Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1995-01-25
2001-01-16
Bryant, David P. (Department: 3726)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C442S246000, C028S107000
Reexamination Certificate
active
06174594
ABSTRACT:
The invention relates to a method and apparatus for the production of a shaped filamentary structure and to filamentary structures made by the method and/or made on the apparatus. A particular application of the invention is in the manufacture of a carbonisable assembly and even more particularly to the manufacture of circular or annular shaped filamentary assemblies. It is to be understood however that in its broadest aspects, the invention is not restricted to any particular type of filamentary material nor to any particular shape of product. The expression “shaped structure” is however intended to exclude the production of mere piece goods.
In the specification of U.S. Pat. No. 5,081,754 (Lawton et al), there is described a method of producing a shaped filamentary structure comprising the steps of: producing segments comprising continuous aligned filaments having staple fibre on top; assembling at least two of the segments in side-by-side contiguous relationship to produce a first filamentary layer of the required structural shape; superimposing at least one of similarly formed filamentary layers on the first layer and needle punching the assembled layers to product cross-linking of the layers by displaced staple fibre being pushed down to extend across and interlink lower layers.
The specific embodiments described in that specification relate to the manufacture of annular preforms made for example from tows of polyacrylonitrile continuous filaments. In a first stage, a sheet of stretched filaments is first submitted to a needle punching process by passing the sheet of filaments through a conventional needle loom, to give the sheet a certain amount of cohesion. Then a web of stapled fibre is needled on top of and partially into the layer of substantially continuous filaments to produce a duplex layer. Segmental shapes, each corresponding to a segment of the finished annulus, are then cut from the duplex layer and these segments are, in a second stage, assembled to form superimposed layers, each comprising an annulus made up of a series of the cut segments, and whilst the thickness of the stack of layers is being built up, the stack is rotated under a segmental needling head, so that the stack is subjected to a further needling process, but the distance between the bottom of the stack and the needling head is progressively increased, so that the degree of needling is substantially constant throughout the process. The needling carries the staple fibre down though the stack such that the staple fibres extend in the general direction of the stack to interlink adjacent layers.
After the final layer has been added additional layers of staple fibre web are added to at least partially replenish the upper duplex layer whose staple fibre has been pushed down into the stack with additional staple fibre.
If desired, the preform can be turned over and additional staple fibre layers can be needled into the other side of the preform layer.
When the preform is not turned over to needle additional staple fibre layers into the stack, at least the lower portion of the stack will have the same strength as the middle portion. When the stack is turned over, an additional manufacturing stage is involved thereby increasing projection time and cost. Furthermore, the density and strength of the upper and lower parts of the preform will be different as the staple fibre at the top is being needled into a region starved of staple fibres and the staple fibre at the bottom has been needled into an already rich region of staple fibre. Furthermore, the needling of the staple fibre into what was previously the bottom of the stack causes the needles to penetrate the stack in a reverse relative direction which has an unknown possibly disadvantageous effect on the preform.
It is also necessary for some purposes (e.g. when the preforms are used in the manufacture of brakes where the carbon—carbon product made from the preform has to withstand high stresses) to ensure that there is a good resistance to inter laminar weakenesses, some of which appear near to the top surface of the finished preform.
According to one aspect of the present invention, a method of manufacturing a shaped fibrous fabric structure from multiple layers of fibrous material comprises building a stack of layers and causing fibres to extend across the layers to interconnect the layers and enriching an outer region of the stack with additional fibres which are caused to extend across a plurality of layers.
The method may comprise enriching an outer region which is the last to be added to the stack. Alternatively, the method may comprise enriching an outer region of the stack which is the first to be added to the stack. The method may comprise enriching the first outer region to be added to the stack before adding the further layers to complete the stack.
The method may comprise the enrichment replenishing a region which is deficient in fibres which extend across layers to interconnect the layers.
The method may comprise needling the layers to cause the fibres to extend across said layers to interconnect the layers and continuing the needling after the final layer of material is added to the stack without varying the distance between the end of the needle stroke into the stack and the opposed end of the stack.
According to another aspect of the present invention, a method of manufacturing a shaped fibrous fabric structure from multiple layers of fibrous material comprises building a stack of layers and causing fibres to extend across the layers to interconnect the layers, enriching initial layers added to the stack with additional fibres which are caused to extend across a plurality of layers, before continuing to add further layers to complete the building of the stack.
The method may comprise the layers including unidirectional filaments and staple fibres with additional staple fibres (which may be in the form of rovings or loose fibre or web) being added to enrich initial layers added to the stack. The unidirectional filaments may be arranged to abut a previous layer.
The method may comprise stacking the layers on top of each other.
The method may comprise needling the layers to cause fibres to extend across layers. The method may comprise increasing the distance between one end of the stack and one end of the needle stroke as the stack is being built. The needling may be continued after the final layer of material is added to the stack without varying the distance between the end of the needle stroke into the stack and the opposed end of the stack. The method may comprise the needles passing completely through the stack as the initial layers are being added, with the needles subsequently reaching substantially the end of the stack after a predetermined number of layers have been added, and enriching the stack with additional fibres extending across a plurality of layers at that stage. The method may comprise maintaining the distance between one end of the needle stroke and the end of the stack substantially constant as initial layers are being enriched.
At least some of the layers may be constituted by a plurality of segments assembled in a substantially contiguous arrangement to form the required shape. The segments may be assembled in a former which locates the segments relatively to each other as fibres are caused to extend across layers.
The layers may be formed into a circular or annular shape. The needling of the circular or annular assembly may be carried out by reciprocating a needling head equipped with needles and causing relative rotary motion about the axis of the circular or annulus being formed relative to the needling head.
At least one of the layers may comprise both continuous filaments and staple fibres which have been needled together prior to assembly in the stack.
The longitudinal axis of the filaments in a subsequently added layer may be disposed at an angle to the axis of those filaments in a previous layer. The longitudinal axis of the filaments in the segments of each layer may be disposed at an angle to those in t
Lawton Peter Geoffrey
Smith Norman
Adams, Schwartz & Evans P.A.
Aerospace Preforms Limited
Bryant David P.
Butler Marc W.
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