Rexnord Industries Inc.
Downers Grove, Ill.
Self-lubricating bearings make sense when relubrication is difficult or when operating conditions compromise liquid lubricants. Such bearings can also eliminate the need for special lubricants in food-processing equipment.
Self-lubricated, nonmetallic Duralon bearings, for instance, use a filament-wound fiberglass epoxy resin matrix with a woven bearing element of Teflon and polyester. The bearings can be made in numerous shapes and inexpensively customized to work in a wide range of conditions, including harsh industrial environments.
For example, pneumatic cylinders fitted with Duralon rod bearings operate a rotary valve actuator on machines that fill "tote tanks" with liquid chemicals including solvents, soaps, oils, vaporous liquids, waxes, and corrosives. The cylinders have successfully completed tests to 80 million cycles at 0.5-in. travel under various load conditions.
Another application for the bearings are in winches and sheaves used aboard large cruising and racing yachts. Here, lubrication can wash out because bearings constantly see fresh or saltwater at temperatures ranging from below freezing to tropical. In this environment, needle bearings tend to bind, while plastic bushings can swell and seize. The Duralon bearings tolerate the harsh conditions and reduce friction.
Self-unloading barges are yet another application for the nonmetallic bearings. The bearings support huge cylinders that position booms as they unload taconite, gravel, calcite, and other bulk mineral cargo. The combined weight of boom and cargo can reach nearly 200 tons.
Lifting and lowering the boom is a hydraulic cylinder mounted above it at the pivot end. The 21-in. bore 125-in. stroke cylinder, weighing more than 22 tons, attaches to the supporting structure by a yoke with a vertical pin. The vertical pin rotates on a Duralon bearing. The bearings see ambient temperatures from over 100°F to under 20°F, plus moisture and dust. The self-lubricating bearings reduce the amount of lubricant needed to prevent corrosion of the large-diameter shafts.
In another application, threesided square Duralon bearings are used in equipment that sprays lubricant on dies between casting cycles. The motor-driven unit moves aside for die removal and replacement. The portion of the machine and manifold supported by the bearings weighs about 500 lb.
The previous design used a cam follower on which the upper part of the machine moved. However, the followers needed periodic lubrication. The open-square bearing, in contrast, needs no external lubrication. It rides on a 0.75-in.-square rail that bolts against a plate, which supports the rail along its length.
A conveyor system uses hexagonal-shaped, nonmetallic bearings to eliminate a separate drive motor. The precision machines deliver plastic, multiwell vessels, from each of three conveyor lanes, to a multisyringe aspirate-dispense instrument.
A variable-speed dc motor drives the shuttle mechanism though a timing belt and hex shaft. Two 0.375-in. hex-bore Duralon bearings epoxy into a crowned aluminum drive tube. The tube slides along the stainlesssteel hex shaft. Linear travel speeds are about 24 ips. The hex bearings let the shuttle move perpendicular to the conveyor lanes and provide power at any point in its travel, without the weight and complexity of a drive motor on the shuttle itself. Less shuttle inertia shortens transfer times and boosts throughput. The self-lubricating bearing material meets critical outgassing specs as well.
Hydraulic cylinder rod ends are yet another application for the bearings. Here, spherical bearings combine with a splitsteel outer race to eliminate metal-tometal wear and galling. Dynamic load capacities to 30,000 psi are possible. Cylinders equipped with the bearings find use in construction equipment, agricultural vehicles, conveyors, packaging machinery, and scissors lifts. Mounted filament-wound bearings can fit round, square or hex shafts, in either two-bolt and fourbolt flange or pillow-block housings. Housings can be cast iron, stainless steel, or plastic. Various other bearing and ball-joint configurations are possible.
When selecting a self-lubricating bearing material, be sure to look at manufacturer test data and evaluate the material's B10 life. Rexnord has successfully tested Duralon bearings to 25 million cycles at a load of 4,000 psi, and 1,000,000 cycles at 20,000 psi, or about 8 longer than competitor composite bearings.
Rexnord Industries Inc., www.rexnord.com