By Jason Industrial
Article three in a series of three
The implementation of a preventative maintenance program including proper belt drive installation, tensioning procedures and best practices will increase productivity, reduce downtime and yield the additional benefit of improved workplace safety.
The majority of power transmission drive problems are attributed to improper installation and maintenance. This article is intended to provide guidance in avoiding drive problems, extending drive life and maximizing performance while maintaining a safe working environment.
When compared to the cost of production downtime and the labor costs associated with a belt failure, the cost of a belt is relatively insignificant. Generally speaking, at any given production facility, 80% of the downtime related to power transmission belts can be found on 20% of the drives in the plant. In other words, 80% of the drives are fine. The remaining 20% are “problem drives” requiring frequent attention and replacement. Additionally, it’s not uncommon for a large industrial facility to spend thousands of dollars annually to determine what type of replacement belt is needed for a particular drive. Worn belts are often difficult to identify as their part numbers sometimes become impossible to read after lengthy service.
Power transmission products are potentially dangerous. Failing to follow recommended application information and procedures for installation, and maintenance of products may result in serious bodily injury or death. Make sure that product selected for any application is recommended for that service. Always follow the recommendations of the original equipment manufacturer. Contact Megadyne for specific information.
- Before doing any maintenance work on power drives, always switch off the power and lockout the drive. A tag should be attached stating, “Danger – do not operate.”
- One should always try to operate the equipment after shutdown to make sure you have locked-out the proper switchbox, ensuring that the switchbox is operating properly and also to release any stored energy.
- Use belt guards to provide protection for personnel from contact with drive components. Never test or operate belt drives without guards in place.
- Always wear gloves to protect from sharp edges and hot surfaces.
- Never wear loose or bulky clothing in close proximity to an unguarded drive where it could become entangled in the drive and cause injury to personnel.
- Always be aware of pinch points where hands and fingers can be injured, especially where the belt enters the sheave or sprocket.
- Always keep the area around the drive free of clutter and debris.
- Never re-use damaged pulleys. They should be replaced if not repairable.
- Always use static dissipating belts in conjunction with industry approved methods to dissipate electrical charges on drives used in hazardous atmospheres.
- Never use Megadyne belts for aircraft applications. Megadyne belts are not designed for or intended for use on aircraft propellers, rotors or accessory drives. Do not use on helicopters or private, commercial, ultralight or any other airborne aircraft application.
Installation & maintenance
Most drives fail due to improper installation & maintenance.
(see Figure 1)
- Good installation & maintenance practices ensure…
- Longer belt life
- Lower maintenance costs
- Longer drive component life
- More efficient drive systems
- Energy savings
- Safe operation
- Increased productivity
- Reduced downtime
After correct installment and alignment of pulleys you can install the belts. Always move the drive unit, usually an electric motor mounted on an adjustable base, to decrease the drive center distance and create slack so you can easily slip the belts onto the pulleys without force. Never force belts onto a drive with a tool such as a screwdriver or a pry bar. Doing so will rupture the fabric cover or break the load-carrying cords inside the belt.
Proper belt tension
Proper belt tension is essential for maximum belt life and efficiency. Improper belt tension is the leading cause of premature belt failure and increased costs. Under-tensioned belts lead to slippage, overheating, excessive pulley wear, rollover and noise, all of which lead to higher maintenance costs and inefficient power transmission. Also, over-tensioning belts leads to premature wear of bearings, shafts and pulleys. The result is more frequent replacement of drive components and costly downtime. Proper tension is the lowest tension at which the belt won’t slip or jump teeth under peak conditions.
V-Belt belt tensioning
V-belt tensioning can be performed using a tension tester gauge using the procedure in Figure 2. After seating the belts in the sheave groove and adjusting center distance to take up slack in the belts, further increase the tension until only a slight bow on the slack side is apparent while the drive is operating under load. Stop the drive and use the gauge to measure the necessary force to depress the belt and deflect 1/64-inch for every inch of belt span (use center belt on multiple belt drives).
For example, a deflection for a 50-inch belt span is 50/64ths, or 25/32-inch. The amount of force required to deflect the belt should compare with the deflection forces noted in Megadyne technical manuals.
- Matching V-Belts. When using multiple grooved sheaves, be sure that all of the belts are the same brand. Always replace complete sets of v-belts even if only one is worn or damaged.
Proper alignment is essential for long belt life. Check belt alignment whenever you maintain or replace belts or whenever you remove or install pulleys.
- Select Correct V-Belts to match Sheave Grooves
- Don’t mix belt brands; stick with one manufacturer
- Don’t mix new & used belts
- Replace worn pulleys after 3 belt replacements
- To check for loose belts, put your fingertips in a sheave groove (after drive shutdown). If sheave is so hot you cannot comfortably keep them there, the belts have probably been slipping.
- Ideal tension is the lowest tension where belt will not slip under peak load.
- Over-tensioning will shorten belt and bearing life.
- Inspect drive periodically. Re-tension the belts if slipping.
- If belts slip, check for adequate tension and/or worn sheaves.
- Never apply “belt dressings” to belts. These compounds are usually made from a petroleum derivative and can have a destructive effect on rubber compounds and other components of the belt.