BEAD REINFORCEMENT CONSTRUCTION

Abstract: The reinforcement for the bead of e.g. a pneumatic tyre, a rolling lobe diaphragm or an air spring is constructed by winding onto a mandrel or former alternate layers of naked wire (13) and flat, uncured rubber strip (12). Rubber (12A) is wound on before wire winding commences and continues after wire winding stops, so that the assembly exposes no cut wire end. After the winding operation the assembly is subjected to heat and pressure so that all the wire is embedded in and surrounded by an integrated, vulcanised rubber body. The rubber layers may be parallel with and on opposite sides of the layers of spaced wire windings or, as shown, a given rubber winding such as (12C) may have wire windings (13A, 13B) and (13C, 13D) on its radially opposite sides. The windings, both of rubber and wire, may be discrete loops or may be made by helically winding a single rubber strip or wire. The shape of the assembly as well as the volume of rubber at any position therein may be controlled by varying the tension under which the rubber strip and/or the wire is wound.

Description: "BEAD REINFORCEMENT CONSTRUCTION" The present invention relates to bead reinforce ent construction and more partic larly to the construction of an annular reinforced bead at the or each orifice of a hollow article fabricated from flexible and/or resilient materials and of a kind adapted to be mounted on a rigid seat, e.g. of metal, to form an air seal therewith. Examples of such articles are air springs, rolling lobe diaphragms and pneumatic tyres. A com mon element in the construction of such articles is a liner or carcass ply made from a sheet of a polymeric material in which reinforcing cords are embedded. This liner or ply is wrapped around a cylindrical former or mandrel to form a tube, a bead reinforcement is constructed near each end of the tube, other bead components such as (in the case of a pneumatic tyre) a bead filler or apex are wound over each bead construction and thereafter the ends of the tube projecting beyond the bead assemblies are turned up to fold over or lock into them. Also in the case of a pneumatic tyre the central part of the tube between the bead assemblies is then bowed outwardly to give the carcass ply a toroidal configuration, breaker, tread and side wall components are added and the completed assembly is cured in a mould. Bead reinforcements of inextensible material such as wire are necessary to preserve the predetermined diameter of each bead of the tyre enabling it to seat on the respective flange of a wheel rim and resisting unintended dismounting especially when the tyre is inflated. The wire is, however, sheathed in natural or synthetic rubber to prevent damage to the carcass ply wrapped around it and to form a consolidated strong loop. Bead reinforcements have been made from a simple loop of wire tape impregnated with rubber, Le. a flat rubber strip in which plural, parallel wires are embedded. The overlapping ends of the loop, however, necessarily produce a circumferential unevenness in the finished bead which is pronounced because of the overlap of the tape end. Efforts to produce a less circumferentially uneven bead have included wrapping round the mandrel a single rubber sheathed wire in such a manner as to give a similar section or regular section with improved joint areas. According to United Kingdom Patent Specification GB- A -2179009 a reinforced bead for a pneumatic tyre may be constructed from superimposed layers of rubber- sheathed wire. This latter proposal has the advantage 'that the shape of the wound bead may easily be varied and both proposals have the advantage that the turned-up carcass ply may be embedded and trapped in the windings of the reinforced bead. However the versatility of the construction even of the latter proposal is limited by the fixed ratio between the volume of rubber and the volume of wire in the finished product imposed by the use of rubber coated wire. Variation of the configuration of the reinforced bead to meet different requirements is also limited by the use of sheathed wire having a predetermined rubber- to- ire volume ratio and spatial relationship. A principal object of the present invention is to improve upon previous proposals by increasing design flexibility in a simple and cost- effective manner permitting the construction of improved bead reinforcements or bead reinforcements better adapted to particular design requirements. In accordance with the present invention there is provided a method of constructing a bead reinforcement which co prises alternately wrapping around a mandrel or former at least one flat strip of uncured polymeric aterial and spaced- apart windings of an inextenable material under a tension such that the polymeric material enters the spaces between the windings and until an annular assembly of the required diametral thickness and cross-sectional shape has been built up in which each winding is surrounded by and embedded in the polymeric material. The method preferably comprises at least partially curing the polymeric material such that the windings are embedded in an integral body of at least partially cured polym ric material-. In preferred embodiments of the invention the polymeric material is natural or synthetic rubber and the inextensible material is naked wire in single-filament or stranded form. At least some of the windings forming one layer thereof transverse of the assembly may be made by helically winding a single filament or strand of the inextensLble material and in this case at least some of the windings forming each layer thereof throughout the assembly may be made by helically winding a single filament or strand of the inextensLble aterial. The windings forming one or each layer thereof transverse of the assembly may be made by si ultaneously helically winding a plurality of spaced- apart single fila ents or strands of the inextensible material, A single flat strip of the polymeric material may be helically wound simultaneously with the winding or windings of the inextensible material such that layers of the inextensible material are sandwiched between layers of the strip throughout the diametral cross section of the assembly. In a given layer of the inextensible material windings transverse of the assembly one or more of said windings may lie on the radially inner side and the remainder may lie on the radially outer side of the same winding of polymeric strip, additional windings of the polymeri strip extending transversely across the assembly both radially inward and radially outward of said layer. During its winding the polymeric strip and/or the inextensible material may be subjected to differential tension thereby to vary the width and/or thickness of the polym ric material interposed between two windings or two layers of windings of the inextensible material. During the construction of the bead reinforcement and before its completion an edge of a carcas ply over which the reinforcement is being built may be turned up and folded over the incomplete reinforcement and the reinforcment may be completed on the radially outer side of the folded back ply edge so that the latter is trapped within the reinforcement. In case the reinforcement is being constructed by continuous to-and-fro helical windings of strip and inextensLble material this will mean that the ply edge must be slit to enable the windings to continue from its radially inner to its radially outer side. Preferred embodiments of the invention will now be described by way of example with reference to the accompanying diagram matic drawings, in which: Figure 1 is a cross section in a radial plane containing its axis of a first embodiment of a bead reinforcement in accordance with the invention, and Figure 2 is a similar view of a second embodiment of a bead reinforcement in accordance with the invention. Referring first to Figure 1, an elongate strip 10 of uncured rubber, preferably in a warm, sticky condition is wound around a mandrel (not shown). If e.g. a pneumatic tyre or a rolling lobe diaphragm is being manufactured this mandrel, or former, will first have been covered with a tubul r carcass ply (not shown) in the form of a sheet of uncured rubber in which reinforcing cords are embedded. The strip 10 is of the width of the intended bead reinforcement and is positioned near one end of the carcass ply so that the end portion of the carcass ply projecting beyond it on the mandrel or former can later be turned up into or over the bead reinforcement. Such techniques are well known per se - see for example United Kingdom Patent Specification No. GB-A-2179009. After the application of a first turn 10 A of the rubber strip to the mandrel or former a layer 11 comprising four spaced-apart wires is applied over it. The four wires 11 are naked ( e. not sheathed e.g. in rubber) and are fed im mediately after application of the first rubber layer 10A. The wires of the layer 11A may be monofilaments or may be strands of several filaments twisted together. The four wires are now wound sLmiiLtaneousLy with the rubber strip to form three further successive layers 10B, 10C, 10 D and 10E of rubber with wire layers 11A, 11B, 11C and 11D interposed. The four wires 11 are stopped before application • of the final rubber turn 10 E so that the wire is fully enclosed by the rubber. The height to which the assembly is built (Le. its radial extent) is determined by the intended dimensions of the bead reinforcement, ore or less wire and rubber turns being applied, although rubber layers will always be provided on the radially inner and outer sides of the assembly. Moreover it should be understood that whereas the acco panying drawings illustrate only bead reinforcements of generally rectangular cross section other cross sectional shapes can be built up by varying the widths of the rubber and wire layers. This can be facilitated either by selecting rubber strip of different widths for different layers or by varying the tension under which the same strip is wound so as to reduce its width. At any chosen moment during the construction of the bead reinforcement the carcass ply end (not shown) over which it is being built may be turnd up and folded over the partially formed reinforcement. The resumption of the winding procedure will entrap the ply end in the reinforcement. The rubber strip and/or the wires are subjected to tension during winding such that the uncured rubber penetrates the spaces between the turns of wire of each layer 11A - 11D. When the assembly is subsequently subjected to curing heat (e.g. after incorporation in a pneumatic tyre which is vulcanised in a mould) each turn of naked wire of each wire layer 11 A - 11 D is embedded in and surrounded by vulcanised rubber and the entire assembly is integrated in that any previous spaces between rubber layers on opposite sides of wire layers have been filled (this includes the spaces at opposite ends of each wire as well as the spaces between the wires of each layer). The fact that all wire included in the assembly is fully embedded in rubber even at cut ends of each wire or strand is an important advantage of the present invention. The exposure of metal at the cut end even of a sheathed wire in previous proposals is a serious weakness since corrosion can set in at this point when stored. Although such cut end is subsequently covered during completion of tyre manufacture there will be an interval of exposure and an air gap adjacent the cut end in the finished product. Even limited corrosion resulting fro this arrangement is deliterious to the finished product. The embodiment of Figure 2 differs from that of Figure 1 primarily in that only a single wire 13 (monofilament or strand) is wound helically, traversing from side- to-side to form the various layers of spaced-apart wire turns throughout the radial extent of the assembly. After a first turn 12 A of rubber is wrapped around the mandrel (or carcass) feeding of the wire 13 com mences at the right-hand side of the assembly, as viewed to make a first turn 13A. Necessarily the second turn 13B of wire is on the opposite side of the second turn 12B of rubber to the first rubber turn 12A. Similarly the third turn 13C of wire is separated from the second turn 13B by the third turn 12C of rubber, and the final turn 13D of wire in the first layer is separated from the third turn 13 C by a fourth turn 12 D of rubber. The direction of traverse of the wire winding head is now reversed. After a fifth turn 12E of rubber has been wound over all the wire turns 13 A - 13 D of the first layer of wire a second layer of wire com ences with a first turn 13E. This is overlaid by a sixth turn 12F of rubber and so on, the second layer of wire with interleaved rubber being constructed similarly but oppositely to the first layer. The process is continued until a bead reinforcement of the desired dimensions is built up. If desired the assembly may be subjected to compacting pressure and to heat to produce an integrated body of v-ilcanised or partially vulcanised rubber in which the individual turns of wire filament or strand are fully embedded even at the ends of the or each wire.

Claims: CLAIMS: 1. A method of constructing a bead reinforcement which comprises alternately wrapping around a mandrel or for er at least one flat strip of uncured poly eri material and spaced-apart windings of an inextensible material under a tension such that the polymeric material enters the spaces between the windings and until an annular assembly of the required diametral thickness and cross-sectional shape has been built up in which each winding is surrounded by and embedded in the polymeric material. 2. A method as claimed in claim 1 and comprising at least partially curing the polym ric material such that the windings are embedded in an integral body of at least partially cured polymeric materiaL 3. A method as cl med in claim 1 or claim 2, wherein the polymeric material is natural or synthetic rubber and the inextensible material is naked wire in single-filament or stranded form. 4. A method as claimed in any one of the preceding claims, wherein at least some of the windings forming one layer thereof transverse of the assembly are made by helically winding a single fil ment or strand of the inextensible materiaL 5. A method as clai med in claim 4, wherein at least some of the windings forming each layer thereof throughout the assembly are made by helically winding a single filament or strand of the inextensible material. 6. A method as cl imed in claim 4 or claim 5, wherein the windings forming one or each layer thereof transverse of the assembly are made by simultaneously helically winding a plurality of spaced-apart single fil ments or strands of the inextensible material. 7. A method as cla ed in any one of the preceding claims, wherein a single flat strip of the polymeric material is helically wound simultaneously with the winding or windings of the inextensible material such that layers of the inextensible material are sandwiched between layers of the strip throughout the di metral cross section of the assembly. 8. A method as claimed in any one of the preceding claims, wherein in a given layer of the inextensible material windings transverse of the assembly one or more of said windings lie on the radially inner side and tire remainder lie on the radially outer side of the same winding of poly ric strip, additional windings of the polymeric strip extending transversely across the assembly both radially inward and radially outward of said layer. 9. A method as clai med in claim 7 or claim 8, wherein during its winding the polymeric strip and/or the inextensible material is subjected to differential tension thereby to vary the width and/or thickness of the polymeric material interposed between two windings or two layers of windings of the inextensible material. 10. A method as cl med in any one of the preceding claims, wherein during the construction of the bead reinforcement and before its completion an edge of a carcas ply over which the reinforcement is being built is turned up and folded over the incomplete reinforcement and the reinforcment is completed on the radially outer side of the folded back ply edge so that the latter is trapped within the reinforcement. 11. A method of constructing a bead reinforcement substantially as hereinbefore described. 12. An article having a bead reinforced by the bead reinforcement made by the ethod cl imed in any one of the preceding claims.

Inventors: HOLROYD ERIC, WRIGHT ANTHONY RICHARD, HOLROYD, ERIC, WRIGHT, ANTHONY, RICHARD
Applicants: HOLROYD ASSOCIATES LTD, HOLROYD ASSOCIATES LIMITED
Application year: 1988
Main classification: B60C15
IPC codes: B29D30, B60C15