GB2185211A - Moulding tyres - Google Patents

Abstract

A method of manufacture of a tyre comprising premoulding and assembling tyre components in a shaped mould 50,60,61 having no strength in itself. The mould is externally supported in a housing 55,65,66 during the moulding operation and assembly and consolidation of components. The mould is then released from the housing and the unvulcanised tyre, in the mould, located in a pressure vessel and subject to all round gaseous pressure, and the tyre is vulcanised by the application of heat in the pressure vessel. There is also described a shaped mould (50) having sufficient strength to support an unvulcanised tyre but having insufficient rigidity in itself to withstand moulding pressures. A housing (55) (65) (66) is provided to support the mould during the moulding operation. <IMAGE>

Description

SPECIFICATION Manufacture of vehicle tyres This invention relates to methods and apparatus for the manufacture of vehicle tyres.

Pneumatic tyres are assembled from many separate components which are each intended to be accurately shaped and precisely located in the finished tyre. However, in conventional tyre moulding and vulcanising presses the hot rubber tends to flow and thus disturb the positions and distort the shapes of components however accurately they may have been placed and shaped during the tyre building operations. This problem is particularly serious in the moulding of large tyres such as truck or earthmover tyres.

In our co-pending UK published application No. 2133357A there is described a method of tyre building in which the unvulcanised tread (and preferably also other components) is or are pre-shaped in the corresponding mould parts so that when the completed tyre is vulcanised no substantial re-shaping is necessary. However, that process still requires the use of a heavy and expensive mould to withstand the moulding pressures.

One object of the present invention is to reduce the mould costs in a process of the kind described in our co-pending UK published application No. 2133357A.

According to the invention, a method of manufacturing a pneumatic tyre comprises premoulding and assembling components of the tyre in a shaped mould having sufficient strength to support the unvulcanised tyre in its required finished state, but having insufficient rigidity of itself to withstand the moulding pressure, said mould being externally supported during the moulding operation and subsequently being released from its external support to convey the unvulcanised but otherwise finished tyre to a pressure vessel within which the mould and tyre are then confined and subjected to gaseous pressure such that the external pressure on the mould is equal to the internal pressure within the tyre, and heating the tyre in the pressure vessel to effect vulcanisation thereof.

The present invention also provides apparatus for manufacturing a pneumatic tyre comprising a shaped mould having sufficient strength to support the unvulcanised tyre in its required finished state, but having insufficient rigidity of itself to withstand the moulding pressure. Means needed to be provided to support the mould during the moulding operation only and to release the mould after the moulding operation so as to enable the mould and tyre to be conveyed to a pressure vessel for vulcanisation of the tyre.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic axial cross-section through part of a tyre mould and associated apparatus in accordance with the invention, showing an unvulcanised but moulded tyre in position in the mould, and Figures 2 and 3 are diagrammatic views in the axial direction showing part of a flexible tread moulding ring.

The tyre 10 shown in its moulded state in Fig. 1 comprises a tread 14, breakers 22, 30, 32, 33, carcass plies 35, beads 36, 37, chafers 39, 40, toe strips 41, 42, and sidewall rubbers 43, 44. The assembly of the tyre is carried out as described in our published UK Application No. 2133357A, using pre-moulded rubber components where possible.

The mould comprises a flexible segmental tread moulding ring 50 formed from plastics material such as polytetrafluoromethylene (PTFE) in which the segments 51 fit together within a steel retaining ring 55 to form a full annulus (Fig. 2) but can be 'unwound' from a finished tyre (after removal of the ring 55 which may be transversely split and releasably clamped to enable this to be done) as shown in Fig. 3.

Sidewall moulding plates 60, 61 are also formed from a plastics material such as P.T.F.E. and are held against moulding pressure by end plates 65, 66 which may be clamped to the ring 55 or held between press platens. Metal bead moulding rings 46 and clip rings 47 complete the assembly.

In operation, the unvulcanised tread 14 is pressed into the moulding ring 50 and the breakers and carcass fitted into the tread as described in published application No.

2133357A, resulting in an accurately moulded and correctly located tread/breaker package into which the carcass 35, which has been separately built on a cylindrical drum, incorporating beads 36, 37, may be expanded.

The rubber bead components 39-42 are pre-shaped and assembled into the bead moulding rings and fitted to the carcass assembly, followed by clip rings 47 to hold the bead assemblies in position. Pre-moulded sidewall components are fitted into (or premoulded) in sidewall moulding plates 60,61 and the whole assembly as shown in Fig. 1 is clamped together and subjected to internal air pressure to finally mould and consolidate the various components of the tyre. Internal air pressure may be provided by means of an inflatable diaphragm (not shown) in known manner, or by simply engaging the bead rings with sealing plates having suitable rubber seals to enable air pressure to be applied directiy into the interior of the carcass.

After the tyre has been fully moulded and consolidated within the mould assembly (at a temperature below that at which vulcanisation takes plate), the end plates 65, 66 and ring 55 are removed and the tyre is conveyed, still within the plastic mould parts 60, 61 and 50 and supported by the bead moulding rings 46 and clip rings 47, to an autoclave or similar pressure vessel where the tyre can be vulcanised under pressure.

Since the tyre components have all been pre-moulded and consolidated together before the final vulcanisation step, no pressure differential between the interior of the tyre and the exterior of the plastic mould parts 50, 60, 61 is required and the supporting structure provided by the end plates 65, 66 and the ring 55 is not needed.

Following vulcanisation, the bead moulding rings 46, clip rings 47, and sidewall moulding plates 60, 61 are removed and the tread moulding ring 50 is detached as shown in Fig.

3.

The invention has the advantage that relatively cheap plastic mould components can be employed for all the functions normally requiring expensive metal moulds. The additional clamping means required during the application of moulding pressure does not need to be occupied by the tyre during the relatively lengthy vulcanising period, and this results in a lower tooling cost for a given production capacity.

Whilst in the drawings a mould for a truck tyre is illustrated, methods and apparatus in accordance with the invention are also particu lady, advantageous in the production of earthmover tyres since the reduction in mould costs is of greater significance with the larger sizes of tyre.

Claims (2)

1. A method of manufacturing a pneumatic tyre comprising pre-moulding and assembling components of the tyre in a shaped mould having sufficient strength to support the unvulcanised tyre in its required finished state, but having insufficient rigidity of itself to withstand the moulding pressure, said mould being externally supported during the moulding operation and subsequently being released from its external support to convey the unvuicanised but otherwise finished tyre to a pressure vessel within which the mould and tyre are then confined and subjected to gaseous pressure such that the external pressure on the mould is equal to the internal pressure within the tyre, and heating the tyre in the pressure vessel to effect vulcanisation thereof.

2. Apparatus for manufacturing a' pneu- maric tyre by a method in accordance with Claim 1 comprising a shaped mould having sufficient strength to support the unvulvanised tyre in its required finished state, but having insufficient rigidity of itself to withstand the moulding pressure, means being provided to support the mould during the moulding operation only and to release the mould after the moulding operation.