A tire building drum has a center section (720) and two end sections
(722,724). Each end section is provided with an expandable bead lock
assembly (726). The center section is preferably expandable. The
expandable bead lock assembly comprises a carrier ring (CR) and a
plurality of elongate links (K) extending between the carrier ring (CR)
and a plurality of radially-expandable segments (S). When the carrier
ring moves inward (towards the center section), the radially-expandable
segments (S) move radially outward, urging a plurality of axially
extending, circumferentially spaced-apart finger segments (F) outward
from a collapsed position to an expanded position, and at least one
position therebetween. In an embodiment of the invention, the bead lock
assembly comprises a cylinder and two pistons (P1, P2) disposed within
the cylinder. The pistons are free to move axially within the cylinder,
in response to pneumatic pressure. The first piston (P1) is constrained
from moving axially inward by rods (R1P1,R2P1,R3P1). The second piston
(P2) is connected by rods (R1P2,R2P2,R3P2) to the carrier ring (CR).
Pressurized air supplied through hoses (H1,H2,H3) and passageways in the
cylinder (73) control the movement of the pistons (P1,P2) so that the
beach lock assembly can be partially-expanded, fully-expanded, and
retracted, unexpanded position.