Synchronous Belts vs V-Belts

There are two major types of power transmission drive belts. They come in many different sizes and constructions but can be broken down into these two groups.

• V-Belt

• Synchronous Belt (also commonly referred to as timing belt)

The V-belt is a friction device that works on the principle of a wedge. It relies on tension to transmit power by creating friction on the side walls of the wheel. The V-belt allows slippage, which may be desirable and intentional in the drive design. For example, on a lawn mower deck, the belt must slide when the blade touches a rock or tree stump, rather than breaking the belt or bending the crankshaft.

A synchronous or timing belt is an active engagement device. It is an efficient power transmission system. It combines the advantages of mechanical and flexible components without drawbacks. All timing belts operate on the principle of forward engagement, as with the chain, where the molded belt teeth engage with the sprocket teeth. The timing belt is wound around the sprocket by bending rather than rotating the hinged parts as in a chain. This eliminates one of the causes of wear and noise. Sync belts are not allowed to slip, because some drive synchronicity is required, and any slip can cause damage. Take, for example, the valve mechanism of an internal combustion engine. If the drive fails to operate in sync, the piston will contact and damage the valve.

V-Belts Applications & Advantages

V-belts are available in a wide variety of cross section sizes and construction types, making them an option for small to high horsepower drives. They can also be used with multiple belt sets lined up side by side for very high horsepower drives. There are usually two types of structures, wrapped and raw edge. The cladding type belt has a fabric cladding that completely covers the outer surface of the belt. Wrapped structures shall be used where maximum slip capacity is required. The primary side structure has no fabric on the sides of the belt in contact with the wheels and has gears, also known as grooves, at the bottom of the belt to increase the flexibility of the winding pinions. Due to the exposed rubber on the side walls, the original structure belt is less prone to slip than the cladded belt. Raw Edge belts are used where high horsepower is required, while still requiring some slippage under peak torque conditions. Because the Raw Edge belt has less slippage than the V-belt and can be mounted on existing pulleys without any component modifications to the drive, the Raw Edge belt can be a very cost-effective system upgrade with significant efficiency improvements.

Advantages of V-Belts

• Lower noise

• Less cost

• Allows some slippage – can act as a safety fuse

Use a V-Belt Drive Where

• Some slippage is desirable

• Low noise is required

• The most economical drive is requested

Synchronous Belts: Applications & Advantages

Like the V-belt, the timing belt comes in a wide variety of sizes and configurations and can be an option for almost any drive. All timing belts are somewhat similar in structure, the differences being the belt body compound used, tooth shape, and type of tensile rope. They can be made of rubber or polyurethane construction. The choice of rubber or polyurethane depends on the type of application. For example, in a production environment, such as the food industry, where cleaning is a priority, a polyurethane strip can be used as it is less likely to shed the material than a rubber-based structure. Conversely, for very high temperature applications, a rubber belt will be chosen because of its greater heat resistance. Compared to triangle belts, synchronous belts also require very low mounting tension, putting much less pressure on driving parts such as shafts and bearings. The tooth shape was chosen according to various conditions. For example, if accurate registration is required, a tooth shape with minimal clearance between the belt teeth and the pulley grooves can be selected. In very high torque drives, a parabolic tooth shape is desirable because it can transmit high power and torque while minimizing the chance of the tooth jumping out of the sprocket and compromising synchronization. Synchronization belts also require less tension maintenance than V-belts. The V-belt must be checked periodically to ensure that the correct tension is maintained, while the synchronous belt often maintains the correct tension after the initial installation of the belt.

Advantages of Synchronous Belts

• Exact shaft synchronization

• Elimination of slippage and resulting speed loss common to v-belts

• Low installation tension means less stress on shafts and bearings

• Less maintenance

• Higher Drive Efficiency

Use a Synchronous Belt where

• There are high torque, low RPM requirements

• Compact drive layout is necessary

• Synchronous transmission between shafts is a must

• High precision positioning of shafts (minimal backlash)

• High mechanical drive efficiency and energy savings required

• Low maintenance is a priority

• Low noise requirements (compared to chain, gears)