Under some circumstances zero speed may be achieved by the drum motor running at zero (detent) speed. If there is no means of positively holding the web, such as a web clamp, brake or layon roller, stall tension controlled by the unwind must balance the torque on the drum.
Stall tension should be used only when there are valid reasons for using it. Stall tension should be set just low enough to prevent pulling the web backward. It cannot tear the web from the core. Stall tension must be low enough to prevent pulling a splice apart.
The drive itself does not require stall tension. Stall tension should be as near running tension as possible so long as the high stall tension value does not create one of the problems listed above. A high stall tension will reduce the transition to running tension once the slitter/winder is accelerating.
Drive speed control is not suitable for stall tension. The unwind drive is normally operated in torque mode when stopped. If speed control is used, the web tension may be undefined. The unwind drive can be engineered to stay in tension through torque control or transition to tension through speed while accelerating.
The stall tension may be maintained until the slitter/winder is running at slightly greater than thread speed.