Belts Versus Chains

This article examines the types, characteristics, advantages, disadvantages and applications of belts and chains for industrial power transmission applications. It compares flat/V-belts, synchronous belts and chains.

Poly belts are available in two types, flat belts – also called V-belts – and synchronous belts. Flat/V-belts wrap around a sheave and rely on friction between the belt and sheave for movement. They require a take-up system or a tension sheave and sprocket alignment within 1/2° for belt performance.

Flat/V-belts are suited for highspeed and relatively low-power applications. Their advantages are that no lubrication is required, they are lightweight, and the belt drives cushion loads and load fluctuation. It’s important to know that a belt will slip when it is overloaded, preventing mechanical damage to shafts and other machine parts.

There are some disadvantages. Flat/ V-belts cannot be used where exact timing or speed is required, because of slippage between the belt and sheave. The belts, which are easily damaged by oil, grease and abrasives, have a limited operating temperature range of -20°F to 140°F (with special materials, the range is -65°F to 185°F). Also, belts can be noisy, and loose or worn belts can be a major cause of machinery vibration.

The most common failure in belt drives is a broken belt caused by improper tensioning. There is a tension at which the belt experiences optimum service life. Above this tension, belt fatigue translates into a decrease in belt life; below this tension, belt slip occurs, resulting in reduced belt life. Belt suppliers strongly recommend operators check the tension using special tools such as a belt frequency meter or plunger-type gauge.

Normal failure is due to a broken belt, which stops the equipment. Since it is difficult to monitor belt wear, operators should track hours or cycles to determine when to replace a belt.

Flat/V-belts cannot be used in applications with fixed-centre distances because they do not allow proper tensioning. Belts always require a take-up system or idlers to provide proper tension on the belts. Also, belts come in set lengths and cannot be adjusted, so the user is required to stock an individual belt for each application.

Synchronous belts provide positive engagement between the mating teeth of a toothed belt and a toothed sprocket. Like flat/V-belts, they require a take-up system or a tension sheave. Centre distances are limited by the belt size.

Synchronous belts are good for highspeed applications, providing a life expectancy of 12,000 operating hours. Sprocket alignment needs to be within 1/4° for belt performance.

Advantages of synchronous belts are that they operate at high speeds, produce less noise at slow speeds, provide positive engagement between the belt and the sprocket, require no lubrication and are light in weight.

Synchronous belts can be used on applications that include positioning, indexing and constant speed, as well as where there is no slippage.

On the other hand, there are some disadvantages to consider: Synchronous belts are easily damaged by oil, grease, abrasives, chemicals, and extreme temperatures of heat and cold. High horsepower and high speed can result in noise problems (sounds like a loud squeal). Alignment is very critical (within 1/4°) for belt performance. Belts exposed to abrasive material will wear out at an accelerated rate.

The most common failure of synchronous belts is a broken belt caused by improper tensioning. There is a tension at which the belt experiences optimum service life. Above this tension, belt fatigue translates into a decrease in belt life. Belt suppliers strongly recommend special tools to check tensioning, such as a belt frequency meter or a plunger-type gauge.

Normal failure is due to a broken belt, which stops the equipment. It is difficult to monitor belt wear, so operators need to track hours or cycles to determine when to replace a belt.

As with the flat/V-belts, synchronous belts cannot be used in applications with fixed centre distances because they do not allow for proper tensioning.

Belts always require a take-up system or idlers to provide proper tension on the belts. The belts come in set lengths and cannot be adjusted, so the user is required to stock an individual belt for each application. The normal operating temperature range is -20°F to 140°F (with special materials, the range is -65°F to 185°F).

Precision roller chain has a positive engagement with the sprocket teeth (so there is no slippage) and is more practical for slow-speed drives. Chain drive efficiency approaches 100%.

Sprocket alignment is within 1/4°. When properly maintained, the standard life of chain is 15,000 operating hours, though more durable chain is available.

Chains offer several advantages: Chains are easier to install than belts. They can be used in applications with fixed centres – the centre distance is unlimited and the length of the chain is adjustable. Proper tensioning is required but not to same precision as with belts. Unlike belts that must be purchased and stored in specific lengths for all applications, chain can be purchased in bulk and cut to length as needed for various applications.

The operating temperature range of standard carbon steel chain is -20°F to 500°F, and for stainless steel chain it is -40°F to 1,000°F.

Chain is normally replaced due to wear. Wear can be monitored by using a Timken Drives EZ Chain Wear Gauge so chain replacement can be planned.

Chains can operate in adverse environments, and around abrasive material, moisture and chemicals (with the proper chain series). Chains can be used in lifting applications and in conveyors with the use of integral, customizable attachments to move the products.

Chains do have some drawbacks: To maximize wear life, the chain should be effectively lubricated. Timken Drives recommends using the Rotalube system, which extends the useful life by allowing the operator to control the speed, frequency and precise location for oil lubrication. Also, chain weight may be a concern and chain drives may be noisy.

See the original article on the MRO website 

Richard W. Neuhengen is product manager, chain, with Timken Drives LLC.