V-belt drive tips
May 1st 2004 Gates Europe nv writes for IP&E about how to get the best from your power transmission
When compared to the lubrication problems associated with chain drives, or the mechanical problems and high costs associated with gear drives, belts are the most cost-effective, reliable means of power transmission. But the life of a transmission depends on correct installation and maintenance of the belts. Hence the importance of preventive maintenance.
Preventive maintenance is only possible if the causes and characteristics of belt failure are known. The largest number of breakdowns are caused by improper maintenance. A lot of belt drives suffer from a tension that is set too low or from pulleys that are worn or misaligned. Another important cause is a poor drive design. The wrong choice belt/pulley combination for example, or wrong use of tensioners. Another factor is environmental influences. Chemical products and oil can damage the rubber and soften it. Heat has the opposite effect and makes the rubber hard and friable. Dust or sand can also speed up the wearing process of both belt and pulley. Finally some belts fail due to other defective drive components. Most of the above problems can be avoided by proper preventive maintenance.
There are two kinds of preventive maintenance: short, regular inspections and thorough inspections with a longer period of machine shutdown. For a critical drive a quick visual and listening inspection may be needed every two weeks. With most drives, such an inspection can be performed once a month. A drive shutdown, for a thorough inspection of belts or pulleys and other drive components, may be required every three to six months. The following factors will influence the frequency of drive inspection: drive operating speed, drive operating cycle, critical nature of equipment, temperature extremes in environment, environmental factors, accessibility of equipment.
Belt tension
Improper tension too high or too low can cause difficulties. A tension that is set too low causes accelerated belt wear. A tension that is set too high causes premature failure of both belt and pulleys. The influence of tension on the efficiency of a drive is still underestimated. Both a tension that is set too high, or a tension that is set too low cause friction losses, that are transformed into heat. In extreme cases, such high friction losses due to incorrect tensioning can go up to 3 or 4 %; on an annual basis a multiple of the cost of new V-belts. Adjusting and checking the correct tension may still seem a difficult task. But in fact the opposite is true. There exist different simple methods to measure belt tension. Mechanical testers measure the deflection force of a belt under tension. Sonic tension meters measure tension by analysing the sound waves a belt produces when strummed.
Belt construction
The construction of the belt is another important aspect to take into account when choosing a belt for a specific application, as it allows major cost savings. Too often, one accepts that the pulleys that are available in the market can perfectly perform with all types of belts. Indeed pulleys with small diameters can be used with all existing belts, but create higher efficiency losses than with raw edge belts.
Pulley alignment
The alignment of belt drive pulleys is usually treated as a second-class problem, but the effects on wear and lifetime are significant. Improper pulley alignment can in the worst case lead to downtime. Correct aligned pulleys have many advantages: lower energy use, less wear and tear on belts and pulleys, less noise and vibrations, higher reliability of the drive, increased belt, pulley and bearing life. Therefore, pulley inspection is a vital element of preventive maintenance of belt drives.
The main causes of misalignment are: pulleys improperly located on the shafts, unparallel motor shafts and driven machine shafts, tilted pulleys due to improper mounting. Before realigning the pulleys, alignment tolerances always have to the checked. The greater the misalignment, the greater the chance of belt instability, increased belt wear and V-belt turnover.
The current method to measure misalignment is putting a straight edge to the pulleys. A much faster and more accurate method is ensured with a laser alignment device, such as Gates new LASER AT-1. The LASER AT-1 identifies parallel as well as angular misalignment between the pulleys and is suitable for pulley diameters of 60 mm and larger.
Condition of the pulleys
Pulleys themselves are also subject to wear and have a specified lifetime. During preventive maintenance one should always check the pulleys for unusual wear or obvious signs of damage. Wear is not always obvious.
Checklist
1. Turn off power to the drive. Lock the control box and tag it with a warning sign
2. Place all machine components in a safe (neutral) position
3. Remove and inspect guard. Check for signs of wear or rubbing against drive components. Clean guard as needed
4. Inspect belts for wear or damage. Replace as needed
5. Inspect pulleys for wear or damage. Replace if worn
6. Inspect other drive components such as bearings, shafts, motor mounts and takeup rails.
7. Inspect static conductive earthing system (if used) and replace components as needed
8. Check belt tension and adjust
9. Re-check pulley alignment
10. Re-install belt guard
11. Turn power on, restart drive. Look and listen for anything unusual
Note: if drives with two or more belts needs replacing, always change all the belts and use only belts for one manufacturer. More articles from Gates Europe NV: | 
