Braided textile sleeves

Abstract: A braided textile sleeve (12) is formed from flexible yarns such as glass fibers and a rigid filament such as a stainless steel wire. The rigid filament reduces the tendency of a braided sleeve to fray at its ends, and can cause the end portions of the sleeve to taper inwardly, which can enhance the thermal insulation properties of the sleeve. The sleeve may be coated with polymeric material.

Description: Technical field of the Invention This invention relates to a braided textile sleeve of the kind commonly used for mechanical, electrical, flame or thermal protection of elongate objects such as pipes or tubes or, more especially, wire bundles, see EP-A-0 249 333. Such sleeves are generally formed from textile yarns which may comprise staple fibres or continuous filaments. Staple fibres are generally relatively short compared with the length of the yarns formed from them and yarns are generally formed by twisting an elongated fibre bundle to form a coherent yarn. Continuous filaments are generally of such length that they extend substantially throughout the length of yarns formed from them. Little or no twist is needed to develop coherency. The textile yarn material from which braided sleeves are formed is generally selected from the group consisting of ceramic, quartz, glass, carbon and engineering plastics (such as for example nylons, polyamides, polyesters, etc.), and mixtures thereof. The construction will generally be selected according to the requirements of the application to which the sleeve is to be put. The number and diameter of the filaments in each yarn, and the number of yarns in the braid and the number of carriers on the braiding machine are factors which can be varied in order to change the flexibility of, and degree of protection afforded by the sleeve. Discussion of the prior art The use of a braided sleeve has the advantage that its transverse dimension can be varied by the application of longitudinal force or outward radial presssure, this being a unique feature of a braided structure. This feature requires that the yarns from which the sleeve is made are able to move relative to one another in a trellis sense, that is by changing the braid angle. This movement tends to cause the yarns to splay radially of the end of the sleeve so that the sleeve frays, and the requirement that the yarn be able to move relative to one another generally means that it is not possible to hem or otherwise to seal the end of the sleeve to prevent such fraying. It is an object of the invention to overcome or at least minimize the effect of this problem. Summary of the Invention According to this invention, a braided textile sleeve comprises (a) first yarns each comprising relatively flexible filaments; and (b) second yarns comprising at least one relatively rigid filament; the second yarns being distributed evenly around the circumference of the sleeve, and the number of second yarns being from about one third to about two thirds of the number of first and second yarns. The second yarn will preferably comprise less than five, more preferably less than three filaments, especially one filament that is sufficiently rigid to prevent the filaments of the first year splaying radially outwardly. Suitable materials for the filaments of the second yarn include engineering plastics and certain metals. A particularly preferred second yarn consists of a single filament of stainless steel. The sleeve of the invention incorporates from about one third to about two thirds of yarns of a relatively rigid filament such as stainless steel wire. Preferably, the number of second yarns is from about 45% to about 55%, especially about 50%, of the number of first and second yarns. Preferably, the yarns are loaded symmetrically on the braider carriers and this can restrict the proportions of first and second yarns in the sleeve, depending on the number of carriers on the braider that is used to make the sleeve. The precise properties of first and second yarns will be selected according to the yarn construction and of the sleeve made from the yarns and, in particular, on the tendancy of the relatively flexible yarns to fray. In addition to reducing the tendency of a braided sleeve to fray, when the sleeves are formed according to the present invention, the inclusion of relatively rigid filaments has the advantage that it tends to cause the end portions of the sleeve to taper inwardly. In use, this inward taper helps to locate the sleeve on an elongate object, for example by gripping the object. The central portion of the sleeve, between the tapered end portions, tends to stand proud of the object. This has the advantage of providing thermal insulation around the object in addition to that provided by the material of the sleeve itself by forming an air pocket around the object. In carrying out this aspect of the invention, it is preferred that the second yarn be comprised of a relatively stiff material such as a single filament wire of stainless steel having a diameter of between about 0.075 mm and about 0.38 mm with a Young's modulus of between about 68x10⁶ KN/m² and about 276x10⁶ KN/m² and an axial stiffness of about 45 to about 3400 kg wherein axial stiffness is defined as the product of the Young's modulus and the cross-sectional area of the wire. In fabricating the sleeve, the wire or other relatively rigid filament comprising the second yarn is prestressed or set, for example by winding it on the braider bobbin in a relatively tight helix. In th braiding operation, the braided tube is formed with the braided structure tensioned or stretched to its minimum diameter. The helix of the second yarn in the braid when so formed should be a minimum of 1.3 times as long and is preferably greater than two times the length of the helix on the bobbin. The pitch angle of the helix of the second yarn in the braid should be a minimum of two times and is preferably greater than four times the pitch angle of the helix on the bobbin. The differences in length and pitch angles selected are dependent upon the size and stiffness of the second yarn and are determinable by a few field trials. With the braid so formed, when tension is released, the relatively rigid preset yarn has a tendency to return to the the configuration it had on the bobbin helix. The braid will then foreshorten and as a braid naturally does when it is longitudinaly compressed, it expands in diameter. In a section of braided sleeve so formed, a reduction of diameter can be seen at the cut ends. Apparently because the non-wire yarn has no integrity, the forces in the wire tend to cause a radial contraction of the end helices. In another aspect, the invention provides a method of making a braided sleeve, the method comprising the steps of braiding together: (a) first yarns each comprising relatively flexible fibres filaments; and (b) second yarns comprising at least one relatively rigid filament, the number of braider carriers bearing the second yarn being from about one third to about two thirds of the total number of carriers used to form the sleeve, and the second yarns being distributed evenly around the circumference of the sleeve. Preferably, the method includes the use of relatively stiff filaments capable of taking a permanent set, such as a single filament wire preferably having a Young's modulus of between about 68x10⁶ and about 276x10⁶ KN/ m² and an axial stiffness of about 45 to about 3400 kg as the second yarn and prestressing the second yarn in helical form, for example by winding the second yarn in a tight helix on the braider bobbins. ''Tight in this context means in relation to the helix of the wire in the braid. In the braiding operation, the braided tube is formed with the braided structure under tension at its minimum diameter. Preferably the helix of the wire in the braid when so formed is a minimum of 1.3 times and most preferably greater than two times the length of the helix of the wire and the pitch of the helix is at least twice that on the bobbin, the selected amount for a given wire and desired product being determined by a few field trials. Preferably, the method is characterised by the further step of applying a polymer coating to the braided sleeve. The polymer coated may be applied to one or both of the principal surfaces of the sleeve; it may be applied by dip coating or by spraying. Description of preferred embodiments In order that the invention be better understood preferred embodiments of it will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic view illustrating the manufacture of braided sleeves formed according to the present invention; and Figure 2 and 3 are views showing the braided sleeve respectively under tension in the braider and in relaxed form cut to a length suitable for use. Figure 1 shows in schematic form a braider 10 which includes a plurality of bobbins or carriers 11 there being wire and non-wire yarn carriers disposed on the braider in predetermined relationship. In a preferred arrangement, every other carrier is a wire carrier, the wire constituting the relatively rigid component of the braided sleeve. As indicated above, sleeve 12 is braided under tension so that the sleeve is braided at its minimum diameter. Preferably the newly braided sleeve is subjected to a heat treatment by heater means schematically represented at 13. Polymer coating may be applied as a spray as indicated by sprayer 14 or by immersion in a bath, (not shown). After drying the finished sleeve is wound on a take-up reel 15. Figure 2 illustrates the sleeve during braiding with the sleeve under tension. Figure 3 shows a section of the same sleeve cut to desired length, as shown in Figure 3, the sleeve in relaxed state axially compresses. This is believed to be due to the tendency for the relatively rigid yarn to return to the form in which it was previously wound as a helix on the braider carrier bobbin helix. As the braid foreshortens, the diameter increases to about four times the diameter of the tensioned sleeve, except at the ends where the forces in the wire cause a radial contraction of the end helices. EXAMPLE A sleeve was braided using a 96 carrier braider from a yarn which comprises two strands of textured fibrerglass, ETG9.0 sold by Owens Corning, and a relatively rigid yarn of a 0.15 mm diameter hard stainless steel wire having a Young's modulus of about 158x10⁶ KN/m ² and an axial stiffness which was determined to be about 295 kg. The yarns were loaded symmetrically on the braider. The length of the helix of the wire on the bobbin was about 5.7 cm and the length of the helix of the same wire in the braid when under tension was about 16 cm. The ratio of wire to total yarn was 50%. A comparison of the sleeve as braided under tension and in its relaxed foreshortened state can be seen by referring to Figures 2 and 3. The thermal insulation properties of the sleeve were compared with those of a sleeve which did not contain wire, and it was found that the sleeve of the invention had the better performance. It is believed that this results from the ability of the sleeve of the invention to trap a pocket of air around the object to be insulated, in turn because of the radial resilience of the sleeve conferred by the relatively rigid wire component.

Claims: A braided textile sleeve, comprising: (a) first yarns each comprising relatively flexible filaments; and (b) second yarns comprising at least one relatively rigid filament; the second yarns being distributed evenly around the circumference of the sleeve, and the number of second yarns being from about one third to about two thirds the number of first and second yarns, said second yarn being prestressed to a relatively tight helical form, and said sleeve being braided under tension sufficient to elongate the helices of the yarns in the braid by at least 30% during braiding. A braided sleeve as claimed in claim 2, characterised in that second yarn comprises a metallic wire. A braided sleeve as claimed in claim 2, further characterised in that said metallic wire has a Young's modulus of about 68x10⁶ to about 276x10⁶ KN/m² and an axial stiffness of about 45 to about 3400 kg. A braided sleeve as claimed in claim 3, characterised in that tension is sufficient to elongate the helix of the yarns in the braid by at least 100% during braiding. A braided sleeve as claimed in claim 4, characterised in that wire is stainless steel. A braided sleeve as claimed in claim 5, characterised in that wire has a diameter of between about 0.75 mm and 0.38 mm. A braided sleeve as claimed in claim 1, characterised in that the first yarn comprises glass fibers. A braided sleeve as claimed in claim 1, characterised in that a polymer coating is applied to the first and second yarns after braiding. A braided sleeve as claimed in claim 5, characterised in that material of the polymeric coating is thermoplastic. A method of making a braided textile sleeve, comprising the step of braiding together: (a) first yarns each comprising relatively flexible filaments; and (b) second yarns comprising at least one relatively rigid filament, said relatively rigid filament preferably having a Young's modulus of about 68x10⁶ to about 276x10⁶ KN/m² and an axial stiffness of about 45 to about 3400 kg, the number of braider carriers bearing the second yarn being from about one third to about two thirds of the total number of carriers used to form the sleeve, and the second yarns being prestressed to a relatively tight helical form and being distributed evenly around the circumference of the sleeve, said sleeve being braided under tension sufficient to elongate the sleeve by at least 30% during the braiding operation. A method as claimed in claim 10, characterised in that the first yarns comprise glass fibres. A method as claimed in claim 10, characterised in that relatively rigid filament is a metallic wire. A method as claimed in claim 12, characterised in that the metallic wire is a single filament wire having a diameter of about 0.075 mm to 0.38 mm. A method as claimed in claim 10 further characterised by the step of applying heat to the braided sleeve. A method as claimed in claim 10 characterised by the step of applying a polymer coating to the braided sleeve. A method as claimed in claim 15, characterised in that the polymer coating is applied to the external surface of the braided sleeve.

Inventors: CONAGHAN THOMAS B, KITE III JOSEPH S, PIOTROWSKI MICHAEL JOHN, TRESSLAR MARIE C, CONAGHAN, THOMAS B., KITE III, JOSEPH S., PIOTROWSKI, MICHAEL JOHN, TRESSLAR, MARIE C.
Applicants: BENTLEY HARRIS MFG CO, THE BENTLEY-HARRIS MANUFACTURING COMPANY
Application year: 1989
Main classification: F16L59
IPC codes: D04C1, B29C53