Slitting and Rewinding Key Processes for High-Performance
Roll Conversion Carlos Muriel, sales and marketing director, Pasaban, S.A.
he term refers to the processes of slitting and rewinding, starting from a parent roll and generating multiple fi nished rolls. Both processes are carried out simultaneously in the same machine, commonly known as slitter rewinders.
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Slitting and rewinding processes can cover a wide range of substrates, such as paper, board, cellulose, non-woven materials, plastic or fi lm, among the most common.
Winders refer to machines that produce large rolls of paper, board, etcetera. Rewinders, on the other hand, process large rolls into smaller ones with specifi c width and diameter, or linear metres. Slitter rewinders play a crucial role after paper or board manufacturing by converting large rolls into smaller ones, which are then processed in other machines, mainly Sheeters, which cut sheets into a specifi c size for various applications, such as printing and the production of folding cartons, poster sheets, etcetera.
The increasing use of various types of packaging in our daily lives, such as in food, pharmaceuticals, perfumes, chocolates, etcetera, has made these machines highly relevant. Today, they are required to operate at high speeds.
The slitting/rewinding concept consists of three fundamental phases: Unwinding, Slitting, and Rewinding. While conceptually simple, modern slitter rewinders incorporate a high level of automation. The key to producing perfectly formed rolls, both in terms of dimensions and side profi le or winding
hardness, requires that the web tension remains at predetermined values and extremely stable at any operating speed, including rapid acceleration and deceleration ramps. Otherwise, the quality of the fi nal rolls will be compromised.
For unwinding, the trend today has been to replace the pneumatic or hydraulic brakes of older slitter rewinders with regenerative electric brakes (AC motors) to minimise maintenance costs associated with high operating speeds. Combined with the precision provided by modern drives, this results in excellent performance.
Regarding slitting, the choice of top and bottom slitters diameters, as well as cutting angles, depends on the substrate and grammage. Decades of
experience in manufacturing these machines provide the necessary expertise to determine the most suitable confi guration for each case.
Rewinding is also a key process and must be designed to absorb even slight vibrations caused by various factors, such as the imperfect geometry (oval shape) of the core at the start of the roll, which can create instability as the roll grows. If the design is correct, the fi nal result will not be aff ected. Otherwise, the fi nished rolls may show signifi cant variations in quality. The rewinding process consists of two roll support drums and an upper pressure roller that ensures the correct pressure at all times.
In some cases, for mark-sensitive materials, rewinding is performed on a central shaft, but in this case, the total width of the winder is smaller. The technology available today makes many aspects highly diff erent compared to equipment from over two decades ago. Precise tension and hardness control ensure exceptional roll quality even at extremely high speeds. Automation in knife positioning, core and tail cutting and gluing, or roll ejection signifi cantly reduces cycle times and setup times.
In conclusion, while the slitting rewinding process has remained conceptually unchanged for decades, it has undergone a huge leap in production capacity, faster setup times, waste reduction and, above all, improved roll quality. Our equipment is designed based on a methodical study of the most appropriate confi guration and layout of components, applying the most advanced control technology to deliver agile, fast and reliable machines for handling a wide range of grammages and substrates.
42
March 2025
www.convertermag.com
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