GB709378A - Improvements in methods of moulding rubber and similar materials - Google Patents

Abstract

709,378. Moulding rubber tyres &c. UNITED STATES RUBBER CO. March 31 1952 [June 21, 1951], No. 8109/52. Class 87 (2) During the shaping of rubbery material, it is subjected to stresses in a direction transverse to the residual stresses, the transverse stresses being of such a magnitude that the effect of the residual stresses is reduced. As applied to the moulding of tyres, strips of rubber 13. 14, Fig. 1, are extruded from a twin extruder 10, 11 and the strips cut longitudinally into two parts 18, 19, Fig. 2, by a rotary knife 16, and transversely into tyre lengths by a rotary knife 21. The part 13 is made of abrasion resistant material and the part 14 of crack resistant material. The ends of a length are spliced together to form annular bands which are then stretched and applied to a core 28. The bands are then moulded under heat and pressure between mould halves 24, 25, Fig. 4, to form of a tyre. The mould is heated by passing a heating medium through channels 45, 46 and' the core and the bands may be preheated. In order to neutralize stresses induced in the material due to the compression moulding, the bands are given a shear stress by rotating the core 28 by means of a hydraulic motor 50 which drives a pinion 51 engaging teeth 32 on a flange 31 of the cores. The Specification gives details of the magnitude of the shear stresses employed. The mould halves are then opened, and by making the core surface of, e.g. polished chromium plate, so that its adhesion to the rubber is relatively small the bands remain in the mould halves. To provide the necessary friction between the core and the bands to produce the shear stress, the core may have slight ridges on its surfaces. A shaped tyre carcass 55, Fig. 6 containing a curing bag 56 is then inserted in the mould and the mould halves closed to within #in. of each other, the bag 56 is then inflated through an opening 57 to expel the air from between the moulds. The mould halves are then closed and the tyre and tread moulded under heat and pressure. The mould halves are then opened and the tyre assembly and curing bag placed between mould halves 60. 61, Fig. 8. having a tread pattern forming design 63. The mould halves 60, 61 have a slightly bigger mould cavity than the previous mould halves. The tyre assembly is then moulded under heat and pressure to form the finished tyre. Alternatively the tyre assembly may be vulcanized in a vulcanizer of the McNeill or Demattia type. The mould surfaces may be of matte surfaced chromium or nickel plated. Specifications 703,973 and 709,387 are referred to.