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Designed to go the distance

DN Staff

June 24, 1996

7 Min Read
Designed to go the distance

A little garlic works wonders on the body--it wards off colds, is good for the heart, and opens the pores. Seven thousand tons a year, however, will turn protected or coated steel into a mass of rust. Just ask the Garlic Co. of Bakersfield, CA.

Chief Engineer Jan von Engel will tell you that the sulfur component in garlic creates caustic fumes devastating to ordinary food-processing equipment. He will also point out that standard bearing housings and bearing inserts, continually exposed to these fumes, as well as processing water and steam washdowns, fail after as little as six months of operation.

Traditional nickel-plated units prove more durable, but don't solve the problem. Even under a rigorous, twice-weekly relubrication schedule, rust on bearing components eventually leads to spalling or other forms of premature failure.

To reduce parts replacement, as well as costly downtime and disruptions in production, the Garlic Co. installs polymer-housed bearings in the belt conveyors that transport the garlic cloves. Made by the Torrington Co., Torrington, CT, the Fafnir Survivora PT-housed units combine the polymer housing with a completely corrosion-resistant bearing insert.

The Fafnir polymer units, von Engel claims, have easily outlasted anything the Garlic Co. had previously tried. "Under our lubrication schedule," he says, "the Survivor PT lasts significantly longer than conventional bearings. We've put these units through their paces, and they've passed every test."

Specifically designed to government standards and other food processing requirements, Torrington's Survivor PT is pre-lubricated with a food-grade grease. Its polymer housing stands up to a broad range of acids and alkalis, as well as steam, and resists shock loads. Housing strength, in fact, exceeds bearing load capacity. Additionally, the units withstand continuous operating temperatures as high as 250F, with intermittent temperatures reaching 320F.

The bearings' insert rings and self-locking collar are coated with Fafnir TDC, a proprietary thin, dense chrome coating that will not crack or peel under known application conditions. All other components consist of stainless steel, synthetic rubber, or other polymeric materials to further enhance corrosion resistance and service life.

The Garlic Co.'s processing line incorporates about 80 pillow blocks, produced by a variety of manufacturers. As corrosion takes its toll on the existing nickel-plated and conventional bearings, von Engel installs more Fafnir polymer units as replacements.

"Our plans also call for the installation of these units in much of the new machinery we design and build in house," he says. Reason? "We anticipate long-term savings resulting from far fewer parts replacement and less production downtime."

Life-extending lubricants. Extended warranties and trouble-free service life can often be credited to a particular lubricant. Designing in the proper lubricant actually increases a part's value by decreasing mainte-nance and service costs. One such ex-ample: DuPont "Krytox" performance lubricants.

Krytox wets metallic surfaces easily, and is compatible with all elastomeric materials and engineering plastics. It also maintains its lubrication characteristics in operating temperatures of -70F to 650F, a range much broader than other synthetic lubricants. These properties, coupled with the material's chemical inertness, make Krytox useful in a multitude of demanding jobs, including one of the auto industry's hottest underhood applications--the cooling fan clutch in light trucks.

Because typical electrically controlled fans aren't powerful enough to provide sufficient cooling under extreme conditions, some truck manufacturers run the fan directly from the engine accessory belt drive. The temperature-sensitive clutch, engaging only when the fan must draw air through the radiator, lowers engine power losses and improves fuel efficiency.

As viscous silicone fluid transmits power within the clutch, however, the shearing action creates heat. This heat, plus that from the adjacent engine block, dictates components that will operate at temperatures to 450F for long periods of time.

"There are only a few lubricants that can perform under these conditions," claims NSK Automotive Applications Engineer Matt Nagel. That's why NSK--headquartered in Ann Arbor, MI, and bearing supplier to two leading U.S. manufacturers of automotive fan-clutch assemblies--specifies Krytox lubricant.

"Many synthetics, even those termed high temperature, can't withstand these extremes," Nagel says. "To ensure high-temperature performance and longevity, you need a fluoroether grease." To date, NSK reports no failures or warranty claims associated with Krytox-lubricated, fan-clutch bearings.

Self-lubricating designs. For applications involving a dry start under load, oscillating and fretting conditions, varying lubrication levels, or frequent start/stop, design engineers increasingly replace traditional bearings with self-lubricating bearings. Garlock Bearings Inc., Thorofare, NJ, offers a full line of bearings designed to reduce or eliminate the need for lubrication.

For example, the company claims its DUbearings have a greater application range than any other self-lube material. Construction features a steel backing, porous bronze innerstructure, and polytetrafluoroethylene (PTFE)-lead reservoir and overlay.

The backing allows high load-carrying capacity, excellent heat dissipation, and dimensional rigidity. The bronze innerstructure, sintered onto the steel backing, conducts heat away from the bearing surface. To complete construction, the PTFE-lead mixture impregnates the porous innerstructure; it also forms a 0.001-inch-thick overlay to coat the mating surface.

During operation, as the overlay is depleted, relative motion of the mating parts draws material from the porous bronze layer, continually restoring the low-friction surface film. When conditions are severe, lubrication actually increases due to the high thermal expansion rate of PTFE.

Garlock's DXa bearings--for slow speed, oscillatory applications, and intermittent operation--feature a steel backing, porous bronze innerstructure, and acetal resin overlay. The latter offers high wear resistance and low friction, even when only minute quantities of lubricant are supplied to the polymer surface. Because they require just a trace of lubricant, DX prelubricated bearings fill the gap between fully-lubricated bearings and dry bearings.

To meet the need for high-load, self-lubricating bearings that provide low wear rates in a wide variety of applications, Garlock Bearings provides two types of filament-wound, composite bearings: GAR-FILand GAR-MAX(R). GAR-FIL's composite structure consists of epoxy-encapsulated, wound glass fibers oriented to provide the radial and axial strength needed to support high bearing loads. For long life without lubrication, a proprietary filled PTFE liner is bonded to the surface.

GAR-MAX bearings feature a combination fiber surface liner which com-prises a controlled, filament-wound pattern of both PTFE and high-strength fibers. These materials are braided to form a cord that is fully encapsu- lated by an epoxy resin. A self-lu- bricating filler provides a wear-resistant bearing surface. Long-term field tests indicate excellent resistance to impact and shock loads.

All told, these lines of self-lubricating bearings give design engineers another means of decreasing unit size, weight, and cost, while increasing longevity and serviceability.

Krytox keeps alternator 'humming'

If the bearing lubricant fails, the bearing fails. If the bearing fails, the alternator fails and the vehicle eventually grinds to a halt. This kind of equipment breakdown in a military vehicle can mean the difference between a battle won and a battle lost.

C.E. Niehoff & Co., Evanston, IL, builds heavy-duty alternators (200-400A) for commercial and military vehicles, such as the Army's High Mobility Multi-Purpose Wheeled Vehicle. As demonstrated during the Gulf War, the "Hummer" must operate in conditions ranging from the desert's dry heat to the sub-zero chill of the Arctic.

"When you talk about quickly mobilizing our fighting forces," explains Issam Jabaji, project engineer at C.E. Niehoff, "there's not a lot of prep time. The Army wants to put this vehicle on an air transport, fly it somewhere, drop it, and begin to use it immediately."

Jabaji claims that organic greases, which perform well in the everyday environment of personal autos, can't handle applications in the heavy-duty alternators built for severe environments. Alternators with Krytox-lubricated bearings, he says, have easily withstood as many as 2,000 hours testing at ambient temperatures ranging from -50F to 230F.

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