Picking a Winner
Do you take your shafts and chucks for granted? It’s probably easy to do, because although they are important components in any web handling or printing operation, they don't tend to elicit much excitement.
For those companies that supply these components, however, shafts and chucks are exciting and require the high level of attention that is afforded any device that carries heavy weights at high speeds around operating personnel.
Mark Fortin, president of Double E Company, points out that the first considerations when specifying shafts has to be structural safety. “That means that the shaft, as a beam, has to be capable of safely supporting the intended roll weight at the design speed of the machine,” he says. “For this, it is important to know the operating conditions that will result in the highest stress and deflection of the shaft. When a machine user plans on running multiple web widths, the heaviest roll will very often not represent the worst shaft bending case.”
Once the shaft strength and deflection are addressed, the next area to consider is to make sure the shaft will be running below its critical speed, especially in high-speed applications. “Today’s higher web speeds and wider web widths can result in vibration that necessitate machine slow downs at minimum roll diameters,” says Fortin.”
One important factor in dealing with the issues of stress, deflection, and critical speeds is the shaft material being used. In addition to high-strength steel and aluminum shaft materials, Fortin points to the variety of high-strength carbon fiber options that can be used to address these issues.
Specifying core chucks
With core chucks, Fortin notes the importance of differentiating between simple unwinding with brakes and regenerative unwinding in which the drive motor also provides the braking action. “The first case is best served with automatic torque-type chucks, while the latter requires pneumatic/mechanical chucks that are controlled to be either on or off,” he states.