Top Web : Torque and Inertia Does a roller require too much torque to make it spin? Is this thecause of scratches or tension mismatches? This TopWeb modeller tells you how to find out. Will my roller scratch my film? Will I have any tension problems caused by rollers? To answer this question you first need to know how much torque drag is caused by a sticky bearing and how much inertia is in the roller. The inertia can be calculated by knowing the Roller ID, Roller OD, Roller Density. To find the torque drag you can either measure it directly using some sort of torque meter or indirectly by setting it spinning at a speed Spin from m/min and Time how long it takes to slow down to Spin to m/min. From the calculated inertia and from the measured time, the program can calculate the torque drag. A large value of Time means that the roller is free running and the torque drag is small. Knowing the torque drag, it’s then easy to calculate whether there is enough grip between web and roller to avoid the web slipping and causing scratches and/or tension variations. The calculation uses the Wrap angle and Friction coefficient from the other module. If you get a Warning: then you need to fix the roller bearing or increase Wrap and/or Friction coefficient. Finally, the increased tension caused by the roller might impact your overall web handling, especially if you have a Number of rollers. At steady running this tension may not be a problem, but if you accelerate the web the inertia of the rollers may cause extra tension which, at the extreme, could cause a web break. The Acceleration is in the apparently odd units of m/min/s, but this makes sense – it’s a measure of how many seconds it takes to increase your web speed by a known m/min.  | 
