On the fast track

July 1, 2006
Belts and chains have unique benefits and limitations. Those differences become more apparent in applications that require fast motion as part of their

Belts and chains have unique benefits and limitations. Those differences become more apparent in applications that require fast motion as part of their operation.

To shed additional light on the topic, we talked to industry experts, asking them what designers need to know to keep their belts and chains happy at high speed. Here's what they had to say.

Can you think of an extreme case where excessive speed caused a chain or belt to fail or degrade power transmission?

Peter/Jason Industrial: A very common example is blower belts on dragster race cars. The blower is driven at 8,000 rpm or more and the load is several times the rated horsepower of the timing belts used for this application. Consequently, the belt sometimes lasts only a couple of races, and many racers use a new belt each time. It is not possible to drive this application with a chain due to the high speed of the drive, centrifugal losses, and lubricant needs.

Steve/U.S. Tsubaki: When selected and lubricated properly, roller chain is very capable of running at high speeds. The difference between success and failure often comes down to using the proper type of lubricating system. When following the selection procedure and referring to the horsepower tables in the manufacturer's catalog, generally there are three distinct types of lubrication requirements:

  • Manual or drip system

  • Oil bath, with the chain enclosed in contained bath

  • Oil bath with pump applying lubricant directly to the chain

Trouble may occur if the application requires oil-bath lubrication, but only manual or drip is applied. There is a very common application referred to as a pin oven: Chain is used in excess of 1,000 ft/min. Its purpose is to convey beverage cans through a drying oven at high speed to cure their painted labels. The lubrication requirement is oil bath due to the speed involved, but unfortunately, only manual drip or spray lubrication can be used. Oil baths allow excess lubricant to contact the product being conveyed and create other problems.

As a result, chain life on this application is only a few months, compared to years for other applications. Problematic high-speed applications are usually avoided by following selection procedure references or consulting with knowledgeable application engineers. In less common cases, endusers may make a selection without utilizing the above resources and very quickly realize an alternative selection is required, at which time they usually refer to the catalog or contact the manufacturer.

Gerhard/Gates Mectrol: The traditional weakness of most urethane timing belts has been their relatively low maximum operating temperature of 70° C. We are seeing new belts coming onto the market with higher operating temperatures, but heat dissipation is still poor. These two factors limit their continuous operating speed.

Most urethane timing belts are employed in conveying and positioning applications where speed is generally not a limitation.

Steve/U.S. Tsubaki: In the case of the pin oven application mentioned, chain load is often around 1,000 lb, considering chain tension and working load to move the 600-ft strand. Speed is generally about 1,000 ft/min. Oftentimes, premature wear can occur: Several months service life is considered premature wear, while a service life of one year or more is often considered acceptable.

Gerhard/Gates Mectrol: Our conveyor application engineers always take a closer look at applications to run at linear speeds over 5 m/sec, and they never recommend conveying components for linear speeds over 10 m/sec. As far as conveying belts go, the speeds involved are no problem. To illustrate: The rotational speed for a 100-mm pulley to move a belt at 10 m/sec is only 1,909 rpm. This is not considered fast for most rubber timing belts.

What construction features in chains and belts most often limit speed, and why?

Gerhard/Gates Mectrol: A high coefficient of friction between the belt and contact surface can limit belt speed. In many conveying applications a slider bed supports the belt. It is recommended that the slider material be an ultra-high molecular weight polyurethane. To further reduce friction, belt teeth can be made with a nylon fabric covering. Welded endless belts also have lower speed limits than truly endless belts, but if a conveyor requires an extremely long belt or odd length, a welded belt may be the only option.

Peter/Jason Industrial: Chain drives are limited by the need to lubricate them, especially at high speeds where centrifugal force throws the lubricant off the chain. Higher-speed chain drives must run in an oil bath. Belt drives have no such requirement and being of less mass, exhibit lower loss to centrifugal tension — and thus, can run at higher speeds than chain.

Steve/U.S. Tsubaki: Roller chain speed is limited by the ability to maintain a film of lubricant in the pin/bushing joint, between wearing components as they articulate when passing over sprockets. At high speed, centrifugal forces fling the lube from these joints. That's where lube baths are essential. Beyond this, roller chain may be limited by centrifugal forces generated at high speed due to its mass. So, at very high speed, smaller-pitch chains of lower mass are used.

What application factors can limit speed?

Peter/Jason Industrial: The size of pulleys, as well as noise, can limit speed. Generally, belts run at higher speeds than chain.

Manufacturer horsepower ratings are sometimes exceeded with a commensurate drop in expected drive life. However, it's prudent to always consult manufacturers for proper recommendations before exceeding published belt or chain drive parameters.

Steve/U.S. Tsubaki: Mass limits speed. If system mass (to be moved) is too great, resulting inertia forces may require a very large or wide multistrand chain size. Silent (also called inverted tooth) chains may be used to overcome this problem. They're capable of operating at very high speed (in a lube bath) and carrying high loads due to their construction: A series of interlaced plates and pins, similar to leaf chain.

What are the main attributes of high-speed belts and chains?

Peter/Jason Industrial: Belts run at high speeds without lubrication. Timing belts also have the advantage of not requiring a tensioning idler. Chains wear causes chain drives to need periodic retensioning. Belt drives can generally be designed to run at higher rpm than chain. In drives where either chains or belts can be used, the chain drive will have the advantage of being narrower than the belt. However, it usually requires more maintenance, such as retensioning and lubrication.

Gerhard/Gates Mectrol: Belts do not require lubrication to perform properly and efficiently, whereas chains do. Belts also tend to be quieter than chains.

Steve/U.S. Tsubaki: Silent chains are also used for high-speed applications, and are designed to be quieter and smoother. Small pitch chains or silent style chains are usually selected for high-speed applications. Small pitch chains are generally lower in mass and generate less inertia force at high speed. To accommodate load requirements, multistrand small pitch chains may be used.

About the Author

Elisabeth Eitel

Elisabeth Eitel was a Senior Editor at Machine Design magazine until 2014. She has a B.S. in Mechanical Engineering from Fenn College at Cleveland State University.

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