WO2014030018A1

WO2014030018A1 - Reinforcing fabric

Info

Publication number: WO2014030018A1
Application number: PCT/GB2013/052238
Authority: WO
Inventors: David Peter TOUGH
Original assignee: Scott & Fyfe Limited
Priority date: 2012-08-23
Filing date: 2013-08-23
Publication date: 2014-02-27
Also published as: GB201215043D0

Abstract

A reinforcing fabric includes at least two sets of inlaid yarns (82, 84) formed of a relatively strong material, such as glass, interlinked with knitted yarn made of a more conformable material, such as aramid. The inlaid yarns follow paths through the fabric that extend to one and then another side of an axis that is generally parallel to a machine direction of the fabric. The inlay yarns contribute to the strength of the fabric and the knitted yarn to its conformability, each factor being adjustable with more independence than known in the prior art. The degree of flexibility in adapting performance characteristics of the reinforcing fabrics allows tailoring to a range of products, in particular pipes, hoses and pressure vessels. In one embodiment, particularly beneficial to glass inlays, changes in direction of the inlaid yarn are accomplished through gradual rotations of successive short inlay segments (87a, 87b, 87c).

Description

REINFORCING FABRIC

This invention relates to a reinforcing fabric. More specifically, it relates to a reinforcing fabric for use in the fabrication of hoses, pipes, other coupling pieces, and the like. It is expected to find particular application in high temperature and high pressure environments, for example in pipes that are to carry hot, pressurised fluids.

Elastomeric and rubber materials are in widespread use, their inherent flexibility associated with a mature processing technology having seen their incorporation in many products. It has long been known that elastomeric or rubber materials can be strengthened by inclusion of a reinforcing fabric. In high-pressure applications such as hose products, such reinforcement is essential to prevent excessive longitudinal and radial expansions when the hoses are subjected to high internal pressures.

Applications for reinforced hoses are becoming increasingly demanding, particularly in the transportation and automotive industries, as exhaust emission targets become more stringent and engine compartment

temperatures increase. Moreover, reinforced hoses are often required to assume convoluted paths, particularly when used in the restricted space of an engine compartment, and, in some instances, couple components having differently-sized inlets and outlets. It is for these reasons that reinforced hoses are often hand fabricated using a mandrel system in order to ensure that the necessary geometric requirements are met.

Two types of reinforcing fabrics are commonly used in the fabrication of reinforced hoses, namely: woven and knitted fabrics. Each type however has its inherent advantages and disadvantages.

A woven material has interleaved warp and weft yarns, which results in a construction that is more resistant to expansion. It can therefore provide the hose with a higher resistance to both radial and longitudinal expansion. On the other hand, the relative stiffness of woven reinforcing fabrics can often cause the hose construction to distort during the fabrication process. It can also make the product less easy to manipulate, with the result that the act of releasing the final hose construction from the mandrel used in fabrication is difficult, sometimes to the extent that the hose may be damaged. The consequent requirement to repair or even to dispose of the hose can prove costly.

The yarns in a knitted material are more mobile and so the use of a knitted reinforcing fabric overcomes some of the distortion and release issues associated with a woven reinforcing fabric. It is more commonly selected therefore for applications in which the form of the hose is expected to change during its manufacture. Conversely however, the lower stiffness of the knitted reinforcing fabric offers less resistance to excessive longitudinal and radial expansions, making rupture more likely.

The selection of a particular type of reinforcing fabric for a particular product application is therefore essentially a compromise between resistance to expansion and conformability. Knitted fabric is widely used as a standard reinforcement for hoses within an automotive engine. Such fabrics are conformable to allow the hoses to be fabricated with specific geometries and, where necessary, to link parts of different diameter. These fabrics are at the same time sufficiently strong to withstand the high pressures and temperatures within the engine

compartment. Increasingly however the standard fabric has been found wanting. The drive to make automotive engines more economical and less damaging to the environment has resulted in engines that burn fuel at a higher temperature. This, combined with the more compact design of the modern engine, has markedly increased the operational temperature and pressure experienced by hoses within. The European Union have set standard targets to be met by new designs of car engine. The Euro 6 standard is expected to be adopted in the near future. Established designs of hoses reinforced with knitted fabrics have been failing the Euro 6 tests. There is therefore a perceived need for a reinforcing fabric that can be incorporated in hose and pipe designs that reduces the degree of compromise required between conformability and stiffness. It is accordingly an object of the present invention to provide a novel reinforcing fabric structure that is highly flexible in its design parameters. In this way, it can be adapted for a variety of applications and, in particular, for use in high temperature and pressure environments such as to be found in automotive engines and the like. According to a first aspect of the invention, there is provided a reinforcing fabric comprising two or more sets of inlaid yarns and a knitted yarn. Each set of inlaid yarns has paths extending to one and then another side of an axis that is generally parallel to a machine direction of the fabric, the paths comprising first and second generally linear regions, with respectively constant positive or constant negative cross-directional components and reversal regions in which orientation of the path with respect to a cross direction of the fabric is reversed. The stitches of the knitted yarn interlink with the inlaid yarns. The "machine" direction of a fabric refers to the direction parallel to the direction of movement followed by the fabric during a machine manufacturing process. As the vast majority of technical textiles are machine-made the terminology is adopted herein, regardless of whether the fabric under consideration has actually been manufactured by machine or otherwise. The "cross direction" is the direction perpendicular to the machine direction. In a woven fabric, machine and cross directions correspond to the warp and weft directions respectively.

A reinforcing fabric in accordance with this invention essentially separates the desired characteristics of strength and conformability such that overall fabric performance is less of a compromise than in the prior art. The inlaid yarns are responsible for the strength of the reinforcing fabric and they are held in place by knitted yarns that offer the potential for good conformability. With this arrangement, the strength of the inlay yarn can be adjusted with minimal effect on the conform ability of the knitted yarn. Conversely, the conformability of the knitted yarn can be adjusted with minimal effect on the strength of the inlay yarn. The benefits of this are considerable. It offers the potential for better-performing fabrics to be manufactured at reduced cost.

This design has an inherent adaptability in design parameters, far exceeding the flexibility afforded by prior art woven or knitted materials. This adaptability enables fabrics to be constructed with properties that are tailored to a particular application.

Ideally, the reversal regions of the inlaid yarn paths comprise at least three short linear inlay sections, each short linear inlay section being oriented at an angle to the previous section such that, overall, a total reversal angle between constant positive and constant negative cross-directional components is described. The angle between adjacent short linear inlay sections is preferably less than 45° and, more preferably, between 2° and 30°. In this manner a total reversal angle of between 90° and 130° may be achieved.

This arrangement avoids sharp bends in the inlay yarn as the cross- directional component is reversed. That is, as the direction in which the, generally stronger, inlay yarn traverses the fabric area is switched. In an alternative arrangement, the inlaid yarns may be laid in an Atlas-type arrangement such that the paths follow a zigzag pattern about the machine direction. The zigzag pattern however includes a single sharp bend, rather than a distribution of the total bend among shallower components. Sharp bends are known to be a source of weakness in some yarn materials, in particular glass, under dynamic loading. A distributed angular arrangement therefore improves the durability of the fabric, particularly if glass is used as an inlay yarn.

The paths followed by each set of inlaid yarns preferably have a repeating unit that is replicated in the machine direction, each unit having forwards and reverse cross directional components. Further, the paths of a first set of the at least two sets of inlaid yarns preferably overlay and are offset in the machine direction from the paths of a second set of inlaid yarns.

In these embodiments, the inlaid yarns, at some point, extend crosswise at an angle to the axis parallel to the machine direction. Due to the adaptability of the design of fabric in accordance with this invention, the angle between yarn direction and machine direction can be varied simply by adjusting the stitch length of the knitted yarns that interlink with the inlay. A longer stitch length results in a more acute angle. Preferably, a substantial section of the paths followed by the inlaid yarns makes an angle of between 25° and 45°, and ideally around 35° with the machine direction.

A cylindrical product, such as a hose, when subject to internal pressures is strained both longitudinally and radially. In the industry, the resulting expansions are referred to as axial and hoop expansions respectively.

Consideration has therefore to be given to how best to resist both axial (longitudinal) and hoop (radial) expansions of the finished product. A fabric with the inlaid yarns extending at a 35° angle to the machine direction is ideally oriented to be included in a cylindrical product in order to balance the hoop and axial expansions.

There is also flexibility in the number of sets of inlaid yarns. The fabric may also include a third, fourth, fifth and even a sixth set of inlaid yarns, each of which overlays and is offset in the machine direction from each of the other sets.

Ideally, the knitted yarn comprises a plurality of yarn chains, each chain having a plurality of linked stitches and extending generally parallel to the machine direction.

The yarn material can also be varied. The inlaid yarns, which give the fabric its strength, are preferably of one or more materials selected from glass, aramid, polyester, polypropylene, nylon, rayon, cotton, basalt, metals, PEEK (polyester ester ketones) and dyneema, depending on application requirements. Ideally, the inlaid yarns are glass. Glass is a far stiffer material than aramid and so is clearly better suited for providing the reinforcing fabric with its integrity at elevated temperatures. However, there exists a strong prejudice against the use of glass in reinforcing fabrics that undergo vibration or movement in use. Aramid yarn is almost universally used for high- temperature applications that require conformability. Although glass has many advantages over aramid, it has one fundamental drawback: that it is fragile when subject to a tight bend. A fabric in accordance with this invention however makes use of inlaid yarns that accordingly follow a relatively straight path along much of their length. The weakness associated with the bends is therefore reduced below that known in the prior art. This, along with the ability of a fabric in accordance with this invention to balance hoop and axial expansions, enables glass to be used as an inlay yarn. For the avoidance of doubt, it is noted that the term "yarn" is understood to have its generic meaning of any thread-like component that can be

incorporated in a fabric. That is, in the case of glass it is not to be limited to a specific meaning of a twisted thread, but is taken to encompass other threadlike products such as glass rovings.

The knitted yarn is preferably aramid, which has the required characteristics for stitching. It could however, for specific applications, also be polyester, polypropylene, nylon, rayon, cotton, metals, PEEK (polyester ester ketones) or dyneema.

In preparation for use as a reinforcing fabric, the interlinked yarns may have an elastomeric coating. The elastomeric coating is preferably of silicone or fluorosilicone. The present invention also provides a hose, pipe or pressure vessel comprising a liner about which is wrapped a reinforcing fabric as described above, the fabric being wrapped such that its machine direction extends circumferentially about the liner. Hoses, pipes and pressure vessels generally have a cylindrical geometry and so a design of reinforcing fabric for use in these fields requires consideration of behaviour under both hoop and axial stresses. A reinforcing fabric in accordance with this invention allows ready balancing of stress responses by, for example, changing the orientation of the inlay through the fabric. . Moreover, in many operational fields, these products also require a reinforcing fabric to have both high strength and good conformability, both of which are provided by a fabric in accordance with this invention.

In a further aspect, the present invention provides a method of forming a fabric for use as a reinforcing material, the method comprising the steps of:

(a) presetting a multi-bar warp knitting machine to operate a first guide bar to create an open lap chain or pillar stitch and to operate two or more remaining guide bars to create an inlay pattern that extends to one and then another side of an axis that is generally parallel to a machine direction;

(b) loading a first yarn into a first shaft position that feeds the first guide bar;

(c) loading two or more inlay yarns into shaft positions that feed respective ones of the two or more remaining guide bars; and

(d) operating the knitting machine.

The multi-bar warp knitting machine may also be preset to operate the two or more remaining guidebars to create a plurality of tricot-type and, optionally, pillar-type inlays in the inlay pattern. These inlay types are arranged to align at shallow angles and thereby to effect a total reversal angle, being the sum of all shallow angles, in the inlay pattern. This presetting step may also include presetting the machine to operate the two or more remaining guidebars to create a plurality of Atlas-type inlays, extending between the other inlay types, in a repetitive inlay pattern.

The invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a known woven reinforcing fabric; Figures 2 and 2a are plan views of known knitted reinforcing fabrics, of different structures; Figure 3 is a schematic diagram illustrating the construction of a hose product that incorporates a reinforcing fabric;

Figure 4 is an illustration of a hose product flexing under (a) hoop and (b) radial pressure;

Figure 5 is a schematic representation of a reinforcing fabric in accordance with a first embodiment of this invention;

Figure 6 is a schematic representation of a reinforcing fabric showing a variation of the embodiment shown in Figure 5;

Figure 7 is a schematic representation of a reinforcing fabric in accordance with a further embodiment of this invention; and Figure 8 is a schematic representation of a reinforcing fabric showing a variation of the embodiment shown in Figure 7.

Figure 1 illustrates schematically the structure of a known woven reinforcing fabric 2 suitable for incorporation in a hose, pipe or similar product. The woven fabric 2 comprises a plurality of substantially parallel longitudinal or warp yarns 4 that extend in a machine direction. A plurality of lateral or weft yarns 6 extend in a cross direction and are interleaved with the warp yarns. In the simple example shown, the warp 4 and weft 6 yarns intersect at right angles and the weft yarn 6 passes above and below alternate warp yarns 4. This example is for illustrative purposes only, in order to bring out the essential differences between knitted and woven fabric structures. As is well known in the art, more complex weaving patterns can be used in many, including reinforcing, fabrics. As is well known in the field, the stresses experienced by a cylindrical body, such as a pipe, carrying a high-pressure fluid are not equally distributed. The hoop stress is twice as large as the axial stress. In order to construct a hose efficiently therefore, so that neither hoop nor axial direction is reinforced more that it need be to withstand anticipated operating pressures, hoop

reinforcement should be twice that of the axial reinforcement. For a filament wound hose in which fibres are laid down at a helical angle a to the longitudinal axis of the cylinder, the angle a at which this is achieved is 54.735°. This is known as the critical balanced angle for fibre wound pressure vessels. It corresponds to the situation in which fibres are inclined just enough towards the circumferential direction to make the vessel twice as strong circumferentially as it is axially.

Conversely, fibres that are not held in the hose at the critical balanced angle will, when subject to hoop and axial stresses as the hose is pressurised, try to align along this balanced direction.

A similar consideration applies to a woven fabric that is conformed to a cylindrical geometry. The warp threads are predominantly responsible for the fabric's resistance to expansion. These should therefore not be aligned circumferentially to form a cylindrical hose, but tilted from the circumferential direction by an angle 35.265°.

In a hose construction therefore, a reinforcing woven fabric is aligned such that the warp threads 4 form an angle (a) approximately 55° to the

longitudinal axis of the cylinder. Or, equivalently, the weft threads 6 form an angle approximately 35° from a square cut edge of the hose. Other bias angles are however used, their selection being based on final product performance: whether resistance to axial or hoop expansion is more critical. In Figure 1 , a dashed line 8 indicates the position of the longitudinal axis of the cylindrical hose, with its alignment at angle a to the warp direction. In typical hose applications polyester and nylon yarns are commonly used for the reinforcement fabric. These materials are however only suitable for lower- temperature applications as they are unstable at high temperatures. If it is to be subject to more extreme conditions therefore the woven yarn is most typically aramid. Glass fibre may alternatively be used but, although stiffer than aramid when straight, it is fragile when subject to a tight bend. This limits its application in reinforcement fabrics.

With reference now to Figures 2a and 2b there are shown two exemplary yarn arrangements for knitted structures. Figure 2a shows a structure 10 formed from a warp knitted chain or pillar stitch. Each yarn 12 forms chains of stitches, each stitch 14a being linked to those above 14b and below 14c. In a chain stitch knit, there are no lateral connections between the wales and so a fabric as such is not created, only chains of disconnected wales. It is therefore not normally used alone but in combination with other stitch types to create a more complex fabric.

Such a fabric is shown in Figure 2b. This structure 16 is an example of a prior art knitted fabric that is used to reinforce pipes and the like. Two yarns 17a, 17b are used to form interlinked chain stitches 18 that define a honeycomb structure. This structure 16 includes many open regions 20a, 20b, which are responsible for the fabric having good conformability and linked chain stitches 18 that contribute to its strength. Regardless of the specifics of the knitted pattern, it can be seen that a knitted fabric comprises a plurality of interlinked loops or stitches 14, 20. Each loop 14, 20 is relatively loosely held, which gives a more open structure 10, 16 than a woven fabric 2. This results in increased flexibility and therefore conformability of knitted fabrics 10, 16, which can be advantageous in some applications. This however is at the expense of a reduction in stiffness and therefore resistance to expansion. Aramid, polyester and nylon yarns are all commonly used as knitted reinforcing fabrics. For high-temperature applications aramid is almost universally employed. In preparation for its use as a reinforcement fabric, both woven 2 and knitted 10, 16 fabrics are coated with an elastomer, such as silicone or other resinous material, using known processes like spread, solution or calender coating. The method selected generally depends on the type of silicone used and product application. The elastomer serves to hold the yarns in place, but allows some movement of the composite during the process of its

incorporation in a product structure and subsequent use. Silicone is advantageous for high temperature applications as it maintains its physical properties over a wide temperature range. As is known, the coating process presents its own difficulties. In particular with a woven fabric 2, the generally dense or tight arrangement of the yarns tends to inhibit penetration of the coating material, making complete coverage difficult. To improve the uniformity of the coated product, the woven fabric 2 requires pre-treatment in order to ensure effective adhesion of the elastomeric coating. Such a pre- treatment process can be costly. Depending on the precise knitted construction of the knitted fabric 10, 16, pre-treatment may similarly be required prior to the coating process.

The details of both the coating and associated pre-treatment process are well known to those skilled in the art and so will not be discussed in more detail here.

In the automotive industry, to which this invention particularly, although not exclusively, applies, a current standard reinforcement material is an aramid knit in which chain stitches are formed into a linked honeycomb structure, such as shown in Figure 2b. It is fast becoming apparent however that this material has a number of shortcomings. Although the honeycomb structure is open, which gives the fabric its high conformability, the small chain stitches used to form it are not. The small stitching involves the yarn looping round many corners, each of which stresses the aramid yarn and so represents a potential source of fabric weakness. Moreover the structure is not sufficiently open to allow efficient coating with the elastomer. Effective adhesion of elastomer may only be achieved following a pre-treatment process . Most significantly, in its established commercially-viable form, the fabric fails to perform to the level set by the Euro 6 standard.

As previously noted, applications for hose products are becoming increasingly demanding on hose performance and capabilities. For example, within an engine compartment, a hose may be required to withstand high temperatures and pressures, often conveying hot gases or oil. It may further be required to assume a convoluted path to straddle engine components and sometimes to connect with inlets and outlets of different diameters.

Increasingly specific demands for hoses or coupling pieces means that they are likely to be hand fabricated using a mandrel system so as to ensure that the final hose construction conforms to a particular geometry.

An example of a process by which a hose, or more general coupling piece, is constructed, incorporating the coated woven or knitted material of Figures 1 and 2, will now be described with reference to Figure 3. This figure is a schematic illustration of the structural layers of a hose product that incorporates a reinforcing fabric.

In order to fabricate a hose product 26 such as shown in Figure 3, a liner 28 is first applied to a mandrel or arbor 30. The mandrel 30 shown in Figure 3 is to construct a simple straight hose, but it could be in any of a number of geometries. The liner 28 may be an extruded elastomer tube or a calendered elastomer sheet wrapped around the mandrel to form a tube. The liner 28 provides impermeability, chemical and heat resistance to the interior of the hose and so the particular liner material used will depend to a large degree on application. For example, fluorosilicone may be selected for use in a high- temperature environment because it remains chemically stable over a wide temperature range. An elastomer-coated reinforcing fabric is then wrapped around the liner layer 28. The fabric may be wrapped once, twice or many times around the liner 28, depending on the performance requirements (primarily burst strength) of the finished product. In Figures 3 only first 32 and second 34 layers of the wrapped fabric are shown for clarity. The elastomer coated layers 32, 34 may, for example, be woven or knitted as described above and / or as shown in figures 1 , 2a or 2b. A typical, prior art, material is woven aramid coated with silicone. It is generally preferred that axial and hoop expansions are balanced. This is achieved in a woven fabric if this is cut on a bias such that when the fabric-reinforced layers 32, 34 are applied to the liner 28, the warp yarns form an angle approximately 55° to a longitudinal direction along the liner surface. These layers 32, 34, as stated previously, strengthen the hose.

The mandrel and layers 28, 32, 34 are then wrapped tightly with a binder tape such as, for example, a polyester film tape. The binder tape is very tightly wound so as to exert a pressure on the layered structure beneath. The whole construction is then heated to a high temperature in order to vulcanise the elastomeric materials within. The finished hose product is then removed from the mandrel by means of a blast of pressurised air. If the hose material is stiff however or the mandrel shape is very convoluted then this removal process may not be successful. The hose may therefore need to be prised off mechanically.

Although this process is known to be able to produce high-strength hose products using woven fabrics as the reinforcement layer, additional problems arise from the stiffness of the woven layer. In the first instance, the stiffness can cause unwanted distortions of the assembled layers 28, 32, 34 during the fabrication process. Tensions are developed in the construction during curing and the lack of conformity in the fabric layers 32, 34 renders them liable to fold and break through the bore surface. There is therefore a structural weakness in and increased pressure drop through the final hose construction. In order to avoid this, additional liner layers 28 may be applied to the mandrel 30, to the extent that fabric-layer 32, 34 distortions are contained within the layer arrangement, ensuring that the hose bore remains smooth and unbroken. The process of incorporating additional liner layers 28 into the final hose construction can however be expensive. Secondly, the stiffness of a woven fabric means that if it becomes necessary to prise the finished construction from the mandrel, internal damage may occur. The release of the finished product is therefore also made more difficult.

These problems in the fabrication process do not generally arise if knitted fabrics, with their improved conformability, are used in the reinforcement layer. As has been made clear above however, the reduced resistance of knitted fabrics to hoop and axial expansion renders them unsuitable for many applications.

Passing pressurised fluid through a hose causes the structure to expand in both hoop and axial directions. The effect of such expansions is shown in Figure 4. Figure 4 shows an end of a corner-shaped hose piece 38 secured to a pipe 40 by means of a retainer 42. In Figure 4a the hose 38 is subject to hoop stress. As the hoop stress varies with flow through the hose 38, the result is an expansion and contraction of the hose walls as indicated by arrows 44 and dotted lines 45. It can be seen that movement is concentrated in the vicinity of the retainer 42. The hose material in this region is therefore subject to the greatest stress as radial movement is countered by the retainer 42. The hose is therefore subject to fatigue in this region, ultimately resulting in hose leakage and failure. In Figure 4b the corner-shaped hose 38 is subject to axial stress. The expansion resulting from this stress is however concentrated in the region of the hose bend, as indicated by arrow 46 and dotted lines 47. If the yarn used in a reinforcement material is particularly fragile, for example glass, then the type of expansion shown in Figure 4a is of more concern. Flexing in this manner repeatedly bends and stresses the yarns, causing them to break. If a fabric incorporating fragile yarns is to be contemplated therefore, it is important to minimise hoop expansion.

Figure 5 illustrates, by means of a binding diagram, a first exemplary embodiment of a reinforcing fabric 50 in accordance with this invention. A binding diagram, as is well known in the knitting field, is a symbolic representation of the movements of the guide bars of a knitting machine as it creates the fabric. From this, a skilled operator can recreate the fabric with a suitably configured machine. Each dot 51 represents one needle head at one point in time. Each horizontal row of dots represents a series of needles during one stitch forming process. That is, one row or course of the fabric. The rows of dots from bottom to top represent a succession of stitch-forming processes. The vertical direction on the page thus corresponds with the machine direction and the horizontal axis with the cross direction, as shown by axes 52. As the machine knits a fabric, the guide bars first form the stitch itself by wrapping the yarn around the front of the needle (the overlap) and drawing it through the previously-formed stitch. They may then move the yarn laterally across the back of the needles to form the underlap. In the binding diagram, the path followed by the guide bars is drawn in front of and behind the needles.

Turning now to the detail of the reinforcing fabric 50 of this invention and as represented in the Figure 5 diagram. The fabric 50 comprises a first plurality of inlaid yarns 54a - 54f arranged as a 9 row Atlas-type inlay. An Atlas-type inlay is one in which the yarn moves continually one needle across the course of the fabric for each successive stitch. After moving 9 needles (taking therefore 9 rows) across the course, the lateral movement is reversed and the Atlas-type inlay proceeds at a reverse angle. The result is that the first plurality 54a - 54f of inlaid yarns follow a sharply alternating course generally proceeding along the machine direction of the reinforcing fabric 50. That is, the first inlaid yarns 54a - 54f follow a zigzag path: they proceed upwards (in the figure) at an angle of around 35° clockwise to the machine direction for a length L (9 rows), they then turn sharply (through about 1 10°) to proceed again generally vertically but at an angle of around 35° anticlockwise to the machine direction again for length L, where another turn is executed and the pattern is repeated. That is, a pattern of triangular symmetry of length 2L and internal angle about 1 10° is repeated along the machine direction of the fabric 50 by the first inlaid yarns 54a - 54f. In this Figure 5, for clarity, only six inlaid yarns of the first plurality 54a - 54f of yarns are shown. In reality, the first plurality of yarns extends across the width of the fabric. Only a small selection of such yarns are however illustrated in order to avoid obscuring further details shown in the Figure.

In this particular example, the 35° angle is intended to correspond so far as possible with the critical balanced angle that is used in fibre-wound hoses to equalise hoop and axial extension. As the inlay moves one needle laterally for each row stitched, this angle is achieved by appropriate selection of needle spacing (gauge) and stitch length.

A second plurality (six shown for exemplary purposes) of inlaid yarns 56a - 56f overlays the first plurality of inlaid yarns 54a - 54f extending across the width of the fabric and also arranged as a 9 row Atlas-type inlay. The second inlaid yarns 56a - 56f therefore also form a pattern of triangular symmetry of length 2L (18 rows) and internal angle 1 10° that is repeated to form a zigzag path generally along the machine direction of the reinforcing fabric 50. The pattern followed by the second plurality 56a - 56f of inlaid yarns is offset from that of the first plurality by a distance of 2/3L (6 rows) in the machine direction. A third plurality (six shown again in this example) of 9 row Atlas-type inlaid yarns 58a - 58f overlays the first 54a - 54f and second 56a - 56f plurality of inlaid yarns and follows a similarly zigzag path generally along the machine direction of the reinforcing fabric 50. That is, the third inlaid yarns 58a - 58f also form a pattern of triangular symmetry of length 2L and internal angle 1 10° that is repeated along the machine direction of the fabric. The pattern followed by the third plurality 58a - 58f of inlaid yarns is further offset from that of the second plurality by a distance of 2/3L (6 rows) in the machine direction. The inlaid yarns are interlinked with warp-knitted chain or open lap pillar stitches. Columns 60, 62 of chain stitching are indicated using standard notation in the Figure 5 binding diagram. In this fabric 50 therefore, the chains of stitches 60, 62 extend along the machine direction, each stitch 64 being linked to those above and below (in the figure) it in the column. That is, the stitched columns 60, 62 each form essentially a one-dimensional chain of knitted fabric. Each stitch 64 loops round one or more of the inlaid yarns 54, 56, 58. In this Figure only five columns of chain stitching are illustrated, again for clarity. In practice, the columns are repeated laterally across the width of the fabric. That is, parallel chains of knitted yarn 60, 62 bind and are interlinked with zigzag arrangements of inlaid yarns 54, 56, 58 across the extent of the fabric.

The interlinked fabric structure of inlaid yarns 54, 56, 58 and knitted chains 60, 62 is coated with an elastomer or other resinous material to form a reinforcement fabric for use in a product, such as that shown in Figure 3.

A fabric structure in accordance with this invention exhibits numerous advantages over the prior art. Fundamentally, it replicates the desirable properties of both the prior art woven 2 and knitted 8 fabrics. The reinforcing fabric 50 can exhibit very good hoop stability, that is resistance to radial expansion, when pressurised and good conformability when relaxed. This is achieved by inlaid yarns 54, 56, 58, which mimic the stiffness of a woven fabric, but these are supported not by forming them into a weave, but by interlinking them with conformable parallel chains 60, 62 of stitches. This advantage over the prior art is notable in itself but fabric constructed in accordance with the present invention is also remarkably adaptable. It has an inherent capacity for structural variation that is reflected in the finished fabric performance capabilities. That is, the basic structure is readily adapted to produce different fabric structures, each with a specified set of characteristics.

In the preferred embodiment described above, the inlaid yarns 54, 56, 58 are aligned to form an angle of 35° (or as close to the critically balanced angle as possible) with the machine direction. This means that in assembling the layers of a hose or pipe product, as illustrated in Figure 3, the reinforcement fabric can be simply wrapped round the liner circumferentially in the machine direction. The strong inlaid yarns 54, 56, 58 are aligned such that in the product assembled in this straightforward manner, they are tilted from the circumferential direction by an angle of around 35°. This is the ideal alignment to equalise hoop and axial expansion and so to form a more efficient pressure vessel product.

Another benefit of the reinforcing fabric 50 in accordance with this invention is that its structure has been found to provide excellent adhesion to an elastomer coating. That is, known coating processes have been found to work well without the need for pre-treatment.

Ideally, the inlaid yarns 54, 56, 58 are glass fibre yarns and the chains of knitted stitches 60, 62 are formed from aramid yarn. The weight of yarn can be selected from the standard range depending on application, typically 68 Tex glass fibre and 33 Tex aramid are used. Glass fibre yarns are very stiff when lying straight, as they are along the majority of the length of the fabric in the orientation of the critical balanced angle. Aramid yarn is highly flexible and able to conform readily to define the loops within a knitted structure, without significantly weakening. Both are suitable for the anticipated high- temperature requirements. The preferred elastomeric coating is, as in the prior art, silicone for high-temperature applications because of its physical stability over a wide temperature range. Other materials can of course also be used, depending on application and cost considerations, but this particular combination satisfies a number of requirements for automotive applications as will be described in more detail below.

As stated previously, a standard reinforcement material for automotive applications in which hot fluids have to be carried under pressure through convoluted pipe work pathways is aramid yarn knitted into a honeycomb structure. This has the necessary conformability and strength to satisfy present requirements. Aramid is almost universally used in fabrics for high- temperature applications that require conformability. Glass has not previously been successfully incorporated in a knitted structure.

The present invention however permits the use of glass fibre inlays. Indeed, this is very much the preferred embodiment for many applications. As can be seen in Figure 5, the glass inlay is straight along the majority of its length. Glass fibre is far stiffer than aramid when straight. Each bend however is a potential source of weakness. It is known that glass fibre yarn is susceptible to fracture under dynamic loading conditions, particularly when subject to tight angles. In the inlay structure of the embodiment shown in Figure 5, the glass is subject to a 1 10° bend at point a. By using the glass inlay however its reinforcement strength is increased (in comparison with aramid). By orienting it at 35° to the circumferential direction, hoop and axial expansion are balanced, which means less strain on the material arising from fibre realignment when pressurised. These two effects combine to significantly reduce hoop expansion of a pipe reinforced using such a material. This reduces the flexing of the material under stress. The degree of movement of the type shown in Figure 4 is significantly reduced. The source of weakness at point a is accordingly more protected than in the prior art, with the result that glass becomes a viable reinforcement yarn. Hoop expansion of the finished product can be reduced still further by aligning the inlays at less than 35°, by increasing the stitch length, the increased axial expansion being, as discussed in connection with Figure 4, less damaging to the pipe material.

Glass fibre yarns possess two principal benefits in comparison with aramid. First, they are around eight or more times stiffer, which significantly improves the performance of glass-reinforced fabrics. Secondly, aramid costs 5 to 6 times more than glass for the same weight of material. Although therefore aramid yarns can be strengthened if necessary by increasing the Tex of the material used, this significantly increases the cost. A cheaper, stronger reinforcement fabric can be obtained if using glass inlays in a fabric structure in accordance with the present invention. A stronger fabric clearly allows a given structure to have a higher burst strength or, equivalently, allows the same burst strength but with fewer layers of reinforcing fabric.

In a fabric designed in accordance with this invention, the inlay yarn takes the bulk of any applied load. The stitching yarn primarily functions as a carrier and takes very little load. It is however highly conformable, which allows the fabric to adapt to different shapes. The weaker, more conformable, aramid yarn is therefore a preferred choice for the knitted yarn, despite its increased cost relative to glass fibre.

It has also been found that the coating of silicone, or other elastomer, is also beneficial to the performance of glass inlays 54, 56, 58. The coating is found to add support to the glass inlays 54, 56, 58 and to reduce the strain experienced under dynamic loading conditions, particularly at the weakened bend. The alignment at 35.265° is the theoretical ideal for balancing hoop and axial expansion. Practically however, for many applications, the two expansions are close enough through a range of orientation angles. It is anticipated that the desirable benefits of the reinforcing fabric 50 can be obtained, to a large extent, if the alignment angle is within the range of 25° to 45°. The angle 35° is specified for the embodiments described herein, although it is to be understood that this encompasses a range of angles that, in a number of applications, have a sufficiently equivalent effect.

In order to create the fabric structure represented in Figure 5, a four bar, single needle-bed, 12 gauge warp knitting machine is used. Beams carrying the required endage of glass yarns are loaded into shaft positions 2, 3 and 4. Beams carrying the required endage of aramid yarns are loaded into shaft position 1. Shafts 2, 3 and 4 feed guide bars 2, 3 and 4, which form the Atlas- type inlays both over and in opposition to one another. Shaft 1 feeds guide bar 1 , which creates an open lap chain or pillar stitch that holds the inlays in place. All four guide bars are operated simultaneously to build up the fabric structure row by row, moving from the bottom to the top of Figure 5.

As will be clear to one skilled in the art other warp knitting machines may alternatively be used, provided they are multi-bar to facilitate simultaneous assembly of inlays with the stitching. The machine may therefore alternatively be a double needle bed model or operate on multiple gauges. As noted previously, this design of reinforcement fabric is readily adaptable, enabling physical properties to be tuned by adjustment of various fabrication parameters. The inlay design represented in Figure 5 is created using 3 bars, each of which lays its yarn in a 9 row Atlas-type inlay. That is, each bar moves the yarn laterally one needle position per row over nine rows. The direction of lateral movement is then reversed so the yarn moves back one needle position over nine rows to its original position. This movement continues for a further nine rows before the direction of lateral movement is again reversed, and so on. The three inlay bars are offset such that the inlay patterns overlap and cover the fabric area, as shown in Figure 5. The fourth bar creates the chain stitch that holds the inlays in place.

An alternative embodiment of an inlay design 68 in accordance with this invention is indicated by the representation of Figure 6. In Figure 6, and indeed in Figures 7 and 8, the knitted chain or open lap pillar stitch is not represented. This is for clarity only, to avoid cluttering these diagrams in which the inlay yarns are shown extending across a greater width than in Figure 5. In all embodiments an additional bar creates the chain stitch that holds the inlays in place across the width of the fabric. It is only the inlay design that is varied between the various embodiments shown in the figures and this is seen more clearly in the absence of the chain stitch representation, although the chain stitching will of course be present in the finished fabric. In a fabric constructed according to the representation 68 of Figure 6, four guide bars are used to create four respective inlays 70, 72, 74, 76. Symmetry constrains an Atlas-type inlay to follow a needle pattern in which the number of lateral shifts from the central position, or equivalently number of rows between lateral reversals is a multiple of the number of bars. In the embodiment represented in Figure 6, each inlay is a 12 row Atlas-type inlay.

The number of bars used to form respective inlays is not limited to 3 or 4, despite the fact that this is what is shown in the diagrams. Increasing the number of bars generally results in longer lengths of straight glass inlay between corners. For example, 9 rows in the 3-bar embodiment of Figure 5 compared with 12 rows in the 4-bar embodiment of Figure 6. Reducing the number of corners reduces the potential sources of weakness, making the fabric more stable. On the other hand, increasing the number of bars makes the fabric more complicated and therefore more costly to fabricate. The preferred range is 3 - 6 bars or sets of inlay yarns. It is further noted that an even number of inlay yarns will distort the stitch to a lesser degree. In Figure 5, it can be seen that a bend in one inlay yarn as it loops around a needle position is not balanced by a similar bend in any other yarn. This will result in a distortion of the chain stitch in the vicinity of that bend. In the Figure 6 embodiment on the other hand, each bend in one yarn is balanced by an oppositely-directed bend in another yarn. See, for example, needle position indicated by reference numeral 78. The forces about the chain stitching in the Figure 6 fabric will be more balanced, resulting in less distortion.

Although both embodiments described have Atlas-type inlays, the invention is not restricted to this, although this is expected to be the preferred embodiment for most applications. As an alternative a tricot-type inlay may be used. With this inlay pattern, the yarn is moved laterally one needle for every two rows of fabric knitted. For the same stitch length shown in Figures 5 and 6 therefore, the angle at point a will be more acute for a tricot-type inlay. This will increase resistance to hoop expansion, but at the expense of a significant loss in resistance to axial expansion.

The range of flexibility inherent in a design of fabric in accordance with the present invention is indicated below. Fabric properties such as resistance to hoop expansion, resistance to axial expansion, burst and pulse strength and yarn density and coating ability along with temperature stability can all be tuned by adjusting parameters within the basic framework described. It is likely therefore that the fabric of this invention can be built to specification and adapted to fulfil any of a vast number of requirements for reinforcing structures. This large market makes it commercially very attractive.

In particular, for the structures shown in Figures 5 and 6, it is envisaged that the parameters set out below may all be adjusted in order to tune the fabric properties as described. Chain stitch length / orientation angle

The orientation of the inlays with respect to the machine direction affects the balance between resistance to hoop expansion and resistance to axial expansion. These parameters are balanced when the angle at point a is 35.625°. Decreasing the angle aligns the inlays more with the machine direction resulting in increased resistance to hoop expansion (at the cost of increased axial expansion) in a product reinforced by wrapping the fabric circumferentially. Conversely, increasing the angle increases resistance to axial expansion (at the cost of increased hoop expansion). In order to change the orientation angle, the stitch length of the chain knit is adjusted. If therefore an application demands a reduction in product hoop expansion, then the stitch length is increased in order to reduce the orientation angle. If on the other hand a product requires more resistance to axial expansion, shorter stitches are used. Number of knitting machine bars

One bar of the machine is assigned to knit the binding chain or pillar stitching. Some or all of the remainder may each be used to include an inlay. An even number of inlay bars results in more balanced stress on the knitted chains; an odd number is more likely to pull them into a zigzag formation. Number of rows in the repeat (2L)

This is of course constrained to some degree by the number of inlay bars. The number of rows before a change in lateral direction should be a multiple of the number of bars. This symmetry enables the inlaid yarns to fill the fabric area more evenly. Thus in a fabric according to the Figure 5 representation, 3 inlay bars are used with L = 9, the offset for each inlay accordingly being 6 rows. The repeat however could alternatively be 12 rows, that is a 12 needle, Atlas-type inlay. The offset between inlay patterns would now be 8 rows. Expanding the pattern in this manner reduces the number of corners for each inlaid yarn, which reduces the number of potential failure points. On the other hand the inlaid yarn density is also reduced. The density of the yarn should be within an acceptable range. As the inlaid yarns predominantly bear the load, reducing their density reduces the burst strength of the fabric. On the other hand, increasing the density may make elastomeric coating difficult. Fabrics according to Figures 5 and 6 have densities within the acceptable range. Gauge

This is defined as the number of needles (or stitches) per inch in the cross direction. This value tends to be specific to the machine used to create the fabric. Changing the gauge will therefore require

reconfiguring the machine or using another machine. Nonetheless, the gauge may be adjusted. Increasing the gauge increases the density of the fabric, with the result that it is stronger but may be more difficult to coat. Yarn weight

Varying the yarn weight offers another mechanism by which to adjust the strength of the inlay yarns and hence of the fabric. Yarn weight is measured in Tex (g km^"1). Yarns however are available commercially only at certain Tex values, which limits the scope for adjustment.

Moving to the next Tex level will provide a marked increase in yarn strength, but this may be more than is required and other mechanisms may provide better options for fine-tuning. Of course one or more of these listed adjustments may be combined to achieve the required result. Yarn material

As noted previously, environmental factors play a significant part in determining the yarn material used. Specialised high-temperature materials are required in many applications. This leaves a choice between glass and aramid. Glass fibre is a very stiff yarn material, but fragile when subject to a tight bend under dynamic loading. Aramid is not weakened to anything like the extent of glass by bending, but it is intrinsically less stiff and more expensive.

Figure 7 is a schematic representation of a second exemplary embodiment 80 of a reinforcing fabric in accordance with the invention. Similar to the first 50 exemplary embodiment of the reinforcing fabric, this reinforcing fabric 80 comprises first 82a - 82d, second 84a - 84d and third 86a - 86d sets of inlaid yarns positioned on top of each other and arranged offset from each other in the lengthwise or the machine direction of the reinforcing fabric 80. In this embodiment 80, each group 82a - 82d, 84a - 84d, 86a - 86d of inlaid yarns consists of a number of yarns, extending across the fabric, that are arranged to follow a repeating pattern at distances of 2L in the machine direction. In this embodiment, the repeat pattern is not a triangular zigzag but a more curved variation.

By use of the term "curved", it is meant that the transition angle of the zigzag (Point a in Figure 5) is not so acute. The inlay yarns do not follow a curved path, as such, as they are still constrained to discrete needle positions by the manufacturing process. As in previous embodiments of reinforcing fabrics, it is necessary to reverse the direction of the angle made by the inlay yarn along a straight part of its length with the machine direction. The zigzag

embodiments achieve this reversal with a single angular change (for example 1 10° at Point a). In this embodiment however, the angular adjustment is not localised at one stitch position, but is distributed over several successive stitch positions. The inlay path therefore, strictly, over a region in which alignment is reversed, is a series 87a, 87b, 87c of short, straight linear sections, the orientation of each linear section being rotated a small, shallow angle from adjacent sections. That is, reversal of the angle to the machine direction is achieved by means of multiple small angular adjustments, distributed across successive stitches 87a, 87b, 87c. This, as can be seen by comparing Figure 7 with the embodiments shown in Figures 5 and 6, gives the inlay paths a more generally "curved" appearance. For brevity, the term "curved" or "generally curved" will be used herein, but this is to be understood to mean a succession of short linear regions, each oriented at a shallow rotational angle from a previous linear region. Each shallow angle must be less than 45° although, ideally, the variation is between 2° and 30°.

Ideally, a substantial part of the inlaid yarns 82, 84, 86 of Figure 7 extends along the fabric at around the preferred angle of 35° (shown in Figure 7 by axes 88 defining angle a). The generally curved path is not therefore sinusoidal, but that is not to say that a sinusoidal variation could not be used. Fundamentally, is the apices of the triangles of the inlay patterns of the first 50 embodiment that have been rounded in this 80 embodiment. As in the previous embodiments, the inlaid yarns 82, 84, 86 are interlinked throughout the fabric by parallel columns (not shown) of knitted chain or open lap pillar stitches.

This arrangement of the inlaid yarns 82, 84, 86 is particularly beneficial to embodiments that use glass fibre inlays. As noted previously, each bend in a glass yarn is substantially weaker than a straight yarn. Glass yarns when subject to dynamic or transient loading, for example in a pressurised reinforced hose, are therefore susceptible to fracture at regions with a high degree of bending. The use of generally curved inlays means that any dynamic loads that are applied to the inlaid yarns 82, 84, 86 are distributed over a greater length of yarn by virtue of the gradual angles to which the yarns 82, 84, 86 are subjected. For this reason, the reinforced fabric 80 provides the additional benefit of reducing the likelihood of fractures arising at areas of high stress concentrations, when compared with the reinforcing fabric 50 illustrated in Figure 5.

The fabric represented in Figure 7 is fabricated using the same machine as used for the Figure 5 representation. That is, a four bar, single needle-bed, 12 gauge warp knitting machine, although other machine configurations can alternatively be used. The first guide bar carries aramid yarn and creates an open lap chain or pillar stitch that holds the inlays in place. Guide bars 2, 3 and 4 each form a generally curved glass inlay both over and in opposition to one another. The curved inlay is more complex to create than the 9 row Atlas-type inlay for the fabric of Figure 5. One example of guide bar movement that can create a curved inlay is the following sequence:

2 rows pillar-type inlay 87b

1 needle, 2 row tricot-type inlay 87a

3 row Atlas-type inlay

1 needle, 2 row tricot-type inlay

The inlay is first laid in this sequence with the lateral movement across the needles from left to right, it is then repeated with lateral movement from right to left. This creates a more gradual curve with repeat half-length L of 9 rows, of the type shown in Figure 7.

As with the previous embodiment, the four guide bars are operated simultaneously to build up the fabric structure row by row, moving from the bottom to the top of Figure 7.

It will be appreciated that the section with the Atlas-type inlay is that in which yarn orientation largely determines the balance between hoop and axial expansion. The precise angle, although around 35° is preferred for the reasons given above, can be selected by varying the chain stitch length. Obviously in this embodiment other orientations of yarn are present in the curved region, which will affect the balance. This disadvantage is however acceptable given the marked increase in burst strength that is obtained in a fabric constructed in accordance with this design.

The properties of the generally curved-inlay embodiment can, like those of the first embodiment, be tuned by varying characteristics of the pattern. Chain stitch length, number of bars, repeat length, machine gauge, yarn thickness and material can all be varied as described previously in relation to the Figure 5 embodiment.

Figure 8 is a schematic representation of a variation 90 of the embodiment 80 of Figure 7. In a fabric constructed according to this representation 90 of Figure 6, four guide bars are used to create four respective inlays 92, 94, 96, 98. Like the Figure 6 4-bar embodiment of the triangular inlay, the inlay in this fabric also has a length of 12 rows between lateral reversals. The novel yarn structures described in relation to Figures 5 to 8 are coated with an elastomeric material to form a reinforcing fabric. Such fabrics are incorporated in hoses, connectors and the like using processes such as that described in relation to Figure 3. Such novel hose structures therefore are also part of this invention.

Claims

1. A reinforcing fabric comprising two or more sets of inlaid yarns (54, 82, 56, 84) and a knitted yarn (60, 62), wherein:

each set of inlaid yarns has paths extending to one and then another side of an axis that is generally parallel to a machine direction of the fabric, the paths comprising first and second generally linear regions, with respectively constant positive or constant negative cross- directional components and reversal regions in which orientation of the path with respect to a cross direction of the fabric is reversed; and stitches (64) of the knitted yarn (60, 62) interlink with the inlaid yarns (54, 82, 56, 84).

2. A reinforcing fabric according to claim 1 wherein the reversal regions of the inlaid yarn (82, 84) paths comprise at least three short linear inlay sections, each short linear inlay section being oriented at an angle to the previous section such that, overall, a total reversal angle between constant positive and constant negative cross-directional components is described.

3. A reinforcing fabric according to claim 2 wherein the angle between adjacent short linear inlay sections is less than 45°.

4. A reinforcing fabric according to claim 3 wherein the angle is between 2° and 30°

5. A reinforcing fabric according to any one of claims 2 to 4 wherein the total reversal angle is between 90° and 130°.

6. A reinforcing fabric according to any one of claims 2 to 5 wherein the inlay reversal regions cover 6 rows: 1 needle, 2 row tricot-type inlay (87c), followed by 2 rows pillar-type inlay (87b) followed by 1 needle, 2 row tricot -type inlay (87a).

7. A reinforcing fabric according to any preceding claim wherein the paths followed by each set of inlaid yarns (54, 82, 56, 84) have a repeating unit that is replicated in the machine direction, each unit having forwards and reverse cross directional components, and wherein the paths of a first set (54, 82) of the at least two sets of inlaid yarns overlay and are offset in the machine direction from the paths of a second set (56, 84) of inlaid yarns.

8. A reinforcing fabric according to claim 7 wherein the fabric also

includes a third set (58, 86) of inlaid yarns, the third set (58, 86) overlaying and being offset in the machine direction from both the first (54, 82) and second (56, 84) sets.

9. A reinforcing fabric according to claim 8 wherein the fabric also

includes a fourth set (76, 98) of inlaid yarns, the fourth set (76, 98) overlaying and being offset in the machine direction from the first (70, 92), second (72, 94) and third (74, 96) sets.

10. A reinforcing fabric according to claim 9 wherein the fabric also

includes fifth and / or sixth sets of inlaid yarns, which overlay and are offset in the machine direction from the first to fourth sets.

1 1. A reinforcing fabric according to any preceding claim wherein the

knitted yarn comprises a plurality of yarn chains (60, 62), each chain having a plurality of linked stitches (64) and extending generally parallel to the machine direction.

12. A reinforcing fabric according to any preceding claim wherein the inlaid yarns (54, 82, 56, 84) are of one or more materials selected from glass, aramid, polyester, polypropylene, nylon, rayon, cotton, basalt, metals, PEEK (polyester ester ketones) and dyneema.

13. A reinforcing fabric according to claim 12 wherein the inlaid yarns (54, 82, 56, 84) are glass.

14. A reinforcing fabric according to claim 12 or 13 wherein the knitted yarn (60, 62) is selected from the group comprising: aramid, polyester, polypropylene, nylon, rayon, cotton, metals, PEEK (polyester ester ketones) and dyneema.

15. A reinforcing fabric according to claim 14 wherein the knitted yarn (60, 62) is aramid.

16. A reinforcing fabric according to any preceding claim wherein the first and second generally linear regions of the paths followed by the inlaid yarns (54, 82, 56, 84) make an angle of between 25° and 45° with the machine direction.

17. A reinforcing fabric according to claim 16 wherein the angle is around 35°.

18. A reinforcing fabric according to claim 1 wherein the inlaid yarns (54, 56) are laid in an Atlas-type arrangement such that the paths follow a zigzag pattern about the machine direction.

19. A reinforcing fabric according to any preceding claim in which the

interlinked yarns have an elastomeric coating.

20. A reinforcing fabric according to claim 19 wherein the elastomeric

coating is of silicone.

21. A reinforcing fabric according to claim 19 wherein the elastomeric

coating is of fluorosilicone.

22. A hose, pipe or pressure vessel comprising a liner (28) about which is wrapped a reinforcing fabric in accordance with any preceding claim, the fabric being wrapped such that its machine direction extends circumferentially about the liner (28).

23. A method of forming a fabric for use as a reinforcing material, the method comprising the steps of:

(d) operating the knitting machine.

24. A method according to claim 23 wherein the step of presetting the multi-bar warp knitting machine includes the step of presetting the machine to operate the two or more remaining guidebars to create a plurality of tricot-type inlays in the inlay pattern, such that successive inlay-types are arranged to align at shallow angles and thereby to effect a total reversal angle, being the sum of all shallow angles, in the inlay pattern.

25. A method according to claim 24 wherein the presetting step also includes presetting the machine to operate the two or more remaining guidebars to create a plurality of pillar-type inlays in the inlay pattern, at least one of the pillar-type and various tricot-type inlays being arranged to align successively at the shallow angles.

26. A method according to claim 24 or 25 wherein the presetting step also includes presetting the machine to operate the two or more remaining guidebars to create a plurality of Atlas-type inlays, extending between the other inlay types, in a repetitive inlay pattern.