Soft Nip Calender Barring - Self Excited Vibration Causes Excessive Maintenance

Single nip soft nip calenders also suffer from barring, resulting in caliper variations and increased roll maintenance. This is also a self-excited vibration with two possible feedback paths, both involving the soft cover. The feedback can be temperature induced cover property variations, or creep in the cover causing minute diameter variations.

The vibration will usually show itself as a barring problem. The barring frequency is always at or close to a resonance in the calender stack or rolls.  The resonance is excited by an integer number of bars around the circumference of the soft roll.

To determine the problem, calender vibration and temperature measurements are made.  When required these are augmented with modal measurements to determine the resonances within the stack.  Finite element calculations are used when redesign is required.