Across all types of industries and applications, synchronous belt failure can have disastrous results, causing increased downtime, high costs, and overall loss of production. Below, we’ll outline seven common causes of belt failure — all of which ultimately stem from either subpar design or improper maintenance — and offer tips on how to prevent failure in the first place.

1. Too Much Power for the Belt to Handle

Synchronous belts, sometimes referred to as timing belts, gain their strength from tensile members or cords comprised of helical strands of material such steel or Kevlar. The size of the belt also plays a role in its strength; the wider the belt, the stronger it is. In high-torque applications, determining proper belt width is critical; if a belt can’t handle a certain torque, it may snap under the tension.

Signs of this issue generally don’t appear until it’s too late. However, regular visual inspections of the belt teeth, and keeping an eye out for signs of damage or excessive wear, can help prevent total failure.

When selecting a belt, be sure to choose one that’ll match the power output of your application, paying close attention to width options. It helps to partner with an application engineer who will work closely with you on drive design while considering critical factors such as alignment and application environment.

2. Power Peaks

Power peaks, spikes in the torque or load on the belt that cause high tension, can leave belts vulnerable to snapping. Peaks may be caused by a range of different issues: For instance, trapped debris, such as rocks in a wood chipper, can cause jams that lead to a snapped belt. Harsh loads taken on all at once can also cause tension peaks.

To ensure your belts run smoothly, check the equipment and work area for debris before startup, and consider placing a guard on the drive to keep out debris during use. If your application involves inevitable power peaks or excessive amounts of debris, a V-belt may be a better option than a synchronous belt as they allow for some slippage and offer self-cleaning pulleys, enabling them to handle larger shock loads.

3. Improper Tensioning

Compared to V-belts, synchronous timing belts require fewer periodic adjustments after installation; this is because the tensioner pulley minimizes the need to make adjustments due to elongation and maintaining tension stability. If improper tensioning does occur, however, failure can ensue.

Under Tensioning

Too little tension may allow the belt teeth to jump the pulley grooves, causing damage to the belt and other equipment; in these situations, the timing belt pulley can destroy the belt.

Under-tensioning can also result in tooth shear, one of the most common belt failure modes. This occurs when belt teeth climb out of the pulley grooves and drive loads are no longer applied at the tooth root. These drive loads, applied further down the belt tooth, can cause the teeth to bend and “shear,” resulting in rubber tearing at the base of the belt teeth along the tensile member and leading to tooth separation from the belt body.

Over Tensioning

Synchronous belts are ideal in that they require less installation tension to maintain maximum performance. Too much tension, however, will put excessive stress on the belt, causing failure; this is also harmful to shafts and bearings.

Belts placed under excessive tension often exhibit signs of excessive pulley wear. This wear can generate cracks at the root of the tooth leading to separation from the main body of the belt.

Following a proper drive design procedure will ensure that you apply the correct amount of tension.

4. Pulley/Belt Mismatch

Selecting proper tooth pitch is critical in preventing belt failure. If tooth pitch is incorrect, installation will be impossible. If the belt width is incorrect, it can cause tooth jump, excessive noise, shortened life, and even instant breakage. Tooth profile is also important, as the belt profile must be compatible with the pulley profile.

Visual inspections allow you to determine whether the belt teeth mesh properly into the pulley teeth. However, conducting thorough preliminary research helps ensure you select the right belt for your synchronous belt drive. Labeling drives to identify which pulleys and belts are required can also help in preventing mismatches during replacement of drive components.

If you are unsure about what type of belt to use, a pitch gauge — which quality suppliers should be able to provide — can also be employed.

5. Using the Wrong Belt Material for the Application

Selecting the right material is critical for preventing belt failure. In high-torque synchronous applications, for instance, rubber belts can withstand high heat, whereas polyurethane belts may melt. However, unlike rubber, which can leave behind dust, polyurethane is a clean material making it ideal for applications requiring optimal cleanliness and hygiene.

In washdown environments — such as automatic car washes or food processing areas — water resistance is key. Working with a polyether polyurethane, in particular, will help. Other environmental considerations, such as chemical exposure, should also be considered when selecting a belt material.

An experienced engineer will be able to guide you through the selection process to ensure you get the right type of belt, made from the right type of material.

6. Pulley Misalignment

Because synchronous belts are much more sensitive to misalignment than V-belts, they should not be used in applications in which severe misalignment is inherent to the drive. Synchronous belt pulley misalignment can result in uneven belt edge wear and cause excessive wear on the pulley, premature tensile failure, and ultimately shortened belt life.

To prevent these issues, ensure that total misalignment is less than 116 inch per foot of the drive center distance. Use of a laser alignment tools or straight edge, even a piece of string, can help ensure optimal pulley alignment.

7. Debris

Synchronous belts are more sensitive to debris than other types of belts; unless a fully enclosed guard protects the drive, debris can become easily trapped between the belt and pulley. V-belts, on the other hand, can eject debris from the sheave grooves as the drive operates.

Dust and debris compacted in the pulley tooth can force the belt to ride out away from the pulley, leading to belt failure and possible drive system damage. In addition to dust and debris, oil and other lubricants can alter belt polymers and degrade the adhesion of belt components. Use of proper drive covers in applications with contaminants and debris will help reduce these risks.

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For over 60 years, the Megadyne Group of companies has been manufacturing power transmission, specialty belting, and conveyor belting for a wide range of industries, from food processing and packaging to paper and print. As an ISO 9001:2008 company and a member of both the National Industrial Belting Association (NIBA) and the Power Transmission and Drive Association (PTDA), we understand the importance of quality and reliability in belting applications.

Looking to get longer life out of your synchronous timing belts? Contact us today to discuss your belting needs with an expert.

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