Power Transmission Belt Failure Modes

Four different types of belt are considered synchronous belts, V-belts, V-ribbed belts and conveyor belts. Each type of belt has a distinct set of failure modes and so each is considered in turn below. Only failures which can be considered to be belt failures have been considered, rather than belt/pulley system failures, so that failures as a result of pulley misalignment, for instance, have not been included. For adhesion related failure modes, methods of predicting belt failure where they have been developed, are outlined. 

The belts are manufactured by first putting a fabric sleeve around a mandrel which has the belt teeth formed in it. The cord is then helically wound along the mandrel (this means that in a finished belt the cords do not lie along the axis of the belt but at a slight angle to it). The rubber compound (mixed but uncured) is then placed around the cord before an outer casing applies pressure to force the rubber compound into position and heat is applied to cure the rubber compound once it is in position. Once the curing process is complete individual belts are cut to width from the stock. Similar methods are used to manufacture most types of power transmission belt. 

Tooth root cracking is the prevalent failure mode for belts and the literature suggests two mechanisms for its generation. The most commonly reported mechanism is fatigue and eventual failure of the facing fabric in the tooth root, followed by rapid crack propagation through the tooth rubber compound, usually across the rubber compound/ 

Fabric separation failure occurs when the belt teeth and fabric land become detached from the belt cords [17] and is essentially seen as purely an adhesion failure, although there may be links between this failure mode and the tooth root cracking failures observed by lizuka [18], originating from cracks developed in the cord itself through internal delamination. Wear causes belt failure through changing the tooth profile to such an extent that the belt teeth can no longer support the required load [25]. 

Overall it is interesting that adhesion within the belt can be the root cause of most types of failure, with fabric fatigue (often accelerated by wear), wear itself, and rubber compoimd cracking, the root causes of those failures not related to adhesion. The observations made by various researchers suggest that both the cord/rubber interface and the fabric/rubber interface are potential failure initiation sites, with interyarn and interfilament adhesion within the cord providing further possible failure initiation sites. 

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