Patent GB-904531-A (GB)
Title: Improvements in or relating to tyre building drums
IPC: B29D30/26
Filed: 1959-11-30
Abstract: 904,531. Tyre-building drums. PIRELLI S.p.A. Nov. 30, 1959 [April 24, 1959], No. 40600/59. Class 144 (1). In a tyre-building drum comprising a flexible cylindrical wall sealed at its ends to the peripheries of a pair of coaxially spaced, axiallyadjustable end discs 7, 8 so as to extend over peripherally-grooved expansible bead-locating rings 3, 4, carried by said discs, the cylindrical wall is reinforced by parallel longitudinal cords extending the full length of the wall so as to be inextensible longitudinally, and a further reinforcement of circumferentially-extending cords is incorporated in a central zone 11 of the wall, the circumferential cords being so formed or built into the wall that in the axially tensioned, uninflated condition, Fig. 1, the wall presents a circular cylindrical surface of a diameter equal to that of the end discs, and in the inflated condition, Fig. 2, with the end discs moved towards each other and bead rings 13, 14 clamped to the tyre plies 12 on the wall by the expanded rings 3, 4, the central zone 11 of the wall assumes a circular cylindrical shape of a diameter greater than that of the bead rings and merges into tht wall portions underlying the bead rings by outwardly convex curved shoulder portions. Such reinforcement of the cylindrical wall provides stability to permit the use of ply-stitching wheels. In manufacture the circumferential reinforcing cords 46, Figs. 4 and 5, may be helically wound over a rubberized ply of longitudinal cords 45 which is wrapped around a former 36 of a diameter equal to the expanded diameter of the zone 11. The cords 46 may comprise highly twisted yarns or a braid of limited stretch surrounding an extensible core, such cords being applied to the former 36 in its maximum stretch condition, or may be inextensible cords wound under tension on to spaced longitudinal strips 50, Fig. 8. In all three cases the assembly is enclosed in an elastic sheath 48 and the former is adjusted to a reduced diameter equal to that of the end discs 7, 8. An inextensible binding is then wound round the sheath 48 and the assembly vulcanized in its low diameter condition. Where braided cords 46 are used they contract on the reduction in diameter of the former, and where inextensible cords 46 are used they tend to fold upon themselves. Such folding is controlled by the strips 50 in that the portions of cord 46 between the strips 50 are prevented from bonding to the ply of cords 45 during vulcanization and are thereby free to move on contraction of the wall. In an alternative construction the wall is built up on the former 36 in its low diameter condition with the circumferential cords wound helically and along a sinuous path, Fig. 10, to permit the desired limited stretch. The former 36, Figs. 4 and 5, comprises spaced hubs 30, each having segments 33 radiating from a flange 31 thereof, the segments being separated by slots 34 which serve to guide radial webs 35 of a series of arcuate plates 36 which together define a cylindrical former surface, the webs 35 have lugs 37 at each end which are slidably clamped on screwthreaded posts 32 radiating from the flanges 31 whereby the diameter adjustment of the former is achieved. The former is completed at each end by a ring 40 bolted to the segments 33 and having a peripheral groove 41 which serves to mould the thickened edges 5, 6, Fig. 1, by which the cylindrical wall is eventually clamped to its associated end discs.