Production of a shaped filamentary structure

Abstract: The invention relates to a method of producing a shaped filamentary structure, particularly a circular or annular structure. The invention is particularly applicable to filamentary structure which can be subjected to further processing to produce a carbon-carbon product. A specific use of the invention is in the production of discs for use in aircraft braking systems. The invention includes assembling filamentary layers one on top of another and then needle punching the assembly of layers, without needing completely through the assembly. However, there is a relative rotary motion about an axis perpendicular to the faces of the filamentary layers between the assembly of layers and the needling head, so that an annulus of the assembled layers is needled together. In the preferred method of carrying out the invention, the layers of filamentary material are supported by a substructure, which permits needle penetration but which can be subsequently detached from the needled assembly of layers. Also in the preferred method, the layers are themselves of annular shape, and are located in an annular mould.

Description: The invention relates to a method for the production of an annular multilayer carbonisable filamentary structure. Patent No. GB-A-1 447 030 discloses a method of manufacturing fibrous sheet material in which a layer of filamentary material is subject to a needle punching operation and then up to four such layers are combined with each other by a subsequent needle punching operation. In some of the layers the filaments extend substantially longitudinally (warp wise) of the sheet, whilst in other layers, the filaments extend transversely (weft wise) of the sheet. If it is required to produce shaped structures from the sheet material made in accordance with patent GB-A-1 447 030, the finished shape must be cut from the sheet material. The patent describes the manufacture of carbonisable sheet material (which is very expensive) and, in fact, this material has been used for the manufacture of carbon fibre reinforced discs for brakes. The method of manufacture of the discs involves cutting annular shapes from the sheet material; assembling a set of these cut-out shapes in a stack; impregnating the stack with resin; clamping it in a mould and baking the assembly in an oven to carbonise the resin and produce a carbon-carbon structure. This process has three serious disadvantages. The moulds used to clamp the assemblies are bulky and typically, two-thirds of the oven space is occupied by the moulds, rather than by useful material; hence, the process is wasteful of energy. Secondly, the moulds are made of graphite and have a short life so that the cost of the moulds is high. Thirdly, because the layers are bonded by the baking process, there is a tendency for delamination to occur, either during the manufacture of the carbon-carbon product, or later if the finished disc is subjected to applied stresses, as occur when the disc is used in say an aircraft braking system. Patent Specification FR-A-2 414 574 describes a method of producing a needled annular fibrous product, in which stapled fibrous material is laid on a "warp" of continuous filament material and the assembly is needle punched to give it dimensional stability. Then complete annuli are cut from the sheet material; several such annuli are stacked one on top of another and the stack is needle punched, but there is no description of the method of needling, which must involve passing the assembly of annuli through a conventional needle loom. U.S. 2 132 530 discloses a process for making decorative needled fabrics in which a fabric is located beneath a needle board which is then reciprocated. The reciprocating needles push fibrous material into a foundation web, and the needles penetrate a lower resilient support. Objects of the present invention include: overcoming the energy waste problem when the resultant product is a carbon fibre reinforced product and overcoming the delamination problem during subsequent processing or when the resultant product is subjected to applied stress. The present invention relates to a method of producing an annular multilayer carbonisable filamentary structure, comprising the steps of: assembling sectors of filamentary material in side-by-side contiguous relationship to produce a first filamentary layer of the required structural shape; laying at least three such filamentary layers one on top of another onto a needle penetrable substructure and needle punching the assembly of layers by reciprocating a needling head equipped with needles in a manner such that the entire assembly of filamentary layers is cross-linked by filaments displaced from the filamentary layers and extending in a direction generally perpendicular to the faces of the layers, causing relative rotary motion between the assembled layers and the needling head about an axis perpendicular to the faces of the filamentary layers when reciprocating the needling head in a manner such that an annulus of the assembly is cross-linked and in that the needle head is reciprocated without needling completely through the assembly of layers with the axis of relative rotary motion being coincident with the major axis of the annulus. A most significant departure from the prior art methods, as disclosed, for example, in GB-A-1 447 030 and FR-A-2 414 574 is the method of needling the layers together by the relative rotary motion. According to a preferred method the needles of the needling head extend substantially entirely across the radial width of the annulus formed by the assembled filamentary layers. According to a preferred method, the first filamentary layer is laid on the substructure, which is rigid enough to support the first layer to allow the subsequent layers(s) to be superimposed on it, at least the initial needle punching of the assembled layers involving penetration of the sub-structure, whereby the assembled layers become a structure, but the attachment of the structure of assembled layers to the sub-structure ensures that the needled assembled layers can be separated from the sub-structure without damaging the shape and stability of the needles assembled layers. According to a preferred feature of this aspect of the invention, the annular layers are assembled in a former which locates the layers relatively to each other during the needle punching of the assembled layers. This method may be carried out by needle punching the assembly after the addition of a layer to one or more already laid layers and superimposing a relative movement between the assembly and the needles (in the same sense as the punching action) on the punching motion, so that the bottom limit of the punching action is moved upwards relatively to the assembly during the formation of the assembly. This superimposed motion can be achieved by lowering a support on which the assembly is resting during the punching operation. A method of manufacturing a carbonisable filamentary assembly for use as a preform, and apparatus for use in carrying out the manufacturing method will now be described by way of example. In the accompanying drawings:- Figure 1 is a diagram illustrating a first needle punching stage of the method; Figure 2 is a plan view of part of apparatus for presenting a sheet of filamentary material to a needle loom; Figure 3 is an elevation looking in the direction of the arrow III in Figure 2; Figure 4 is a plan view of a sheet of filamentary material showing the cutting of sectors from the sheet; Figure 5 is a plan view of an assembly of sectors to form an annular layer of sheet material; Figure 6 illustrates diagrammatically the method of needle punching an assembly of sectors; Figure 7 shows a first stage in an assembly needling operation; Figure 8 is a cross-section through the assembly at the end of the needling operation; Figure 9 is a general elevation of an annular needle punching machine; Figure 10 is a detail view to a larger scale, partly in section, showing a rotatable receptacle and associate part used in the machine shown in Figure 9; and Figure 11 is a detail view, to the same scale as Figure 10, of the driving mechanism for the apparatus shown in Figure 9. The specific example relates to the manufacture of a "preform" made of oxidised polyacrylonitrile filaments. Such a preform may be carbonised, impregnated with a resin and then baked at a very high temperature, so that both the fibrous filaments and the resin are changed to a carbonaceous form, hereby there is produced a shaped article made of carbon reinforced with carbon fibres - such a product is referred to as a carbon-carbon product. The technique of converting polyacrylonitrile fibres to carbon fibres by heat treatment is well-known, as are the techniques for production of carbon-carbon products and hence it is not necessary to describe these techniques in detail. The polycarylonitrile material is rendered suitable for carbonising by at least partial oxidation effected by passing the material through a furnace containing an oxidising atmosphere. It emerges from the oxidation process in the form of a continuous single filament textile fibre, that is to say, it is flexible and capable of being woven. However, the filamentary material has a highly polished surface sheen and is consequently quite difficult to handle. For use in the process of the invention, the material is obtained in tow form and in a specific example, each tow is constituted by some 320,000 continuous filaments. It is necessary to assemble the filaments in the form of a uni-directional sheet (warp). The filament should be held taut and touching each other to produce total "cover" of the planar area of the sheet and, in a typical example, the thickness of the sheet of filaments is about 3 millimetres. One way of producing this initial layer or sheet of filaments is to wind a series of tows on to the drum of a conventional warping machine. However, it has been found that a better prepared sheet of filaments can be formed using a special preparation apparatus shown in Figures 1,2 and 3. This spreader device does not form part of the present invention. Referring first to Figure 1, the required number of tows 10, each carried by a short flanged drum 12, is mounted end-to-end on a single stationary beam 14. From this beam 14, the filaments are drawn in warp sheet form (indicated at 16) through a needle loom 18, and on to a take-up roller 20. Arrangements for letting off filaments in warp form; drawing them through processing equipment and winding them up on to a take-up roller, are well-known in the textile industry and therefore require no detailed description here. It should be mentioned, however, that the take-up roller 20 should have a driven spindle (flanged) to ensure that the necessary tension is applied to the filamentary sheet. The needle loom itself is only very diagrammatically illustrated in Figure 1. Instead of the flanged drums 12, the individual tows may be drawn directly from the cartons in which they are normally supplied. Between the beam 10 and the needle loom 18, there are two parallel rods 22 and 24, which will be referred to as the spreader rods. Special flanged spreader devices 26 are mounted on the rods 22 and 24 and the arrangements of these devices is such that the tow from a single drum 12 or carton is received between the flanges of a single spreader device, and the spreader devices themselves alternate across the width of the apparatus on the spreader rods 22 and 24, ie a first spreader device 26a is on the rod 22, the next spreader device 26b is on the rod 24, the next on the rod 22 and so on. Essentially, each spreader device 26 comprises a cylinder able to turn on the rod 22 or 24, the periphery of the cylinder being slightly bowed (banana-shaped) - this shaping of the cylinder is exaggerated in Figure 3 for illustrative purposes. Locking means (not shown) are provided for locking each device 26 in a selected angular relationship to the rod on which it is mounted. Considering the spreader device 26b this is illustrated with its maximum radius on the top side of the rod 22. It will be observed from Figure 1, in that the sheet of filaments 16 is stretched over and engagement with the cylinders of the spreader devices 26. Now, if a particular tow passes over a device 26 orientated on its rod 22 or 24 as at 26b, the effect will be to cause the filaments to spread laterally (because they tend to slide away from the high centre point towards the flanges of the device 26). The opposite extreme is illustrated at 26a, where the smallest radius of the cylinder is at the top, and consequently, there is a tendency for the filaments to slide towards the centre and therefore to be compressed laterally. It will be appreciated that it is possible to adjust the present orientation of the spread devices at any angular disposition between the extremes shown at 26a and 26b - (including the halfway position at which no lateral spreading or compressing force is applied to the filaments) to present a warp sheet issuing from the spreading arrangement which is as consistent as possible in terms of a lateral density of the filaments and the tension in the filaments. The needle loom 18 is conventional in construction and operation. A set of barbed needles 28 is mounted in a vertically reciprocable needle board 30, and those needles are arranged in a plurality of rows each extending across the full effective width of the machine (ie the maximum overall width of the filamentary sheet 16). The needle loom has the conventional bed plate 32 and stripper plate 34, both of which are perforated to allow passage of the needles 28 when the needle head 30 descends, and the path of the sheet 16 is between these plates. In operation, the needles 28 penetrate the filamentary sheet 16 on their descent and are then drawn out of it on their ascent. The barbs of the needles catch some of the filaments and pull those filaments downwardly, so that the caught filaments are severed (because they are held taut) and form generally vertical fibres which tend to bind the filaments of the sheet 16 together. As a result of this needling operation, the sheet 16a issuing from the needle loom and wound onto the take-up spindle 20, has changed from an arrangement of longitudinally extending filaments completely separate from each other into a "fabric" mainly comprising longitudinally extending filaments (and therefore having very good dimensional stability in the longitudinal direction) but with these longitudinally extending filaments sufficiently bound together by the displaced filaments to give the "fabric" some degree of stability in the lateral direction. It will be appreciated that the lateral stability is quite poor, but it is sufficient to allow the "fabric" to be manipulated for subsequent processing, so long as it is not subjected to severe lateral stress. The next stage in the manufacturing process is illustrated in Figure 4, and this is a cutting stage. The sheet 16a is placed on the bed of a cutting machine (not shown) equipped with shaped knives for cutting sectors 36 and 38 out of the sheet. Such cutting machines are used in garment manufacture or in the manufacture of footwear. The result of the cutting process is to produce a multiplicity of sectors of an annulus, six of which can be assembled as shown in Figure 5, in a side-by-side arrangement, to produce a flat annular-shaped assembly or fabric layer. The preform which is made by the exemplary method herein described is intended to be used as the basis of a carbon fibre reinforced disc for a brake particularly suitable for aircraft use, and this product requires the annular shape shown in Figure 5. The annular shape in turn determines the shape of the sectors 36 and 38 - though it is to be understood that more or less than six such sectors could be used and this would alter the dimensions and precise shape of the sectors. It is a significant feature of the process that the sectors are cut from the needles filament sheet 16a. One advantage of the sectorial structure method will be immediately apparent, in that it is possible to produce the required shape (in this case an annulus with relatively little wastage of the filamentary sheet. Since the oxidised polyacrylonitrile material is very expensive, this is a great advantage. The actual technique of laying out the sectors on the sheet is well understood in the garment and footwear industries. However, there is another advantage to the sectorial construction method, which is well illustrated in Figure 4, in that the sectors 36 are cut in such a way that the majority of the filaments extend substantially radially of the eventual annulus (see segment 36a in Figure 5), whereas the sectors 38 are cut so that the majority of the filaments extend substantially cordially of the annulus (see segment 38a in Figure 5). Clearly the sectors 36 will have their greatest dimensional stability in the radial direction, and the sectors 38 will have their greatest dimensional stability in the chordal direction. The sectors are assembled into the annular shape on a support 40 (see Figures 6, 7 and 8) which is made of foamed polyethylene, formed to the same annular shape as that required of the finished preform. The method of assembling the sectors on the support 40 will be hereinafter described, but for present purposes it will suffice to say that the sectors are laid in the side-by-side arrangement shown in Figure 5 on the support. The first layer of sectors thus laid up on the support may comprise a set of sectors 36 with the filaments of all the sectors radially disposed, or it may comprise a set of sectors 38 with the filaments of all sectors cordially disposed, or it may comprise segments 36 alternating with sectors 38. At that stage, with a single layer of sectors on the support 40, a needle punching operation, using barbed needles as in the needle loom, is carried out on the support and the first layer of sectors. The needles displace some of the filaments into a generally vertical disposition, and this has two effects:- (i) it further stabilises the sectors themselves; and (ii) it binds a needles assembly of sectors on to the support 40 because, as shown in Figures 7 and 8, some of the filaments are displaced into the foamed support. It may be found advantageous to lay two layers of sectors, one on top of the other, before this first needle punching operation. In that case, it is preferred to arrange sectors with one orientation of filaments on top of sectors having the alternative filament orientation; but it is also preferred to lay up the second layer so that its radial joints do not coincide with the radial joints of the first layer. The use of a foamed needle-penetrable support in a needle punching operation is an important feature of the process, because it ensures the stability of the assembly of sectors in the required structural shape at a stage in the manufacturing process, when the sectors are both relatively fragile and very difficult to manipulate. A second layer of sectors similar to the first layer is then laid on top of the first layer of sectors and the needle punching operation is repeated, using a small, vertically reciprocable needling head 42 illustrated in Figure 5, but the assembly of sectors is rotated about its own vertical axis during the needling so that the complete annulus of assembled sectors is subjected to the needling process. This has the effect of crosslinking the two layers of sectors by vertically disposed filaments; further consolidating the first layer of sectors; increasing the thickness of the total assembly of sectors and further securing the assembly to the support 40. It will be appreciated that the sectors of each layer may themselves be formed of two layers of individually cut sectors. Now the sectors of the second layer are selected and arranged so that the filaments in the second are differently orientated than those in the first layer - eg a sector with cordially arranged filaments is disposed over a sector with radially arranged filaments. However, it is also preferred to arrange that the radial joints of the second layer do not coincide with the radial joints of the first layer. This process of adding layers of sectors and needling them continues until the required overall thickness of the preform is arrived at as shown in Figure 8. The depth of stroke of the needles is kept constant during the addition of the layers of sectors but as each layer is added, the stroke of the needles is displaced upwardly approximately the thickness of a layer of sectors. In other words, there is superimposed on the vertical reciprocation of the needle head 42 a slow upward translatory motion, so that the extent of the needle stroke is always rising. The result is that all the eventual mass of filamentary material is cross-linked by vertically displaced filaments, but towards the upper end of the range, the needles are not penetrating the support 40. Therefore, only the lower layers of sectors are themselves crosslinked to the support and the top and bottom layers are not directly crosslinked, although the whole mass is well bound together. It has been found that if the included angle of each of the sectors is 68°, it is possible to arrange a multiple layer of sectors one on another without any two radial joints being aligned with each other. It will be appreciated that, if the sectors subtend 68°, then instead of forming a complete first layer and then laying a second layer on top of it, as has been described above for simplicity, what actually happens is that a larger number of sectors together for a helix which is continuously laid up on the support 40, with one convolution lying on the next and the needling operation is carried out in a continuous fashion by turning the support 40 about the vertical axis of the annular shape to bring all parts of the assembly under the needling head 42. When the structure of filamentary material on the support 40 is of adequate thickness and has been sufficiently needle punched, the whole assembly of the support and the preform can be stored and/or transported. It will be appreciated that, if the filamentary structure is of relatively low density and/or quite thin, it may be still quite limp, and somewhat difficult to manipulate by itself, but the polyethylene support 40 gives it a good degree of rigidity. However, in many instances, the preform will itself have adequate rigidity to allow it to be manipulated without the polyethylene support. The filamentary preform is peeled off the support 40 prior to carbonisation. It has been found that the filaments inserted into the support are not too firmly embedded therein to prevent their withdrawal and providing the needling into the support is properly controlled, it is quite possible to peel the preform from the support. This was a surprising discovery, which enabled the use of the foamed but relatively rigid support. The oxidised preform is then placed in a carbonising oven and at this stage it is possible to use a lightweight mould only to achieve a controlled fibre volume fraction. This is because the needle punching has given the preform adequate stability, compacted it and introduced cross-binding filaments. The preform is sufficiently rigid to allow it to be placed in a furnace entirely without moulds for the formation of the matrix. After matrix formation in the furnace, the resulting carbon-carbon product (now quite rigid) can then be machined if necessary and provides a disc for use in high duty brakes for vehicles. In fact, it is suitable for use on aircraft undercarriages. It has been found that a disc made by the method of the invention is particularly well adapted to resist applied stresses as applied in braking without delamination or other structural failure. In addition, it will be appreciated that the method is cheaper than prior art methods, because of the saving of material and energy. Turning now to Figures 9, 10 and 11, there is shown a machine which is adapted to carry out the segment assembly and needle punching technique described in general terms previously, with reference to Figures 6, 7 and 8. It has also been found possible to vary the density of the needled assembly by increasing or decreasing the needling action - an increase in needling increasing the bulk density of the product. Because the product is inherently less liable to delamination than similar products made by the known methods, relatively low densities may be used, with consequent saving in material. The machine has a stationary plinth 50, to which there is rigidly attached a stationary drive housing 52. An open topped rotary receptacle 54, in which the sector assembly and needle punching takes place, is mounted for rotation about its own vertical axis on top of the drive housing 52. The machine also has a needle punching head 56 slidably mounted upon the plinth 50. The open-topped receptacle 54 is cylindrical and has a closed bottom 56; it is secured on a circular drive plate 58 by screws 60. The drive plate 58 forms part of the driving mechanism of the machine to be hereinafter described, but the receptacle 54 can be removed by unfastening the screws 60, and replaced by an alternative receptacle. A cylindrical core 62 has end plates 64 and 66, and is secured on a core spindle 68 so as to be rigid with that spindle. At its lower end, the core spindle 68 has a flange 70 which can be secured by screws 72 to the drive plate 58. By unfastening these screws 72, it is also possible to remove the core 62 from the drive plate 58. It will be appreciated that, since both the receptacle 54 and the core 62 are secured to the drive plate 58, they rotate together with that plate. In use, the core 62 defines the internal diameter of an annular sector assembly, and the peripheral wall of the receptacle 54 defines the outside of the sector assembly. Mounted within the annular space in the receptacle 54 is an annular false bottom 74. A false bottom lowering member 78 has a cylindrical lower section 77 from which three equi-angularly spaced driving columns 79 project upwardly. The false bottom 74 is secured by screw 76 to the top ends of the driving columns 79. Each of the columns 79 extends through a bearing arrangement 80 in the drive plate 58, so that when the drive plate 58 is rotated, the driving columns 79 rotate with it, and consequently, the false bottom 74 is also rotated with the receptacle 54 and the core 62. Hence, there is provided a rotary receptacle arrangement to contain the assembly of sectors as that assembly is being built up and needle punched. The false bottom is capable of vertical motion with the lowering member 78 (as will be hereinafter described) from a top position illustrated in full lines in Figure 10, to a lowered position illustrated in chain-dotted lines in Figure 10. The particular receptacle 54 illustrated in Figures 9, 10 and 11, can only be used to produce an annular assembly of specific dimensions. In practice, the machine illustrated can be used to manufacture annular assemblies having a range of dimensions, because it is possible to completely remove the receptacle core and false bottom, and replace these by an alternative receptacle arrangement having different dimensions appropriate to another size of finished needled product. For the purpose of driving the drive plate 58 (and therefore rotating the receptacle 54), a small variable speed receptacle drive motor 82 is secured to a stationery element within the drive housing 52. The motor shaft is connected directly to a worm shaft 84 in a receptacle drive gearbox 86. The worm shaft 84 meshes with a worm wheel 88 mounted on a primary shaft 90 which is journalled in bearings 92 and 94 carried by stationary parts of the drive housing 52. A driving pinion 96 is keyed on the primary shaft 90, and meshes with a large spur gear 98 keyed on the outside of a main drive spindle 100 which, as is clear from Figure 11, essentially comprises a cylinder. The main drive spindle 100 is itself journalled in bearings 102 and 104 which are located in stationary elements of the drive housing 52. It will be appreciated, therefore, that when the motor 82 is operated, drive is transmitted through the worm gear reduction box and the primary shaft 90, to the spindle 100, which rotates at a relatively low speed. The drive to the spindle 100 is controlled through an electrical control system (not shown) which is set to ensure that the assembly of sectors accumulating in the receptacle 54 is rotated at a speed required to produce adequate needle punching of the sectors as those sectors pass underneath the needling head 55. It has already been mentioned that the false bottom 74 is rotated with the receptacle 54, by virtue of the drive transmitted through the bearing arrangements 80 to the driving columns 79. However, the driving arrangement also incorporates a mechanism for raising and lowering the false bottom 74 in accordance with the requirements of the needle punching and assembling operation. To this end, a small variable speed elevation motor 106 is provided within the lower part of the drive housing 52, and the motor shaft is directly connected to a worm shaft 108 of an elevation gearbox 110 secured to stationary parts of the drive housing 52. The worm shaft 108 meshes with a worm wheel 112 keyed onto a screw shaft 114 which is coaxial with the vertical axis about which the receptacle 54 rotates. At its lower end, the screw shaft 114 is journalled in bearings 116 in a stationary part of the drive housing 52. The upper end of the screw shaft 114 is journalled at 118 in a cap 120 which is secured by screws 122 to the top ends of three stationary pillars 124 the bottom ends of which are welded to a stationery part of the drive housing 52. Consequently the pillars 114 provide mountings for the top cap 120, the purpose of which is to provide a top journal mounting for the screw shaft 114. The main portion 126 of the screw shaft 114 is screw threaded, and an elevation nut 128 engages with this screw threaded main portion 126. The nut 128 is secured by screws 130 in a slider 132. The slider 132 is generally cylindrical, with an inturned flange at its lower end, and the pillars 124 extend through bearings 134 in this inturned bottom end. It will be recalled that the pillars 124 are fixed at their lower ends to a stationary part of the drive housing 52, and hence do not rotate. The bearing arrangement 134 prevents rotation of the slider 132, which in turn prevents rotation of the nut 128. However, the bearing arrangement 134 permits the slider 132 to slide vertically on the pillars 124. Hence, as the screwed shaft 114 is rotated-, the nut 128 being prevented from rotating, moves longitudinally of the screwed shaft (ie it moves vertically). The slider 132 is provided with top and bottom bearing flanges 136 and 138, and an annular drive member 140 is located between these flanges 136 and 138. The cylindrical lower section 77 of the lowering member 78 is secured by pins 142 to the annular drive member 140. By virtue of this connection, the annular drive member 140 has to rotate with the lowering member 78 and, therefore, with the receptacle 54, but bearings between the annular drive member 140, on the one hand, and the slide member 132 with its flanges 136 and 138, on the other hand, ensure that the member 140 is able to rotate, despite the fact that the slider 132 is non-rotatable. The end flanges 136 and 138 are the means whereby the axial motion of the nut 128 is transmitted to the lowering member 78. It will be appreciated that this axial motion of the member 78 with its columns 79 produces the elevation and lowering of the false bottom 74 within the rotary receptacle 54. The mounting for the needling head 55 comprises a long slide 150 having dovetail cross-section slide bearings (similar to those used on machine tools) engaging in a stationary mounting 152 on the plinth 50. Thus, the slide 150 is able to move in a longitudinal direction indicated by the arrow A, that is radially with respect to the rotational axis of the open-topped receptacle 54. A transversing screw 154 is journalled in an extension of the mounting 152, and is controllable through a handwheel 156. The split nut 158 is secured by screws 160 to the slide 152, and this nut engages on the screw 154. Rotation of the handwheel 156 therefore causes sliding motion of the slide 150 in or out with respect to the vertical axis of the receptacle 54 according to the direction of rotation of the handwheel. (As an alternative to the handwheel 156, or in addition thereto, there may be power-driven means for rotating the spindle 154 to produce the radial motion of the slide 150). The slide 150 carries a stop rod 162, on which are adjustably mounted stops 164 and 166 adapted to cooperate respectively with limit switches 168 and 170 to indicate the inner and outer extremities of motion. As illustrated in Figure 9, the slide 150 is shown at the inner end of a preselected movement, with the stop 164 engaging with the limit switch 168. A signal initiated by the limit switch 168 will indicate to the setter, that the needling head 55 has been correctly located with respect to the receptacle 54. It will be appreciated that, when an alternative receptacle 54 is fitted to the drive plate 58, it is necessary to adjust the position of the stops 164 and 166 accordingly. The needling head 55 has a variable speed driving motor 172, on the motor shaft extension of which is a driving pulley 176 of a toothed belt drive 178. The driven wheel 180 of the belt drive is keyed onto the driving shaft 182 of the needling head 55. It is unnecessary to describe the mechanism of the needling head 55 in detail, because, essentially, this mechanism is the same as that of a dabber brush as used on a Noble comb in the combing industry. Suffice it to say for present purposes, that there is a vertically reciprocable needle carrier 184, which is operated by the drive from the motor 172. Various sizes of needle board 186 can be fitted to the lower end of the needle carrier 184, each of these needle boards being similar to the needle boards used on a conventional needle loom, excepting that they are much smaller in area than those used on a needle loom. For any particular application, the needle board 186 has to be able to fit in the annular space between the core 62 and the wall of the receptacle 54, in order to carry out the needling operation. Each needle board 186 is provided with the usual barbed needles (not shown) as used in a needle loom for penetrating a fibrous mass. The electrical control system is so arranged that the needle board 186 always comes to rest in the raised position where the needles are clear of the top of the receptacle 54. It will be appreciated that, with the needling head 55 in the innermost position, as indicated in Figure 9, it is possible to carry out a needle punching operation on filamentary sectors or assemblies of such sectors located on the false bottom 74 within the receptacle 54. Moreover, as the receptacle 54 is rotated under the stationary needling head 55, the complete annular assembly is subjected to the needling action. One of the important features of the present invention is the carrying out of a needle punching operation on filamentary material, where the material traverses a recirculating path (namely, the rotation about the vertical axis of the receptacle 54) under a stationary needling head. This is in contradistinction to the ordinary needle loom arrangement, such as that shown diagrammatically in Figure 1, where a continuous length of filamentary material moves in rectilinear fashion under a needling head. It will be noted that there is no stripper board, as used in conventional needling looms, although if it is found necessary to use such a stripper board, it can be mounted from the stationery parts of the needling head 55. Provision is also made in the machine for automatic control of the elevation and lowering of the false bottom 74 within the receptacle 54. For this purpose, a speed reduction gearbox 190 is attached to the underside of the worm gearbox 110, and a train of speed reduction gears 192 transmits driving motion from a driving pinion 194 mounted on the bottom end of the screw shaft 114 to a pinion 196 meshing with a rack 198 attached to a control rod 200; this control rod 200 is mounted for axial sliding motion and is driven through the gearbox 190 whenever the screw shaft 114 is rotated. The gearing is so arranged that the stop rod moves to the right, as seen in Figure 11, when the false bottom 74 is being lowered. Closely adjacent to the stop rod 200 is a switch mounting rod 202, which is fixed to the casing of the gearbox 190. Consequently, the switch mounting rod 202 has no motion, and, therefore, there is relative motion between the stop rod 200 and the switch mounting rod 202. A pair of dogs 204 and 206 is attached to the stop rod 200, and these dogs are adapted to cooperate with a series of switches 208, 210, 212, 214 and 216 adjustably mounted on the switch mounting rod 202. The switch 210 is adapted to be tripped by the dog 204 whenever the screw 114 has been rotated to bring the false bottom 74 into the lowest operative position and is referred to as the "DOWN" switch. The switch 216 is adapted to be tripped by the dog 206, should the switch 210 fail to operate to protect the machine parts. Closure of the switch 210, which is referred to as the "DOWN" switch should terminate the electrical supply to the elevating motor 108 to prevent further downward motion of the false bottom 74, but if for some reason the false bottom continues to descend, closure of the switch 216 by the dog 206 will cut off the electrical supply. The switch 216 is therefore referred to as the "OVERRUN DOWN" switch. The switch 212 is adapted to be operated by the dog 206 when the false bottom is elevated above the starting position, to a discharge position where it projects above the top of the receptacle 54. The switch 212 is referred to as the "UP" switch. The switch 214 is adapted to be tripped by the dog 206, when the false bottom is in the starting position illustrated in Figure 10 and therefore this switch is referred to as the "START" switch. When this switch is tripped, it is adapted to cause the operation of the driving motor 82 for rotating the receptacle 54, and also for operating the elevation motor 106 for commencing the lowering of the false bottom 74. Finally, the switch 208 (which is referred to as the "UP OVERRUN" switch) is adapted to be tripped by the dog 204 if the false bottom should be elevated to a position above the normal up or discharge position. When the machine illustrated in Figures 9, 10 and 11 is to be operated, the correct size of receptacle 54 is bolted to the drive plate 58, and the appropriate size of the needle board 186 is fitted to the needling head 55. As has already been mentioned, the machine is equipped with electrical control circuit which receives signals from the switches 168 and 170 operated by the in and out feed of the needling head 55, and from the switches 208, 210, 212, 214 and 216. The control circuit is set to bring about a sequence of operation as follows:- In the starting position, the false bottom 74 is located (as shown in Figure 10) about ten millimetres below the top lip of the receptacle 54. This location is suitable for receiving the polyethylene support 40, and the support is placed on the false bottom, where it is located by the wall of the receptacle 54. The slide 150 is then actuated by turning the handle 156, to move the needling head 55 into the operative in position, as illustrated in Figure 9. When the needling head arrives at the in position, the switch 168 is closed, and this permits electrical power to be supplied to the two variable speed motors 82 and 106 of the machine. The first layer of sectors 36 and 38 is then laid manually on the support 40, with their edges in abutting arrangement, as illustrated in Figures 5 and 6 (as has been mentioned, this first layer may, in practice, be constituted by two layers laid one on top of the other). When this first layer of sectors has been laid on the support 40 in the receptacle 54, the driving motor 82 is operated, and the receptacle 54 begins to rotate. At the same time, the motor 172 driving the needling head 55 is operated, and consequently, the needling head begins to carry out a needle punching operation on the filamentary sectors located beneath it in the receptacle 54. The needles carried by the needle board 186 penetrate the portion of the first layer of sectors which lies under the needling head, carrying those fibres which are caught by the barbs of the needles vertically downwards from the plane of the sectors 36 and 38 into the needle penetrable support 40. Although the needles themselves withdraw from the support 40, and from the filamentary sectors 36 and 38, the filaments which have been displaced into this vertical position remain embedded in the support 40. As the receptacle 54 rotates, it carries the first layer of sectors under the needling position, and after a single rotation, all the first layer has been subjected to a needle punching operation, and it is secured to the support 40 by those filaments which have become embedded in the support. At the end of a single rotation of the receptacle 54, a limit switch (not shown) is tripped and this causes actuation of the elevation motor 106 for a predetermined period of time. As a result, the elevating mechanism is operated to lower the false bottom 74, through a distance which is approximately equal to the thickness of a single layer of the needled filamentary sectors. Further sectors are then fed one at a time onto the first layer of sectors as the receptacle 54 continues to rotate. Since the rotation will be relatively slow, it is possible to carry out this feeding of the segments by hand. The feed position may be located immediately in advance of the position at which the needling head 55 operates. As these further sectors pass under the needling head 55, they too are needle punched and this has the effect of crosslinking the sectors to the sectors of the first layer, and of course, further binding the assembly of sectors to the needle penetrable support 40. It will be appreciated that, as each succeeding layer of sectors passes under the needling head 55, it becomes crosslinked by the vertically displaced filaments to the layers underneath it, and since the support 40 is descending in stepwise fashion, once every revolution of the receptacle, the penetration of the needles into the support 40 is progressively reduced. Eventually, when the thickness of the assembly of sectors on the false bottom exceeds the depth of penetration of the needles into the assembly of sectors, there is no further crosslinking of the filaments into the support 40. The operation continues until a sufficient thickness of filamentary material has been built up into an annular structure supported by and bonded to the support 40. At that stage, the dog 204 will actuate the DOWN switch 210, terminating the supply of current to the driving motors 82, 106 and 172. Consequently, all the operations of the machine are brought to a halt. In practice, after all the sectors have been fed into the receptacle 54, needling is continued until the entire preform constituted by the needled assembly of filamentary sectors is clear of the needles, thus ensuring uniform density throughout the thickness of the filamentary preform. Before the preform can be removed form the receptacle 54, the handwheel 156 has to be turned to retract the needling head 55 from the operative position, to a retracting position. When the switch 170 is operated by the arrival of the needling head at the retracted position, the elevation motor 106 is then operated in the direction opposite to that which caused lowering of the false bottom 74, but at a high speed, to produce rapid upward motion of the false bottom. This motion continues until the dog 206 operates the UP switch 212, at which point the power supply to the elevation motor 106 is terminated and the false bottom is arrested in the UP position, where it projects above the lip of the receptacle 54. It is then possible to lift the preform together with the needle penetrable support 40 as a unit off the thus elevated false bottom 74. As has been previously mentioned, the support 40 is useful in subsequent manipulation of the assembly, but it is possible to peel the needled assembly off the support 40 when required. To restart the machine, the operative presses a control button (not shown) which operates the elevation motor 106, to lower the false bottom 74 into the START position. This completes the full cycle of operations of the machine. It will be appreciated that the needle punching operation carried out in the machine illustrated in Figures 9, 10 and 11 results in a degree of compacting of the filamentary sectors, such as is normally obtained by a needle punching operation. This is useful in the provision of a well bonded together filamentary product provision of a well bonded together filamentary product, and indeed the degree of needle punching can be such that the original laminar construction of the product is virtually broken down due to the intense crosslinking vertically displaced filaments. This is useful not only in the provision of a preform which can be placed into a matrix forming furnace without the necessity for clamping, because it also helps to ensure that there is no delamination of the eventual disc, under applied stress. Moreover, it will be appreciated that by suitable control of the machine, it is possible to vary the fibre density of the preform by adjusting the speed of rotation of the receptacle 54 relatively to the speed of operation of the needle punching head and/or by adjusting the rate of descent of the support 74. It should also be mentioned that experiments have shown that a preform made in accordance with the invention will have much greater strength than preforms made by known techniques. Consequently, it is possible to effect large savings in material costs, because the density of the preform can be substantially reduced compared with the preforms made by the known techniques. For example, it has been found that a preform formed in accordance with the invention and having a fibre volume of 15% is stronger than the present commercially available preform, which had a fibre volume of approximately 35%. It is expected, therefore, to be able to obtain satisfactory results with a fibre volume of between 15% and 24%.

Claims: A method of producing an annular multilayer carbonisable filamentary structure comprising the steps of: assembling sectors of filamentary material in side-by-side contiguous relationship to produce a first filamentary layer of the required structural shape, laying at least three such filamentary layers comprising filaments (36, 38) one on top of another onto a needle penetrable substructure (40) and needle punching the assembly of layers by reciprocating a needling head (42) equipped with needles in a manner such that the entire assembly of filamentary layers is cross-linked by filaments displaced from the filamentary layers and extending in direction generally perpendicular to the faces of the layers, causing relatively rotary motion between the assembled layers and the needling head about an axis perpendicular to the faces of the filamentary layers when reciprocating the needling head in a manner such that an annulus of the assembly is cross-linked and in that the needle head is reciprocated without needling completely through the assembly of layers with the axis of relative rotary motion being coincident with the major axis of the annulus. A method of producing a multilayer carbonisable filamentary structure as claimed in Claim 1, in which the needles of the needling head (42) extend substantially entirely across the radial width of the annulus formed by the assembled filamentary layers. A method of producing a multilayer carbonsiable filamentary structure as claimed in Claim 1 or Claim 2, in which the first laid filamentary layer is laid on the substructure (40), which is rigid enough to support the first layer to allow the subsequent layer(s) to be superimposed on it, at least the initial needle punching of the assembled layers involving penetration of the substructure, whereby the assembled layers become a structure, but the degree and density of the penetration being limited, to ensure that the needled assembled layers can be separated from the substructure without damaging the shape and stability of the needled assembled layers. A method of producing a multilayer carbonisable filamentary structure as claimed in Claim 2, in which the annular layers are assembled in an annular former (54, 220) which locates the layers relatively to each other during the needle punching of the assembled layers. A method of producing a multilayer carbonisable filamentary structure as claimed in any one of Claims 1 to 4, in which the assembled layers are needle punched after the addition of a layer to one or more already laid layers and in which there is superimposed on the punching motion a relative movement between the assembly of layers and the needles (in the same sense as the punching action), so that the bottom limit of the punching action is moved upwards relatively to the assembly during the formation of the assembly. A method of producing a multilayer carbonsiable filamentary structure as claimed in Claim 5, in which the superimposed motion is achieved by lowering a support (40) on which the assembly is resting during the punching operation.

Inventors: LAWTON PETER GEOFFREY, SMITH NORMAN, LAWTON, PETER GEOFFREY, SMITH, NORMAN
Applicants: AEROSPACE PREFORMS LTD, AEROSPACE PREFORMS LIMITED
Application year: 1987
Main classification: D04H18
IPC codes: D04H18, F16D69, D04H3