Features Equipment & Systems
Paper Week Review: Preventing failure

HOW OFTEN should you repair a machine, before finally consigning it to the garbage and opening the chequebook? Joe Cooper from the Domtar pulp and paper mill in Espanola, ON, attempted to answer the question in his presentation at Exfor 2002. The decision very much depends on which machine is under consideration said Cooper. Kiln or chippers are not likely to be treated as motors do, the smaller 5 to 50 HP models in particular.

“We just had too many failures on our motors”, said Cooper. Over the years the company had accumulated an excess of totally enclosed fan-cooled motors (TEFC). Many were old, had multiple re-winds and bearing changes, they did not run efficiently, or broke down soon after repair.

Due to repeated motor failure, the Espanola mill decided to embark on a consignment spare program of IEEE-841 TEFC motors from 5 to 50 HP — the Institute of Electrical Engineers (IEEE) created the new standard, IEEE 841 motor, in 1986. The mill chose these motors because of their reputation for increased efficiencies and decreased noise levels. They are also frequency drive rated, possess lower bearing temperatures and a five-year warranty. And the move proved to be a success. “We’ve only had one motor failure in 152 installations over three years,” said Cooper. Savings on energy and inventory costs, coupled with shorter downtime, have offset the increased costs of purchasing the new motors.

R. Da Prat, from Rockwell Automation, offered a presentation on application considerations in the use of variable frequency drives in the pulp and paper industry. He pointed out that 50% of the motors in the pulp and paper industry are used for the operation of fans, blowers and pumps, and that this represents potential savings. There are two methods to alter a pump’s characteristics and vary flow, throttling valve control and variable speed flow control. Da Prat said that most of the northern Ontario pulp and paper mills sent a positive feedback on the use of variable frequency drives to control centrifugal pumps. Variable speed drives are claimed to allow optimum operation on fan and pump systems, with additional benefits such as extended bearing life and improved process control.

Pete Pelletier, product applications sales engineer at Toshiba International Corporation, focused his presentation on a practical overview of common application problems and solutions. “Electric motors play an extremely important role in large industrial production facilities,” he said. He examined the reasons why motors fail and suggested practical solutions and alternative methods. He mentioned particularly bearing and insulation failures. He advised delegates to pay particular attention to the greasing activities in a mill. “We would definitely recommend greasing as opposed to not greasing at all. The goal is to spread greasing intervals as far apart as possible,” he explained.

Pelletier also suggested that botched belting applications are possible instigators to premature bearing failures. “Sheave size and width, sheave placement on the shaft, sheave alignment and belt tension may all lead to premature bearing failure,” he said, excessive starting may also contribute to motor failure.