Printing

In flexo and gravure printing, steady tension and a straight web path are preconditions for print quality, and unwind and rewind equipment shapes both.

On roll-to-roll presses, flexographic and gravure (rotogravure) alike, the material is unwound, passes through the print units and the drying section, and is then rewound onto a new roll. For a sharp print with colours landing in register, the web has to travel the length of the line at constant tension and along a straight path. That makes the mechanical equipment at the unwind and rewind an unseen but decisive part of print quality.

Roll handling on a printing line

As a roll unwinds, its diameter keeps shrinking. If brake torque is not adjusted to match, tension rises or falls, leading to stretching, slackness and misregister. Fixing the lateral position of the web before the print units keeps colour and edge alignment in check. At the rewind, the printed web needs to be wound without creases and with straight edges, ready for the next process, whether that is laminating, slitting or bag making.

Which equipment goes where?

Air shaft: Grips the core at the unwind and rewind and keeps it centred. For light to medium rolls an aluminium air shaft is a common choice; for heavier, wider rolls a steel air shaft is worth considering.
Safety chuck: Connects the shaft to the machine and transmits torque, allowing the shaft to be removed quickly and safely at each roll change. Depending on the frame, frame-mounted or inside-frame types are used.
Brake: At the unwind, a pneumatic brake applies controlled resistance to the web being paid out.
Tension control: A tension controller uses load cell or dancer feedback with PID control to drive the brake, unwind or rewind, helping to prevent misregister.
Web guiding: A web guide controller tracks the web edge or a printed line with a colour sensor or fork sensor and corrects lateral drift.

What to consider when selecting

At high press speeds, shaft balance and runout have a direct effect on vibration and print defects.
The tension range calls for the brake and the controller to be selected together; a brake should not be sized in isolation.
Where the shaft or core comes close to the printed surface, both need to be clean and undamaged.
With frequent roll changes, shaft weight and ease of use of the safety chuck become more important.
Shaft journal and safety chuck dimensions should be checked against a drawing of the existing machine.

For size options see the technical dimensions page, or request a quote for your press through our contact page.