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Maintaining older gear units: part three

World Cement,

Case study: membrane replacement

The city of Nimbahera in India is known for its so-called ‘Nimbahera’ stone – a special sort of limestone. It is not surprising that several cement production facilities are located in this region. A Symetro gear unit has driven one of the ball mills in the Nimbahera area since 1987. During an inspection in 2002 it turned out that the low-speed membrane on the mill side was no longer in good condition and had to be replaced. In July 2006 this exchange took place and during the same visit damage to the membrane on the gear side was discovered.

Nevertheless, vibration monitoring showed acceptable values and, thanks to regular inspections, it was possible to run the gear unit in that condition until July 2015, when a planned shutdown to replace the membrane took place. As the gear side low speed membrane was bolted into the balance wheel, the balance wheel itself had to be removed to change it. The customer decided to perform a complete disassembly and inspection of the gear unit at the same time as the necessary work. During this inspection it was proven that the gear was in very good condition with perfect tooth contacts.

The low speed membranes have to transmit the total torque from the balance wheel to the mill. To do this efficiently, the coupling hub and the membrane are fitted together with fitting bolts. The membrane replacement kit was therefore supplied with new bolts and the required drilling tools. Once the old membrane was disassembled from the balance wheel, it needed to be sent to a local workshop where the coupling hub was dismantled from the original assembly and placed onto the new membrane. After alignment, the new holes were drilled and the bolts were fitted directly into the new assembly.

After this operation, the new membrane assembly was sent back to the cement plant and the reassembly of the gear unit was started. Internal and external alignments were checked during the final inspection. Once the Symetro was connected to the drive motor the mill could be restarted at 100% load.


The Symetro gear unit in Nimbahera is only one example showing how important the regular maintenance and professional inspection of key components is. If discovered in time, a gear unit can even run with small damage for a limited time. Breakdowns and expensive emergency repairs can be avoided and the gearbox can run smoothly for many decades.

This is part three of a three-part article written for World Cement’s December issue and abridged for the website. Subscribers can read the full issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the December 2015 issue here.

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