2016 Slitting and Rewinding Q&A for Flexible Packaging
What’s new in slitting rewinding? How can slitter rewinders minimize inefficiencies? Why are alignment and tension control so important? In the Jan/Feb 2016 issue of Flexible Packaging magazine, Catbridge president Michael Pappas answers these and other questions. See an excerpt from the interview below:
Q: What’s new when it comes to slitting/rewinding?
A: New technologies and developments focus on a number of areas. One is safety. Safety concerns are not new, of course, but the technologies used are constantly advancing. For example, safety PLCs are now being employed by premier builders. While there is an associated cost, the benefits in safety and operator process control are more than justifiable.
Wind quality is another area of focus. Edge quality continues to improve as tension control and rewind shaft technologies improve. Roll build can be better than ever due to consistent tension achieved through recipe-controlled, precise taper-tension programs. Better roll build can greatly reduce unwind problems for customers using automatic roll dispensing machinery.
For turrets, new technologies at the start and end of roll rewinding further improve quality. The latest automated turret designs offer a tail tie to core process that all but eliminates the problem of the roll being slightly off core at the first wrap. The new process also provides proper alignment at the last wrap, which, importantly, eliminates the need to detach, realign, and then re-secure the last wrap. The savings in operator time and the improved finished roll appearance to the customer are significant.
Additionally, many exciting technologies are being developed for duplex slitter rewinders. As duplex slitters get faster, core placement and finished roll removal processes must also get faster. The new technologies do both tasks more simply, without expensive systems that are often dedicated to just one slit size.
Q: What’s being done to minimize inefficiencies?
A: Inefficiencies from downtime originate from four main sources: loading new parent (jumbo) rolls, stopping and splicing for flags, knife setup changes, and downtime between finished sets (when the machine stops to discharge rolls, place new cores, and attach tails). Shaftless floor pickup unwinds, auto knife placement systems, auto core loading, and roll pushers address three of these inefficiencies.
For the fourth, flags, one solution is programming the PLC. Flag positions on a jumbo roll can be entered in when the roll is loaded so that the machine slows down and then stops at a flag. From there, the right type of splicing equipment, often used in conjunction with an integrated scrap winder, can help the operator save time.
From a broader perspective, eliminating the need for flags has the most beneficial effect in the slitting department. This means fixing the problem at the source, during a previous process such as printing or laminating. When this is not possible, some companies turn to the intermediate step of a “roll editor”. This is a machine specifically designed to deal with bad material, removing defects before the roll gets to the converting department. This adds a step to the process, of course, but time studies in some plants have shown this approach to be a significant net gain.
Q: Why are alignment and tension control so important in slitting/rewinding, and what should converters be doing to better account for these factors?
A: As mentioned above, tension control and alignment are critical in two areas: finished roll build quality and edge quality. However, proper tension and alignment control also impact a third, important area: the speed at which material can be run. Speed can be a major efficiency factor as finished roll length increases. Modern, well built, well controlled slitters should be able to run most all materials at 2,500 to 2,800 fpm. That can make a huge throughput difference on longer rolls. For example, a 20,000 foot finished roll running at only 1,500 fpm would take roughly 14 minutes to run. The same roll at 2,500 fpm would take approximately 8.5 minutes to run (accel and decel curves a variable). That is a savings of more than 5 minutes a set, every set, every shift, every day. Even at shorter roll lengths the gains of speed must not be ignored.
For the complete Q&A, visit the Flexible Packaging magazine website: