According to TAPPI testing guide (Technical association of the pulp and paper industry) when controlling the web tension, a general guideline is to apply 5% ~ 25% of the maximum web strength, and around 0.5 ~ 1 PLI/mil of thickness.
Web tension control could be categorized into 3 main zones, unwind, internal and rewind. Each zone is independent therefore each zone could have its own tension. The torque required to provide a certain level of tension is measured by the total tension applied x the roll’s radius. Therefore, during production, the torque required at the unwinder will decrease as the roll diameter decreases and the torque required at the rewinder will increase with the increase in the roll diameter. The tension at the unwind and internal zones should remain constant throughout the production. However, this is not the case for the rewind zone. When the web is rewinded at the end of the production. As each layer builds up compressive forces which can cause the inner layer to wrinkle. Therefore, the tension reduces as the rolls build up. This process is called the Taper tension.
It is important to control the tension. Some of the equipment for measuring web tension on a roll to roll solution include load cell, at the dancing roller, the fish scale method at the unwind zone…