WO1998054393A1

WO1998054393A1 - Cutting heat-shrinkable fabrics

Info

Publication number: WO1998054393A1
Application number: PCT/GB1998/001451
Authority: WO
Inventors: Charles Davies; Ian Clive Drinkwater; Derek Lewis; Ronald Alec Page; Alan George Ryder; Sean Michael Lewington; Martyn David Priddle
Original assignee: Raychem Limited
Priority date: 1997-05-30
Filing date: 1998-05-20
Publication date: 1998-12-03
Also published as: GB9711160D0

Abstract

Fraying of hoop filament loops from cut ends of heat-shrink fabric sheaths is controlled to prevent snagging during placement on hoses or other conduits to provide abrasion protection etc. The hoop filaments nearest the cut ends of the tubular sheaths are retained in the fabric by (a) projecting end portions of the length filaments, preferably formed by cutting and removing one or two hoop filaments, or (b) binder applied to the fabric, preferably in lateral or longitudinal stripes, or (c) fuzzy or tacky gripping materials incorporated in the filaments (pref. length filaments) themselves, or (d) filaments fused together within the fabric near the cut ends.

Description

CUTTING HEAT-SHRINKABLE FABRICS

This invention relates to circumferentially-heat-shrinkable sheaths of woven fabric capable of use on conduits, for example to provide abrasion protection to the conduits, which may be fluid or electrical conduits, or other elongate guiding forms, such as electrical wiring bundles or harnesses, or electrical or optical cables. Mechanical protection of conduits such as hoses etc. is often found to be necessary because it is difficult to provide all of the desired properties in a single material. For example, a hose must in general be impermeable to fluids, flexible and heat-resistant. The preferred materials for providing those properties often have poor abrasion and cut-through resistance.

US-A-5413149 (Bentley Harris) discloses a flexible, kink-resistant shaped fabric product for protecting and/or covering cables, conduits and wiring. The shaped fabric has a wall portion comprising a filament resiliently set in a spiral configuration with respect to the longitudinal axis of the shaped product. The wall portion may also comprise a filament in the form of circumferential hoops substantially conforming in shape and size to the cross-sectional configuration of the shaped product. To achieve the resilient set, thermoplastic filaments are heated to a temperature above their glass transition point and are then cooled to cause recrystalization or "set" of the filaments. The resulting product then has the desired spiral resilient bias. This is stated to be an "elastic memory". Whilst the products disclosed in US 5413149 are satisfactory for many purposes, we have found that it may be difficult to locate the products on the conduit to be protected. In general some fixing means such as a small length of heat-shrinkable tubing will be required at each end of the product.

A further prior art product, known as "Expando", is also disclosed in US-A- 5413149. This product is an open braid that when compressed longitudinally expands radially, and vice versa. It is therefore longitudinally compressed, pushed over a hose to be protected, and then longitudinally stretched. The ends must, however, be secured in position by some additional means. An alternative approach to provision of abrasion resistance and other functions, which makes use of heat-shrinkage of a fabric product, is further improved by cutting the sheaths according to the present invention. It should be noted that, although "heat- shrinkage" makes use of the property of "elastic memory", the resilient set disclosed in US-A-5413149 does not result in a heat-shrinkable sheath. In fact, since it is a spiral configuration that is locked in by the process of setting, the effect of heat on the prior art product would, if anything, result in its radial expansion. In this respect, and in others, the prior art clearly teaches away from the present invention.

The sheaths may be cut to length from a longer feed roll and one possible method of cutting involves use of a hot blade, which welds the filaments together at the cut ends of the sheath to prevent fraying. This is effective for various end uses, but can cause difficulties when cutting tubular sheaths in automated or high-speed environments such as vehicle component production lines, since the cut ends of the sheaths tend to become partially sealed shut, thus hindering subsequent fitting of the sheaths onto pipes or cables etc. to be protected. Cold cutting (i.e. at temperatures below the filament softening or melting temperature) is therefore preferred for many such end uses of the sheaths. This eliminates the undesired end closure effect, but has problems of its own, owing to uncontrolled fraying of the cut fabric, as hereinafter described in more detail.

The present invention addresses these problems by providing a circumferentially- heat-shrinkable sheath of woven fabric, capable of use on a conduit as aforesaid, for example to provide abrasion resistance, wherein the sheath provides a substantially unobscured outer fabric surface and comprises hoop filaments extending substantially circumferentially around the sheath, at least some of which hoop filaments are heat- shrinkable, and length filaments extending substantially along the sheath, which length filaments are preferably dimensionally substantially heat-stable, and wherein the sheath has cut ends formed by cold cutting across the length filaments and the cut ends incorporate retaining means arranged to retain substantially within the fabric at least the uncut hoop filaments thereof nearest to the cut ends, the retaining means being selected from (a) end portions of the length filaments projecting beyond the uncut hoop filament nearest to a cut end to a projecting length greater than the portion of the sheath length occupied by the said nearest hoop filament;

(b) binder material applied to the woven fabric which binder material holds the hoop filaments and length filaments together at least near the cut ends, and which binder material, at least after heat shrinking of the sheath, leaves a majority or substantially all of the outer fabric surface substantially unobscured;

(c) gripping structures and/or materials incorporated in at least some of the filaments (preferably length filaments) prior to weaving of the fabric whereby the length filaments grip the hoop filaments and/or vice-versa; and

(d) filaments heat bonded together within the fabric.

It will be understood that the reference to circumferentially-heat-shrinkable sheaths does not necessarily limit the invention to tubular sheaths of substantially circular cross- section. Sheaths of square, triangular, hexagonal, or any other desired tubular cross- section, whether woven as tubes or formed by wrapping around and fastening a fabric originally woven as a sheet, may be included, provided that they are heat-shrinkable in the direction of the perimeter so as to narrow the tube, thus enabling them to contract around and grip the conduits on which they are used. The requirement that the sheath provides a substantially unobscured outer fabric surface will be understood as excluding sealed heat- shrinkable fabrics whose external surface is covered with a layer of polymeric material of at least 0.03 mm thickness, as described for example in EP-A-0117026 (RK176), but may include fabrics with coatings from which at least parts of the filaments project to perform their abrasion-resisting contact or other function.

The hoop filaments extend substantially circumferentially around the sheath, as distinct from the helical filaments of a braid, which extend very noticeably along the sheath as well as around it. The length filaments of the fabric according to the present invention extend substantially along the sheath, preferably substantially parallel with the sheath tubular axis, although a certain amount of helical curvature of these length filaments may be tolerable in practice and is to be understood as included within the expression "substantially along the sheath". It is generally preferred, though not essential, that the hoop filaments are provided by the weft of the fabric and the length filaments are provided by the warp of the fabric.

When the binder material (b) is used as the retaining means according to the present invention, it is applied so as to leave the outer fabric surface substantially unobscured, either by applying the binder to restricted areas of the fabric, leaving the remainder of the outer fabric surface to perform its abrasion-resisting or other function, or by applying the binder in such a way that any quantities thereof on the outermost surfaces of the fabric have a negligible or acceptable effect on the abrasion-resisting or other function. It is preferred to apply the binder in such manner and in such quantities that the fabric texture remains substantially completely visible and thus unobscured before heat shrinking of the sheath, but it would be possible to apply heavier coatings of binders which, upon heat-shrinking of the sheath, flow and penetrate further into the fabric so as to leave the fabric texture sufficiently unobscured after heat-shrinking to perform its abrasion-resisting or other function.

In one embodiment of the invention, the weft-retaining projecting end portions (a) of the length filaments are formed by deliberate cutting and preferably deliberate removal of portions of at least one, preferably up to two, hoop filaments originally closest to the cut end of the sheath. Since the hoop filaments may not necessarily lie exactly at right angles to the longitudinal sheath axis, it is possible that a transverse cutting operation may sever one or more of the hoop filaments before or simultaneously with the deliberate cutting and removal of one or more hoop filaments. The deliberate cutting might therefore include cutting fractions of a hoop filament in some cases. Removal of cut portions of up to three, preferably up to two hoop filaments from the reasonably closely woven fabrics described hereinafter has been found to produce projecting end portions of the length filaments which are both attractive in appearance and capable of retaining the next-closest hoop filament in the fabric in use. The cut hoop filament portions could be left in place, but would tend to come out during handling, which may be undesirable, even though snagging of uncut loops would still be avoided.

Such retention of the hoop filaments closest to the cut ends of the sheaths is desired in all forms of the present invention to reduce the risk of fraying loops or ends of hoop filaments obstructing the insertion of the conduits to be protected into the sheaths on the aforementioned vehicle component production lines or in other automated or high-speed environments. This retaining fringe of projecting end portions (a) may be achieved by cutting the sheaths in several ways, for example by angled cutting at either edge of a flattened sheath or by cutting in a direction parallel with the length filaments, in either case preferably simultaneously with the main transverse cut as hereinafter described. Alternative patterns of cutting include castellated, wavy, or preferably zig-zag cuts, and a particularly preferred pattern involves cutting across the length filaments at a slight angle to the normal, preferably less than 20 degrees, more preferably within the range from 5 degrees to 15 degrees. As will be explained hereinafter, this angled cutting can be used to retain the hoop filaments within the fabric while simplifying the cutting operation and equipment. Punch cutting involving impact of a blade edge on a substrate supporting the fabric may be used, but it has been found that shear cutting is surprisingly effective and reliable in the present context, even for high speeds and long production runs involving thousands of cuts.

In especially preferred forms of the invention using the binder material (b) as the weft-retaining means, the binder is applied in a fluid state to the fabric (preferably to the outer surface of the fabric) at a temperature below the fabric threshold shrinkage temperature (that is the temperature at which shrinkage begins), preferably in the form of an aqueous latex, more preferably an ethylene/ vinyl acetate copolymer latex. The binder coatings could if desired be applied to the inner surface of the tubular sheath, but application to the outer surface will usually be more convenient in practice. Binder materials other than those indicated above may readily be selected, for example waxes, polyolefins, solvent-based materials, for example hair-sprays and the like, and hot-melt adhesives having sufficiently low melting temperature to permit melt coating of the fabric below its threshold shrinkage temperamre. The binder material, and indeed the fabric itself, will preferably be flame-retarded by incorporation of suitable flame-retardant additives, many examples of which are known per se and may be compounded by known methods into the polymers concerned or included in the latex or other liquid coating composition. Any convenient method may be used for applying the binder to the fabric, for example roll or spray coating, and the binder will be solidified after application, for example by allowing it to cool in the case of a melt coating or by evaporation of the liquid carrier such as the water of the preferred latex. The binder will preferably be applied in quantities not greatly exceeding the minimum necessary to retain the hoop filaments in the fabric, which can readily be determined by simple trial and error.

It has been found particularly useful in practice that the binder material (b) is in the form of one or more stripes whose length extends either at least part-way along the sheath or around an end region of the sheath. The exact shape or pattern of application of the binder material is not critical, provided that there is sufficient binder present in the cut end regions of the sheaths to retain the hoop filaments as aforesaid. The preferred stripe coatings of the binder may thus be applied by any convenient technique, preferably to provide two or more stripes extending lengthwise along the sheath, and preferably uniformly spaced around its perimeter. Such stripes may extend continuously along the sheath, thus allowing for cutting of various lengths from a supply roll of the flat or tubular fabric, or the stripes may be applied discontinuously if the cutting regions can be predicted in advance. For predictable cutting positions, the alternative of stripes extending across the sheaths in a direction substantially parallel with the hoop filaments is also possible, cutting on such a stripe thus producing two cut ends each with its own portion of the retaining stripe of binder material. The stripes of binder material could be provided in the form of pressure-sensitive adhesive tapes applied to the inner or outer surface of the fabric, which tapes might be removable after the heat-shrinking operation in use when their hoop-filament-retaining function has served its main purpose and the shrink-tightened fabric will be less likely to fray.

In further alternative embodiments of the invention, the gripping structures and/or materials (c) comprise fuzzy or hairy filaments, tacky filaments, or heat-softenable or heat-tackifiable filaments having a softening or tackifying temperature below the fabric threshold shrinkage temperature. Filaments which are thus capable of gripping one another may thus be woven into the fabric of the sheaths. It may be preferable in many cases for these gripping structures to be provided by the length filaments, leaving the hoop filaments free to perform their heat-shrink function, but gripping structures may alternatively or in addition be provided by the hoop filaments, provided that this does not unacceptably compromise their shrinking ability. It may be preferable in many cases to use only one kind of the gripping filaments incorporating a single one of the aforementioned gripping structures, but there is no reason in principle why combinations of fuzzy, hairy, tacky, softenable, and tackifiable filaments may not be used.

In another alternative embodiment of the invention, the heat-bonded filaments (d) used to retain the hoop filaments may be formed by heat sealing the fabric, preferably only or mainly in its outer surface regions, for suitable time, at suitable temperature and pressure, to bond the filaments together within the fabric, at least in the regions near the cut ends. Suitable times, temperatures, and pressures are readily determined by simple trial and error. The desired filament bonding may be achieved by hot pressing a sheet fabric, or by hot pressing opposed exterior surface regions of a tubular fabric so as to bond filaments together in regions near the fabric surface while avoiding sealing the tube wholly or partially shut. Such undesired end sealing of the tube may be avoided by controlling the surface sealing temperatures, times, and pressures to avoid fusing the interior surface of the fabric filaments. Alternatively, a non-stick sheet or other surface may be provided between the opposed parts of the tube interior, but this will usually be less convenient in practice. Other heat sealing techniques, for example lasers or infrared, may be used according to convenience. The filament bonding is preferably effected only in the regions near the cut ends, and may be done during or after, but preferably before, the cutting operation. It is especially preferred to make surface seals by hot pressing at appropriate positions on the fabric, then to cut through the resulting "sear" marks, thus leaving both cut ends sealed to retain the adjacent hoop filaments.

In a further embodiment of the present invention, the fabric sheath may include means for resisting animal or insect attack, possibly comprising filaments carrying chemical repellents (the preferred flame-retardant additives may have some effect in this connection). Such sheaths may help to overcome a problem which is understood to be unique to Germany, caused by sharp-toothed animals known as pine martens ("mardens" in German) entering the warm engine compartments of parked cars and gnawing on the polymer materials of pipes and cables, thus preventing or interfering with subsequent operation of the vehicle. The abrasion-resisting sheaths without such chemical repellents may also be effective to some degree in resisting such attacks.

The invention also includes a method of making the sheaths hereinbefore described by deliberately cutting the hoop filaments originally nearest the cut ends of the sheath, wherein that cutting is performed by at least two blades acting in unison across the hoop filaments, preferably two blades respectively near opposite edges of the flattened tubular sheath and/or preferably in unison with a blade cutting across the length filaments to sever the sheath, and the deliberately-cut pieces of the hoop filaments are subsequently allowed to fall out or preferably deliberately removed, for example by brushing and/or suction. The cutting of the hoop filaments could of course be performed before or after the main transverse cut which severs the sheath from a supply roll, but it is more efficient in practice to perform the two cutting operations, that is the transverse cut and the deliberate hoop-filament cut, simultaneously using suitably formed blades or suitable combinations of blades.

The invention also includes a method of making fabric sheaths, preferably sheaths as hereinbefore described, wherein sheaths of predetermined length are made by cutting from a longer tubular feedstock thereof in flattened form, and before the cutting operation the feedstock is constrained into partly-open tubular form by means which result in the sheaths remaining partly open after cutting. This setting of the sheaths in partly-open form could for example be achieved by creasing the tubular fabric so as to form an angle in each of its originally flattened sides. Such creasing could be achieved by various arrangements of pinch rollers or pressing devices. Preferably, the constraining operation includes the insertion of a suitably shaped former into the tubular feedstock which then passes over suitable rollers or support surfaces en route to the cutting operation so that the insert is progressively pushed back along the interior of the approaching feedstock, thus progressively opening it as it approaches the cutting operation. The cutting equipment could be arranged in such a way that the cutting operation flattens the feedstock in a sense transverse to its originally flattened form. In other words, the cutting pressure may be applied towards the opposite edges of the originally flattened form (preferably after partial opening as above), thus temporarily flattening it transversely with two new flattened edges midway between the original flattened edges. The resultant creasing effect of the cutting operation, together with the natural resilience of may fabric filaments, may result in at least the ends of the cut sheaths remaimng partly open. With some such opening means, the sheaths may be successfully cut using hot blades or wires without incurring the aforementioned self-sealing problems, but cold cutting is preferred for simplicity and reliability.

The present invention includes the use of the fabric sheaths to provide abrasion resistance to a conduit such as a pipe or flexible hose. The invention may alternatively or additionally be used to provide other forms of protection, such as impact protection and cut-through protection.

Various fabric designs may be employed in the present invention, but it is preferred to use a weave, in particular a plain weave, although other weaves such as a 2/2 twill would be suitable. When using a weave, it is preferred that one set of fibres runs substantially parallel to the length of the sheath, and another set of fibres runs substantially circumferentially of the sheath. If the sheath is to be made continuously in line, it will be desirable (at least when using a narrow fabric loom) for the warp fibres to become the longitudinal fibres of the sheath, and the weft fibres to become the circumferential fibres of the sheath.

By using a fabric for abrasion resistance, it is possible to select as circumferential fibres those that are ideal for the provision of heat-shrink properties, and to select for the longitudinal fibres those which are ideal for provision of abrasion-resistance, for example toughness, resistance to notch propagation, low coefficient of friction, impact resistance, and high temperature performance. Such fibres preferably predominate on an external surface of the sheath. Thus, it is preferred to use high density polyethylene (HDPE) as the circumferential fibres and to use a polyester, such as polyethylene terephthalate, or a nylon in the warp direction. Other suitable circumferential fibres include polyolefins such as low density polyethylene, medium density polyethylene, polypropylene/polyethylene copolymers and fluoropolymers such as polyvinylidene difluoride (PVDF) and ethylene chlorotrifluoroethylene (E-CTFE). Other suitable longitudinal fibres include poly aery onitrile and copolymers thereof, polyphenylene sulphide, cellulose acetate, aromatic polyamides, eg Kevlar, natural fibres and fluoro polymers. The longitudinal abrasion-resistant fibres are preferably able to flatten-out and/or to move under the influence of an adjacent surface. This ability to flatten-out or to move results in that surface causing less damage to the fibres. To this end it is preferred that the longitudinal fibres comprise multi-filament bundles since the filaments within each bundle will be able to move slightly with respect to one another. At present it is preferred to use a co- mingled yarn. A further advantage of multifilament bundles is that cut-through of any filament results in less overall damage to the product. The circumferential, heat- shrinkable, fibres may comprise simple monofilaments.

Various preferred characteristics of the product can be achieved by suitable selection of the weave density, weave design, and weaving process. For example, in order to protect the underlying hose against abrasion or cut-through by sharp objects, it is preferred that a high-density weave, or weave using fibres of high tex value, be used to achieve a high optical coverage. Optical coverage is a well-known term that simply relates the percentage of a plan view of a fabric that is taken up by the fibres themselves, rather than by the interstices between then. The optical coverage, at least after shrinkage is preferably at least 75%, more preferably at least 95%, most preferably substantially 100%.

A second preferred characteristic of a fabric is that it be ribbed, preferably warp ribbed. This means that the fabric will have a surface relief comprising a series of parallel ribs. If the hose is to be protected from abrasion caused by an adjacent surface moving longitudinally with respect to the hose, it will generally be preferable for ribs to be provided that run circumferentially of the hose. Ribbed fabrics are well understood in the weaving art, and warp ribbed fabrics may be constructed by inserting several weft picks in succession into the same shed of an ordinary plain weave. A warp ribbed fabric will in general be woven with a larger number of ends than picks. The weft yarn generally has less twist than the warp yarn and is of heavier linear density, and if it is a single monofilament it will have zero twist. Crimp is another characteristic of the fabric that may be considered. Preferably the crimp is predominantly in the longitudinal direction of the sheath.

Although it will depend on the tex value of the fibres, for most purposes the following weave densities will be suitable. 25-60, particularly 35-45 warp ends per cm, and 3-20, particularly 10-15 weft picks per cm. As mentioned above, the circumferential fibres are preferably monofilaments, and the longitudinal fibres preferably comprise multifilament bundles. More particularly, the longitudinal fibres comprise five to ten fold (particularly about seven fold) bundles, each of the fibres within each bundle again comprising a bundle of very fine filaments. Each of the folds is preferably 10-20 tex, (preferably about 17 tex (tex being the ISO standard for linear density of textile strands and is the weight in grams of 1000 m) and each of those filaments preferably comprises 30-40 very fine filaments. This results in longitudinal fibres of great flexibility and of great ability to flatten out and to move under the abrading effect of an adjacent surface. Damage to any one filament will not of course be catastrophic. The circumferential fibres preferably have a tex value of 5-200, more preferably 20-100, especially 30-60.

One advantage over the cited prior art was stated above to be that the sheath of the invention is easy to secure in place around the hose to be protected. The sheath may be produced in long lengths, cut to length, slid over the hose and then heat-shrunk around the hose to locate it in position. The desired shrinkage ratio for this purpose is from 1.2:1 to 5: 1. The lower value will be suitable where the hose to be protected is straight and where installation at low tolerances is simple. Shrink ratios greater than, say, 5:1 might be difficult to achieve in practice and might result in instability or uneven shrinkage during installation. In general It is preferred a shrink ratio between 1.5:1 and 4: 1. Where the sheath is to be installed around a shaped, non-linear hose it may be desirable to provide some longitudinal shrinkage to avoid wrinkling at the bends in the hose. To this end I can include heat-shrinkable fibres in the longitudinal direction. A longitudinal shrinkage ratio of from 1-20%, more preferably 2-10% , will generally be suitable. Shrinkage when expressed as a ratio means a dimension before shrinkage compared to the dimension after shrinkage. When expressed as a percentage it means the change in a dimension, based on the dimension before change.

Where the sheath is produced in long lengths it will usually require cutting according to the present invention before installation. If hot-blade cutting were involved, it might have ben desirable that the fibres be thermoplastic, and therefore not excessively cross-linked during their manufacture. Some degree of cross-linking of at least some of the fibres of the sheath may be desirable to render the sheath heat-shrinkable. The circumferential fibres, which by virtue of their heat-shrinkability, drive shrinkage of the overall product, are preferably stretched before weaving of the fabric and may be crosslinked before, or preferably after, weaving. They may be cross-linked and then stretched at an elevated temperature and then cooled, or the heating, stretching and cooling may preferably precede the cross-linking. Generally it will be desirable to weave the fabric from heat-shrinkable fibres, although in some circumstances it may be preferred to produce the fabric from heat-stable fibres, and then stretch the fabric. Depending on the temperature performance of the product it may be desirable to cross-link the fibres which are, or are to become, heat-shrinkable before weaving in order that the longitudinal fibres may remain uncross-linked. In this way, the longitudinal fibres can readily be welded at their ends by the hot-knife cutting. Alternatively, for example where higher temperature performance is required, it may be desirable to cross-link the overall fabric (either by cross-linking separately all of the fibres from which it is to be made, or preferably by cross-linking the woven fabric) in order to ensure that all of the fibres retain their integrity at high temperatures.

The sheath may be produced in the form of a tube, or other structure closed in cross-section or it may be woven as a sheet and later formed into a tube either before or during installation. A product formed into a tube during installation, known as a "wraparound sleeve" may be provided with a so-called closure mechanism to hold it in the wrapped around configuration around the hose. If desired the sheath may be provided with some form of visual marking either for identifying it or as a means of determining when it has been subjected to abrasion. For example, a logo of distinguishing colour may be woven into the sheath using for example a Jaquard mechanism on a narrow fabric or other weaving machine. Such a logo may serve to identify the product as that of a particular company, it may be provided for aesthetic reasons, or it may be provided to indicate the nature of the fluid that the underlying hose is carrying. For example, hoses containing dangerous fluids or hoses that will become hot during use may be provided with a marking in red etc. by way of a warning.

Indication of abrasion may be provided as follows. Abrasion-susceptible fibres may be woven into the sheath such that they predominate on the external surface of the sheath that is likely to become abraded. If these abrasion-susceptible fibres are of a distinguishing colour with respect to the remainder of the sheath then the appearance of the sheath will change as it becomes abraded. Full protection of the underlying hose may continue to be provided long after the sacrificial fibres have been destroyed. Thus, periodic inspection will reveal that abrasion has occurred and will alert someone to take suitable action, either to prevent a further abrasion or to replace the now partly worn sheath.

Various other characteristics may be built into the design of the sheath depending on the nature of the hose to be protected. For example, the materials may be chosen to ensure high temperature performance, oil resistance, acid resistance, and resistance to a variety of other chemicals.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying schematic drawings, wherein: -

Figure 1 illustrates a cut fabric sheath having loose ends or loops of hoop filaments formed by fraying at its cut end;

Figure 2 illustrates angled cutting across the hoop filaments at the edges of a sheath; Figure 3 illustrates removal of severed hoop filaments from a cut sheath of Figure 2;

Figure 4 illustrates one form of cutting blade for use in cutting sheaths as illustrated in Figure 2;

Figure 5 illustrates the possibility of multiple cuts severing hoop filaments in a tubular fabric sleeve;

Figure 6 illustrates the possibility of hoop filament cutting as in Figure 5 with simultaneous transverse cutting to sever the sheath;

Figure 7 illustrates the removal of the multiple sections of cut hoop filament provided by cutting as in figure 5 or 6;

Figure 8 illustrates a preferred form of cutting blade having only two transverse blades for cutting hoop filaments;

Figure 9 illustrates striped application of retaining binders in coating or tape form to the fabric sheaths;

Figure 10 illustrates the alternative of striped application of binder across the tubular fabric at a preselected cutting point;

Figure 11 illustrates schematically the use of a progressively sliding former inside the fabric sheath to open it before the cutting operation;

Figures 12A, 12B, and 12C respectively illustrate schematically the aforementioned castellated, wavy, and zig-zag alternative cutting patterns;

Figure 13 illustrates schematically an angled cut at the locking-thread edge of a tubular sheath according to the invention; and

Figure 14 illustrates schematically the preferred straight cut angled across the whole width of the sheath.

Referring to Figure 1 , tubular fabric sheath 10 has frayed at its cut end to produce hanging end 12 and loop 14 of hoop filaments which have become dislodged from the projecting ends 16 of the length filaments after cutting. The trailing hoop filament portions 12 and 14 are likely to interfere with efficient insertion of hoses, cables, or other conduits into the sheath as hereinbefore mentioned. Manual trimming of the hanging hoop filament portions is usually not cost effective in production-line circumstances. Figures 2 to 4 illustrate one approach to solving this problem, wherein the fabric sleeve 20 is cut by a blade 40 as shown in Figure 4 having angled end portions 42, which produced angled cuts 22 across a few of the hoop filaments immediately adjacent to the main transverse cut. As shown in Figure 3, the deliberately-severed hoop filaments 30 may then be removed to leave a projecting fringe 32 of length filaments whose projecting length b is sufficient to retain the remaimng hoop filaments 34 within the fabric by friction.

Figures 5 to 8 illustrate alternative ways of deliberately cutting the hoop filaments. Figure 5 shows a first stage in which several cuts 50 are first made substantially parallel with the length filaments of the fabric sleeves to sever about four hoop fibres, whereafter a transverse cut may be made by a blade 60 as shown in Figure 6 across the previously made cuts 50 of Figure 5. Alternatively, those hoop-fibre-severing cuts may be made simultaneously with the main transverse cut by means of transverse blade segments 62 as shown in Figure 6. Figure 7 illustrates the subsequent removal by suction of the many small severed sections 70 of the deliberately-cut hoop filaments. Figure 8 illustrates a preferred form of cutting blade 80 having only two transverse blade sections 82 near its respective ends for cutting about two hoop filaments on either side of the main cut simultaneously effected by the blade 80 in use.

Figures 9 and 10 illustrate various applications of binder material to retain the hoop filaments near the cut ends of the fabric. Figure 9 shows a continuous stripe 90 of aqueous latex binder as aforesaid applied along the length of the tubular fabric so as to retain the hoop filaments at cut edges anywhere along the tube. In practice, there would normally be at least one, preferably at least two or three, other such stripes so as to retain the hoop filaments at sufficient points around the circumference of the tube. The alternative possibility of using pressure sensitive adhesive tapes to provide the binder is illustrated by continuous length of pressure-sensitive adhesive tape 92, corresponding to the latex stripe 90, and the shorter stripe 94 illustrating the possibility of discontinuous application of binder at pre-determined cutting points. Such application of binder only at pre-determined cutting points is further illustrated by the transverse stripe of latex binder 100 which has been divided by the sheath-severing cut in Figure 10. The various forms of hairy, tacky, or softenable gripping means incorporated in the filaments as hereinbefore mentioned are not illustrated in the drawings, since their operation, for example by hairy entanglement, or by adherent contact on gentle heating of the fabric before or during or possibly immediately after the cutting operation, will be sufficiently understood by persons familiar with this kind of technology.

Figure 11 shows a supply roll 110 of tubular fabric 112, which is fed towards the cutting operation in flattened form and is then opened by suitably shaped insert 114 whose elongate cross-section 116 (shown in the inset) is retained upright in a sense transverse to the originally flattened plane of the fabric 112 by means of V-shaped rollers 118. Retaining roll 120 engages the fabric just beyond the end of the insert 114 which is closest to the cutting machinery, so as to retain the insert 114 in place as the fabric progressively passes over it towards the cutter. The action of the former together with the V-shaped rollers is sufficient to retain the fabric tube in partially open form as it progresses to and passes beyond the cutting operation.

Figures 12A to 12C show the aforementioned alternative cutting patterns in a manner which is self-explanatory. These patterns may be preferred over that illustrated in Fig. 6, owing to the greater facility with which the Fig.12 patterns may be used with intermeshing shear-cutting blades or blocks bearing the complementary halves of the pattern.

Figure 13 shows, in exaggerated scale for clarity, a blade having an angled portion 130 severing one of the hoop filaments 132, the severed portion of which can be removed from the cut ends of the length filaments 134 left by the straight portion 136 of the blade. A small portion 138 of the cut hoop filament is retained by the locking catch thread 139 which closes the tubular sheath along its edge. The next adjacent hoop filament 133 is shown as uncut and will be retained in the fabric by the projecting ends of the length filaments 134 remaining after the cut hoop filament portion 132 has been removed. In Figure 14, a fabric sheath similar to that of Fig.13 is shown being cut across by a straight blade 140 at an angle α to the normal (exaggerated for clarity). The resulting cut hoop filament portions 132 can thereafter be removed and the adjacent uncut hoop filament 143 will be retained in the fabric in a manner similar to that described for Fig.13. On the opposite side of the cut, the severed portions 144 of the hoop filaments are held by the locking catch thread 146 and so will remain in the cut sheath. While their cut ends may become disclodged to project somewhat from the cut end of the sheath, these will not cause snagging problems to the extent which could result from a projecting closed loop of hoop filament. The adjacent uncut hoop filament 145, however, is held over a majority of the fabric width by a sufficient length of the projecting cut ends of the length filaments 148 to resist dislodgement, thus avoiding formation of a potentially snagging loose loop. It has been determined that a cutting angle α of less than 20 degrees is preferable to avoid unsightly degrees of belling or flaring in the longer portion of the sleeve when it is shrunk around conduits in use. Cutting angles within the range from 5 to 15 degrees are especially preferred, the lower angles possibly being more desirable at lower sheath diameters. In general, cutting angles within this range, especially 5 to 10 degrees, tend to produce an advantageous balance of "fluffiness" and resistance to flaring. In all aspects of the invention, a degree of "fluffiness", produced by the controlled fraying of the cut ends, imparts a pleasant feel to the product, enhancing operator acceptance during installation on conduits, and can be unexpectedly attractive in appearance. It will be understood that the successive cuts, across the length filaments of a length of the sheath fabric fed from a supply roll, are preferably made parallel with one another, so that the successive severed sheaths have a parallelogram flattened shape. However, the cuts may be made alternately at reverse angles, for example one cut at +20 degrees to the normal, the next at -20 degrees to the normal, and so on, so that the severed sheaths have a trapezoidal flattened shape.

A further preferred coating material (b) for the present invention may be crosslinkable after application to the fabric. For example, a 52% solids self-crosslinking dispersion of a copolymer of vinyl acetate and ethylene (Vinnapas EN133 Trade Mark from Wacker) may be dip coated onto the fabric, squeezed to remove excess, and dried at 120°C for 5 minutes.

Claims

1. A circumferentially -heat-shrinkable sheath of woven fabric, capable of use on a conduit, wherein the sheath (at least when shrunk on the conduit) provides a substantially unobscured outer fabric surface and comprises hoop filaments extending substantially circumferentially around the sheath, at least some of which hoop filaments are heat- shrinkable, and length filaments extending substantially along the sheath,

and wherein the sheath has cut ends formed by cold cutting across the length filaments and the cut ends incorporate retaining means arranged to retain substantially within the fabric at least the uncut hoop filaments thereof nearest to the cut ends, the retaining means being selected from

(a) end portions of the length filaments projecting beyond the uncut hoop filament nearest to a cut end to a projecting length greater than the portion of the sheath length occupied by the said nearest hoop filament;

(c) gripping structures and/or materials incorporated in at least some of the filaments (preferably length filaments) prior to weaving of the fabric, whereby the length filaments grip the hoop filaments and/or vice-versa; and

(d) filaments heat bonded together within the fabric.

2. A sheath according to claim 1, wherein the projecting end portions (a) of the length filaments have been formed by deliberate cutting (and preferably removal) of portions of at least one, preferably up to two, hoop filaments originally closest to the cut end of the sheath.

3. A sheath according to claim 1 or 2, wherein the sheath has been either

(i) cut across the length filaments at an angle to the normal less than 20 degrees, preferably within the range from 5 to 15 degrees; or (ii) cut in a zig-zag pattern across the length filaments.

4. A fabric sheath according to any preceding claim, wherein the binder material (b) has been applied in a fluid state to the fabric (preferably to the outer surface of the fabric) at a temperature below the fabric threshold shrinkage temperature, preferably in the form of an aqueous latex, more preferably a ethylene/ vinylacetate copolymer latex.

5. A sheath according to any preceding claim, wherein the binder material (b) is in the form of one or more stripes whose length extends at least part-way along the sheath, or at least part- way around an end region of the sheath.

6. A sheath according to claim 5, wherein the binder material is in the form of a pressure-sensitive adhesive tape.

7. A sheath according to any preceding claim, wherein the gripping structures and/or materials (c) comprise fuzzy or hairy filaments, tacky filaments or heat-softenable or heat- tackifiable filaments having a softening or tackifying temperature below the fabric threshold shrinkage temperature.

8. A sheath according to any preceding claim, wherein the heat-bonded filaments (d) are provided by hot pressing opposite exterior surfaces of a tubular fabric sheath using temperatures, pressures, and times selected to bond the filaments within the fabric without sealing the tabular ends wholly or partially shut.

9. A fabric sheath, preferably according to any of the preceding claims, for use in providing abrasion resistance to a conduit, wherein the fabric is capable of resisting animal or insect attack, preferably comprising filaments carrying chemical repellents.

10. A method of making a sheath according to claim 3, wherein the said cutting of hoop filaments is performed by a single substantially straight blade acting across the hoop filaments or by a combination of such a blades or blade portion acting in unison with a blade or blade portion cutting substantially straight across the length filaments to sever the sheath, preferably followed by removal of any unsecured cut pieces of the hoop filaments, preferably by brushing and/or suction.

11. A method of making fabric sheaths, preferably sheaths according to any of claims 1 to 9, for use in providing abrasion resistance to a conduit, wherein sheaths of predetermined length are made by cutting from a longer tabular feedstock thereof in flattened form and before the cutting operation the feedstock is constrained into partly- open tabular form by means which result in the sheaths remaining partly open after cutting.

12. The use of a heat-shrinkable fabric sheath according to any of claims 1 to 9 to provide abrasion resistance to a conduit.

13. The use according to claim 12, in which the conduit comprises a flexible hose.

14. The use according to claim 12 or 13, or a sheath according to any of claims 1 to 9 in which the fabric after shrinkage has an optical coverage of at least 75 % .

15. The use according to any of claims 12 to 14, or a sheath according to any of claims 1 to 9, in which the sheath has a circumferential shrinkage ratio of from 1.5:1 to 4:1.

16. The use according to any of claims 12 to 15, or a sheath according to any of claims 1 to 8, in which the sheath has a longitadinal shrinkage ratio of from 1 to 20%.

17. The use according to any of claims 12 to 16, or a sheath according to any of claims 1 to 9, in which the fabric has a crimp that is predominantly in the longitadinal direction of the sheath.

18. The use according to any of claims 12 to 17, or a sheath according to any of claims 1 to 9, in which the fabric is ribbed, having its ribs running substantially circumferentially of the sheath.

19. The use according to any of claims 12 to 18, or a sheath according to any of claims 1 to 9, in which the fabric is a weave having its warp in the longitadinal direction of the sheath.

20. The use according to any of claims 12 to 19, or a sheath according to any of claims 1 to 9, in which the longitadinal fibres comprise co-mingled yarn.

21. The use according to any of claims 12 to 20, or a sheath according to any of claims 1 to 9, in which the circumferential fibres comprise monofilaments.

22. The use according to any of claims 12 to 21, or a sheath according to any of claims 1 to 9, in which the fabric comprises a weave having 25-60 warp ends per cm.

23. The use according to any of claims 12 to 22, or a sheath according to any of claims 1 to 9, in which the fabric comprises a weave having from 3-20 weft picks per cm.

24. The use according to any of claims 12 to 23, or a sheath according to any of claims 1 to 9, in which fibres which predominate on an external surface of the sheath comprise a polyester or a nylon.

25. The use according to any of claims 12 to 24, or a sheath according to any of claims 1 to 9, in which the sheath is heat-shrinkable by virtue of heat-shrinkable polyethylene fibres thereof.