GB1397583A - Cast pneumatic tyre and a method of producing said tyre - Google Patents

Abstract

1397583 Tyre moulding BRIDGESTONE TIRE KK 4 Oct 1972 [7 Oct 1971] 45725/72 Heading B5A [Also in Division B7] A pneumatic tyre 1 comprises an annular portion 4 cast or moulded from a material having a Shore A hardness of 50-75 degrees and forming the whole, as shown in Fig. 1, or part, as shown in Fig. 5, of the tyre tread, and a portion 3 bonded to the portion 4 and forming the remainder of the tyre, the portion 3 being cast from a material which is different to that of the portion 4 and which has a modulus of elasticity at 50% elongation of 140-650 Kg/cm<SP>2</SP>, the tyre containing as reinforcements except for a pair of bead wires 2, 2<SP>1</SP>. The portion 4 has grooves 5 which extend inwardly from its ground contacting surface to leave a thickness of material of 10-40% of the groove depth between the groove bases and the junction between the portions 3, 4. The material of the portion 4 may be styrene-butadiene or natural rubber, and that of the portion 3 an ether type polyurethane. The tyre may be manufactured using the mould apparatus shown in Figs. 11 and 13 whereby firstly the portion 4 is made by casting curable material into a cavity formed by positioning an annular core 7 in a space defined by side parts 9, 9<SP>1</SP>, an outer split ring 6, 6<SP>1</SP>, and an inner split ring 8, 81 of the apparatus; then, when the portion 4 is partially cured, the core 7 is replaced by a core 10 which defines with the parts 9, 9<SP>1</SP> and rings 6, 6<SP>1</SP> and 8, 8<SP>1</SP> a cavity into which curable material is cast to form the portion 3; and finally curing of the two portions 3, 4 is completed during which process they become chemically bonded together. The mould cores 7, 10 may be closed hollow structures as shown in Figs. 11 and 13, or may be hollow structures as shown in Figs. 11 and 13, or may be hollow structures open at their inner periphery such that they have a pair of spaced apart bead portions provided with bead cores 14, 14<SP>1</SP> as shown in Fig. 14B. In both cases the cores may be pressurized with gas and may contain a reinforcing layer, e.g. 13<SP>1</SP>, or fibre cords or canvas. The above described apparatus and method may be modified such that the portion 3 is cast before the portion 4, in which case the core 7 is not needed, but another mould part is used to set the radially outer limits of the portion 3 during its casting. In a further method of producing the tyre a portion 4 in partially cured form is produced by moulding, e.g. from extruded or unvulcanized rubber tread stock, and is then placed in a mould apparatus in which an already cast and partially cured portion 3 is contained or in which the portion 3 is then cast.