Top Web : Wound Rolls

Are your rolls badly wound, too tight or too loose?

This TopWeb modeller lets you find out how to wind a better roll.

It also does all those tricky little calculations of weight and diameter of rolls given density and length, or vice versa.

We can do some simple, but convenient calculations on roll Weight, Core diameter, Roll diameter, Length, Density, Thickness, and Basis weight. Changing any one of these values will calculate the others (where appropriate).

More complex is to evaluate the Winding behaviour of our rolls. Winding gives a Radial pressure (squashing the roll) and a Tangential stress (stretching or shrinking the web). Stress and pressure are interchangeable terms in this context, but it seems more natural to talk of radial pressure and tangential stress. These values depend on many aspects. We use a modified Hakiel model for the calculations.

The Tension during rewind is, of course, important and usually these are Tapered in one of 3 ways: Linear Radius (i.e. the tension decreases in proportion to the radius), Linear Length (i.e. the tension decreases in proportion to the length of the wound film) and Constant Torque where, as the diameter of the roll D increases from the initial value Dcore the tension decreases by a factor Dcore/D. In the linear cases you need to know to what value of tension the taper is heading – that’s set by the Tension To % setting – if you set this to, say, 40, then the tension will start at 100% and decrease to 40%. The graph of Wind Tension shows you the profile you have chosen.

If you have a nip roller on the rewind, the effective wind tension is increased (if you have no nip roller enter a value of 0). This extra tension is a product of the nip load (Nip Load N/m) and the coefficient of friction (Friction Coef.) between the roller and the web. If you don’t know this, 0.3 is a reasonable value to enter. It is convenient here to provide another calculation. The Hertzian Nip Stress is calculated from the nip pressure and the width of the contact line, Contact Width mm which is usually found using pressure paper. It’s called Hertzian stress because the basic theory of roller contact was first formulated by Hertz.

The graph of radial pressure and tangential stress should be self explanatory