The appts. (30) comprises essentially an anvil (32) and an opposed strap engaging member (80), with serrated faces (34, 112) through which the strap (U,L) passes. Anvil (32) has positioner that allows it to squeeze strap (U,L) against member (80) and plunger (92) at a first position, against plunger (92) only at a second position, and to disengage wholly at a third position. Strap engaging member (80) has a coaxial spring-loaded plunger (92) and is mounted on bearings (60) in cavity (54) of drive shaft (46), which itself is mounted on bearings (44) in bore (42) of support frame (40). The axis (58) of member (80) is offset (X) from the axis (48) of drive shaft (46), so rotation of the drive shaft confers an orbital motion to member (80). When the motion is applied to strap (U,L) clamped between anvil (32) and member (80), it creates friction between the strip faces and forms a friction weld conventionally. When anvil (32) is moved to the second position, the orbital motion is disengaged and smooth-faced plunger (92) maintains pressure on strap (U,L) while the weld cools.
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