by William Goodwin

In many industrial applications, powered machinery is by far the largest, most inefficient consumer of energy. These losses can be reduced with proper maintenance. Here are some tips to keep belts, bearings and chains in top operating condition.

Belt maintenance
Belt guards: Anything accumulating on a belt guard tends to insulate it. This can cause the drive to run hotter, which shortens belt life. Keep drive train guards free of dirt and grime.

The guards’ main function is for protection and safety of workers and machines, but they can help increase drive belt efficiency. All belt drives lose some energy to windage (the air disturbance caused by turning sheaves). Properly installed guards break up the effects of this windage. Check the guard for wear or rubbing against drive components before removing it for belt inspection.

Belt inspection: First inspect the belt while the equipment is still running with the guard in place. Look and listen for unusual movement or vibration, chirping, squealing or grinding noises. Smell for warm rubber or oil. Look for accumulations of suspicious dust or particles.

After turning off the power and locking out the unit, remove the guard and look for oil drips or grease stains (possibly from over-lubricated bearings). Drive belts and their sheaves must be free of oil or grease. Look and feel for unusual abrasion patterns or signs of burning, fraying and cracking.

In synchronous belts, look for sheared or asymmetrically worn teeth. Any sign of belt deterioration means two things: the belt must be replaced; and you must identify and eliminate the source of the deterioration (such as a misaligned or damaged sheave).

Belt replacement: Always replace a damaged belt. Period. It’s safer and more efficient than waiting for failure.

To replace belts, loosen the motor mounts until the belt is slack enough to easily come off the sheave. Never use screwdrivers or crowbars to pry off an old belt or to force a new belt onto the sheave. In a set of drive belts, do not mix new and used belts; they will be different lengths. Replace the whole set for optimum performance.

When installing a new belt, the top of the belt should be flush with the outer edge of the sheave. If the top surface of the belt is below the outer edge of the sheave, you have excessive groove wear. The sheave should be replaced.

When replacing belts, hold the dressing. Belt manufacturers generally advise against applying dressing to drive belts because it does nothing to help a properly installed belt function and because they are petroleum products, may shorten belt life.

Sheaves: Pulley sheaves should be checked for dirt, damage and wear each time the belts are maintained or changed. Sheaves that are less than perfect will substantially shorten belt life. Dirt in the grooves abrades belt covers while oil attacks belt materials and contributes to slippage. Nicked or gouged sheaves can cut the belt. Worn grooves allow the belt to bottom out or slip, which causes glazing or burning.

Disconnect power to the machine before removing or cleaning sheaves. Conventional mount, split-taper and taper-lock sheave hubs require slightly different removal/replacement procedures. Carefully follow sheave manufacturer replacement directions.

Remove sheaves from the shaft for thorough inspection and cleaning. Use a stiff brush to clean off rust and dirt and wipe the sheaves clean of oil and grease. After cleaning, use a sheave groove gauge to check the entire circumference of each sheave for voids. Any space around the gauge indicates dishing or other abnormal groove wear.

Alignment: Belts tolerate misalignment better than chain systems, but that doesn’t make sheave alignment less important. Misalignment cuts into belt life, causes more running noise and sucks energy. It may also cause uneven wear on one side of the belt, make the belt roll over in the sheave or place all the load on one side.

Check alignment every time you perform drive train maintenance and whenever belts or sheaves are replaced. After tensioning, recheck alignment. A misalignment of more than half of a degree (one-tenth of an inch per foot of drive center distance) is enough to spell trouble for most drive belts. Synchronous (timing) and some other types of belts, however, are even less tolerant of misalignment.

Properly aligned sheave shafts must be parallel and sheave grooves must be in line. To check, place a long, rigid straight edge in contact with the sides of both sheaves. If the straight edge contacts two points on the outer-most surface of each sheave, they are aligned. If only one point touches on either or both sheaves, they are out of alignment. Adjust sheave accordingly.

Check other drive components. While the power is off and the guard removed, check bearings for proper alignment and lubrication; motor mounts for correct tightness; and take-up rails for cleanliness.

Belt tensioning: Usually the final step of a drive component inspection is checking belt tension. Too little tension causes belt slipping, shortens belt life and erodes sheaves. Too much tension stretches belts, hastens belt deterioration and shortens bearing life. The ideal tension is the lowest tension at which the belt will not slip under peak load conditions.

Experienced mechanics sometimes feel confident enough to check belt tension with a thumb, but why guess when simple and accurate methods are available? The time-tested deflection method requires only a long straight edge, a small tension tester and a table of recommended values available from belt manufacturers and distributors. Another method uses a battery-powered sonic tension meter that can be linked to a computer. After installing a new belt, check tension frequently during the first 24 hours of run-in operation.

Tip for saving energy and increasing belt life: Increasing belt speed by using larger sheaves and longer belts, if space allows such a change, often saves energy. Larger sheaves also place less flexing stress on the belts and require less tension. These factors help increase belts and bearing life.

Information for this article was provided by Gates Rubber Co., Goodyear Rubber and Tire Co. Commercial Belting Division and American Bearing Manufacturer’s Association.

This article appeared in the February/March 1998 issue of MRO Today magazine. Copyright, 1998.

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