Tips

Differential rewind shafts are typically much more complex and cost much more than their locked core counterparts. So, why would you go through all of the trouble and expense associated with outfitting your slitter rewind with differential rewind shafts? The answer is simply that you may need to use them to build your multiple slit width rolls properly.

When parent rolls are slit, each slit width then becomes its' own parent roll. Each slit width must be treated as an individual roll. Most of the time parent rolls have slight thickness variations (or gauge band variations) across their width. When parent rolls are slit, these thickness variations will cause slit widths to be rewound at slightly different roll diameters. If the slit widths are wound with locked core shafts, most of the web tension will be delivered to the largest rolls making them very tight and smaller rolls will be extremely loose. Telescoping, dished rolls and completely unstable rolls will result from trying to wind slit widths on a locked core air shaft.

You may be thinking, "Well our parent rolls don't have any gauge band variations, so this shouldn't be a problem". Are you sure? Keep in mind just a very slight variation can make a huge difference in roll diameter build. Thickness variations are cumulative with each wrap of the rewind. A thickness variation of .00001" quickly builds to .001" of an inch difference in roll diameter through just 100 layers in a rewound slit width.

Bottom line, differential rewind shafts work so well at combating this problem because they are designed to allow each slit width to slip independently. In essence, each rewound slit width has its' own individual clutch, allowing the best possible tension control for each width. This improved control will allow you to build the best possible rolls on your slitter rewind.

Written By: Jeffrey Damour, Sales Engineer, Converter Accessory Corporation, Wind Gap, PA, Phone - 800-433-2413