Can You Trust (Web Handling) Equations?

Presented by David R Roisum, Ph.D., Finishing Technology, Inc.

Equations have been used for more than two millennia by mathematicians and scientists alike. Newton’s Laws have been used to predict everything from cannonball trajectories to the orbital mechanics needed to put a man on the moon. Yet, as we will see, the practitioner must not only double check the inputs, they also need to have a level of understanding such that they could derive the equations and checked the results themselves. That is because an equation is a simplified model of reality, not the same thing as the messiness of reality itself.

We begin what is probably the oldest and certainly most used web handling equation: calculating the length of a wound roll given diameter or vice versa. This requires ‘effective’ wound thickness which is not the same as measured in the test lab. For certain web products, the prediction using lab thickness will get you close. However, for other web products the error could be 50% or more.

From there we return to the century old traction equation and find difficulties getting the COF that is a required input. Then we cover curl and roller sizing all the way up to the series of equations needed for wound roll accretion models.