When winding hard rolls of film, the high-caliper areas build on each other.
The rule of thumb for the maximum oscillation speed is 25 mm (1 in.)/min per 150 m/min (500 ft/min) of winding speed.
The rise and fall time of current pulses varies with the winding inductance.
First, we keep the width of the pulses short, to about 300[micro][s.sup.21] Second, we reverse the polarity for every other pulse through the same winding, which cancels any small motion that may result from the first pulse.
When winding inelastic webs, nip is the dominant principle used to control roll hardness.
The challenge for winding is to have sufficient nip to remove the air and wind hard, straight rolls without introducing too much in-wound tension in order to prevent roll blocking or deformation of the web over the high-caliper area.
Buckled rolls are a more severe case of starred or spoked rolls, where compression becomes so intense that the core itself is deformed, often making it impossible to remove the rolls from the winding shaft.
If idler, nip, or lay-on rollers aren't parallel to the winding core or don't apply pressure evenly, stresses will pull the web to one side.
Higher winding speeds and better tension control are "changing the paradigm," notes Mirek Planeta, president of Macro Engineering & Technology.
Precision load cells and newer roller configurations allow much lower winding tensions.
The ability to produce larger rolls at higher speeds is partly owing to new carbon-fiber composite winding
shafts, which are stiffer and less prone to deflection than traditional steel or aluminum shafts.
This flaw affects all winding
applications, but it's especially important for very thin films such as those under 7[mu].