Winder vibration poses special diagnostic challenges way beyond any other web machine . The reason has to do with the wound roll itself. The wound roll is a complicated element because it will have an imbalance and out-of-round much larger than any decent roller. Second, it changes rotational frequency during the course of the winding cycle due to increasing diameter. Thus the forcing function ‘sweeps’ out a range of frequencies rather than being single valued such as a roller. This means there is a much greater chance of exciting a resonance. Third, the wound roll can literally change shape during winding. Thus, for example, a roll can change from one sided (egg shaped) to two sided (oval) to three sided or more sided and/or back. This behavior again increases the chance of exciting resonances. Finally, the misshapen roll can excite vibration that pounds the misshapen roll further out of shape in a self-exciting fashion.
Another necessary concept is that of ‘bouncing’ grades . There are certain grades that are notorious for generating wound roll vibration on almost any winder they are wound on and under almost any winding condition (though winding tighter is usually the best strategy). In paper, these grades include book, kraft, NCR, tissue and others. Sometimes a subtle change of chemistry, such as additives of a few pounds per ton, or a loading change on the paper machine’s calender can switch vibration on and off like a light switch. However other materials such as nonwovens and textiles also tend to vibrate if they are wound at higher speeds. What connects (most or) all of these materials together are two properties: high web-web COF and high ZD compressibility. To make a very long story short, these properties tend to make a wound roll get out of round due to self-excitation. A bump makes the roll bounce, and the bounce makes the bump worse etc.
The question will come up, “whose fault is it.” Despite the enormous complexities of the mechanics, this has a relatively simple test and answer . Does the winder vibrate much when it is run at full speed, but without a wound roll? If so, the winder is clearly deficient. If not, the winder itself may be fine, especially if your product is known to be a bouncer, especially if other materials can be wound without such trouble. In that case, the wound roll is the exciting force, the wound roll is the primary mass in motion and the wound roll has the lowest spring rate of any member of the structure. All the winder is doing is going along for the ride, especially if it is a layon roller or rider roller moving in the direction that it must for roll build. This is one of the toughest problems in the web industry because it is so constrained. Almost the entire set of most important vibration factors belong to the roll product, which presumably can’t be changed, rather than the winding machine.
An analogy might be helpful. Consider a car and a road. Can the car run full speed? Yes, IF the road is straight and smooth. Here, the road is analogous to the wound roll and the car is winder. Those who wish to study further should consider the following classic articles.
Roisum, David R. Winder Vibration Can Reduce Operating Efficiency and Increase Maintenance. Tappi J., vol 71, no 1, pp 87-96, January 1988.
Olshansky, Alexis. Roll bouncing. TAPPI J, vol 80, no 2, pp 99-107, February 1997.
Roisum, David R. Tissue Winder Vibration. Perini J., vol 13, no 8, pp 33-36, August 1998.