Shaping drum for crown reinforcement plies

A process for assembling a tyre, comprising a separate step of producing the crown of said tyre on a drum of variable diameter (1) of generally cylindrical form, said drum comprising a set of first holding means (3) arranged circumferentially at the equator EE′ of said drum and suitable for making that part of the ply arranged level with these means adhere to the drum (1) and comprising a set of second holding means (4) suitable for making that part of the ply placed level with said second means (4) alternately adhere to or slide freely on the drum, and which are arranged circumferentially and axially on either side of the equator EE′ over the entire surface of said drum (1),

• characterised in that it comprises the following steps:
• positioning the drum (1) at a first diameter D1,
• depositing a first crown belt ply N1 composed of reinforcement cables coated in a rubber mix forming a given angle α1 with the circumferential direction, by activating the first and second means so as to make the entire ply adhere to the surface of the drum,
• depositing a second crown belt ply N2 composed of reinforcement cables coated in a rubber mix forming a given angle α2 of opposite sign to the angle α1 with the circumferential direction,
• making the second ply N2 adhere to the first ply N1,
• while keeping the first means (3) in the preceding configuration, activating the second means (4) so as to permit sliding of the first ply level with said second means (4),
• positioning the drum at a second diameter D2 greater than the first diameter D1,
• activating the second means (4) so as to make the ply adhere to the surface of the drum,
• depositing the other plies and the other profiled products constituting the crown of the tyre,
• gripping the crown thus produced with a transfer ring and depositing the crown on a tyre blank of toroidal form.