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Case study: Roller chain applications in minerals processing plants

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As technologies mature and modernise, manufacturers expect more from less.

More power from a smaller footprint.

Greater power from fewer materials.

Synchronous belt technology has evolved, matching the performance of roller chain while reducing weight, mess, and maintenance.

A roller screen being used at an Australian coal wash plant for ROM (run of mine) coal screening, was being driven by roller chains running in an oil bath.

A re-circulating pump was installed down the drive end and a sump fitted underneath the feed end to store the oil.  

The pump would come on every 30 minutes and pump the oil into the chain guard at the discharge end.

The chains would drive the oil to the feed end with the natural motion of the drive.

It used 16B duplex roller chain on 19 tooth sprockets on a roller screen, running 7.5kW @ 138rpm

Chain is well-suited for hostile environments.

It can withstand temperatures above 80°C; it tolerates, oily, dusty, dirty and corrosive atmospheres, albeit at the sacrifice of longer life.

Roller chain drives can also tolerate fluctuations in centre distance caused by a non-rigid or compliant drive mounting.

The problem
In this Australian coal wash plant roller screen, the existing roller chain drives were stretching, breaking and needed to run in an oil bath or be heavily greased.

There were 39 chains that required replacement in one year on the screen creating significant costs in maintenance and downtime.

There are a number of characteristics which make chain drives less than ideal for many power transmission applications.

The most significant factors include chain stretch or elongation, the need for lubrication, and high noise.

Stretching, or elongation, results from pin and bushing wear at the articulated joints of the chain.

Chain elongation results in the need to take up slack or retension the chain at regular intervals.

Lubrication is essential to the proper functioning of a chain drive.

Without proper lubrication, chains and sprockets wear out quickly, forcing replacement.

At a time when maintenance personnel are being pushed to their limits, lubricating roller chain is an unwelcome chore.

To compensate, (as in this case) equipment designers may include an oil bath or oil spray system, or they may specify lube-free chains on their drives, adding to the cost of the system. 

The manufacturer of the screen recognised the cost and constant maintenance required to the roller screen and welcomed a solution.

Belts have been developed with polyurethane bodies and carbon fibre tensile cords.

These belts can compete with standard roller chain in a wide range of power transmission applications.

When used in a dynamic application such as the tensile member of a synchronous belt, carbon fibre delivers a number of performance attributes.

The use of carbon fibre tensile cords has dramatically increased the load carrying capacity of synchronous belts to the point where they can replace roller chain width-for-width.

In this case, Gates Poly Chain GT Carbon belts replaced the chains on the roller screen drive.

Poly Chain GT Carbon belts require no lubrication, a key advantage over the most problematic aspect of a roller chain drive. However when first installed, the Poly Chain GT Carbon belts were running in the oil bath without any issues and without compromising their performance.

In addition, once a belt drive is installed and properly tensioned and aligned, it never needs re-tensioning. 

Roller chain, no matter how well maintained and lubricated, eventually elongates, requiring periodic take-up and re-tensioning.

A synchronous belt drive system is essentially maintenance-free.
The drives on the roller screen have run for 24 months without requiring any maintenance.

The benefit of replacing the chain drive with the Poly Chain GT Carbon belts has been the significant reduction in maintenance costs due to eliminated need for regular chain replacement.

The success of the conversion has resulted in the screen manufacturer making Poly Chain GT Carbon the original equipment
design, to optimise the screening process.

Poly Chain GT Carbon belt drives are the ideal replacement for roller chain drives.

They offer similar, or better, performance capabilities while reducing weight, mess and maintenance, while lasting up to four times longer.

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