FABRIC SLEEVE FOR A RUBBER TUBE

Abstract: A protective fabric sleeve (1) for a rubber tube comprises heat-recoverable interlaced strands forming an elastically deformable tubular structure, the strands comprising at least one monofilament yarn (2) and at least one multifilament yarn (3). Use especially for a coupling in a fluid circuits of a motor vehicle.

Description: Fabric Sleeve for a Rubber Tube The present invention relates to a fabric sleeve for a rubber tube, especially for a rubber coupling fitted in a fluid circuit in a motor vehicle engine. It also relates to a process for manufacturing such a rubber tube surrounded by a fabric sleeve according to the invention. It is known to reinforce rubber tubes, intended to be fitted in fluid circuits, with a fabric mechanical reinforcement embedded in the thickness of the tube. This fabric reinforcement makes it possible to increase the resistance of the tubes to the internal pressure exerted by the fluid. The conventional processes for manufacturing such reinforced tubes mainly comprise the extrusion of a rubber tubular substrate, the winding, overbraiding or overknitting of a fabric fibre on this substrate, and then the extrusion of a new rubber layer in order to embed the fabric reinforcement. Furthermore, it is known to use a mechanical protective sleeve placed around the rubber tube, which sleeve makes it possible to protect the rubber tube from external attack and to improve its abrasion resistance. Such an external protective sleeve is, for example, described in document US 5,366,771. It comprises a woven fabric, which mixes heat-recoverable yarns and heat-stable yarns, the fabric itself being embedded in polymer film. This fabric is manufactured in the form of a sheet and is would around the tube, the longitudinal edges then being fastened to each other in order to form a tubular sleeve around the tube. The object of the present invention is to propose a fabric sleeve which makes it possible, in particular, to simplify the way it is fitted onto a rubber tube and to make it easier to manufacture the rubber tube itself. The fabric sleeve for a rubber tube according to the invention is characterised in that it comprises heat-recoverable interlaced strands forming an elastically deformable tubular structure, the strands comprising at least one monofilament yarn and at least one multifilament yarn. Although this sleeve is tubular, its elastic structure makes it easier to fit onto the rubber tube, this structure allowing it to deform while it is being slipped onto the tube. Furthermore, the heat recovery of the strands allows the design of a sleeve which has a diameter greater than the external diameter of the tube, before recovery of the strands, and consequently is simpler to slip onto the tube. The tubular sleeve according to the invention is therefore perfectly adapted to being slipped onto rubber tubes of varied shape, and especially those having many bends. By virtue of the tubular shape of the protective sleeve and of the use of at least two types of different yarns, one being a monofilament and the other a multifilament, an external sleeve is obtained which allows both mechanical protection against abrasion of the rubber tube and reinforcement of the tube with respect to the internal pressure exerted by the fluids. The monofilament yarn allows the sleeve to be held elastically against the rubber tube, which thus develops a force sufficient to reinforce the tube with respect to the internal pressure. Furthermore, the monofilament yarn holds the multifilament yarn so as to bear on the rubber tube, thus increasing the ability of the multifilament yarn to protect the rubber tube from external attack and from the risk of wear. Apart from the advantages relating to the fitting of the sleeve and to the reinforcement to the rubber tubes, the fabric sleeve according to the invention also makes it possible to dispense with inserting a fabric reinforcement into the mass of rubber forming the tube. The manufacture of the latter is thus greatly simplified. According to a preferred version of the invention, the heat-recovery ratios of the monofilament yarn and of the multifilament yarn are approximately equal. The heat recovery of the fabric sleeve around the tube therefore takes place uniformly over all the strands, thereby avoiding the appearance of wrinkles on the surface of the sleeve, which would reduce its abrasion resistance and facilitate its deterioration. Preferably, the recovery ratios are less than 40%, that is to say the difference in length of a yarn before and after heat recovery remains less than 40% of its initial length. The Applicant has in fact found that, above this threshold value, and unless the diameter of the fabric sleeve is very greatly increased, the heat recovery of the latter may cause the rubber tube to deform and, in particular, may modify its path or restrict its internal diameter. According to an advantageous version of the invention, since the recovery ratios of the monofilament and of the multifilament are not strictly equal, the recovery ratio of the monofilament yarn is slightly greater than the recovery ratio of the multifilament yarn. This provision also prevents the formation of wrinkles on the surface of the fabric sleeve after recovery. This is because the multifilament yarn, being more compressible than the monofilament yarn, can absorb, by being compressed, a slight additional recovery of the sleeve caused by the monofilament yarn beyond its intrinsic recoverability. According to an advantageous version, which provides the fabric sleeve with great flexibility and elasticity making it easier to fit it, the strands are interlaced in the form of a flexible tubular braid, the diameter of the said braid increasing with the longitudinal compression of the said braid. Preferably, the monofilament yarn is made of polyethylene terephthalate having great elasticity and the multifilament yarn is made of a high-tenacity polyamide. This composition of the fabric sleeve is well suited to its double function of reinforcing the tube with respect to the internal pressure and of mechanically protecting this tube. According to another aspect of the invention, a process for manufacturing a rubber tube protected by a fabric sleeve according to the invention is characterised in that is comprises the following steps: - extrusion of a rubber tube; - shaping of the said tube; - fitting the fabric sleeve, the diameter of the sleeve being slightly greater than the diameter of the rubber tube; and - vulcanisation of the tube covered by the fabric sleeve, causing heat recovery of the fabric sleeve. This manufacturing process makes it possible to manufacture the rubber tube by continuous extrusion, unlike the conventional manufacturing processes which require successive extrusions in order to embed a fabric reinforcement in the rubber tube. Furthermore, the sleeve is recovered during the vulcanisation step at elevated temperature and consequently does not require an additional step compared with the conventional processes for manufacturing the rubber tubes. According to a third aspect of the invention, a rubber hose, especially a coupling used in a fluid circuit of an engine, is characterised in that it is formed by a rubber tube covered by a fabric sleeve according to the invention. This rubber hose is thus externally reinforced with a fabric sleeve which perfectly matches its shape and creates no additional thickness, nor puckering, on its surface. Further features and advantages of the invention will also appear in the description below. In the appended drawings, given by way of non-limiting examples: - Figure 1 is a view illustrating a fabric sleeve according to the invention; - Figure 2 is a perspective view of a rubber hose according to the invention; and - Figures 3A, 3B, 3C, 3D and 3E illustrate the manufacturing process according to the invention. The fabric sleeve according to the invention will firstly be described, with reference to Figure 1. This fabric sleeve 1 is suitable for covering and protecting rubber hoses, such as couplings used in fluid circuits in motor vehicles, for example. This fabric sleeve 1 comprises heat-recoverable interlaced strands 2, 3, that is to say exhibiting heat-recoverability. This recoverability of each strand may be measured using a recovery ratio, corresponding to the maximum difference in length of the strand, before and after recovery, with respect to its initial length before heat recovery. Throughout the rest of the description, the recovery ratio corresponds to a recoverability measured in a dry oven at 200°C. The interlaced strands 2, 3 form an elastically deformable tubular structure. In this example, the strands 2, 3 are interlaced in the form of a flexible tubular braid, the diameter of the tubular braid increasing with the longitudinal compression of the braid. Of course, any type of fabric construction forming a tubular sleeve structure which is elastically deformable, diametrically and longitudinally, may be suitable. In particular, the fabric sleeve may be formed from knitted strands, the strands 2, 3 being knitted in the form of a flexible tubular knit, the diameter of the knit increasing with the longitudinal compression of the knit. As well illustrated in Figure 1 , the strands comprise a monofilament yarn 2 and a multifilament yarn 3. The heat-recovery ratios of the monofilament yarn 2 and of the multifilament yarn 3 are approximately equal, and remain less than 40%. Apart from the fact of avoiding deformation of the tube during recovery of the fabric sleeve, keeping the recovery ratio at a significant, but not too high, value prevents the recovery of a shaping tool inserted into the tube, such as a mandrel, from being impeded. Since the recovery ratios of the monofilament yarn 2 and of the multifilament yarn 3 are not equal, it is preferable for the recovery ratio of the monofilament yarn 2 to be slightly greater than the recovery ratio of the multifilament yarn, the latter being less sensitive to the formation of wrinkles since it is slightly compressible. Thus, the recovery ratio of the monofilament yarn 2 is between 1 times and 3 times the recovery ratio of the multifilament yarn 3, and preferably between 1.5 times and 2 times the recovery ratio of the multifilament yarn 3. More generally, the recovery ratio of the monofilament yarn 2 may be between 0.5 times and 4 times the recovery ratio of the multifilament yarn. The recovery ratio of the monofilament yarn 2 is between 3% and 40% and the recovery ratio of the multifilament yarn 3 is between 1% and 20%. More particularly, the recovery ratio of the monofilament yarn 2 is between 5% and 30% and the recovery ratio of the multifilament yarn 3 is between 5% and 15%. In this example, advantageously, the recovery ratio of the monofilament yarn 2 is between 15% and 25% and the recovery ratio of the mulifilament yarn is between 8% and 15%. The proportions of monofilament yarns and of multifilament yams in the fabric sleeve may vary over a wide range since the elasticity of the sleeve remains sufficient to allow easy fitting. In general, the interlaced strands comprise between two monofilament yarns 2 per one multifilament yam 3 and one monofilament yarn 2 per ten multifilament yarns 3, and preferably between one monofilament yarn 2 per one multifilament yarn 3 and one monofilament yarn 2 per four multifilament yarns 3. In this example, the proportion is advantageously one monofilament yarn 2 per three multifilament yarns 3. It could also be one monofilament yarn 2 per two multifilament yarns 3. In general, a monofilament yarn with a very high modulus of elasticity will be present in a lower proportion than a monofilament yarn having a lower modulus, with respect to the total weight of the multifilament yarns employed. The monofilament yarn 2 used for its elasticity will preferably be made of polyethylene terephthalate. It may consist of any polymer having a high modulus of elasticity, such as olefin polymers, polyesters, polyphenylene oxides and sulphides, silicone-carbonate block copolymers, polyketones, polysulphones, polycarbonates, polyamides, epoxy resins and blends of these materials among themselves. The multifilament yarn 3 used for its abrasion resistance will preferably consist of a polyamide, such as a nylon-6 or a nylon-6,6. Any other type of polyamide polymer or of abrasion-resistant polymer may be chosen. This fabric sleeve 1 is fitted onto a rubber tube according to a manufacturing process illustrated in Figures 3A to 3E. As shown in Figure 3A, a rubber tube 4 is extruded by a conventional extrusion technique. Unlike the prior art, in which a fabric support is embedded in the mass of the tube 4, the latter maybe extruded continuously because of the subsequent use of a fabric sleeve 1 according to the invention. Downstream of the extruder 5, a cutting device 6 allows the rubber tube 4 to be cut to a predetermined length. In a shaping step, illustrated in Figure 3B, the rubber tube 4 is preferably slipped onto a tubular mandrel 7. Figure 3C then illustrates the fitting of the fabric sleeve 1 on the tube 4, the diameter of the sleeve 1 being slightly greater than the diameter of the rubber tube 4. The fitting operation is all the easier because this fabric sleeve 1 is elastically deformable, as explained above, allowing it to increase in diameter by longitudinal compression. Next, the rubber tube 4, fitted onto the mandrel 7 and covered by the fabric sleeve 1, is vulcanised as illustrated in Figure 3D, preferably in an autoclave oven 8. This vulcanisation causes heat recovery of the fabric sleeve 1, which thus perfectly matches the external surface of the rubber tube 4. In this method of implementation, the vulcanisation is preferably carried out at a temperature of approximately 180°C. The vulcanisation temperature depends, of course, on the type of rubber used for manufacturing the tube 4. Next, the mandrel 7 is removed, as illustrated in Figure 3E, after the vulcanisation step. As explained above, the recovery ratios of the strands making up the fabric sleeve 1 are not too high so that the heat-recovery force generated by the fabric sleeve 1 does not impede the operation of removing the mandrel. Thus, as illustrated in Figure 2, a rubber hose formed form a rubber tube 4 covered by a protective sleeve 1 is obtained. The characteristics of this protective sleeve 1 allow it to match the external surface of the tube 4 without puckering, nor areas of additional thickness, especially in the bent portions of the hose.

Claims: Claims 1. Fabric sleeve for a rubber tube (4), characterised in that it comprises heat- recoverable interlaced strands (2, 3) forming an elastically deformable tubular structure (1), the strands comprising at least one monofilament yarn (2) and at least one multifilament yarn (3). 2. Sleeve according to Claim 1 , characterised in that the heat-recovery ratios of the monofilament yarn (2) and of the multifilament yarn (3) are approximately equal. 3. Sleeve according to Claim 2, characterised in that the recovery ratios are less than 40%. 4. Sleeve according to one of Claims 1 to 3, characterised in that the recovery ratio of the monofilament yarn (2) is slightly greater than the recovery ratio of the multifilament yarn (3). 5. Sleeve according to one of Claims 1 to 4, characterised in that the recovery ratio of the monofilament yarn (2) is between 1 times and 3 times the recovery ratio of the multifilament yarn (3), and preferably between 1.5 times and 2 times the recovery ratio of the multifilament yarn (3). 6. Sleeve according to one of Claims 1 to 5, characterised in that the recovery ratio of the monofilament yarn (2) is between 3% and 40% and the recovery ratio of the multifilament yarn (3) is between 1% and 20%. 7. Sleeve according to Claim 6, characterised in that the recovery ratio of the monofilament yarn (2) is between 15% and 25% and the recovery ratio of the multifilament yarn (3) is between 8% and 15%. 8. Sleeve according to one of Claims 1 to 7, characterised in that the interlaced strands (2, 3) comprise between two monofilament yarns (2) per one multifilament yarn (3) and one monofilament yarn (2) per ten multifilament yarns (3). 9. Sleeve according to Claim 8, characterised in that the interlaced strands (2, 3) preferable comprise one monofilament yarn (2) per two multifilament yarns (3) or one monofilament yarn (2) per three multifilament yarns (3). 10. Sleeve according to one of Claims 1 to 9, characterised in that the strands (2, 3) are interlaced in the form of a flexible tubular braid, the diameter of the said braid increasing with the longitudinal compression of the said braid. 11. Sleeve according to one of Claims 1 to 9, characterised in that the strands, (2, 3) are knitted in the form of flexible tubular knit, the diameter of the said knit increasing with the longitudinal compression of the said knit. 12. Sleeve according to one of Claims 1 to 11, characterised in that the monofilament yarn (2) is made of polyethylene terephthalate. 13. Sleeve according to one of Claims 1 to 12, characterised in that the multifilament yarn (3) is made of polyamide. 14. Process for manufacturing a rubber tube (4) protected by a fabric sleeve (1) according to one of Claims 1 to 13, characterised in that it comprises the following steps: - extrusion of a rubber tube (4); - shaping of the said tube (4); - fitting of the fabric sleeve (1), the diameter of the sleeve (1) being slightly greater than the diameter of the rubber tube (4); and - vulcanisation of the tube (4) covered by the fabric sleeve (1), causing heat recovery of the fabric sleeve (1). 15. Manufacturing process according to Claim 14, characterised in that in the shaping step, the tube (4) is slipped onto a tubular mandrel (7), the said mandrel being removed after the vulcanisation step. 16. Manufacturing process according to either of Claims 14 and 15, characterised in that the vulcanisation step is carried out at a temperature of approximately 180°C. 7. Rubber hose, especially a coupling used in a fluid circuit of an engine, characterised in that it is formed by a rubber tube (4) covered by a fabric sleeve (1) according to one of Claims 1 to 13.

Inventors: ANDRIEU HUBERT, DROMAIN LIONEL, LAURENT BENOIT, ANDRIEU, HUBERT, DROMAIN, LIONEL, LAURENT, BENOIT
Applicants: ANDRIEU HUBERT, DROMAIN LIONEL, FEDERAL MOGUL SYS PROT GROUP, LAURENT BENOIT, ANDRIEU, HUBERT, DROMAIN, LIONEL, FEDERAL-MOGUL SYSTEMS PROTECTION GROUP SAS, LAURENT, BENOIT
Application year: 1999
Main classification: D04C1
IPC codes: D04C1, F16L11