Bearing Swap: If You Can’t Take the Chill, Get Out of the Cooler

Packaged and unpackaged foods are traveling from place to place on conveyors with hardly any human intervention. Until conveyer bearings start to wear, that is. One company facing multishift shutdowns twice a year to change worn bearings decided there had to be a better way.

In the plant, conveyorized coolers chill some sterilized foods to 100°F before labeling and packing. The cooler lines are 90 to 100-ft long and operate around the clock at least five days each week, apart from periodic cleaning shutdowns. The equipment sees water at up to 200°F sprayed to sterilize and seal some containers as they enter the coolers, not to mention subsequent temperature drops as the packages cool. The conveyors are also exposed to chlorine wash downs.

The 5997 MatTop chain from Rexnord Industries LLC, Milwaukee, moves the filled containers through the coolers. The 2.2-lb/sq-ft chain is supported by 5-in.-diameter stainless-steel rollers with 0.75-in. shafts, on 6-in. centers and travels at 4 to 5 fpm. Bearings support the 100-lb rollers, the chain, and food on the conveyor.

The conveyor-roller shafts originally rode on wood-and-resin bearings that relied on moisture for lubrication. But the conveyor’s loads led to uneven bearing wear, specifically elongation of the inside diameter because the bearings remain stationary while the roller shaft spins.

The original bearings failed in as little as six months. The maintenance supervisor explained, “Sometimes bearings would wear right through, and metal-onmetal contact would cut into the stub shafts on the rollers.” Replacement of bearings meant shutting down the line for up to three days, causing production losses as well as maintenance expense.

The firm tried Rexnord Duralon bearings in the cooler and in hot water spray. Inspections after an eight-month trial revealed no visible wear, so the company planned to replace the remaining bearings.

Duralon bearings have a filament-wound fiberglass structure bound with an epoxy resin. The bearing element itself is woven Teflon and polyester. Bearings are 1-in. long, 1.5-in.-diameter tubes with 0.75-in. bores.

Their simple design requires no adjustment, alignment, or maintenance. Two parallel grooves cut partially through the OD keep each bearing from rotating inside its holder. The bearings do not require additional lubrication which could cause contamination in a food-processing environment. The bearings are not affected by periodic wash downs which can wash away secondary lubricants.

All the rollers on three of the plant’s four coolers have been equipped with the new bearings, 1,150 bearings in all. The Duralon bearings have lasted over 18 months to date, with the original test bearings working for nearly 4 yr. Although they can be rotated 180° in their holders if their bores become elongated from wear, company mechanics say this has not been necessary.