Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1998-08-24
2000-11-21
Ball, Michael W.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
1562742, 156294, 285 212, 219535, 219544, 219547, H05B 306, B32B 3124, F16L 1302
Patent
active
061497568
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to a method for joining a plastic pipe, a joint ring, and a plastic pipe joint, wherein either a smooth pipe or a non-smooth pipe, such as a ribbed pipe, a corrugated pipe or the like, is attached to the inner surface of another plastic pipe or a sleeve.
BACKGROUND OF THE INVENTION
A conventional fastening manner in sleeve-coupling type joints is a joint utilizing a rubber ring, wherein one or several rings are positioned between the ribs of a ribbed pipe or the corrugations of a corrugated pipe, for example, and the rings are pressed to the inner surface of the sleeve or pipe to be joined, the surface being formed to correspond to the profile of the rubber ring.
In addition to the rubber ring joints, ribbed pipes and corrugated pipes are also joined by welding. This is applicable especially for polyolefin pipes, which have excellent weldability properties. In the future, electric welding will be used more often. The essential feature in welding is that the temperature exceeds the melting point of plastic and that the welding pressure is sufficient. Known welding methods are disclosed for example in European patent application 531 750, U.S. Pat. No. 4,234,781 and in Finnish patent 87 685. In these methods, welding is performed by means of a welding ring placed between the pipes to be joined and electric current to be conducted to the ring. In the arrangement according to the aforementioned European reference, the required pressure is produced by moving the parts to be welded axially in relation to each other, whereas in the arrangements according to the aforementioned US and Finnish references the pressure results from the expansion of the welding ring.
However, the above-described welding manners are not applicable as such to the sleeve couplings of ribbed pipes, corrugated pipes or the like, intended for rubber ring joints, since the plastic welding ring to be tacked to the pipes to be welded cannot be placed in the space between the ribs of the ribbed pipe or the corrugations of the corrugated pipe even though this would be the best place for it in order to prevent the occurrence of detrimental axial forces in the joint. Another problem related to the welding of such light-construction pipes is that the welding pressure may deform a thin-walled pipe too much (cf. the support sleeve in Finnish patent 87 685).
SUMMARY OF THE INVENTION
The object of the present invention is to develop an alternative joining manner, based on the above-described arrangements, for the above-described pipe joint to supplement the conventional rubber ring joint.
A preferred and simple implementation of the invention is welding performed by means of only a plastic-coated resistance coil. This coil can easily be stretched over the ribs or corrugations and placed between them. The coil should naturally be such that its structure provides the necessary strength and the flexible properties. The invention can naturally also be applied in a joint wherein a welding ring is placed in a groove (gasket groove) provided in a sleeve or a pipe in order to weld a pipe with smooth walls. The welding ring can be successfully placed in the aforementioned groove if the ring bends sideways or inwards so that its circumference can be decreased.
A resistance coil coated preferably with plastic is placed around a flexible ring before it is mounted. When the welding ring thus consists of an inner part made of for example rubber, thermoplastic rubber or flexible plastic, and of a resistance coil wound around the inner part in the form of a coil, the inner part stretches and the coil gives in, so that the welding ring can be pulled over a rib or a corrugation without problems. The ductility of the inner part is typically in the range of 10 to 15% and the tensile strength is such that the aforementioned operation can be performed manually. In this structure, the flexible inner part produces a sufficient welding pressure both against the sides of the ribs or corrugations and against the inner surface of the
REFERENCES:
patent: 4234781 (1980-11-01), Flink
patent: 4852914 (1989-08-01), Lyall
patent: 5386101 (1995-01-01), Steinmetz et al.
patent: 5407520 (1995-04-01), Butts et al.
patent: 5410131 (1995-03-01), Brunet et al.
Ball Michael W.
Tolin Michael A
Uponor Innovation AB
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