What Works: No more bearing failures for one Memphis plant
Memphis, Tenn.-based Buckeye Technologies Inc. develops and manufactures cellulose-based specialty products at plant sites in the United States, Canada, Germany and Brazil. Its Memphis plant produces cotton-based fiber products used in fine writing papers, filters, acetate films, thickeners, pharmaceuticals and many other applications.
The manufacturing process uses multiple refining technologies to mechanically modify the cellulose fibers. Given the specialized nature of the products at the Memphis plant, the site is sensitive to refiner reliability problems. “You could count on frequent refiner failures,” says Eddie Kelly, Crew Leader of the Maintenance Technology Group and 29-year plant veteran.
The root cause of the failure was lube oil contamination entering the bearing housing assembly. Buckeye personnel knew breakdowns were going to occur but weren’t able to predict when. Failure meant a shutdown for as long as eight hours to change the bearing housing assembly.
In the 1980s, when the refiner was manufactured, the OEM used labyrinth seals to protect the bearings, which were installed next to the packing gland. Over the years, the refiner kept failing and Buckeye tried a number of other sealing methods, including double lip seals with a grease barrier, which simply didn’t last.
The best contact seals have a mean life of about 1,844 hours, or 77 days of operation, according to their manufacturers. Adjustments such as tightening might renew a seal, but only for a relatively short period of time. Fibrous packing, flingers, lip seals and simple labyrinth seals don’t eliminate the root cause of equipment failure – contamination entering the bearing environment and loss of lubricant.
Invented in 1977, the bearing isolator is a non-contact, non-wearing, permanent bearing protection device. It has a rotor and a stator, and the two are unitized so they don’t separate while in use. Typically, the rotor turns with the rotating shaft while the stator is pressed into a bearing housing. The two components interact without contact to keep contamination out of the bearing enclosure and the lubricant in. The bearing isolator makes no contact, never wears out and can be used repeatedly for many years.
Bearing isolators protect motor and pump bearings, machine tool spindles, turbines, pulpers, refiners, conveyor idlers, fans, gearboxes, paper machine rolls and a growing list of rotating equipment.
The Buckeye Electrical and Instrumentation (E&I) Department had been using bearing isolators for years on its IEEE 841 motors. The IEEE 841 motor is an upgrade to the EPAct mandated motor that improves reliability, efficiency and performance by establishing simple design guidelines. One of these guidelines includes using bearing isolators for bearing protection.
Kelly saw how bearing isolators provide increased reliability and longer motor life. He also knew that Goulds ANSI 3196 or 3175 paper stock pumps came with bearing isolators from Inpro/Seal (www.inpro-seal.com) as standard equipment.
Using premium motors, pumps, bearing isolators and other upgrades is part of Buckeye’s Precision Maintenance program. (Precision Maintenance Training is a specialty of Reliability Solutions LLC (www.reliabilitysolutions.net), which has been working with Buckeye’s Memphis Plant to improve its maintenance systems.) Kelly says the extra dollars invested have paid big dividends over time, and his group decided to try Inpro/Seal’s PMR bearing isolator on the refiners. Originally designed for paper machine rolls, the PMR was developed on an end user’s request for a bearing isolator that could increase reliability and extend the service life of paper machines.
On the wet end rolls (breast, table, press, wire return), water, pulp and paper stock are prevented from entering and contaminating the bearing housings. On the dry end rolls (calendar, coating, queen, suction, starch, drum, end), where oil can ruin the product, they eliminate leaks from oil-lubricated bearings.
Inpro/Seal engineers modified the PMR design for the refiners by adding a flange that provides a secure fit, registering it directly to the bearing housing, where it is bolted on. The design can accommodate the axial movement of as much as 1.5 in. when the refiner plate loads up and its plate shifts.
Since installing the flanged PMR bearing isolator 14 months ago, Buckeye hasn’t had a shutdown on the refiner. The backup refiner, maintained in the store room for emergencies, hasn’t been used. As part of its “Precision Maintenance” Program, Buckeye plans to add more bearing isolators as breakdowns occur.