The challenge

At Ash Grove Cement Company, the Symetro-driven mill was stopped due to an unforeseen event in the mill system, which had a negative impact on the gear unit. 

The visual inspection in March 2008 showed the gear unit to be in critical condition; two broken teeth and cracks were found on the low-speed pinions.

The gear specialist was asked about the lifetime of the Symetro which is difficult to estimate and subject to many influences. Experiences have shown that Symetro gear units can last forever if running under normal conditions. The one at Ash Grove was installed in 1977 and a visual inspection in 1997 confirmed it was still in a very good condition.


It can take up to 12 -13 months to deliver a new set of rotating parts. Our gear specialist recommended Ash Grove to purchase our new TSHH Plug and Play, in order to secure mill operation. Installation of a new set of rotating parts itself only takes about a fortnight. 

Broken teeth experienced at the Ash Grove

Implementing a "Plug & Play" solution


After the service engineer's visit, Ash Grove decided to purchase new TSHH Plug and Play rotating parts. The package included new rotating parts with new balance wheel membrane, new lube oil system, new oil level indicator and PCH-1008 vibrations monitoring.


In January 2011 the new parts were successfully installed and the balance wheel membrane was also successfully replaced at the same time. Despite the short downtime of 16 days for replacement work, the gear unit was not started up immediately due to the winter outage.


The final commission took place in March 2011. The gear unit was successfully started up, all parameters were checked and were within the specified tolerances.

Perfect tooth contact check

About the customer

No inspection has been made since 2011. However, according to the customer, the gear unit is in very good overall condition and has been running well. The customer continuously monitors the gear unit and is pleased with its performance.

After a successful replacement, the plant manager provided a letter of endorsement stating that the company was very happy with the outcome of the project.

Likewise, following a project for Holcim Cilacap, Indonesia, Mechanical Engineer Mr. Arie Setiaaji Ibrahim, commented:

After installation of the new lubrication unit for Symetro gear we have experienced a drop in the oil temperature from 58 °C to below 50 °C and the contamination is maintained low

Per Lykkebæk Larsen and Simon Pedersen reflect on the success of a ‘plug and play’ solution for rotating parts

Since 1926, more than 1600 MAAG® Symetro™ gear units have been sold around the world. The first Symetro gear units were manufactured almost 90 years ago, and there are still some going strong even after more than 60 years of operation. To keep them running well, we offer a "plug & play" solution for rotating parts, as well as a range of accessories. 


We offer customers unique, modularised and compact solutions combined with the ultimate in gear precision and accuracy, ensuring that the installed base is maintained and can be upgraded with the latest technology.


New rotating parts: plug & play

To keep the Symetro gear unit "young and strong", new rotating parts based on TSHH technology are the ideal "plug & play" solution. Installing the new solution as standard only takes up to 12 days and customers can start the mill with 100% load. All the pinions are case-hardened (carbonized) and ground with a hardness of up to HB 550. The pinion teeth mesh with the high-grade, through-hardened, ground teeth of the gear wheels, which have a hardness of up to HB 360, offering pitting resistance and excellent strength properties, combined with a very high service factor.


The high-speed pinion is tooth-flank ground with helix-angled modification to obtain superior load distribution on the teeth during full load, and all wheels are ground with top and bottom profile relief to minimize vibration and noise. All parts benefit from MAAG’s core competence and state-of-the-art technology in heat treatment, gear cutting and assembly.

quality control of a high-speed pinion
Quality control of a high-speed pinion


In addition to new rotating parts with TSHH technology accessories are offered for Symetro gear units, which will improve the protection against failures and unavailability of the mill system:

  • An electrical oil level switch to stop the gear unit before an oil level decrease results in any damage
  • A lubrication unit controlling viscosity and contamination of the Symetro oil
  • Vibration monitors to detect abnormal increases in the vibration level and trip the mill motor after a suitable delay before severe damage occurs
  • A barring device for use when mill or gear unit maintenance occurs
  • A comprehensive gear inspection program with vibration and trend analysis
  • Various training programs to enable staff to optimally handle the Symetro gear unit (e.g. lubrication training to learn about suitable additives) 

Short payback


The new TSHH technology rotating parts offer an attractive investment with a short payback time. In addition, having the parts available as insurance spares can help secure the mill operation and avoid costly, unscheduled downtime. Furthermore, when quoting for the new rotating parts, we will investigate the possibilities to increase the production of the old mills and thereby generate a return on investment.


The company visits customers in order to go through all the techno-commercial benefits of the new TSHH Plug & Play solution. During onsite visits, drive station opportunities for ball mills, vertical mills and kilns in terms of service, maintenance, retrofit concepts and new solutions are discussed.

The company visits customers in order to go through all the techno-commercial benefits of the new TSHH Plug & Play solution. During onsite visits, drive station opportunities for ball mills, vertical mills and kilns in terms of service, maintenance, retrofit concepts and new solutions are discussed.

Published for World Cement Review, December 2013

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