Problem-Solver, Series 15
Over the past six years a mid-western chemical plant has been plagued with lost production and high maintenance costs associated with the operation of six pellet pulverizing mills.
Problems started at installation.
Plant safety personnel were concerned that the open gear set could produce enough heat to cause an explosion.
To eliminate this possibility a phenolic plastic pinion was chosen to drive the gear.
This solution produced a new problem. The pinion wear life was limited to one or two months and frequent failures occurred at start-up.
The next try utilized a 901 nylon gear on steel hubs.
A dramatic increase in life was realized, but breakage during the normal start cycle continued.
A Rexnord distributor, aware of these problems, met with his customer to determine the action needed to provide the solution.
After extensive meetings it was determined that the wear life was satisfactory but the nylon pinions could not withstand the high starting torque capacity of the drive motor.
The distributor suggested installing a True Torque fluid coupling between the motor and the Falk
gear drive.
Current Problems
High failure rate of the nylon open gear pinion. The high starting torque capability of the AC motor causes severe shock loads and excessive torque on the
non-metallic pinion.
Mill locking pin interlock failure or over-ride. The AC motor is started with the locking pins in place.
The AC motor's full starting torque capability causes pinion tooth failure.
Mill overload conditions occur demanding full AC motor capacity. This condition severely overloads the pinion leading to rapid failure.
The True Torque Solution
The True Torque Fluid coupling tames the AC motor by controlling the
maximum starting torque. The starting shock load is eliminated and the
acceleration torque is controlled providing smooth acceleration.
The True Torque fluid coupling, even at 100% stall, has internal baffles limiting the maximum delivered torque to a known acceptable value.
The True Torque fluid coupling protects the driven equipment, while under acceleration. It also limits the amount of power transmitted during high overloads.
Implementation
The Rexnord representative suggested a 370HFN20 True Torque fluid coupling complete with an explosion proof thermal trip switch.
The switch prevents loss of fluid and automatically shuts down the motor in the event of high fluid temperature due to overloads.
The customer was assured that the True Torque fluid coupling operates normally in the required vertical motor shaft down position.
The Rexnord representative also offered their shop services to mount the coupling, trip switch and to make the necessary modifications to the AC motor mounting bracket and the coupling guard.
The customer was enthusiastic about the solution and immediately sent a drive for modification. The
True Torque fluid coupling solved the problem by providing smooth controlled acceleration and overload protection.
The elimination of pinion failure resulted in increased productivity and minimized costs to routine inspections.
CONTACT YOUR REXNORD FLUID COUPLING DISTRIBUTOR FOR THE SOLUTIONS TO YOUR POWER TRANSMISSION PROBLEMS.
Form 890401
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