Process and apparatus for manufacturing tyres

A process for producing tyres wherein building of each tyre comprises:

• separately manufacturing a carcass structure and a belt structure,
• joining the belt structure with the carcass structure, wherein manufacture of said belt structure comprises the steps of:
• providing a forming drum externally having a substantially cylindrical laying surface;
• forming at least one first annular insert of elastomeric material around the laying surface;
• applying a plurality of strip-like elements on the forming drum carrying the at least one first annular insert,
• wherein during said applying step the strip-like elements are laid in mutually approached relationship according to the circumferential extension of said laying surface, to form at least one first belt layer;
• wherein said at least one first annular insert of elastomeric material is formed on the forming drum set to a minimum diameter;
• wherein before starting the applying step, the whole laying surface of the forming drum is expanded from the minimum diameter to a first work diameter, at a value such that each of the strip-like elements applied thereto, on the laying surface, subtends an arc of a circumference of a width corresponding to a submultiple integer of the overall circumferential extension of the laying surface;
• and
• further comprising a step of making at least one second belt layer at a radially external position to said first belt layer;
• wherein after making said at least one second belt layer, the forming drum is radially expanded while keeping the laying surface thereof at a substantially cylindrical shape, up to a predetermined second work diameter, to determine a permanent expansion of said first and second belt layers.