Washington, PA--Metal shredders made by Lincoln Hydraulics Inc. reduce valuable machined chips to approximately 1/8 their original volume. This process makes the chips easier to handle and transport. A typical shredder consists of a hopper and shredding knives coupled to the input of a 150:1 double-reduction worm drive by a flex coupling. Lincoln uses a 1.5-hp, size 56C, 1,725-rpm motor to drive the unit.
From time to time, hardened or oversized pieces can jam the shredding knives. When a motor remains connected to the reducer input, a jamup will cause a tremendous input torque spike. Because many drive gearboxes provide ratios of 100:1 or greater, the system magnifies the already high torque spike. Damage to the shredding knives and the system's gear drive almost always occurs.
Lincoln's new shredders eliminate this type of damage by taking advantage of an Overload Protection System made by Horton Industrial Products Division, Minneapolis, MN. Installed at the input side of the shredder's double-reduction wormgear drive, the system can immediately disconnect the input drive power from the gearbox when an overload above a preset value occurs.
The protection system consists of an electronic controller and two proximity sensors. Horton engineers place one sensor on the input of a friction clutch located between the gearbox and power input. The second sensor is mounted on the clutch output. During shredder operation, the controller constantly compares inputs from the two sensors. "The sensors count targets on each side of the clutch," says Edd Brooks, Horton's manager of business development. If the input side count exceeds the output count by more than a pre-set amount (18, 20, or 24, for example), the controller interprets that difference as excessive slip. It then dumps clutch air pressure, and the spring-released clutch interrupts power transmission to the shredder.
After clutch disengagement, an operator can re-engage the clutch at any speed. Re-engagement can occur without regard to the relative positions of the friction interface.
Target sensors and control electronics respond to notch-type targets (like sprockets) mounted externally to the clutch body. Only one requirement exists: one target must be on the clutch's drive side, the other on the downstream side.
Chippers in sawmills
Horton's engineers made the dropout slip amount selectable mainly to permit equal levels of protection at different rpm. "Some processes also involve 'normal' torque-pulse levels," says Brooks, "and the machine operator needs adjustable controls to avoid nuisance shutdowns."
Currently, Horton offers the complete overload protection system in its FMCE model clutch size 625. Control electronics come either in a NEMA enclosure or as a stand-alone printed-circuit board ready for installation on a machine's main control panel.
Additional details...Contact Edd Brooks, Horton Industrial Products Div., 1170 15th Ave. S.E., Minneapolis, MN 55414, (612) 378-6401.