By Fredrik Franding, Global Manager, Certified Programs, SKF Group
ATLANTA,
Nov. 24, 2008 (Industry Executives) -
To the ear of a paper mill manager, the hum of a healthy electric motor is pure music.
A mill may have up to 10,000 motors in operation. They include large dc types that drive the plant’s rollers and smaller ac motors that power auxiliary equipment, such as fans and pumps. All are important and many are essential to the papermaking process. When a critical motor catastrophically fails, production stops at an equipment downtime cost that’s estimated between $20,000-$30,000/hr.
For this reason, electric motor reliability has become a top priority throughout the paper industry. One reliability factor that has emerged with especial prominence in recent years concerns the quality of motor repair services. A case in point: A large papermaker initiated an assessment program for the shops that its mills could employ for electric motor repairs. The initiative came after an internal study that showed:
• Electric motor failure was consistently among its mills’ top five reliability incidents.
• The incidents were causing millions of dollars per year in downtime.
• A major portion of the incidents could be eliminated by addressing non-production related failure causes, including substandard motor repairs.
The assessment initiative would require motor shops to meet challenging criteria pertaining to repair quality. Meeting the criteria would mean wholesale upgrades in how the shops processed repairs. In support of the shops, the papermaker partnered with rotating equipment technology supplier SKF USA Inc. The paper maker would conduct independent assessments, while SKF managed shop audits, training, procedures, equipment and engineering support. The partnership proved beneficial to both the papermaker and the repair shops that participated in the program. In just one year, the manufacturer reduced reliability incident costs associated with electric motor failure by 10%. Additional savings are immanent.
In addition, the paper producer reduced its purchases of new motors by 39% and slashed repair purchases by 45%. Benefits to participating repair shops were equally impressive. Etheredge Electric Company, Inc., with facilities in Shreveport, LA, and Tyler, TX, took advantage of the services offered. Under the program, Etheredge successfully met the paper manufacturer’s assessment standards and in the process became a Certified Electric Motor Repair Shop, one of just 20 in the industry. The certification entailed sweeping changes in the ways Etheredge conducted its operations. A contaminant-free, climate-controlled bearing room was established, for example, which Etheredge says ultimately contributes to the end user’s electric motor reliability.
Other improvements now guarding against contamination at Etheredge include motor disassembly and assembly being completed in different areas, and bearing grease stored in a separate climate-controlled, contaminant free location. Proper bearing installation is a key practice and expert shops will value the importance of achieving accurate bearing fit tolerances. Etheredge Electric uses digitally controlled, degaussing bearing heaters in place of standard models.
“Bearings can pick up a magnetic field when heated with conventional units and attract tiny particles of metal,” company president Mike Etheredge explains. “As the bearing rotates in the motor, that metal can create grooves in the bearing race, leading to premature failure. When you degauss a bearing prior to installation, you eliminate the magnetic field.”
Electric motor shops that provide expert services will typically excel in the area of acceptance testing, including vibration analysis and balancing. Vibration analysis produces a signature that can later be used as a benchmark in the paper mill’s condition monitoring program. Balancing ensures that a motor’s rotor and fan have the proper weight center.
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