Plastic and nonmetallic article shaping or treating: processes – With twining – plying – braiding – or textile fabric formation
Reexamination Certificate
1998-04-24
2001-08-07
Morris, Terrel (Department: 1771)
Plastic and nonmetallic article shaping or treating: processes
With twining, plying, braiding, or textile fabric formation
C264S134000, C264S136000, C264S137000, C264S257000, C264S258000, C264S314000
Reexamination Certificate
active
06270706
ABSTRACT:
This invention relates to methods of forming or treating an article or preform, and to articles and preforms so produced.
An elongate structural component such as a strut or any hollow or solid prismatic member may be made from fibre reinforced composite material, in which a plastics resin or matrix is reinforced by suitable reinforcing fibres such as glass fibres or carbon fibres. Where such a component is intended to withstand compression loads, it is usually made with the fibres aligned in the direction of the load, to provide a preferred structural configuration. In tubular structures it may be advantageous to incorporate additional fibres in the off-axis directions to confer torsional properties such as stiffness and strength. The failure strength of such components, when loaded in compression, depends on the straightness of the fibres in the load direction. Minimising the deviation or waviness can improve the structural performance.
In one known arrangement, small diameter rods, typically 1 to 2 mm diameter, containing very precisely aligned fibres are employed (e.g. Graphlite (TM) from Neptco Incorporated) These rods are intended to be incorporated into composite structures to provide highly directional and controlled orientation of the reinforcing fibres. However, although these rods provide the facility for precise alignment, a potential problem arises in the incorporation of such rods into practical structures due to the need to ensure that the rods are precisely aligned in the structure and integrated with the resin matrix with minimal voids.
We have determined that the structure may be improved by consolidating or compressing the article or preform prior to curing, In one proposal, we prepare a sealed tube or mandrel by coating with PTFE, A first layer of UD tape, i.e tape comprising unidirectional reinforcing filaments is then wrapped around the mandrel and the rods are positioned around the UD tape, with the longitudinal axes of the individual rods parallel to each other and to the longitudinal axis of the component. A further layer of UD tape is wrapped around the rods and the assembly is then put into a silicon bag. The bag is then evacuated and/or subjected to an external gas pressure. Although this technique works well and provides a finished article with good structural properties, the production method is time-consuming and not particularly well suited to continuous production.
We have therefore developed an innovative method of forming or treating an article or preform to subject it to a compression load.
Accordingly, in one aspect, this invention provides a method of forming or treating an article or preform, which method includes the step of providing around at least part of said article or preform a generally tubular element whose effective cross-section tends to reduce on extension of said tubular element, and thereafter applying an extension load to said tubular element thereby to apply a compression load to the exterior of said article or preform.
This arrangement provides a method whereby a compression load can be applied to consolidate the article or preform by applying an extension load to the tubular element. Although the tubular element could be used merely for the purpose of applying the compression load and then discarded afterwards, as described below it is preferred for the tubular element to form an integral part of the finished article, In this preferred aspect, therefore, at least part of the compression required for consolidation may be achieved by means of an integral part of the article or preform.
There are a variety of ways of applying an extension load to the tubular element. In one arrangement, one end of the tubular element is clamped with respect to the article or preform, and the extension load is applied across the remainder of the tubular element. However the extension load may be applied successively across increments of the tubular element, or it may be applied by contacting the exterior of the tubular element with a friction member and moving said friction member away from said one end of said tubular element towards the other end, progressively to apply an extension load along the length of the tubular element. The friction member may take many forms, but in a preferred aspect, the friction member may also apply a compression load to said tubular element and the article or preform beneath. The friction member may comprise an inflatable cuff disposed around said tubular element, operable both frictionally to engage the exterior of said tubular element and also to apply a compression load.
Alternatively, in a preferred embodiment of the method more suited for continuous production, the tubular element may be formed in situ around said article or preform and subjected to an extension load. The article or preform may be continuously fed into the interior of the formed tubular element. In one example, the tubular element may be spun, woven or braided onto or around the article or preform by an applicator head which remains relatively fixed as the article or preform and the formed tubular element progress past it, with an extension load being applied between the applicator head and the formed tubular element on the article or preform.
As noted above, it is particularly preferred for the tubular element to be an integral part of the finished article. Thus said tubular element may be of braided or woven material, advantageously of reinforcing fibres. In this way the tubular element may provide additional important structural properties to the formed article.
It will be appreciated that the above method may find applications for a wide range of manufacturing processes but it is particularly advantageous for the production of fibre reinforced composite structures.
Accordingly, in a particular example, the article or preform comprises an assembly of aligned reinforcement fibres or rods, and the above method provides a transverse contraction which consolidates the structure and maintains the location and position of the reinforcement fibres or rods.
The article or preform may have various shapes, typically of hollow or solid prismatic shape. Where the article or preform is hollow it is preferably formed on a mandrel element.
If required, one or more further tubular elements may be applied to said article or preform to allow application of a further compression load thereto. Thus successive tubes may be provided over the exterior of the article or preform at successive stages of manufacture.
The invention also extends to an article or preform when made or treated in accordance with the method as set out above.
In another aspect, this invention provides a method of producing a structural component of fibre reinforced plastics material, which comprises providing a preform including a plastics matrix material and a plurality of reinforcing fibres, applying around said preform a generally tubular element whose effective cross-section tends to reduce on extension of said tubular element, applying an extension load to said tubular element thereby to compress said preform, and thereafter curing said preform to produce said article.
Whilst the invention has been described above, it extends to any invention combination or sub-combination of the features set out above or in the following description.
REFERENCES:
patent: 4348247 (1982-09-01), Loyd et al.
patent: 5409651 (1995-04-01), Head
patent: 97 08422 (1996-08-01), None
patent: 2 298 214 (1996-08-01), None
BAE Systems plc
Guarriello John J.
Kenyon & Kenyon
Morris Terrel
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