Tyre carcass forming method and drum

A method of forming a tyre carcass, the method comprising the steps of:

• providing a drum having a longitudinal axis and comprising two half-drums and two turn-up bladders, each of which is mounted on a respective said half-drum and comprises an intermediate portion and an annular portion, wherein the annular portion is arranged, at rest, in contact with the respective half-drum and at least partially beneath the intermediate portion;
• the half-drums being of fixed axial length, being movable, in opposite directions along the longitudinal axis, to and from a centre plane of the drum, and being covered externally with the respective turn-up bladders;
• winding a body ply about the drum, so that two annular lateral portions of the body ply lie on at least part of the respective turn-up bladders;
• fitting a respective bead bundle on each half-drum and respective annular lateral portion;
• each annular lateral portion extending outwards of the respective bead bundle;
• clamping each bead bundle in position on the respective half-drum;
• forming an annular central portion, extending between the two bead bundles, of the body ply into a toroidal shape by moving the two half-drums towards each other;
• once the annular central portion is shaped, applying air inflation pressure to expand the turn-up bladders to expand the annular lateral portions outwards and up about the respective bead bundles;
• further applying air inflation pressure to distend, on each half-drum said annular portion of the respective turn-up bladder;
• and
• controlling distension of said annular portion using guide means, which are axially fixed with respect to the half-drum, are rigidly connected to said annular portion so as to move therewith and respond solely to application of said air inflation pressure;
• and in such a manner as to move said annular portion into a final position, and to cause said intermediate portion, extending between said annular portion and the toroidal said annular central portion, of the turn-up bladder to roll outwards along a respective sidewall of the toroidal annular central portion;
• wherein the guide means are rigidly connected to the half-drum at a fixed point which is axially arranged outside the respective annular portion when the annular portion is both at rest and distended;
• and
• wherein the guide means are axially more rigid than the turn-up bladders to result, when each turn-up bladder is distended, in the guide means acting as a substantially conical brace to prevent substantially axial movement, and only permit substantially radial movement of any point of the annular portion along a substantially radial trajectory with respect to the longitudinal axis, and also to result in the intermediate portion being axially pushed towards the respective sidewall.