Improvements in or relating to the vulcanisation of rubber articles

In bonding an unvulcanized natural rubber member to an unvulcanized natural rubber article, the areas of the surfaces to be adhered together are limited by interposing an unvulcanized Butyl rubber element between surface areas not to be bonded, whilst vulcanizing the assembly, and subsequently removing the vulcanized Butyl rubber element. In the manufacture of a dual chamber tube for a pneumatic tyre and comprising inner and outer tubes joined together at their inner peripheries to form a common base, annular strips 2, Fig. 1, of unvulcanized Butyl rubber are placed circumferentially around the exterior of an unvulcanized natural rubber inner tube 1 at the desired lateral limits of the common base. Two annular fillets 3 of unvulcanized natural rubber are then arranged so that a part of each covers a strip 2 and the other part is adhered to the tube 1. The latter is then inflated and the assembly is partially cured in a mould of toroidal shape so that the part of each fillet 3 covering a strip 2 is formed into an annular portion 6, Fig. IV, whilst the other part of each fillet is incorporated into the wall of the tube 1. The Butyl rubber strips 2 are not adhered to the tube 1 by the partially curing process and are now removed. The base portion of the tube 1 between the portions 6 is then buffed, coated with rubber solution and secured by vulcanization to a natural rubber outer tube 7, Fig. V. Alternatively the Butyl rubber strips 2 are located in unvulcanized natural rubber fillets 4, Fig. VI, of substantially U-shaped cross section, and two unvulcanized natural rubber base strips 5 of tapering cross-section are placed around the inner tube 1 between the fillets 2 as shown. The manufacture of the dual chamber tube is then completed in the same manner as in the process described with reference to Figs. I, IV, and V. Base strips may also be used in the construction illustrated in the latter Figures, but are not essential.