An accumulating festoon design allows inline sheeters to closely match the speed of down line processes, thereby maintaining accurate sheet length. The system provides a closed loop tension control for the roll stand, accommodating immediate speed changes that would otherwise be impossible because of the weight of the unwinding roll.
The design employs an air cylinder that spreads the festoon rolls apart or draws them together, a transducer, an electrical – pneumatic converter and the roll stand’s tension control to automatically compensate for rapid changes in web speed. As the rolls get closer together the roll stand brake pressure is reduced, as the accumulator’s rolls spread apart, the unwind tension is increased.
The e-p converter changes the roll stand’s tension control setting to a pneumatic output that adjusts the air pressure in the cylinder, tightening or slackening the web around the accumulator rolls. A transducer monitors the movement of the roll frames feeding back the information to the roll stand’s tension controller adjusting brake pressure until the preset tension is regained.