Oil-Shear Brakes Cure Headache
EP Editorial Staff | November 14, 2018
Running three shifts around the clock throughout the week doesn’t allow production downtime on the anodizing line at the Southern Aluminum Finishing Co. (SAF) site in Atlanta (saf.com). In the past, however, that line frequently ground to a halt due to demand for maintenance on its cranes’ dry-clutch brakes.
The situation was a constant headache for Josh Berris, the general manager of the Atlanta operation. It was such a headache that he dedicated a member of his team to primarily repairing/rebuilding those brakes. Eventually, Berris decided to replace them with units featuring oil-shear technology from Force Control Industries, Fairfield, CT (forcecontrol.com). Equipped with Force Control’s MagnaShear brakes, the site’s anodizing line has been back up and running, 24 hours a day, five days a week,
The anodizing line’s cranes are used to manually guide parts through a process that involves continual starting/stopping/jogging items into position. With a 1-ton capacity and independent front and back action, a crane performs as many as 20 clicks per move, and many hundreds of moves per shift. To stop and position the load, Baldor 5-hp motors from ABB Motors and Mechanical Inc., Fort Smith, AR (baldor.com) are mounted with the brakes.
The equipment’s old dry-clutch brakes had been failing every other week. Dry brakes, by their very nature, employ a sacrificial surface—the brake disc or pad—to engage the load. Without a good way to remove the heat caused from engagement between the disk and plate, this sacrificial material absorbs the extremely high temperatures, which degrades the friction material.
As the brake friction surface wears away and begins to glaze, the spring force is also reduced, causing torque fade. This results in positioning errors that typically require adjustment or replacement of the friction surface. In addition, manual jogging that engages a brake multiple times per move will quickly wear down dry brakes.
Given their heavy loads and rigorous use, the dry brakes required constant attention. Production, in turn, would come to a complete stop for the time a maintenance person needed to disassemble a brake, replace the disc, and reassemble the brake—and do it all at height.
Brake repair was more than just a nuisance. The resulting downtime added up to serious backups and loss of production time. Its cranes are set up with two overlapping brakes so SAF can operate with just one, but productivity is limited, with as much as 30% less efficiency.
Berris and his team purchased and installed five MagnaShear MSB4 oil-shear brakes. All five have operated flawlessly. In these brakes, a film of automatic transmission fluid (ATF), flowing between the friction surfaces, is compressed as the brake is engaged. The fluid’s particles in shear then transmit torque to the other side. This torque transmission causes the rotating surface to slow, bringing it to a stop. Since most of the work is done by the ATF particles in shear, by the time the surfaces actually meet or lock up, wear is virtually eliminated.
Beyond transmitting torque, the ATF helps to dissipate heat, due to a patented fluid-recirculation system. Along with torque transmission and heat removal, the fluid also lubricates all components, thus extending their service life. In addition, oil- shear technology provides a cushioned stop that reduces shock to the drive system—further extending service life.
Unlike dry-clutch brakes, the totally enclosed oil-shear system is impervious to external elements, including wet, dusty, or dirty environments. Since the layer of oil eliminates wear, MagnaShear brakes also offer long service life.
While the initial purchase price was higher than the dry brakes SAF replaced, the MagnaShear units have paid for themselves several times over in longevity and subsequent maintenance savings. By avoiding brake failures and production downtime, they’ve allowed SAF to keep up with its high production standards and maintain its reputation of excellence. EP