Productivity is always a major point of emphasis, and one that has led some manufacturers to process multiple rolls of material through a machine (that was originally designed for one roll) at the same time. If multiple rolls of material can be processed side by side within a machine; to ensure high quality results, tension must be measured, and controlled on each roll separately. In applications like this, multiple webs of material should not pass over/utilize the same load cell roll.
If they do, accurate tension measurement and control, is often very difficult; potentially causing a tremendous amount of web tension related issues from inaccurate tension readings, poor controls, material quality issues, finished roll quality issues and a high level of scrap.
So why can’t multiple, separate rolls of material utilize the same load cells?
Outside of a specially designed segmented load sensing roller, a pair of load cells cannot be configured to independently measure multiple places on a roll and thus sends a singular measurement to the tension controller throughout the process. They simply don’t know if it’s one web or twenty webs.
If running multiple webs over the same load cell roll, the load cells are essentially measuring the AVERAGE tension of the multiple webs. The controller then uses this average to control the torque device (brake/clutch) and tension.
Because each roll of material will most likely be at a different tension level as it reaches the load cell roll, utilizing average tension means none of the webs will be controlled at your desired tension set point, affecting processing and end product quality. For example if one web is slack while the other is tight the controller has no way of regulating them independently as it controls based on the average tension of these two webs, thus requiring the operator to compensate & manually adjust the torque device.
Regardless of whether you are unwinding/rewinding multiple rolls from the same shaft (and torque device), or are utilizing multiple shafts (multiple torque devices), utilizing the same load cell for each web will create wide tension variations and affect product quality.
Multiple rolls of material can be run together on the same machine, but in order to ensure you are maximizing your process and end product quality always utilize independent load cell rolls for each roll of material you are running.