Pipes and tubular conduits – Flexible – Braided – interlaced – knitted or woven
Patent
1996-04-22
1998-01-13
Brinson, Patrick F.
Pipes and tubular conduits
Flexible
Braided, interlaced, knitted or woven
138126, 138137, 138141, F16L 1108
Patent
active
057068658
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pipe for high pressure fluid, and more particularly for conveying a fluid that changes state, such as a refrigerator fluid.
BACKGROUND OF THE INVENTION
Present pipes for refrigerator fluid such as Freon (in its most recent version known as R134a) are made of multilayer elastomer comprising reinforcement embedded in the rubber and secured to the various layers when vulcanization takes place.
Some such pipes include an inside lining formed by a layer of plastics material such as a polyamide in order to increase the impermeability of the wall relative to the refrigerator fluid being conveyed, whether in the liquid state or in the gas state.
A major drawback of such pipes lies in their weight, their bulk, and their lack of flexibility.
SUMMARY OF THE INVENTION
The present invention seeks to remedy those drawbacks by separating the elements designed to provide a barrier against the refrigerator fluid from the elements for withstanding pressure. The invention thus proposes a pipe having an inner core which performs a multilayer barrier function and an outer portion for withstanding pressure.
The nature of the inner core and particularly the nature of the material forming its outer layer constitutes a constraint on how the outer portion of the pipe can be made. In general, said outer surface is a polyamide to which it is practically impossible to bond a filamentary reinforcing structure. After numerous tests, the invention proposes a specific bond between said inner structure and the filamentary reinforcement which, in addition to being of high quality, and in particular under high temperature and high pressure, also enables the pipe to be made with a relatively thin wall, thereby conferring great flexibility thereto.
To this end, the invention therefore provides a pipe comprising an inner core whose outer structure is made of polyamide that provides an effective barrier function, and outer reinforcement that withstands pressure, the reinforcement comprising a filamentary reinforcing structure such as a weave, a braid, or a knit that is placed around the core, an outer covering layer of thermoplastic rubber based on polyolefin or on polyprobutyl, and at least one agent for ensuring bonding at least between said filamentary structure and the inner core. Given the low degree of compatibility between the outside surface of the core and the nature of the threads used (aromatic polyamides or polyesters), numerous tests were performed to discover that the effective bonding agent had to be either a hot melt polyurethane, or a hot melt polyamide, or else a thermosetting polyester.
Preferably the inner core includes, three layers of polyamide, with the outer layer made from a polyamide elastomer, e.g. a copolyamide elastomer of the type ELY 60 or ELX23NZ, products developed by EMS CHEMIE AG of Zurich, Switzerland. The core is made by coextrusion and constitutes an advantageous solution to the problem of conveying a refrigerator fluid in a flexible pipe while retaining excellent barrier and chemical resistance qualities. It may also incorporate a coextruded layer of EVOH, either between two layers of polyamide or outside said layers.
In a first method, the outer reinforcement is made by extruding hot melt polyamide or polyurethane or thermosetting polyester onto the core and then installing the filamentary structure (wrapped around, weave, braid, or knit made from aromatic polyamide or polyester fibers) and then extruding a second layer of hot melt polyamide or polyurethane or thermosetting polyester thereon preferably with coextrusion of maleic acid to reinforce the bonding with the outer layer of thermoplastic rubber.
In a variant of this method, it suffices to deposit only one layer of bonding agent between the core and the filamentary structure. In another variant, the bonding agent may be placed between the filamentary structure and either the outer layer or the core, providing the viscosity of said bonding agent enables it to be sweated through the filamentary structure to rea
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Database WPI Week 9115, Derwent Publications Ltd., London GB ; AN 91-107547 & JP,A,3 051 596 (Nitta KK) 5 mars 1991.
Brinson Patrick F.
Nobel Plastiques
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