Rebuilding ATOX® gear to new standards

June 19, 2014 Gert Hansen

Quinn Cement in the Republic of Ireland recently replaced the old spline connection in its ATOX gear with the new torque ring concept and took the opportunity to carry out a complete overhaul of the gearbox, significantly reducing any future risk of unscheduled downtime.

Quinn Cement, a greenfield FLSmidth plant producing 4,000 tpd, had been running an ATOX gear with a spline connection since 1998. Over the years, both FLSmidth and the plant staff had identified pitting in the gear and the plant was concerned that the worn gear would negatively affect mill performance.

The original spline connection is very costly to maintain and has a limited lifetime (between 5 and 25 years). The dynamic from the mill operation and the tilting of the grinding table, in combination with inadequate grease lubrication, generates wear and increased backlash. This leads to uneven tooth flank pressure and overload, and the spline connec-tion changes from working as a fixed spline to a flexible spline, for which it is not de-signed. The result is that, over time, the spline ring and the low speed shaft develop cracks.

In partnership with FLSmidth, Quinn Cement decided to reverse the gear wheel of its heavy-duty ATOX TTVL gear by 180 degrees, replace the old spline connection in its ATOX gear with the new torque ring concept including all the gear bearings and, if necessary, the high pressure pads.

“With the flexible torque ring, wear, damage and maintenance are reduced. Once and for all, these problems are solved as there are no longer any movable parts from gear to mill. The torque ring is flexible – and thus a stable connection between the gear and the mill is created,” explains Gert Hansen, FLSmidth senior field engineer and supervisor of the gear overhaul.

Maintenance-free design
The design of the flexible torque ring is taken from the well-known SYMETRO™ gear and it fully meets plants’ requirements for increased gear reliability under all running conditions. The torque ring has a shrink-fitted shaft with case-hardened pins and can be retrofitted to all TTVL-A gear units in as little as 2 weeks. The torque ring is maintenance-free because the shrink fitted parts do not require lubrication.

Despite the rainy Irish weather requiring temporary roofing to be erected to protect the work, the gear overhaul at Quinn Cement ran smoothly. FLSmidth supplied all the equipment for the gear retrofit, including jacks, chain blocks, heavy-duty spanners and measuring equipment. A subcontractor supplied the electric blankets for the heating process.

Read more about on-site services provided for the Vertical Mills>>

All the spare parts for the torque ring solution were also supplied by FLSmidth and were available in the plant store during the retrofit. Flexible torque ring spare parts include: 

• Output shaft with split thrust ring
• Torque ring with case-hardened shrink fit pins and tight-fitting bolts
• Retainer plate with bolts and cover
• Connecting flange with slide ring

Support and collaboration
The gear overhaul provided some good insights for Quinn Cement: “We realised that whatever we have been doing we will continue to do, since the gearbox was actually in good condition,” explains Paul Carron, Mechanical Manager at Quinn Cement. “We decided against replacing the high pressure pads, due to their good condition.” “Gert Hansen helped to plan the job ”, says Paul Carron, and he has been in touch regularly since completion regarding the subsequent operation of the gearbox.”

Quinn Cement continues to improve the plant and has recently invested in an incinerator for alternative fuels. This green investment will save money used for coal firing and is an on-going project with FLSmidth. “I believe that we have always had a good relationship with FLSmidth over the years and they have never let us down. Going forward, we will continue to use FLSmidth’s expertise in all aspects of the plant operation,” concludes Paul Carron.

The gear overhaul process involves
• Jacking up the grinding table
• Pulling out the gearbox from the mill
• Dismounting the wheels
• Dismounting the old bearings (at Quinn Cement they were flame cut because they were not going to be reused)
• Replacing the roller bearings
• Reversing the wheels and mounting them on the new shaft in the gearbox
• Mounting the connecting flange with the new torque ring
• Cleaning and adjusting the gear and measuring vibrations

Read more about the ATOX Raw mill>>


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