Pipes and tubular conduits – Flexible – Spirally wound material
Reexamination Certificate
1999-03-01
2001-05-29
Hook, James (Department: 3752)
Pipes and tubular conduits
Flexible
Spirally wound material
C138S137000, C138S148000, C138S154000, C181S196000, C181S224000
Reexamination Certificate
active
06237642
ABSTRACT:
TECHNICAL FIELD
This invention relates to sealing-tight pipes for the transport of gaseous fluids. Amongst such pipes, the invention relates to those which are of the type having acoustic damping, i.e. they have the property of attenuating the noise level generated by resonance of the stream of gaseous fluid at each of its own nodes.
The invention is applied preferably, although without limiting force, to the use of this pipe for admission of air for combustion into a motor vehicle heat engine. In this specific applicatior, it is well known that it is important not only not to allow any penetration of liquid, inter alia water, inside the pipe carrying the air for combustion, but also to limit as far as possible the noise generated by the stream of gaseous fluid itself as a result of its natural resonances.
The object of the invention is to provide a pipe of this kind which has excellent acoustic damping properties and which is of simple and hence relatively uncomplicated structure.
DISCLOSURE OF THE INVENTION
To this end, the pipe according to the invention is characterised in that it comprises a first layer of a porous material permeable to the gaseous fluids and a second layer consisting of a thin film attached to the first layer and not adhering thereto, of a flexible fluid-tight material which is mechanically deformable reversibly.
Preferably, the second layer is an outer layer, so that an additional energy dissipation can be obtained by the vibrations of the gaseous fluid through the first porous inner layer. Also, because the two layers are not connected, the second layer, which has no rigidity, can therefore be kept in a position which is fixed by the first layer which, itself, can be rigidified to a varying degree.
However, in some applications it is also possible for the second layer to be an inner layer.
The material constituting the second layer is preferably of the visco-elastic type so that optimal acoustic damping is obtained, in co-operation with the porous nature of he first layer, which actively participates in the damping due to its porous nature creating a pressure loss.
This material of he second layer can be polyurethane, a polyolefin, e.g. polypropylene, PVC, or an elastomer, e.g. latex of the nitrile or neoprene type.
Advantageously, the material of the first layer is fibrous or formed by an open-cell foam.
In manner known per se the first layer can be formed by helical winding of a strip of porous material on itself, the helix turns preferably partially overlapping.
To gave the pipe good radial rigidity, it is possible to interpose a helical reinforcing filament, e.g. of metal or plastic, between the overlapping turn parts.
The second layer preferably is in the form of a tube in one piece, i.e. it is not wound helically.
For its assembly on the first layer the second layer is joined to the latter only at points, e.g. at the ends of the pipe.
The Invention also relates to a specific method of producing this pipe.
According to this method, it comprises making the first layer at least partly from thermofusible fibres, and heating and subjecting the assembly of the two layers to deformation so that, on cooling, the thermofusible fibres, on the one hand, bond to one another and to the other fibres, and on the other hand the second layer, by plastic deformation, assumes the final shape of the first layer without adhering.
For example, the first layer is based on polyester and contains about 20% by weight of copolyester fibres having a melting point of about 140° C., the remainder being polyester fibres having a melting point of about 200° C.
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Hook James
Renner Kenner Greive Bobak Taylor & Weber
Westaflex-Automobile
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