V-belts will continue to transmit torque even if they are slightly slipping. A properly tensioned drive should have an efficiency of slightly over 96 per cent. If improper tensioning allows a four per cent slip, efficiency drops off to approximately 92 per cent. As the slip drops to the six per cent range, an excess amount of heat is generated.
The condition becomes even more serious as the belt approaches eight per cent slip. At eight per cent slip, drive efficiency has dropped off to 80 per cent. At this point the drive will not function.
Belt tension can only be properly checked with a belt tension checker. It is important that all the belts on the drive have the same tension. Do not over tension! Be sure to recheck frequently during the first 24 to 48 hours. It is also a good practice to check tension on a periodic basis. These inspections should be in the order of every 3000 hours running time, and should never exceed 6000 hours of operation.
WORN PULLEYS
Before installing a new set of belts, the pulley walls should always be checked for wear, rust, damage or porosity. Through continuous use, the pulley walls become ?dished? out, which reduces the ability of the belt to wedge in the groove.
Pulley wear is much less apparent than belt wear, yet equally critical. Generally, when pulley sidewall wear exceeds 0.06mm when measured with a feeler gauge and a straight edge or pulley profile gauge, the pulley should be replaced.
MISALIGNMENT
Misalignment is another V-belt maintenance condition that can cause a loss of efficiency. Misalignment can cause belt slip, resulting in belt heat build up. These conditions dramatically decrease belt drive efficiency. Drives should be checked to assure the parallel position of the pulley shafts and correct alignment of the pulley grooves. A simple, effective means of checking drive alignment is to use a straight edge or a tight cord across the pulley faces to assure four point contact. A more accurate method is to use laser alignment tools. There are several types that measure alignment along the face of the pulley but the most accurate method is to use a system that measures from groove centre line to groove centre line (see Figures 1 and 2).
LARGE DRIVE INSTALLATIONS
For large belt drives it is often difficult and very time-consuming to both fit and re-tension drives as the weight of the motor to move for tensioning and alignment can be excessive, involving lifting equipment and several fitters; therefore the job does not get done or it is not done properly. In these cases, a specially manufactured motor base can be utilised that once aligned, future belt refits and tensioning is a simple matter. The only time realignment would be necessary is when a new pulley is fitted.
Source: SKF