Torque Limiters Tag-team to Prevent Overloads

For Elmar Industries, mechanical stops alone could not sufficiently halt the upward travel of the adjusting column with every cycle on one of its 100+ models – the Monoblock custom filler/capper
systems. At times, the upward force would overpower the mechanical stops, jarring them loose and sometimes knocking them off the system. The downward motion could develop too much force if the limit switch failed and the column bottomed out. This would jam-up the system. “What’s critical is to be able to control both upward and downward travel to avoid both of these problems even if the over-travel switches fail,” said Russell Wozniak, project engineer for Elmar.

Wozniak’s team turned to an alternative method for overload protection. Elmar now uses mechanical torque limiters because of their simplistic, fail-safe operation. On its Monoblock filler/capper systems, two different Zero-Max Torq Tender torque-limiting devices safeguard two separate machine functions. Both devices provide fail-safe jam-up protection.

The Zero-Max H-TLC torque limiter provides overload protection in the bottle height adjuster mechanism.

“We use the H-TLC-500 torque limiter in the motorized height adjustment mechanism, which raises and lowers the center column to adjust for different bottle heights,” reported Wozniak. This device prevents over-travel of filler heads. At the high and low point of travel of the filler head are mechanical stops. The motor-driven height adjuster assembly has a rotating shaft that connects to the elevation device at one end and the H-TLC torque limiter at the motor end. The H-TLC is located between the motor that powers it and the shaft leading into the height adjuster mechanism. It operates on a spring-loaded convex pin and detent design, which reacts to pre-determined overloads. When the load reaches the preset limit, a pin disengages from the detent, shutting down the system. Once the overload condition is corrected, the torque limiter can be reset fast and the system restarted. The H-TLC can quickly be adjusted for changes in torque as needed.

The Zero-Max face-mount Torq Tender is the second torque-limiting device in the system.  It
connects to the primary drive train that moves the bottles through the system for filling, and protects the timing screw mechanism in the main gear drive from any kind of jam-up. Steel springs within the unit force metal slides against each side of a hardened cast steel pawl, holding it rigid with one end seated in a detent on the outer drive housing. During normal machine operation, the Torq Tender functions as a positive drive coupling. Input power transfers into the central assembly through this pawl. The outer drive housing and its driven shaft then rotate.

1. During normal machine operation, a hardened cast steel pawl is held rigidly between metal slides, with one end seated in a detent on the outer drive housing. 2. The pawl rotates out of its detent when excessive torque overpowers the springs.

When a load exceeds the rating determined by the precision tempered torque springs, excessive torque overpowers the springs, and the pawl rotates out of its detent. The central assembly is disconnected from the outer drive housing. This cuts power in the system, shutting it down.

Wozniak said that prior to the Torq Tender, a shear pin protected the feed screw drive. This was a problem because it required time to replace it following a jam-up. The Torq Tender, however, re-starts quickly, and it does not require tools. “You can manually re-set the torque springs of the Torq Tender with a simple full turn of the device. This puts the pawl back in its detent, and it re-engages the drive shaft. What’s more, Wozniak reported, “Once installed, you can forget about the Zero-Max torque limiters because they never need service. Ours have performed without problems for over five years with many installations operating twenty-four hours a day, seven days a week.”

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