Patent GB-1403441-A (GB)
Title: Tyre retreading process
IPC: B29C33/02
Filed: 1972-09-11
Abstract: 1403441 Retreading tyres VAKUUM VULK HOLDINGS Ltd 11 Sept 1972 [11 Sept 1971] 42100/72 Heading B7C A worn tyre carcass 3 is retreaded by roughening the radially outer surface of the carcass; covering the roughened surface with a layer 2 of unvulcanized rubber bonding material; superposing a vulcanized tread 1 on the layer 2; adhesively bonding the tread 1 to the carcass 3 by pressing the tread and carcass together so that the bonding material flows to completely fill the space between the tread and carcass, thereby excluding gaseous matter from between the tread and carcass; and permanently bonding the tread 1 to the carcass 3 by vulcanizing marginal portions of the layer 2 adjacent the lateral edges of the tread 1 before vulcanization of the remainder of the layer 2, so that a permanent vulcanized bond at each lateral edge of the tread retains the tread and carcass together during vulcanization of the remainder of the layer 2. The vulcanization of the marginal portion of the layer 2 is effected so rapidly that a permanent bond between the tread and carcass at these portions is formed before any decrease in the adhesive forces exerted by the layer 2 occurring during vulcanizing can cause separation of the tread and carcass. The tread 1 may be applied as an endless ring, as a strip wound round the carcass to form a ring, or as segments which together form the complete tread, and in the last two cases the tread will have further edges in addition to its lateral edges and the portions of the layer 2 adjacent these further edges of the tread may also be rapidly vulcanized prior to vulcanization of the remainder of the layer 2. Rapid vulcanization of the marginal portions of the layer 2 may be effected by spraying a hot fluid, e.g. air, steam, glycerine, on to the marginal portions through a nozzle or nozzles 39, Fig. 17, whilst moving the nozzle or nozzles and/or the tyre so each marginal portion is heated over its whole circumference. Alternatively the marginal portions may be rapidly vulcanized by rotating the vertically disposed tyre assembly whilst immersing it in a bath of hot liquid to a depth sufficient to cover the marginal portions (Fig. 16, not shown). Rapid vulcanization of the marginal portions may also be effected by irradiation, passing heated rollers around the marginal portions, or heating the marginal portions by electrically heated wires. The layer 2 of bonding material may incorporate, or be coated with, a vulcanization accelerator in its marginal portions in order to effect rapid vulcanization of the marginal portions. The tread 1 may be pressed on to the carcass 3 prior to vulcanization by means of the apparatus shown in Fig. 9, whereby a roller 6 first presses the central area of the tread on to the carcass and is then moved axially to stitch the remainder of the tread in so doing displacing frustoconical rollers 5 from between the tread and the carcass, which rollers 5 are initially placed between the carcass and tread to provide gaps for the exit of gases. The beads of the carcass 3 may be forced apart, Fig. 10, to cause the radially outer surface of the carcass to assume a flat or concave profile during application of the tread to the carcass, or may be forced together to cause the radially outer surface of the carcass to assume a convex profile during such application. The tread 1 may be placed under vacuum by use of a flexible sheath 24, Fig. 12, during pressing of the tread on to the carcass, several forms of sheath being disclosed in the Specification. Alternatively a rigid ring or rings (Figs. 2 and 11, not shown) or an inflatable bladder (Fig. 15, not shown) surrounding the tread may be used to press it against the carcass. Pressure may be applied internally of the carcass, e.g. by rollers or fluid, as well as to the tread to press the tread and carcass together. A plasticizer, e.g. benzine, benzene, turpentine or a resin, may be added to the layer 2 to facilitate adhesive bonding on pressing the tread and carcass together. Specification 1,150,809 is referred to.