What’s TNT Winding Principles

Tension, nip and torque are winding principles which are summarized in the acronym for “TNT”, these principles are commonly used for various materials to assist in optimizing the roll structure with proper hardness and without defects. Tension refers to the winding web tension which is used for slitting and spreading, and controlled by surface drive. Nip refers to the nip of the pressure roll or drum, controlled by the lay-on roll loading. The torque is from the center drive or torque drum.

Tension principle of winding

Web tension is the significant winding principle that is used to control hardness of roll when winding elastic materials. The winding web tension is generally determined empirically. The more tension means the more stretch put on the web before winding process, and the wound rolls tend to harder at the end.

However, The web tension will depend on the type and the thickness of the material being wound. The amount of web tension must be between 10% to 25% of the material’s elastic limit. When we control roll density through tension, the winding tension will be tapered smoothly as the roll diameter increases. The tension taper should be between 0 and 50% in general. Taper tension can reduce telescoping, end crowning, starring and buckling problems.

Nip principle of winding

When winding inelastic materials, nip is the significant winding principle that is used to control roll hardness. The sufficient nip can remove the boundary layer of air following the web into the winding roll. The harder the nip, the harder the winding roll will be. The rolling nip also induces in-wound tension into the roll, The rule of thumb is to use as little nip as possible to achieve a firm roll with the desired roll hardness, winding rolls too tightly can cause problems such as the deformation or roll blocking of the web over the high caliper areas.

The nip must be applied where the material enters the winding roll. The weight of winding material and lay-on roll, and the web tension, should not affect the nip loading. Nip load should be tapered as roll winds to prevent starring and telescoping. However, larger winding roll’s diameter drags more air and produces a nip taper loading with a constant loading pressure.

Torque principle of winding

Through tightening the web layers as the roll diameter builds, the hardness of roll is affected by the amount of torque being supplied by the center drive. When winding in the center or surface mode, winding tension generally starts at 25 to 50 percent greater than the incoming web tension. This is then tapered as the roll builds in diameter to a value at or less than the incoming web tension. The surface drive will regenerate or pull negative torque when the winding tension is greater than the incoming web tension. As the winding roll builds larger in diameter, the surface drive will gradually provide less braking until it reaches zero torque when the winding tension equals the web tension. If the winding tension is programmed to go below the incoming web tension, then the surface drive will pull positive torque to make up the difference between the lower winding tension and the higher web tension.

The setting and programming of the TNT will vary depending on many factors such as design of the winding process,  type of web material, width of the rolls being wound and the speed of the winding operation. Proper roll hardness is extremely important to ensure the high quality of rolls, slitter and winder manufacture like LEAP uses one or more of the TNT winding principles to build roll hardness.