A practical alternative to mechanical braking and non-regen drives systems in the converting, packaging, wireforming and printing industries.
During the operation of any converting machine, whether for film, foil, wire, paper or board, plus most large printing presses, rolls of materials are handled by unwinds, often still driven by pneumatically operated braking systems. The traditional tension control system for an unwind stand is a simple mechanical brake. In principal, the unwind brake mechanically operates much like the braking system on your car, with a disk, caliper and pads, but is controlled by a tension sensor linked to a setpoint controller. As the roll unwinds, the tension is maintained by the brake for smooth passage of the material through the dies or rollers, resulting in better package alignment, less wrinkling, better print registration, even more consistent wire dimensioning and other production positives. These mechanical brake unwinds are effective in controlling the tension, but have inherent problems of heat and power loss, plus mechanical wear and constant maintenance needs, substantially impacting machine uptime.
The typical mechanical brake is pneumatically controlled and may utilize several sets of friction pads to control the web tension as the roll dimension decreases. Plus, a reasonable pressure range in many applications might be from 15-90psi or a 6:1 drop, a range significantly less than the core to full roll ratio for most jobs, an obvious inefficiency in operation.
To affect good tension control on the brake, these friction pad sets need to be manually changed in an out of the brake assembly, depending on the desired operating tension and the roll diameter changes involved. Often, the adjustments are several per roll during this manual changeover. Because the mechanical brake creates the unwind tension through friction, it generates substantial heat and often requires a separately powered fan for cooling to operate effectively. This friction also means the pads are subject to rapid wear, requiring frequent and time-consuming changes or maintenance checks.