The tensile force acting along a web of film or foil as it is unwound, transported or rewound through packaging equipment.
Also called: film tension; foil tension; rollstock tension; web tension control.
Web paths and tension zones
Tension is tensile loading along a web, not travel distance. A line can have separate unwind, transport and rewind tension zones. A value for one span should not silently describe every other span.
The forming and lidding reels are separate web paths. Identify the material, span, measurement unit and operating condition. A brake or drive setting is a control input, not automatically a direct measurement of tension in the relevant web.
Tension variation can stretch or wrinkle the web and change repeat geometry or alignment. Startup behaviour may differ from steady running, so the conditions when an offset appears help identify the relevant mechanism.
Record whether an offset appears at startup, during steady running or across a roll change, together with the actual web and zone. Compare those observations with the registration reference and intended advance. Increasing tension indiscriminately is not a general remedy; material deformation is itself part of the problem being assessed.
Is there one correct tension for every blister laminate?
The required tension depends on material behaviour, the controlled span and reel conditions. Forming and lidding webs may therefore need different control conditions on the same line.