Head for sealless strapping machine

In a strapping head for a strapping machine, in which a sealless connection is made in two overlapped layers of a tensioned loop of steel strap, a combination comprising:

• (a) a pair of sealing jaws mounted in the strapping head for pivotal movement about parallel sealing jaw axes, each sealing jaw having a driving end and a working end respectively on opposite sides of one of the sealing jaw axes, the sealing jaws being pivotable between opened positions and closed positions;
• (b) slitting dies mounted rigidly to the working ends of the respective sealing jaws,
• (c) cam followers mounted operatively to the driving ends of the respective sealing jaws;
• (d) a sealing yoke mounted in the strapping head for movement longitudinally between a withdrawn position and an extended position, the sealing yoke having a driving end and a working end, the sealing yoke having intermediate positions including a sealing jaw-pivoting position between the withdrawn and extended positions and being adapted to be driven between the withdrawn and extended positions;
• (e) means linking the sealing jaws to the sealing yoke so as to cause the sealing jaws to pivot from the closed positions to the opened positions upon movement of the sealing yoke from the sealing jaw-pivoting position to the withdrawn position and so as to allow the sealing jaws to pivot from the opened positions to the closed positions upon movement of the sealing yoke from the withdrawn position to the jaw-pivoting position,
• (f) cams provided on the sealing yoke and adapted respectively to engage the cam followers on the respective sealing jaws upon movement of the sealing yoke between the withdrawn and extended positions, the cams being profiled so as to cause the sealing jaws to pivot from the opened positions to the closed positions upon movement of the sealing yoke from the withdrawn position to the sealing jaw-pivoting position, so as to cause the sealing jaws to remain in the closed positions upon movement of the sealing yoke between the sealing jaw-pivoting and extended positions, and so as to allow the sealing jaws to pivot from the closed positions to the opened positions upon movement of the sealing yoke from the sealing jaw-pivoting position to the withdrawn position;
• (g) a punch holder mounted in the strapping head for movement longitudinally in relation to movement of the sealing yoke, the punch holder having a driving end and a working end;
• (h) a slitting punch mounted rigidly to the working end of the punch holder;
• and
• (i) means connecting the driving end of the punch holder to the sealing yoke so as to allow lost motion between the sealing yoke and the punch holder;
• the punch and dies being adapted to punch interlockable slits into the overlapped layers of the tensioned loop of steel strap, when such layers are disposed between the punch and dies and the sealing yoke is driven from the withdrawn position, through the sealing jaw-pivoting position, to the extended position, whereby the sealing jaws are pivoted so as to close the dies and the punch holder is moved so as to drive the punch into the dies, and whereupon such slits interlock, under retained tension in the loop of steel strap, when the sealing yoke is driven oppositely so as to withdraw the punch from the dies and so as to pivot the sealing jaws from the closed positions.