IE77039B1

IE77039B1 - Braid structure

Info

Publication number: IE77039B1
Application number: IE11691A
Authority: IE
Inventors: David S Brookstein; Donald Rose; Robin Dent; John Dent
Original assignee: Albany Int Corp
Priority date: 1990-01-15
Filing date: 1991-01-15
Publication date: 1997-11-19
Also published as: ATE136068T1; CA2073965A1; ES2085984T3; IE910116A1; DE69118362T2; PT96479B; EP0511248B1; EP0511248A1; CA2073965C; PT96479A; DE69118362D1; WO1991010766A1; DK0511248T3; GR3019966T3

Abstract

The invention concerns a braid structure comprising a plurality of braided layers of stranded material in which said layers are laid down in a single pass of a braiding machine with at least one strand of each layer extending into a contiguous layer to form and interlock between the said layers. The invention also concerns a machine and a method of making the structure by supplying groups of strands (R, B, G, O, W) to a braid forming station whereby each group of strands forms a braid layer thereat; a strand (R) from one of the groups passing into or through the strands (B) of a group of an adjacent layer to form an interlock therebetween.

Description

This invention is concerned with the production of a braid structure which has a plurality of layers of stranded material which are laid down in the form of a hollow structure. Multi-layer braided material is made conventionally by forming a first layer of braid and then sequentially forming further layers over the original layer. Braids are currently produced using a maypole type of braider where an annular bedplate has a serpentine path formed by a pair of intersecting, serpentine tracks formed in it and movable package carriers adapted to travel along said tracks, each carrier carrying a package of stranded material which material forms the braid crossing the strands thereof from the various package carriers over each other at the intersections in said serpentine paths. The braid can be reinforced by having further static strands supplied from static carriers, i.e. carriers which are fixed in their location to the serpentine paths. Such a . static strand is incorporated within the resultant braid structure to form a longitudinal strand. The braid is usually - 2 formed generally centrally of the bedplate and usually on its longitudinal axis.

To form a multi-layer braid, a series of maypole braiders may be set up with a common longitudinal axis and the braid as formed is passed serially through successive braiders so that separate layers are laid down one upon another. Alternatively, such a multilayer braid may be passed the requisite number of times through a single braider to build up the required number of layers. The braid thus formed can have any number of layers depending on the number of maypole braiders employed or the number of passes made as the case may be.

Multi-layer braid structures may be formed on a mandrel of a suitable shape, which mandrel can be removed subsequent to the formation of the structure, to result in the formation of a shaped, braid structure.

As an alternative to the maypole type of braider, it has been proposed to form a hollow braid in braiding machines of a tubular type such as is described, for - 3 example, in U.S. Patent Nos. 4621560 and 4753150 assigned to Atlantic Research Corporation. In the machine disclosed in these patents the internal Λ surface of a cylinder constituting the apparatus is composed of a plurality of ring members, each of a similar size which are axially arranged with respect to each other and each having a yarn carrier which can be moved axially of the cylinder. The ring members are adapted for rotation about the axis of the cylinder and the carriers are moved axially to interbraid the filaments. Stops are provided to limit and control the amount of axial movement. These machines, however, operate by discontinuous or integer motion of the members and carriers and in consequence are slow in operation. This in turn limits for practical purposes the uses to which such machines can be put and hence the nature and type of braided structures which can be produced.

A major problem of multilayer braids of the type described above is the tendency for the resultant braid to delaminate in service. Such braid structures are used in so-called composites formed, for t example by impregnating such a braid structure with a - 4 resin material. While such a composite exhibits good mechanical properties in terms of tensile strength and tensile modulus in the plane of the layer, the mechanical properties of the composite transverse to the layer rely only on the shear strength of the matrix material and the braid strength between the matrix and material and the fibre layers since this is all that physically unites adjacent layers in the structure. Thus, when the composites are subjected to transverse loads there is a risk of inter-lamina failure between the layers of the braid.

Proposals have previously been made to overcome the de-lamination problem by introducing additional strands of material which extend transversly of the layers, during the braiding process. Some of these strands have been introduced randomly, whilst others have been introduced on a systematic radial basis by providing a mandrel which has apertures through which radial strands project. Such radial strands impart a degree of coherence between the . braid layers, but their presence makes it difficult to interbraid the various strands from the package carriers and as a - 5 result the rate of formation of the braid slows down.

Another attempt to overcome the problems of delamination has been by introducing strands in a stitching operation which will unite and reinforce the layers of braid. This, although partially successful, does not give the level of strength or consistency which is required in many applications of such braid structures or of the composites formed therefrom.

In order to have an effective braid structure it is desirable for the various layers of the braid to be positively interlocked. The present invention seeks to provide a multilayer braid structure in which the layers are interbraided and which exhibits substantially uniform or predetermined properties. The invention also sets out to provide an improved form of braid structure which can be used also as a basis for a braided composite which is able to be constructed cheaply and swiftly and thus is economic in its manufacture. - 6 According to the present invention there is provided a braid structure comprising a plurality of layers of stranded material in which said layers are laid down in a single pass of a braiding machine and in which in each layer at least one strand of that layer extends into a contiguous layer to form an interlock between the said layers.

As used herein, the term strand is to be understood to include filaments, monofilaments, slit tape, rovings, multifilament yam, braids or other longitudinal textile products. i The interlock between the layers may be a direct interlock in which the interlocking strand passes from a first layer to a contiguous second layer, and passes around at least one strand in said second layer.

Alternatively the interlock between the layers may be an indirect interlock in which an interlocking strand passes from said first layer through the second layer to another, not necessarily contiguous layer in the structure, and passes around a strand in said other layer to serve to bind the first layer and said other layer together and at the same time to bind the layers therebetween.

The braid structure in accordance with the present invention may be hollow and and may be of a circular or of an irregular cross-section. In a further aspect of the invention the braid is a collapsed braid.

The invention includes a composite material comprising a braid structure in accordance with the invention having a matrix of resin material dispersed and/or distributed within the interstices of the braid. In another aspect of the invention, there is provided a composite material comprising a braid structure having a plurality of layers of stranded material in which said layers are laid down in a single pass of a braiding machine and in which in each layer at least one strand of that layer extends into a contiguous layer to form an interlock between the said layers, and a matrix material incorporated at least in the interstices of the said braid structure. - 8 At least some of the strands may comprise a resin compatible with said matrix material. Such strands may be preimpregnated. The preimpregnation may be by coating the strands with a resin layer or coating.

Alternatively, the strands may include or comprise the resin material.

After formation of the braid, it may, with or without a matrix material be subjected to a treatment in which the resin material component of said strand may permeate the interstices of said braid structure.

The matrix material of the braid composite may be either a thermoplastic or a thermosetting resin. The composite after formation, may subsequently be subjected to shaping, for example, by the application of heat and pressure in a mould.

In another aspect of the present invention, there is 20 provided a method of making a multilayer braid structure which method comprises supplying groups of strands to a braid forming station whereby each group of strands forms a braid layer thereat in which a strand from one of said groups passes into or through the group of an adjacent layer to form an interlock therebetween.

The present invention also provides a method of making a multi-layer braid structure which method comprises :(i) feeding a plurality of strands of material from a first set of movable package carriers to a braid-forming area to form a braid layer thereat in which each movable package carrier traverses a predetermined first serpentine path. (ii) feeding a plurality of strands from a second set of movable package carriers to said braid-forming area to form a braid layer thereat in which each movable package carrier of said second set traverses a predetermined second serpentine path, wherein each of said serpentine paths is arranged so that at least one package carrier of each set can' carry a strand of material from its respective layer into the other layer to interlock with said other layer.

In one aspect of the present invention said second layer may be contiguous to said first layer, whereas in an alternative embodiment of the invention said second layer may be spaced from said first layer and have a number of intermediate layers interposed therebetween. In these circumstances a strand associated with the package carrier moving between the first and the second layer is caused to pass through all the intermediate layers prior to forming a positive interlock with said second layer.

Strands of material from static" package carriers may also be fed to the braid forming area in respect of each layer for interbraiding with the strands from said respective movable package carriers.

A mandrel may be positioned at the braid-forming area in order to form a hollow braid structure and the first layer of the braid is then formed on the mandrel and second, and subsequent layers are formed over said first layer. The mandrel', which may be of circular or other cross section, may be moved through the braid-forming area as braiding takes place to build up a continuous hollow braid structure.

The method also includes the step of laying down all the layers of the multi - layer braid structure in one pass of the braiding machine.

The invention further encompasses a method of making a braid structure having a plurality of layers, each layer being constituted by interbraided strands of material with at least one strand of each layer interlocking with strands of another layer and includes, in respect of each layer, the steps of feeding a plurality of strands of material from a plurality of package carriers to a braidforming area and causing or allowing those strands to be interbraided by moving a respective set of package carriers along a predetermined path in respect of each layer, and feeding strands in respect of each layer to the braid forming area so that the layers are overlaid one on another, wherein the strands fed to the braid forming area for each layer include strands from a plurality of static package carriers, and the strands from the sets of static and movable package carriers for each layer are interbraided by causing or allowing the movable package carriers to traverse a predetermined serpentine path, and each serpentine path is arranged so that at least one movable package carrier of each set carries the strand of material from its respective layer into another layer to interlock with strands of said another layer.

In one embodiment said at least one movable package carrier returns the strand to its originating layer. In smother embodiment the serpentine path of the movable package carriers of an intermediate layer 5 may move from said intermediate layer to carry a strand of material from that layer into both contiguous layers and returns to the said intermediate layer to interlock the strands of the intermediate layer with each contiguous layer.

Where the braid structure to be manufactured includes a plurality of intermediate layers, a movable package carrier may traverse from one serpentine path to a next adjacent serpentine path to carry a movable strand from a layer associated with the package carrier into layers beyond the immediate contiguous layers and to return the package carrier to the original serpentine path thereby interlocking the layers through which the strand from the movable package carrier has passed. -13The braid structure may be of hollow form and may be formed over a mandrel, which can be positioned at the braid-forming area. Typically, the mandrel moves through the braid-forming area as braiding takes place to build up a continuous hollow braid structure thereon with all the layers of the braid structure being interlocked.

The invention further provides a method of making a braid structure having a plurality of layers of stranded material, each layer being constituted by interbraided strands of material, in which a plurality of strands of material are fed to a braid forming area from a plurality of package carriers and those strands are cuased or allowed to be interbraided by moving package carriers along paths therefor arranged on the internal surface therefor of a tubular braiding machine, wherein a plurality of static strands of material are fed to the braid-forming area from a first set of static package carriers whereby the said static strands are interbraided with further strands from a corresponding set of movable package carriers, each movable package carrier traversing a predetermined first serpentine path to interbraid the strands of the first set of movable package carrier with the strands from the first set of static package carriers to form a first braided layer; feeding simultaneously to the braid-forming area, strands from a second set of static package carriers for - 14 interbraiding with strands from a corresponding second set of movable package carriers, each movable package carrier of the second set traversing a predetermined second serpentine path which interbraids the strands from the second set of movable package carriers with the strands from the second set of static package carriers, to form a second braided layer on the first braided layer and arranging each serpentine path so that at least one movable package carrier of each set of movable package carriers carries a strand of material from its respective layer into another layer to interlock with that other layer before returning the strand to its own originating layer so that at least one strand of each layer interlocks with or passes through strands of a contiguous layer.

The braid forming area is preferably situated at the longitudinal axis of the tubular braiding machine and, as the braid structure is formed it is moved through the tubular braiding machine along the longitudinal axis thereof.

The tubular bed of the tubular braiding machine may be of circular cross-section or may be ellipsoidal or any other closed or multisided shape.

The invention also includes a braiding machine for forming a multi-layer hollow braid which machine comprises:means . for supplying groups of strands of material to a braiding station to form a layer of braid at said station associated with each group of strands and means, effective during braiding, to cause or allow a strand from one layer of braid to pass into or through a next adjacent layer to form an interlock between said layers.

The invention further includes a machine for forming a multi-layer hollow braid in accordance with the invention, the braid structure having a plurality of layers each constituted by interbraided strands of material with at least one strand of each layer interlocking with the strands of a contiguous layer, which machine comprises a hollow tubular member, two apertured end plates securing the hollow cylindrical member between them, a plurality of serpentine paths circumferentially formed on the inner surface of the tubular member, a plurality of intermeshing horn gears, a plurality of movable package carriers, each arranged for movement over a serpentine path in a sequence predetermined by rotation of the horngears, and changeover track means effective between adjacent serpentine paths for the movement of a movable package carrier from one circumferential serpentine path into said adjacent serpentine path.

This movement preferably occurs at least once during a single passage of the package carrier around the tubular member.

The machine may include a serpentine path disposed adjacent each end plate and an intermediate serpentine path in which a movable package carrier in the intermediate path is transferred by the horngears to travel into the serpentine path of each contiguous - 17 serpentine path at least once during a single passage of the package carrier around the tubular member.

The tubular member may be circular, ellipsoidal or multi-faceted in cross-section.

The machine may further include a plurality of intermediate serpentine paths in which a movable package carrier in at least one of the intermediate paths is transferred by homgears to travel into a plurality of said serpentine paths during a single passage of the package carrier around the «cylindrical member.

Each sepentine path is defined by a pair of intersecting zig-zag or generally sinusoidal tracks disposed in the base plate in which the part is located. Each pair of tracks between adjacent intersections effectively defines a generally lemon shaped island portion. The movable package carriers are mounted for sliding movement along in the tracks and are driven by the homgears disposed thereunder, the arrangement being such that the array of homgears disposed beneath the serpentine tracks serves to drive the package carrier in contrary directions in each track. Thus, at any one crossover point the horngears will serve to drive a package carrier in a first direction across an intersection and subsequently a second package carrier across the same intersection in an approximately orthogonal direction.

This arrangement is well known in a standard braiding machine and movable package carriers in such a machine are restricted to movement solely in the single track of the serpentine path pair within which it is located. In accordance with the present invention two or more serpentine paths are arranged in juxtaposition to provide an array of island portions extending as columns generally across the direction of movement of package carriers in each track. Thus, all the islands in a first serpentine path would be in register with all the islands of the second and subsequent serpentine paths i.e. to form columns extending substantially normal to the line of the serpentine track. In accordance with the present invention, at intervals between two adjacent paths, islands are modified to define part of a crossover track between the adjacent serpentine paths.

The homgears are arranged under the serpentine paths to provide an array of gears with basically one gear arranged under each island. Thus, while gears along each serpentine path intermesh at the crossover points to effect a changeover point between the intersecting tracks of said path, the gears between adjacent paths also intersect, not only along the path lengths, but laterally along the columns. Thus, at the changeover point between the adjacent paths there is positive drive between the homgears disposed therebeneath and the package carrier can move smoothly between one serpentine path to the next via the crossover tracks which feed from one path into an adjacent path, thus permitting a package carrier to move from one path to an adjacent path and carrying the yam with it, thereby effecting movement of the strand from one layer to a next adjacent layer. It will be appreciated that a variety of different interlocking patterns can be produced between adjacent layers in this way.

The di mensions between each island portion and the dimensions between each crossover point in a given serpentine path remain substantially constant; a pair - 20 of standard adjacent island portions in contiguous serpentine paths may be exchanged for a pair of modified islands which define part of the crossover track between them. Since island portions are readily interchangable it will be appreciated by a man skilled in the art that a large variety of patterns and changeover arrangements are possible.

In a further aspect of the present invention the apparatus comprises a tubular and preferably substantially cylindrical body member adapted to carry about its surface a plurality of intermeshing homgears. Each homgear is in direct meshing relationship with the next homgear in a given path, but homgears within a given path (or row) may intermesh at an angle one with respect to the other.

The internal surface of the cylindrical bedplate may be provided with a plurality of track forming elements or track plate comprising standard track forming elements each of which define the' extremity of a track portion of a serpentine path, each element being curved to correspond with the curvature of the bedplate. External track forming elements may serve to - 21 define either standard elements which in juxtaposition produce a standard serpentine path without crossover points or may be modified to provide a crossover section.

The intermeshing homgears are mounted externally of the cylindrical bedplate. The drive means for the gears may be mounted on one of the end plates. The drive means may include principle driving gears mounted on one of the end plates and disposed at 90° with respect to each other and these may be driven by a single prime mover. Coupling means may be provided between the drive gears on each end plate.

In addition to the movable package carriers described above, fixed or static package carriers may also be provided such that they introduce strands at points on the surface of the cylindrical member. In accordance with one aspect of the present invention, such static package carriers may be arranged to provide a strand of braidable material to ’ the braid area or station of a braiding machine via hollow axles of each of the homgears.

Machines in accordance with the present invention can produce either a collapsed or a hollow form of braided structure. Where a hollow form or structure is produced, the machine may include a mandrel movable longitudinally along the central axis of the cylindrical member. In this case, strands from the movable package carriers may be fed to the movable mandrel to form a braid structure thereupon.

It will be appreciated from the foregoing that the flexibility of the structure in accordance with the present invention permits a large variety of different braid structures to be produced. The invention includes the braiding or interbraiding of different types of strands; laminated braid layers may be formed with an interlocked configuration by providing each principle layer of the braid structure with strands of braidable material of one set of properties and adjacent braid layers being formed of strands of material of different properties, while at the same time allowing a predetermined degree of interbraiding between the layers. - 23 Following is a description by way of example only and with reference to the accompanying drawings of methods of carrying the invention into effect.

In the drawings: Figure 1 is a front view of braiding machine in accordance with the invention and for producing a hollow braid structure.

Figure 2 is a detail of Figure 1 showing the drive arrangement therefor.

Figure 3 is a longitudinal cross-sectional view of the 15 machine showing the lay out of gearing.

Figure 4 is a detail of the internal surface of the machine indicating a general layout of the serpentine tracks.

Figure 5 is a typical intermediate track plate.

Figure 6 is a typical end track plate.

Figure 7 is a side view of Figure 6 indicating the curvature of the plate; and Figure 8 is a schematic diagram showing part of a typical layout of homgears and illustrating the serpentine tracks for enabling the invention to be effective.

The machine illustrated in the drawings comprises a pair of end plates 10, 10' each plate having a substantially circular opening 11, a top edge 12, a bottom edge 13 and pair of side edges 14. Each comer is provided with a chamfered portion 15 which, together with the top edge 12 and side edges 14 defines a generally eight sided periphery for each end plate 10, 10'.

Each end plate 10 is secured to a generally cylindrical bedplate 16 formed of‘a plurality, in the specific example forty eight, of flat elements, each interconnected one to the other, so that each flat element is disposed at an angle of 7.5° to its - 25 neighbour. Each flat element comprises a central bore 18 which receives and retains a shaft bearing 19 of a homgear 20. Each homgear 20 has a peripheral tooth portion 21 which is adapted to a mesh at 22 with the corresponding tooth portion of each adjacent gear in the circumferential array. In this example, each homgear 20 has two orthogonal diametric slots' in the surface thereof which is disposed towards the centre of the machine.

Each shaft bearing 19 carries a drive shaft for driving a respective homgear 20. Each homgear 20 is journalled for rotation about a hollow tube 23 which latter serves to support island plates 27 or 28 (See Figure 4).

A plurality of horngears 20 is arranged about the circumference of bedplate 16 to provide a plurality, in the case of the specific example in the drawings forty eight linear columns of horngears, each column extending longitudinally of the- cylindrical bedplate 16, the arrangement being such that the intermeshing gears within each columm lie within a plane. - 26 Each column comprises five horngears which when considered circumferentially constitute five circumferentially disposed rows of horngears, each row comprising forty eight gears. Each circumferential row corresponds to a serpentine path extending circumferentially of the cylindrical bedplate 16 the arrangement being such that the horngears of the array intermesh one with respect to another. Each homgear in an intermediate row meshes with four other gears, i.e. two gears in its own row and a gear from each adjacent row. Each homgear in an edge row meshes with three adjacent gears, i.e. the two adjacent gears in its own row and the adjacent gear in the next intermediate row. This is best seen from Figure 3 in which horngears 31, 32, 33, 34 and 35 intermesh one with respect to another in a plane and the gears 31, 32, 33, 34 and 35 together constitute one column of the 48.

Referring now to Figure 4, it will be appreciated that each serpentine path comprises a' pair of intersecting tracks. Thus, the first serpentine path 29 comprises generally sinusoidal path tracks 72 and 73. The tracks are defined by outer plate 25 which has a contoured track edge 53 which serves to define the outer edge 53 of track 73. Inner edge 36 of the track is defined by guide plate 27 which is a standard island plate having a generally lemon- shaped configuration. It will be seen that the tracks 73 and 72 intersect at 65 and the arrangement is such that a strand package carrier (not shown) moving in direction of arrow A passes along path 73 and crosses over intersection 65 and is then followed in time by a yam package carrier moving along in the direction of arrow B in the opposite sense. Thus, it would be appreciated that in the standard serpentine path formed solely of island plates 27 the crossovers 64, 65 all lie within the same row. Guide plate 28, however , is an island crossover plate; it has one edge 36 contoured to correspond with edge 36 of island plate 27 while the other edge 37 is contoured to define a crossover 66 together with the intermediate track plate 26 and corresponding island plate 28'. It will be noted that island plate 28' is provided with two crossover edges 37 to provide· systematic crossover along a column. - 28 It will be appreciated that the plates 27, 28 and 28' are selectively interchangeable, together with plates 25, 26 and other variants thereof to enable a complete interlocking matrix or array of interlocks either along columns or between rows to provide interlocks between adjacent layers or alternatively to provide interlocks passing through an intermediate layer to provide the positive interlock on the next adjacent layer.

Four drive units 41, 42, 43 and 44 (Figure 1) are situated in the comers of drive plate 10 and these are coupled together by means of a continuous chain 45. The chain 45 is driven by a suitable prime mover, such for example, an electric or pneumatic motor.

In order to distribute the load on the array of homgears, corresponding drive units 41a, 42a, 43a and 44a are provided on the other end plate 10' of which only one, 43a, is shown in Figure 3. These are interconnected by means of a shaft 46 which serves to ensure that all the drives and homgears are synchronised by providing positive drive at 8 points - 29 through the gear array so that the applied torque on individual gears is reduced.

Each serpentine path track is adapted to contain a plurality of package carriers. Each package carrier has a depending lug which is engaged by slots in each of the homgears and as each of the gears rotates the slolis co-act with the lug to drive the package around the track. The track plates 25, 26, 27 28 and 28' serve to constrain the movement of the carriers to a given track and the carriers will be retained in a given track of that path passing sequentially over crossovers with the other track of the same path. When the package carrier enters a track portion of a serpentine path giving a column crossover to an adjacent serpentine path, crossover will be effected by means of a crossover, such as crossover 66 in Figure 4 to the next adjacent path.

It will be appreciated that the movement of the package carrier can be controlled so as to direct the carrier along one given serpentine path or to transfer it between adjacent paths, depending on the layout of the track plates for any particular design of braid - 30 construction. In use a series of movable package carriers axe mounted on the five serpentine paths or rows of the machine and the strands from each carrier are lead to a central mandrel which extends longitudinally of the axis of the machine. The strands are secured to the mandrel together with the strands from any static package carriers which may extend through tubes 23. Such staticpackage carriers may be located on the island plates.

When all the strands have been secured to the mandrel the drive means is started which serves to rotate the horn gears to cause movement of the movable package carriers along the serpentine paths in the manner described above. The design of the paths is such that braidable strands of material from various carriers move between the layers defined by each path to form an interlocked braid structure. The braid structure so formed thus has multiple layers which constitute a three-dimensional braid having strands passing from layer to layer thus increasing the strength of the structure against delamination. . Since carriers are moving in all five rows of all forty eight columns simultaneously, the braid structure is continuously - 31 laid down as a three dimensional braid with all the layers interlocked.

This is further illustrated in Figure 8 of the accompanying drawings which shows five rows of gears 100, 200, 300, 400 and 500 each row having 48 gears disposed around the circumference of the machine. Corresponding gears in adjacent rows namely, 101, 201, 301, 401 and 501 each together define a column.

Thus, the machine comprises five circumferential rows each containing 48 gears or 48 columns each containing 5 gears, a total of 240 gears in all. In Figure 8 common gears in a row are prefixed by the first digit, common gears within a column are prefixed by the third digit.

Columns of gears may be arranged in sets and in the particular embodiment shown in Figure 8, the columns 101 to 501, 102 to 502, 103 to 503, 104 to 504 constitute a single set. The columm 105 to 505 and so on constitute the next adjacent set. Hence in the specific example of which there are five rows of 48 columns, there are 12 sets of gears in the total array of 240 gears. - 32 In Figure 8, the horngears which rotate in a clockwise direction are indicated by shading and the gears which rotate in a counter clockwise direction are those which have no shading. Thus, each gear will rotate in a contrary direction to its neighbours meshed with it. Slots in the horngears are indicated diagrammatically by circles on the periphery of the gear and it is these slots which at any time are occupied by a movable package carrier.

Turning now to the first column of horngears 101 to 501, if we consider the homgear at R carrying a red strand, we see from the solid small circle that this is positioned at the far left hand position of gear 101 as seen in Figure 8; as 101 rotates the package carrier will be carried generally clockwise through 180° to the crossover point with the next gear 102 in the same row. Gear 102 is rotating in a counter clockwise direction and the package carrier R is thus carried by gear 102 to a crossover point between gears 102 and 202, i.e. the crossover point between adjacent rows within the same column. Continued rotation of gear 102 results in movement of the package carrier substantially clockwise thereabouts to - 33 the crossover point between gears 202 and 203, i.e. in adjacent columns, but in the same row. A crossover takes place as the package carrier is moved by gear 203 through an arc of 180° to a crossover point between gear 203 and 204, i.e. a crossover point between adjacent columns within the same row. Gear 204 rotates clockwise and carries the package carrier through an arc of 90° to a crossover point between gears 204 and 104, i.e. to effect a crossover in the same column but between different rows, where the package carrier is then rotated clockwise about gear 104 through an arc of 90° to a crossover point with gear 105 and the sequence starts once again.

Thus, it will be seen that the strand from the package carrier, starting with gear 101, moves along its row 1 to column 2 and then has crossed over in column 2 from row 1 to row 2; it is then moved along row 2 via gear 203 and back to row 1 via column 4 thus completing an interlock sequence. By following the remainder of the lettered package carriers within Figure 8 it will be seen that the same sequence is repeated but staggered, for each of the rows, thus producing a three dimensional braid structure. - 34 In operation of the machine a mandrel is located substantially centrally of the cylindrical bedplate 16. This mandrel (not shown in the drawings) is moved generally along the longitudinal axis of the machine as the braid is built up. The mandrel may be a rigid mandrel or one that is capable of being collapsed to enable the braid to be released from the mandrel after formation. It will be appreciated by the man skilled in the art that the shape of the mandrel depends on the shape of the product required, although it is normally of a circular cross section.

The braid structure produced in the manner described above may be subsequently impregnated with a matrix material such as thermoplastic or a thermosetting resin to make a durable braided composite structure. In the alternative, the strand material itself may either be impregnated by a matrix binder which may subsequently be activated or may be composed of components of matrix material. Due to the truly three dimensional structure of the resulting braid, the braid exhibits a much enhanced strength against delamination than has been experienced hitherto. - 35 The method and apparatus of the invention has been found to be suitable for the braiding of ceramic fibres such as those of silica, glass and carbon, as well as standard textile fibres including fibres such as KEVLAR.

Claims

1. 5 1 5 second braided layer into a further braided layer, thereby indirectly interlocking the second braided layer between the first and further braided layers.

1. A braid structure comprising a plurality of braided layers of stranded material, characterised in that strands that are braided together to form one braided layer include strands that also cross over at intervals into another braided layer to interlock said one and said another braided layers of the structure.

2. A braid structure as claimed in claim 1, in which the strands cross over at intervals into a second braided layer adjacent to the first braided layer and

3. A braid structure as claimed in claim 1, in which the strands cross over at intervals through a

4. A braid structure as claimed in any preceding

5. A braid structure as claimed in any preceding claim, in which strands that cross over from one layer to another form two intralayer crossovers between each interlayer crossover, an intralayer crossover being a crossing of one strand with another within the same layer to contribute to the braiding of the layer and an interlayer crossover being a crossing of a strand from one layer to another to contribute to the interlocking of the layers. 10

6. A braid structure as claimed in* any preceding claim, in which, in addition to strands that cross over at intervals from said one layer to said another layer, there are strands that are braided together to form said another braided layer including strands that also cross over at intervals into said one braided layer.

7. A braid structure as claimed in any preceding claim, in which a matrix of resin material is dispersed and/or distributed within the interstices of the braid structure.

8. A braid structure as claimed in claim 7, in which the strands include or comprise the resin material.

9. A braid structure as claimed in any preceding claim, in which the braid structure is hollow. - 38 10. A braid structure as claimed in claim 9, in which the braid structure is of a circular or of an irregular cross-section.

10. (70, 71) cross over to said one set of intersecting tracks (72, 73). 10 second braided layer that is adjacent to the first layer to a further set of intersecting tracks associated with a further braided layer, thereby indirectly interlocking the second braided layer between the first and further braided layers. 10 cross back at intervals from the second braided layer into the first braided layer thereby interlocking the first and second braided layers.

11. A method of forming a braid structure comprising a plurality of braided layers, wherein strands braided to form the braided layers are supplied from package carriers which move along a plurality of juxtaposed sets of intersecting serpentine tracks (72, 73 and 70, 71), each set of intersecting tracks being associated with a respective braided layer of the braid structure in that the strands from the carriers moving along each set of intersecting tracks form strands of the respective associated braided layer, and wherein package carriers moving along one set of intersecting tracks (72, 73) and supplying strands forming part of the braided layer associated with said one set of intersecting tracks (72, 73) cross over at intervals to another set of intersecting tracks (70, 71) associated with another braided layer to interlock said one and said another braided layers of the structure.

12. A method as claimed in claim 11, in which package carriers moving along a first set of intersecting tracks (72, 73) and supplying strands forming part of a first braided layer associated with the first set of intersecting tracks (72, 73) cross over at intervals to a second set of intersecting tracks (70, 71) associated - 39 with a second braided layer that is adjacent to the first layer and also cross back at intervals to said first set of intersecting tracks.(72, 73). 13. , in which package carriers crossing over to said another set of intersecting tracks move along said another set of intersecting tracks and supply strands forming part of said another braided layer.

13. A method as claimed in claim 11, in which package carriers moving along a first set of intersecting tracks and supplying strands forming part of a first braided layer associated with the first set of intersecting tracks cross over at intervals through a second set of intersecting tracks associated with a 14. , in which package carriers which cross over at intervals from one set of intersecting tracks to another, move over two intersections within a single set of intersecting tracks between each crossing from one set of intersecting tracks to another. - 40 16. A method as claimed in any one of claims 11 to

14. A method as claimed in any one of claims 1 1 to 15. , in which further strands for the braided layers are supplied from static package carriers.

15. A method as claimed in any one of claims 1 1 to

16. , in which at a crossover point (65, 67) where package carriers moving along said one set of intersecting tracks (72, 73) cross over to said another set of intersecting tracks (70, 71) package carriers moving along said another set of intersecting tracks 17. , in which each set of intersecting tracks comprises a pair of intersecting tracks.

17. A method as claimed in any one of claims 1 1 to

18. A method as claimed in any one of claims 1 1 to

19. A braiding machine for forming a braid structure comprising a plurality of interlocked braided layers, the braiding machine comprising:

20. A braiding machine as claimed in claim 19, in which the tracks for the package carriers are arranged such that package carriers moving along a first set of intersecting tracks cross over at intervals to a second set of intersecting tracks that are adjacent to the first set and also cross back at intervals to the first set of intersecting tracks. 20 a plurality of package carriers for carrying supplies of strands to be braided, a plurality of juxtaposed sets of intersecting serpentine tracks (72, 73 and 70, 71) along which the package carriers are mounted for movement, each set of intersecting tracks being associated with a respective layer to be braided, and drive means for moving the package carriers along the tracks, wherein the arrangement of the serpentine tracks and the package carriers is such that package carriers driven, in use, along one set of intersecting tracks (72, 73) for supplying strands forming part of the layer associated with said one set of intersecting tracks cross over at intervals to another set of intersecting tracks (70, 71) associated with another braided layer to interlock the braided layer associated with said one set of intersecting tracks (72, 73) with the braided layer associated with said another set of intersecting tracks (70, 71). 20 claim, in which the strands that cross over at intervals from said one layer to another layer are further braided to form part of said another layer. - 37

21. A braiding machine as claimed in claim 19, in which the tracks for the package carriers are arranged such that package carriers moving along a first set of intersecting tracks cross over at intervals through a second set of intersecting tracks adjacent to the first set to a further set of intersecting tracks. - 42 10

22. A braiding machine as claimed in any one of claims 19 to 21, in which the tracks for the package carriers are arranged such that package carriers which cross over at intervals from one set of intersecting tracks to another move over two intersections within a single set of intersecting tracks between each crossing from one set of intersecting tracks to another.

23. A braiding machine as claimed in any one of claims 19 to 22, further including static package carriers supplying further strands for the braided layers.

24. A braiding machine as claimed in claim 23, in which the static package carriers are surrounded by tracks for moving package carriers.

25. A braiding machine as claimed in any one of claims 19 to 24, in which the tracks for the package carriers are arranged such that at a crossover point where package carriers moving along said one set of intersecting tracks (72, 73) cross over to said another set of intersecting tracks (70, 71), package carriers moving along said another set of intersecting tracks (70, 71) cross over to said one set of intersecting tracks (72, 73). - 43

26. A braiding machine as claimed in any one of claims 19 to 25, in which the plurality of juxtaposed sets of intersecting tracks extend around a longitudinal axis of the machine with one set of tracks axially displaced from another.

27. A braiding machine as claimed in any one of claims 1 9 to 26, in which the drive means comprises an array of intermeshing horn gears (20), and means for rotating the gears (41 to 45), points of intersection of intersecting tracks (65, 67) and points of4crossover (66) from one set of tracks to another being at positions corresponding to points of meshing of adjacent horn gears. 28. ), each of which separate a first track from a second track of the same intersecting set of tracks between their intersections.

28. A braiding machine as claimed in claim 27 when dependent upon claim 23 or 24, in which the static package carriers are arranged to supply strands of material for braiding via tubes about which horn gears rotate.

29. A braiding machine as claimed in any one of claims 19 to 28, in which the intersecting serpentine tracks are defined by gaps between a plurality of plates (25 to 28) the edges (36, 37, 53) of which define the boundaries of the tracks. - 44

30. A braiding machine as claimed in claim 29, in which the plates (36, 37, 53) include island plates (21,

31. A braiding machine as claimed in any one of claims 19 to 30, in which each set of intersecting tracks comprises a pair of intersecting tracks. 10

32. A braid structure according «to Claim 1 substantially as herein described.

33. A method of forming a braid structure according to Claim 1 1 substantially as herein described with reference to the accompanying drawings.

34. A braiding machine for forming a braid structure according to Claim 19 substantially as herein described with reference to and as shown in the accompanying drawings.