Problem-Solver, Series 13
A quarry in mid-eastern Alabama was "cooking" the windings of a high horsepower, low speed motor on their ball-mill all too frequently.
As the motor was old and the application severe, both from a duty cycle and environmental standpoint, a
Rexnord distributor was called to quote a replacement.
The quoted motor was very expensive and would require a long lead time. The quarry operators were concerned as the existing motor wouldn't last much longer.
The distributor salesman had some ideas on how to solve the customer's problem. He held a meeting with the plant engineer and discussed the following points:
Current Problems
The motor was special because of its low speed. Rewinding it was expensive and the downtime which was required for the reworking caused too much loss of production.
Contract deliveries had to be made for the up-coming summer season.
The high inertia of the ball-mill kept the motor in the high amp draw part of its curve, causing severe heat build-up and loss of expected service life.
High concentrations of highly abrasive dust and high shock loading transmitted by the ball-mill was causing the premature failure of many seals and bearings in the motor as well as the rest of the drive system.
The True Torque Solution
The distributor salesman suggested the customer use a standard 1775
rpm, NEMA B design motor and a True Torque drive to drive this ball-mill. Lower
maintenance and higher reliability would more than outweigh the cost of
this new equipment.
A True Torque fluid coupling added to this system would allow the motor to come up to speed unloaded, reducing the heat produced in the windings, extending service life of the new motor.
Since the True Torque fluid coupling transmits torque through a fluid, it will cushion impact-induced shock loading.
True Torque fluid couplings have as standard seals which are made of viton. Viton has higher abrasive resistance than ordinary Buna-N lip seals.
Implementation
The customer purchased a standard 300hp, 1775 rpm, NEMA B motor, a Rexnord 425A2 drive and a 480HFD-20 fluid coupling.
Rexnord delivered the drive within 2 weeks.
The distributor supplied the fluid coupling from stock and got the motor on site 2 days before the drive arrived.
The motor now starts unloaded and is past its break-down point in less than 3 seconds.
The ball-mill starts in 22 seconds and the customer now says the equipment runs smoother than ever.
Let us show you how to smooth out those major ups and downs that adversely affect the life of your equipment.
CONTACT YOUR REXNORD FLUID COUPLING DISTRIBUTOR FOR THE SOLUTIONS TO YOUR POWER TRANSMISSION PROBLEMS.
Form 870713
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