Oil Shear Cuts Machine Downtime
- Published: Wednesday, 01 September 2010 08:00
- Written by CP Staff
Ohio's Reading Rock had limited idle time throughout a four-year stretch when the market was at or near peak, producing 22 million 8-in. block Û enough units, placed end-to-end, for a round-trip to the Golden Gate Bridge from the company's suburban Cincinnati plant with sufficient leftovers to build several large schools. Brakes and clutch-brakes incorporating oil shear technology proved instrumental in the producer's block machinery running up to three shifts, six to seven days a week.
Pretty much everything in the plant that has a motor is equipped with a Force Control clutch-brake or brake, notes Reading Production Manager Phil Thacker. Oil shear technology is employed in the braking systems to transmit torque between lubricated surfaces. The circulating fluid cools and lubricates friction surfaces to eliminate wear and dissipate heat. Without direct contact between friction surfaces during acceleration or deceleration, adjustment or replacement of discs is unnecessary.
By contrast, dry-clutch and conventional brakes curtail uptime, since they employ a sacrificial surface (typically, a brake disc or pad) to engage load. Lacking means to remove heat generated by disc/plate engagement, brake materials must absorb the heat; and, extreme temperatures lead to surface-material degradation and glazing. The ensuing torque fade causes positioning errors, which require adjustment or friction-surface replacement.
Since Reading Rock operates a single production line, i.e., one pathway is defined from dry-materials batching and mixing to final exit of pallets carrying cured block, faulty functioning of any component will bring the entire process to a halt. Consequently, the producer chose to equip its main drive with a Posidyne clutch-brake to control indexing of the machine for pallet conveyance, bringing in molds, and depositing concrete. After the mix is placed, vibrators shake the forms to ensure proper density of the block; once completed, the main drive indexes again, and the cycle repeats. Clutch-brakes cycle faster than most prime movers, Force Control affirms, increasing block machine speeds and productivity per shift.
The Posidyne clutch-brakes at Reading Rock use oil shear technology to provide a fluid film between friction surfaces. As the brake is engaged, automatic transmission fluid is compressed and its particles sheared, thus transmitting torque to the other side. Torque transmission causes the stationary surface to turn, accelerating to the same speed as the moving element. Since fluid particles in shear bear the brunt of acceleration, Force Control explains, wear and tear are virtually eliminated by the time the surfaces actually meet or lock up.
Besides transmitting torque, oil shear technology dissipates heat by a patented fluid-recirculation system. Moreover, the fluid continually lubricates all components and 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 found in wet or dusty plant environments.
Additionally, using a Posidyne clutch-brake offers potential energy cost savings, due to lower inrush currents and reduced power factor imbalance. Torque on the clutch-brakes can be adjusted by the actuation system to provide proper acceleration and deceleration. Posidyne oil shear clutch-brakes are also employed on the vibrator drive to settle concrete in block molds. When vibrator shafts are driven by a clutch-brake, the motor runs constantly. No starting and stopping with a clutch-brake-driven assembly ensures smoother, constant operation and decreased cycle time, Force Control asserts, plus extended motor service life.
Upon completion of the vibration cycle, the brake is released and weights drop into the bottom position, owing to the assembly's built-in neutral gear. Both weights thus remain synchronized during start-up, imparting vibration of predetermined amplitude to the shaft Û preferable to starting the cycle with weights in varying positions and imparting more (or less) severe amplitude, causing shock to the system, shortening component life, and compromising block density.
The Ê- to 5-hp motors driving the conveyor, elevator and finger cars are equipped with MagnaShear brakes featuring a totally enclosed oil shear design. Force Control product engineers observe that MagnaShear brakes are used in all areas of green and cured block handling, due to their oil shear durability, electric actuation, simple control logic and spring-set load holding.
HALF-BLOCKS, FULL TREATMENT
To fill half-block forms, Reading Rock used SmartPac vibrator shafts for mold vibration. Previously, actuating the system directly from the motor allowed only on or off vibrator operation. More recently, a technology upgrade enabled personnel to regulate amplitude and frequency. Now, the plant enjoys greater flexibility, double the service life of earlier designs, and rapid compaction and finish times. Further, maintenance requires only greasing a bearing every eight hours and periodically tightening mounting bolts. Overall, Reading Rock attributes increased operational uptime to Force Control Oil Shear technologies.