Pipes and tubular conduits – Flexible – Braided – interlaced – knitted or woven
Patent
1997-05-01
1999-05-18
Brinson, Patrick F.
Pipes and tubular conduits
Flexible
Braided, interlaced, knitted or woven
138130, 138124, 138137, F16L11/08
Patent
active
059041846
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a flexible tube, in particular for use in oleodynamic circuits subjected to very high pressures, comprising a substrate shaped in the form of a tubular core around which at least one reinforcing layer is arranged.
The aim of the present invention is to provide a flexible tube which has the properties necessary for the use indicated above, with respect in particular to mechanical and chemical resistance, and which at the same time has a simple structure compatible with the usual techniques employed in the production of flexible tubes.
This aim is achieved by means of a flexible tube of the type indicated above which is characterised in that the substrate comprises a radially internal layer of elastomeric material extruded longitudinally and a radially external layer obtained as a result of winding a strip of rubber-coated fabric spirally around the internal layer.
The substrate has, overall, a thickness which is preferably between 0.5 and 6 mm, and the ratio between the thicknesses of the radially internal and external layers is preferably between 0.1 and 10.
Each of the two layers forming the core of the tube of the invention confers on the tube some of the properties necessary to satisfy requirements in use.
To be more specific, the extruded internal layer ensures complete impermeability to the fluid flowing inside.
This impermeability could not be reliably ensured by a wound internal layer because of the possibility of errors occurring during its manufacturing process. This process provides that a strip of material is wound spirally around a central spindle, partially overlapping adjacent turns in the direction of the width of the strip. If, however, the overlapping is not carried out correctly, leaving a gap between adjacent turns, the fluid flowing in the tube may pass through the gap and damage the structure of the tube irreparably.
The fact that the external layer of rubber-coated fabric is wound clearly does not jeopardise the impermeability of the tube but, rather, confers an advantageous firmness to its structure owing both to the possibility of using elastomeric materials that differ from those of the internal layer and therefore have the necessary mechanical characteristics, and to the presence of the reinforcing fabric associated with the rubber.
This structure of the external layer is thus capable of withstanding satisfactorily the stresses which are transmitted to it both during the vulcanisation phase and during use, especially when high-performance steels capable of withstanding extremely high loads are used in the reinforcing layer(s).
More generally, the external layer of the core confers on the tube according to the invention excellent properties of mechanical strength while the internal layer confers on it excellent sealing and chemical resistance properties.
This functional separation can advantageously be optimised by using different materials for the compositions employed in the manufacture of these two layers.
For example, it is possible to use for the internal extruded layer compositions having excellent resistance to oils of vegetable origin, the use of which is becoming ever more widespread, even if these compositions have a reduced mechanical strength, because this latter property is conferred to a sufficient degree by the external wound layer.
The double-layered structure of the substrate, shaped in the form of a tubular core, of the tube according to the invention also constitutes intrinsic security against possible defects in one of the two layers, by guaranteeing that the tube performs its function even if there are such defects.
One or more reinforcing layers which are preferably produced by coiling and/or braiding technology are arranged coaxially around the substrate of the tube of the invention.
In this last case in particular high-pressure tubes are obtained which are capable of withstanding high torsional and bending stresses, with the external layer of the core, which layer acts as a support for the braided reinforcing layer lying over
REFERENCES:
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patent: 4488577 (1984-12-01), Shilad et al.
patent: 4499926 (1985-02-01), Friberg
patent: 5660210 (1997-08-01), Ikeda et al.
Polini Ernesto
Seghi Paolo
Brinson Patrick F.
Manuli Rubber Industries, S.p.A. Zona Industriale Campolungo
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