Pipe joints or couplings – Deformed
Reexamination Certificate
2000-05-02
2003-06-24
Lavinder, Jack (Department: 3613)
Pipe joints or couplings
Deformed
C285S256000
Reexamination Certificate
active
06581982
ABSTRACT:
The invention relates to a process for connecting a pipe in the region of its pipe end to a pipe coupling, comprising at least one support sleeve with an engagement means, wherein the pipe and the support sleeve are first pushed into one another, the pipe then being pressure deformed, thereby bringing about a form-fitting connection with the engagement means and bringing about a sealing relationship with sealing surfaces, mutually adjoining one another in axial direction. The invention relates furthermore to a connection brought about by the aforesaid process as well as to a pipe coupling suited therefor.
Pipe couplings are known for the connection of pipe ends of two pipes or—in the case of branchings—of more than two pipes. The pipe couplings are so designed that they can be brought to overlap the pipes by sliding one into the other. In the overlapping region both sections are subjected to radial pressure deformation which results in bringing about a fluid impermeable connection between the pipe coupling and the pipes.
Depending on the material of the pipes, different pipe couplings are employed according to the state of the art. In the case of metal pipes, sleeve-like press fittings are used, comprising annular bulges at their ends projecting radially outwardly, into which sealing rings are inserted on the inside. Into the press fittings pipes are pushed from both sides. The annular bulges are then pressure deformed radially inwardly by plastic deformation both of the press fitting and also of the pipe, i.e. by means of a pressing device suited for this purpose. An example of such a connection is apparent from EP-A-0 198 789.
The use of sealing rings involves a number of drawbacks. On the one hand, there is no guarantee that the sealing ring remains intact when pushing the pipe into the press fitting, as its diameter is smaller than the outer diameter of the pipe. On the other hand, the chemical and thermal stability of such sealing rings over extended periods is not sufficiently ensured. As such pipe connections are employed in particular in the sanitary and heating sectors, presupposing a useful life of 50 years, high demands are made on the long-term stability of the elastomer used for the sealing ring. For heated and, in particular, chemically aggressive fluids, the working material of the sealing ring must be chemically and thermally resistant and must not lose its sealing capacity even if frequent temperature changes occur.
In order to avoid the use of sealing rings, a pipe connection is proposed in DE-U-94 19 106.9, wherein the press fitting is provided with an elastic plastics or rubber coating. For bringing about the connection, the pipe—this may be a metal or a composite pipe—is expanded and pushed over the press fitting. One or more annular beads are subsequently pressed into the pipe exterior so that the pipe material penetrates into the elastic coating of the press fitting. However, a connection of this type has only a limited useful life and is, above all, not suited for plastic pipes.
For connecting plastic pipes, made, for example, of crosslinked polyethylene or polypropylene, as well as of composite pipes, comprising successively from inside towards the outside a plastics layer, a metal tube or a metal coating and—as a protective cover—yet another plastics layer, two-part or three-part pipe couplings are proposed (EP-A-0 582 542, WO 92109840; DE-A-44 41 373; DE-C-196 27 608; JP-A-08 326 974). These pipe couplings include an interior component, from the central part of which one or more support sleeves extend, onto each of which a pipe can be pushed. Onto the pipe exterior a single pressure sleeve, engaging over two support sleeves (EP-A-0 582 543) is pushed, or separate pressure sleeves each (WO 92/09840; DE-A-44 41 373; DE-C-196 37 608; JP-A-08 326 974) are pushed onto the pipes and are then pressure deformed radially towards the interior, so that the terminal regions of the pipes between the pressure sleeve(s) and the support sleeves are in each case clamped over a relatively long distance. In order to improve the clamping action, grooves are moulded at least into the support sleeves —partly into the pressure sleeves as well—, into which the plastics material of the pipes is pressed so that a wave-like pattern of the pipes in the clamping regions results, bringing about sealing surfaces adjoining one another in axial direction. In DE-A-196 37 608 specific embodiments of annular grooves in the support sleeve are proposed, into which the plastics material is pressed in order to subsequently bring about a sealing relationship within these grooves.
Such pipe couplings do not require additional sealing rings so that the above described problems do not occur here. On the other hand, their manufacture is more complex as their construction requires them to consist of a plurality of parts, necessitating additional processing steps in order to mould in the grooves. A considerable drawback resides further in the thermal performance of pure plastics or even composite pipes. It shows its negative effect in particular in the case of such pipe ducts which are exposed to considerable temperature fluctuations—such as heating or hot water pipes. During heating, the plastics expands more than the metal of the pipe coupling, resulting in the occurrence of very high tensions in the regions of the clamped pipe, causing plastic flow, i.e., in particular, if the regions of the clamped pipe completely take up the space between the pressure sleeve and the support sleeve. The plastics then literally flows from these pipe regions and therefore out of the pipe coupling. In the course of subsequent cooling, the plastics contracts again, however, due to exceeding the flow limit, it no longer possesses the initial dimensions. The initial clamping pressure between the pipe and the pressure and support sleeve is no longer attained. If a relative movement has taken place between the pipe and the support sleeve, destruction of the plastics along the groove-like sealing points may occur as well.
Even more serious is the fact that the plastics may act like a kind of pump during the expansion and shrinking processes. Should a liquid film have formed in the gap between the upper limiting surfaces of the plastics and the support sleeve, liquid is locked in at indefinable points during heating and therefore expansion of the pipe. This, in turn, results in an increased expansion, as the volume of the enclosed liquid takes away space from the pipe sections clamped there. With repeated heating and cooling cycles, the plastics gradually looses its inherent tension and the original dimensions so that the tightness over extended periods is no longer ensured. One has therefore reverted to ensuring the tightness of the pipe connection by additionally providing sealing rings (WO 92/09840), having to accept once again their above described drawbacks.
When employed in drinking water supplies, a further problem resides in that no cavities must occur in the region of the pipe coupling, as small living organisms, such as germs or the like, may gather and live there. In pipe couplings taking the form of press fittings, in particular, such cavities exist between the press fitting and the pipe end regions. In addition, sealing rings become porous with time, which favours the presence of such living organisms. As far as plastics pipes are concerned, gaps and cavities come about by the above described expansion and shrinking processes, being in direct contact with the liquid. Furthermore, dissolved materials, such as for example magnesium or calcium carbonate, may also enter into the cavities and deposit there, thereby displacing the interface between the pipe end sections and the support sleeve. This promotes the penetration of water.
It is an object of the invention to so design a process of the type set out in the opening paragraph that reliable sealing between the pipe coupling and the pipes, in particular of plastics and composite pipes, is ensured in the long term. It is furthermore an object of the inventio
King Bradley
Lavinder Jack
Liniak, Berenato & White, LLC
Novopress GmbH Pressen und Presswerkzeuge & Co. KG
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