Q: How can downtime be reduced in slitting/winding?

Michael J. Ducey, Consulting Technical Editor 415/928-7297 paperfo@earthlink.net -- Converting Magazine, 4/1/2001

A: One effective method to reduce downtime in slitting/winding operations is to coordinate the paper grade application with the shear-cutting system. Converters can set up a small program that can accurately predict the knife life of each paper run, which will reduce downtime and set-up times, extend blade life and reduce paper dust. Knife system vendors offer in-house training and automated systems today to "jump start" the process at moderate cost and with excellent returns.

Paper dust and knife life are the two major issues in paper slitting. Mechanically, paper dust is caused by old, loose knife holders, poor set-ups and dull knife blades. Physically, paper dust problems can increase with large variations in moisture, poor formation (especially in 100% recycled-content grade), excessive variability of roll hardness (probably caused by poor winding at the mill) and other large variations in process parameters (caliper, weight, etc.). Paper mills track all of this information with digital computer control systems, so it should be accessible to customers. Customers can use this data when seeking claims for excessive dust and poor blade life.

Checking the knife system

It is useful for converters to track paper grade use by brand name and weight against knife life and dust in a spreadsheet over time. Each paper grade should have its own data line and the goal should be consistency. Of course, the other factors in knife life would have to be considered before results are concluded.

The quality of materials used in knife production are very important in determining knife life optimization. Material hardness unfortunately varies directly with price, so it is easy to follow. Hardness increases should mean increased life, but other factors in shear cutting can be equally important.

Converters should be familiar with the basics of shear cutting. Factors that influence shear cutting include blade overlap, shear angle, side-load pressure, and blade bevels. Once you have found the toughest blade for your jobs, it is equally important to know how that blade should be set for maximum life. The quickest way to reduce downtime is by reducing knife changes, which stop the web and can lead to other problems. Finding the right blade for the right paper and then setting it up properly will keep the web humming along until jobs are changed-at big savings and efficiency gains for the plant.

Knife holders, mounting methods and positioning systems also need attention when reviewing and establishing a good downtime reduction and dust-prevention initiative. Knife holders needs to be sturdier than ever, given the high speeds, roll weights and upstream demands of the converting line. The holder is the key to maintaining precise settings, which is a major factor in keeping the blade sharp. Increasing blade sharpness leads to longer life, which reduces down time and paper dust. There are methods to test durability of the holders available from vendors which will accurately predict just how tough the holder is and when it might become unstable-contributing to dust and downtime.

Automation in paper slitting

The microchip has had a fantastic impact on slitting/winding operations for paper mills and converters alike. At the paper mill, high technology has increased winding speeds in excess of 8,000 fpm, provided detailed information on every roll manufactured, and has enabled the tracking of that roll right up to the customer's roll stand. In this way, the paper roll arrives at the customer location protected and undamaged, and with data that allows the customer to set his system up for effective and efficiency application. That's the theory, anyway!

Best practices in roll handling at the plant ideally would have an inventory system employing highly-trained forklift operators (largest source of damage to rolls), humidity controlled storage, proper alignment of rolls (FIFO or LIFO consumption scheduling), and a good tracking system on performance for every roll, with feedback available to the mill representative. This information exchange between the converter and mill is a "win-win" situation, resulting in lower prices or product upgrades, or just strengthening the business relationship.

At the converting plant, there are many new technologies that can be applied to reduce paper dust and extend blade life, in particular tied to the slitting system. Today's automated positioning systems are designed for great precision and accuracy. Operator error is virtually eliminated and set-up time reduced dramatically. Positioning systems are now available as turnkey projects and retrofits, providing a good alternative to new winding systems.

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For more information on slitting/rewinding, check out the online version of our 2001 Slitter/Rewinder Technology Supplement-Technical Forum Edition. Point your browser to www.convertingmagazine.com and click on the orange tab labeled "Slitter/Rewinder."