Process and expandable forming drum for building tyres for vehicle wheels

A process for building tyres, comprising:

• arranging an expandable toroidal forming drum in expanded configuration such to externally have an abutment surface defined by a plurality of circumferentially consecutive sectors;
• and
• applying at least one elementary semifinished product of a tyre around said forming drum, by pressing said at least one elementary semifinished product towards the abutment surface,
• wherein
• each sector has first coupling portions circumferentially opposite to second coupling portions, each of said first and second coupling portions comprising circumferential projections alternated with circumferential cavities,
• the circumferential cavities are each axially delimited between lateral walls of two axially consecutive circumferential projections,
• the circumferential projections of each sector are slidably engaged in the respective circumferential cavities of circumferentially adjacent sectors,
• the first coupling portions of each sector include at least one support wing extending integral from at least one of said circumferential projections according to an incident direction with respect to one of the lateral walls thereof, as a continuation of the abutment surface,
• each support wing has a first side and a second side that are respectively opposite,
• a thickness of each support wing is defined between the first side and the second side in a direction perpendicular to the abutment surface,
• the first side of each support wing coincides with a portion of said abutment surface extending between portions of the abutment surface defined by two axially adjacent circumferential projections,
• each support wing defines, by its second side together with the lateral walls belonging to two axially adjacent circumferential projections, a containment seat, and
• the containment seat slidably houses one of the circumferential projections belonging to the second coupling portion of a circumferentially adjacent sector.