Textiles: weaving – Special-type looms
Reexamination Certificate
2001-09-19
2002-12-17
Calvert, John J. (Department: 3765)
Textiles: weaving
Special-type looms
C139SDIG001
Reexamination Certificate
active
06494235
ABSTRACT:
BACKGROUND OF THE INVENTION
Technical Field
The present invention relates to the technical field of weaving, and more particularly it relates to the field of fabric intended for industrial use.
Although such a technical field appears to be the most preferable, it should be understood that the present invention can be implemented in other fields, and does not exclude furnishing fabrics or clothing fabrics, for example.
In the preferred field, it is known that the disposition of fibers in a fabric has great influence on the performance of the fabric both in terms of strength in one or more preferred directions, and of suitability for fitting closely over surface shape, particularly when such fabrics are used as reinforcement when making a composite material in association with a matrix, e.g. of resin.
Such abilities are recognized and sought out in order to obtain structural engineering parts of more or less complicated shape by means other than conventional machining, embossing, or stamping which are difficult, lengthy, and expensive to perform, and sometimes also difficult to carry out when the material that is to be used, although of suitable strength, constitutes an insurmountable obstacle because of its mass.
At present, the technique of manufacturing composite material parts is particularly suitable for making engineering parts of more or less complex shape that need to present both light weight and good strength.
Merely as an indication, this applies to hulls, floats, rocket fairings, shrouds for drive units, etc.
Once an attempt is made to comply with the constraints required by such a manufacturing technique, it is clear that optimizing structural characteristics necessarily involves ensuring that the reinforcement constituted by the fabric extends in the proper direction(s) so that the fibers can take up the stresses which will subsequently be imposed on the resulting part in or along the appropriate direction.
Similarly, it is necessary to be able to satisfy the requirement for fitting closely to the shape of the part that is to be obtained, which shape is generally represented by a positive or negative mold on or in which the composite material is to be placed so as to reproduce accurately the shape of the pattern.
SUMMARY OF THE INVENTION
This ability to fit closely to the shape of the pattern is generally referred to in the art as “drapability” or “layability”, which is a quality that an engineering fabric must be capable of presenting in association with the preceding requirements.
All of these reasons mean that as a general rule attempts are made to use a fabric whose individual yarns are not interlaced or crossed in conventional manner whereby some of the yarns, generally referred to as “warp” yarns, extend lengthwise relative to the woven cloth while others, generally referred to as “weft” yarns, extend crosswise, i.e. across the width of said cloth.
In practice it is often desirable to be able to have fabrics in which individual yarns extend on the bias relative to the above two fundamental directions, with such bias, although generally ±45° bias, naturally being capable of being subjected to angular variations that facilitate angular spreading of one of the categories of yarns.
PRIOR ART
In order to satisfy such a requirement using traditional textile manufacturing techniques, proposals have been made to cut individual strips of fabric at an oblique orientation, e.g. at an angle of 45°, out from a piece of cloth woven in conventional manner. Each strip can then be referred to as a “bias” fabric suitable for being oriented in such a manner that some of its component yarns are placed parallel to certain stresses to which the final part will be subjected.
Such a method is penalizing in several ways.
Firstly, it is clear that the individual strips of bias fabric produced in this way are of finite length, at best equal to the diagonal of a square corresponding to the width of the woven cloth when the orientation used is ±45°. This gives rise to a large fraction of scrap which is very penalizing on the cost price of bias fabric, in particular if the fiber constituting the yarns is expensive to produce.
Another drawback comes from the fact that it is then necessary to place such cutout strips of bias fabric side by side in order to cover a large area, and more particularly a long length. If a uniform structure is to be obtained, the question which then arises is clearly that of making connections between adjacent edges, where such connections must be made in such a manner as to present the same laying, draping characteristics, and also the same strength as that of the fabric. It must be understood that the proposals which have been made for this purpose do not enable the requirement to be satisfied when the composite material for use as reinforcement can or must be formed as a single layer of engineering fabric embedded in a resin matrix. The only way in which adjacent strips can then be connected is to superpose, at least locally, a plurality of layers of bias fabric to form a kind of sandwich at the adjacent edges, thereby significantly increasing the cost price of the final part and giving it dimensional characteristics and strength characteristics that are locally heterogeneous.
Various other propositions have been made in the prior art in attempts to answer the problem as posed above.
Mention can be made of the method of obtaining bias from a unidirectional fabric made up of warp yarns that are small in number relative to the weft yarns.
Such a technique consists in causing the traditional woven cloth to pass between presser rollers beyond which the cloth is taken up by a take-up roller whose axis is inclined at a given angle relative to the direction of the presser rollers.
In order to ensure that the expected results can be obtained durably, it will be understood that it is necessary to make use of fixing or bonding means in the portion lying between the presser rollers and the take-up roller, e.g. means acting where the yarns cross in order to fix the yarns in the newly-imparted orientation. Whatever the means used, such a requirement leads to the bias fabric having significant stiffness so that it is no longer capable of satisfying the requirement of being easy to drape or to lay.
Furthermore, the method used for fixing generally implies adding a bonding material whose presence can have a harmful effect on subsequent behavior of the fabric where it bonds with the matrix of the composite.
Finally, biasing such a conventional fabric necessarily reduces the width of the piece of cloth as initially produced.
Furthermore, such a method gives rise to a fabric in which only one yarn direction is on the bias, which is not exactly the intended object.
Another proposal in the prior art consists in making a fabric with conventional weft yarns and warp yarns but which is produced in the form of a continuous tubular sheath. The principle then consists in cutting such a sheath along a helical path, e.g. oriented at 45°, so that a woven sheath is obtained which, once opened and laid out flat, has its yarns oriented on the bias. Such a sheath can be produced using a conventional loom or a circular loom.
That technique can be considered as constituting an advance over the preceding technique, but it nevertheless suffers from certain drawbacks.
These include the reworking operation constituted by cutting out helically, which operation must be performed accurately in order to obtain rectilinear selvages. For this purpose, it is necessary to implement means for holding and cutting out both the tubular sheath and the separated portions thereof, which represent a non-negligible industrial cost.
Another drawback relates to the feed means used for feeding the weft yarns, both with a conventional loom and with a circular loom.
As a general rule, such yarns are fed either from spools or previously-prepared bobbins possessing limited winding capacity which means that they must be changed periodically, with the need to be able to reestablish yarn continuity by butt-join
Bruyere Alain
Debaille Christian
Perret Franck
Calvert John J.
Dennison, Schultz & Dougherty
Hexcel Fabrics (Societe Anonyme)
Muromoto Jr. Robert H.
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