Tyre building drum for building an unvulcanised tyre

Tyre building drum (1) for building an unvulcanised tyre using rubber tyre components, wherein the tyre building drum comprises a central drum shaft (4) and two drum halves (5, 6) arranged at least almost substantially symmetrical with respect to the centre (3) of the tyre building drum (1) and around the drum shaft (4), wherein in the drum shaft (4) one threaded spindle (7) is arranged, wherein on either side of the centre (3) of the tyre building drum (1) the thread has an equal-sized pitch yet in a mutually opposite axial direction of the one threaded spindle (7), wherein on either side of the centre (3) of the tyre building drum (1) a respective one from a pair of driving nuts (8) is arranged on the one threaded spindle (7), wherein each driving nut (8) is fixedly connected to a respective one of the drum halves (5, 6) via a respective connection part (9), wherein the drum shaft (4) is provided with two drum shaft slots (10), each one accommodating a respective one of the connection parts (9), wherein both drum halves (5, 6) are movable in an axial direction of the tyre building drum (1),

• wherein each drum half (5, 6) comprises a folding arm unit (11) with folding arms (12) that are connected to a respective one of the drum halves (5, 6) so as to swing, wherein each folding arm unit (11) is movable in the axial direction of the tyre building drum (1), wherein each drum half (5, 6) further comprises a bead ring core clamping unit (15), intended for supporting and clamping a bead ring core (16), wherein each bead ring core clamping unit (15) is arranged on a respective cylindrical part (17) of its drum half (5, 6), each cylindrical part (17) being arranged around the drum shaft (4), wherein each cylindrical part (17) is provided with a respective cylinder slot (18) for accommodating the connection part (9) of its drum half (5, 6), wherein each driving nut (8) is fixedly connected to the folding arm unit (11) of its drum half (5,6) via the connection part of that drum half (5,6) so that the connection part (9) of that drum half (5, 6) and the folding arm unit (11) connected thereto are movable in the axial direction of the one threaded spindle (7) with respect to said cylindrical part (17) of that drum half (5, 6), wherein each of said cylindrical parts (17) is provided with a locking mechanism (19), wherein each locking mechanism (19) can be brought into and out of engagement with the drum shaft (4), wherein at engagement of each locking mechanism (19) with the drum shaft (4) the cylindrical part (17) associated with that locking mechanism (19) and the bead ring core clamping unit (15) associated with that locking mechanism (19) are fixed in the axial direction of the tyre building drum (1) while, at the operation of the one threaded spindle (7), each connection part (9) is arranged to move its folding arm unit (11) over the fixed cylindrical part (17) of its drum half (5, 6) with respect to the fixed bead ring core clamping unit (15) of its drum half (5, 6) in the axial direction of the tyre building drum (1) such that the folding arms (12) of its drum half (5, 6) are swung upwards, wherein, in the position in which the locking mechanisms (19) are out of engagement with the drum shaft (4), at the operation of the one threaded spindle (7) the connection parts (9) are arranged to move their respective drum halves (5) in the axial direction of the tyre building drum (1).