Tim Taylor is a field application engineer with Gates Corporation. He holds a bachelor’s degree in mechanical engineering from Colorado School of Mines. For more information, visit www.gates.com/belt-pm to download a free copy of Gates Belt Drive Preventive Maintenance and Safety Manual.
Second of Three Parts
Belt drives are a cost-effective, reliable means of transmitting power between shafts. That is why they are found all over the oil patch—mud pump drives, shale shaker screens, pump jacks, compressors, injection pumps, accumulator units.
Just because V-belt or synchronous belt drives are prevalent does not mean everyone knows how to care for them. The “If it ain’t broke, don’t fix it” mentality often prevails, which can be costly. A misaligned or improperly tensioned drive invites downtime.
Begin thinking PM—preventive maintenance. The benefits will be:
- Longer service life
- Trouble-free operation
- Improved uptime and productivity
- Energy conservation
- More efficient power transmission
- Longer component life
Basic PM programs include:
- A safe working environment
- Regular drive inspections
- Proper drive installation
- Proper belt storage and handling
When working around and with belts and drives, begin with a safe working environment. Wear proper clothing (not too bulky or loose-fitting), eye and hearing protection, safety shoes and gloves. Keep the area clean and uncluttered for easy access. Be careful to keep hands and fingers out of pinch points as the belt enters the sheave, and keep drives properly guarded from weather, debris and damage. Follow these guidelines:
- Use OSHA approved guards
- Keep the drive completely enclosed
- Use accessible inspection doors or panels
- Maintain good ventilation
- Allow for easy removal and replacement
As part of the normal routine, look, listen, feel and smell. Look for a loose, damaged or dirty guard. Listen for unusual noise and use your nose to detect any unusual smells, like burned rubber. Feel the drive to make sure the motor and drive mountings are tight.
Occasionally (every three to six months) schedule a complete shutdown and thorough inspection. The frequency depends on several factors:
- Critical nature of the equipment
- Drive operating cycle
- Accessibility of the equipment
- Drive operating speeds
- Environmental factors
- Temperature extremes
- Drive history
Here is a checklist for conducting a thorough PM inspection:
- Test to make sure that the power is off. Lock the control box and tag it.
- Lock down all machine components, and put them in a safe or neutral position.
- Remove the guard and inspect it for damage.
- Inspect the belt for excessive wear or damage, and replace as needed.
- Inspect the sheaves or sprockets for excessive wear or damage, and replace if worn (always wear gloves when inspecting metal parts to prevent cuts).
- Inspect other drive components (such as the bearings, shafts, etc.).
- Inspect the static conductive grounding system, if present.
- Check the belt tension and adjust, as needed.
- Recheck the sheave or sprocket alignment and adjust, if necessary.
- Repeat the previous two steps as needed until tension and alignment are properly adjusted.
- Reinstall the belt guard.
- Turn on the power, and restart the drive.
How do you inspect a belt, and for what should you be looking? First, remove the belt drive guard and mark a point on the belt. Work around the belt and look for cracks, frayed spots, cuts, missing teeth (if it’s a synchronous belt) or unusual wear.
Check the belt for signs of exposure to excessive heat. High heat is a belt killer. Rubber belts will harden, develop cracks and “chunk out” in pieces. The upper ambient temperature limit for a V-belt is 160 degrees F (230 degrees F for a V-belt constructed with EPDM rubber material). Synchronous belts have an upper limit of 185 degrees F. Use an infrared thermometer to check the surface temperature of the belt. Replace the belt if signs of wear are obvious.
Misalignment between the belt and sheaves (or sprockets) can wear out belts quickly. Misalignment can be angular or parallel. You can use one of several methods to check alignment:
- Straight edge
- Laser alignment tool
Ensure that the misalignment is not caused by sheaves or sprockets that are tilted on the shaft due to incorrect installation of the bushings.
Over- or under-tensioned belts can also cause premature wear and early failure. Under-tensioned V-belts slip against the sheave sidewalls and overheat. The teeth of synchronous belts jump or skip over the sprocket teeth, or they experience “hook” wear. Over-tensioned belts can damage the bearings as well as the belt itself.
There are two common methods of measuring belt tension:
- Force/deflection method
- Span vibration method
The force/deflection method relies on measuring deflection force with a pencil gauge or spring scale. The span vibration method uses a sonic tension meter. Both techniques should only be performed while the belt is at rest or when the drive is off.
Belt Drive Installation
Installing a new belt (V-belt or synchronous) is part and parcel of a PM program. Proper installation will ensure maximum life from the belt and sheaves (or sprockets).
First, follow the safety steps noted in the “Regularly Scheduled Inspections” section (power off, equipment locked and tagged). Remove the belt guard and place it in a safe location. Loosen the motor mounting bolts or adjusting screws and move the motor until the belt is slack. (Never pry or force a belt off the sheave or sprocket.)
Remove the old belt and inspect it for unusual wear. This process can provide clues to a problem with the drive. Also, inspect the sheaves or sprockets for signs of unusual wear. For V-belt sheaves, use a sheave gauge.
For synchronous sprockets, run a visual check and drag a straight edge across the grooves to inspect for wear. Look for rust or pitting on the sheaves or sprockets. Also, check the sprocket flanges for damage or looseness. Discard the old belt and replace the sheaves or sprockets, if needed. If the sheaves or sprockets are in good condition, wipe them down with a cloth and a light, non-volatile solvent.
Before replacing belts on a multiple belt drive, ensure that the belts match. Major manufacturers have matching systems to ensure that the belts are from the same batch. Replace all the belts on a multiple drive system at one time, or use a tie band belt.
For single or multiple belt drives, first ensure that there is sufficient clearance for installation. Do not pry or roll belts onto the sheaves or sprockets. Adjust the belt tension. Measure the tension as noted above with a pencil or spring gauge, or sonic tension meter. Rotate the drive by hand for a few revolutions, then recheck and adjust the tension as needed. Be careful to keep hands and fingers out of pinch points. Also, recheck the alignment, and continue rechecking tension and alignment until properly set.
Finally, secure the motor mounting bolts, and recheck the tension and adjust, if needed. Replace the belt guard, start the drive and observe. Look and listen for any unusual noise or vibration. If available, use an infrared thermometer to check the motor and bearings for excessive heat.
Run-in V-belt drives for 24 hours under full load to ensure that the belt is seated in the sheave groove and the initial stretch has been removed. Then recheck and adjust. Failure to recheck will result in an under-tensioned belt and shortened life. If a 24-hour run-in is impractical, any period is better than none.
Storage and Handling
Sometimes, belts fail prematurely because they were not stored and handled properly. Storage and handling guidelines should be part of any PM program.
Store belts in a cool, dry place protected from direct sunlight. On or off the drive, heat and ozone are a belt’s enemies, so keep belts away from heat sources or direct airflow from heating devices. Do not store belts near equipment that generates ozone, such as transformers or electric motors, and keep them away from areas where they might be exposed to solvents or chemicals in the atmosphere. Also, avoid storage where they could be physically damaged. Do not store belts near windows to avoid exposed to sunlight or moisture. Storage temperature should be less than 85 degrees F (30 degrees C) and relative humidity less than 70 percent.
Belts should be stored on shelves or in boxes or containers. V-belts may be hung on a wall rack, but the saddle should have a diameter greater than the recommended sheave or sprocket diameter for the belt’s cross section. Otherwise, the belts will be crimped, damaging the tensile cords and leading to premature failure. To avoid crimping a belt, never tape or wrap the belt too tightly or hang it from a small peg.
Longer V-belts may be stored coiled in large diameter loops. Polyurethane synchronous belts should be stored in their boxes.
Follow these simple PM procedures to gain the maximum life from the V-belt or synchronous belt and drive components.
Upstream Pumping Solutions, Summer 2011