manufacturing a preform of plastic, and forming an additional layer on top of it. The invention further relates to a pipe fitting comprising a preform made of plastic, and an additional layer mounted on top of the preform.
BACKGROUND OF INVENTION
Finnish Patent Application No. 912498 discloses a multi-layer sleeve connection, whose layers are made by extruding, injection molding, or by a crosslinking process. One layer is a reinforcement layer which may also contain metal. The sleeve further comprises resistance wire winding mounted on its inner surface for welding the sleeve to the pipe connected to it.
Application EP 055 891 discloses the technology that is most commonly used at present. This technology comprises manufacturing at first a preform by injection molding, winding a resistance wire on the preform, and injection molding a reinforcement layer on top of the preform and the resistance wire, whereby the preform and the reinforcement portion are at least partly welded together.
Application GB 2 232 330 discloses a sleeve manufacturing method comprising winding a thermoplastic tape which is obtained from an extruder and which is in a molten or soft state on a mandrel, and fusing the edges of the windings together.
Prior art solutions are also disclosed in DK 162588 and WO 9515253.
One of the drawbacks of the prior art solutions mentioned above is that it is uneconomic to manufacture particularly large branch fittings with the above-mentioned conventional methods, since a large amount of material to be injected requires a long cooling time. In addition, the structures are often massive in order for the required strength to be provided, and the tool costs as well as investments in the injection molding machines are extremely high.
SUMMARY OF INVENTION
It is an object of the present invention to obviate the above-mentioned drawbacks. This is achieved with the method of the invention, which is mainly characterized by forming the additional layer by winding a film on the preform until the desired total wall thickness is reached, and that the film is wound using at the same time pre-tensioning in a desired direction. Correspondingly, the pipe fitting is characterized in that the additional layer comprises an oriented plastic film wound on the preform.
With the solution of the invention, in which the film to be wound is oriented in the desired direction by means of pre-tensioning in a suitable tensioning direction, a smaller total layer thickness is achieved than with a sleeve made entirely by injection molding. A film or tape to be wound is not obtained from the extruder as a semi-finished product, but for instance on a storage reel as a product that has gone through all manufacturing steps. In the case of GB 2 232 330, in which the tape to be wound is obtained directly from the extruder while still soft and obviously thick, such a result is not achieved; in this case, the tape cannot be tensioned and thereby oriented in the same way as in the present invention, and it has not even been attempted. In addition, the lack of a preform complicates the manufacturing process.
The speed of the method of the invention mainly depends on the speed of the winding process, not on the cooling times, which is a significant advantage over all the prior art solutions described above.
Furthermore, the winding of the invention allows the film that is wound to consist of one or several different plastic films optionally reinforced with plastic, glass or carbon fibers, for example, or with a wire mesh, or a suitable combination of these.
Resistance means are preferably mounted between the preform and the additional layer, and connected to contact pins provided at the ends of the preform. By means of the resistance means, the pipes to be connected by the pipe fitting can be welded together, as stated above in connection with European Patent Application No. 055 891. It is also possible to weld the preform and the additional layer together when the pipes are connected; this property can be utilized in the present invention when bent fittings are required, for example. The position of a fitting can be steplessly adjusted to a desired angle and locked by resistance heating: the fitting is heated until even the film windings are at least partly welded to each other.
REFERENCES:
patent: 4265951 (1981-05-01), Yates et al.
patent: 4329193 (1982-05-01), Sznopek et al.
patent: 5169176 (1992-12-01), Brossard
patent: 5255943 (1993-10-01), Keller et al.
patent: 162588 (1991-11-01), None
patent: 1373761 (1974-11-01), None
patent: 2090558 (1982-07-01), None
patent: 2232330 (1990-12-01), None
patent: 9533109 (1995-12-01), None
Ladas & Parry
Sells James
Uponor Innovation AB
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