Tech tip: Tendency Driven Idler Rollers

Web tension is cumulative in your machine. Every time your web wraps around and effectively drives an idler roller, that idler roller adds some amount of web tension to your process. There is no such thing as completely friction free bearings, so whatever torque is required to drive the idler roller and in turn the bearings on which it is mounted, is supplied by the web in the form of web tension. More idler rollers means more web tension. Sure, you can take measures to ensure the least amount of tension is accumulating in your process. Measures like utilizing low friction bearings, using light oil instead of grease in your bearings, maintaining your idler rollers to ensure they are rotating properly will help ensure your web accumulates the least amount of web tension.

There is one more step that may help. You can tendency drive idler rollers in your machine. Tendency drive simply means that you drive the center shaft of your normally dead shaft idler rollers. In other words, the construction of your dead shaft idler rollers typically remains the same or very similar to their current construction. There is a center shaft (normally mounted, rigidly, in mounting blocks or bolted between machine frames) and an aluminum (or other material) roller face, mounted in ball bearings to the center shaft. However, instead of mounting the center shaft, rigidly; the center shaft of a tendency driven idler roller is mounted in its own set of ball bearings. That center shaft is then driven, in the web direction, by an external drive.

Since the roller face is not rigidly connected to the center shaft, the drive system can be a relatively simple one because accurate speed synchronization is not necessary. In fact a slight, constant, over-speed is recommended. Since the rollers will rotate in the web direction, they will be a positive driving force on the web but the only positive tension delivered to the web is whatever the frictional losses are in the ball bearings on which the roller face is mounted. This type of system can be very effective to assist in handling very light tension web processes.