This is an abridged version of the full article, which appeared in the December 2012 issue of World Cement. Subscribers can view the full article by logging in.
A damaged girth gear at a Saudi Arabian cement plant had resulted in a dramatic drop in production. In order to get the plant back up to full production, the owners brought in Germany-based repair and maintenance experts Teutrine (acquired by FLSmidth in September 2012). After just 20 days of working around the clock, the kiln was restarted.
Girth gears are widely used in the cement industry to rotate kiln drives. They are easily installed and maintained, but incorrectly aligned, inadequately lubricated or worn girth gears can negatively affect kiln performance. At best, this can result in a severe drop in production rates, or worse – costly and prolonged downtime.
Sure signs of a worn girth gear are loud knocking noises and severe vibrations. After the operators at the Saudi Arabian cement plant heard these distinctive sounds and felt the vibrations, they discovered that the tooth flanks of the girth gear were pitted and skewed. In order to prevent any further damage, they were forced to significantly reduce the rotation speed of the plant’s rotary kiln. As a result, the plant’s cement production instantly fell by 50%. To bring the kiln up to its full production capacity of 5000 tpd, the girth gear had to be reversed and realigned with the kiln’s centre of rotation.
A demanding job
Girth gear reversal is a challenging process that requires both specialist equipment and skilled craftsmen. Teutrine’s particular specialisation is mobile service solutions such as repair and refurbishment projects for both cement plants and mineral processing plants. The company had previously carried out work in the Middle East region, and so it was called in to find a solution to the plant’s girth gear problem.
The first obstacle Teutrine’s team encountered was the hard surface of the spring plates and girth gear itself. As the team began drilling new boreholes for the girth gear bolts, the pneumatic drill’s reamer blades wore very quickly. As a result, the boreholes failed to meet the precise size requirements.
After the first half of the girth gear was successfully dismantled, a great deal of force was required to remove the old girth gear bolts. Before the second half was dismantled, a temporary girth gear fixing system was fitted to the kiln to keep the gear in place until it could be fully removed.
The girth gear was then secured both axially and radially using several alignment supports, and the spring plates were pressed into the shell using cleats. Torsion stoppers were used to hold the girth gear in place while the kiln was rotated into position. This auxiliary structure allowed the lower half to be secured to the foundation using a support stand, and special lifting eyes were used to secure and lift the girth gear’s halves.
Unable to drill new bore holes into the spring plates and on the girth gear, the team smoothed the existing holes with sandpaper and finger sanders. The new bolts were then trimmed to size, and Teutrine constructed a hydraulic press onsite to press the new bolts into the boreholes.
Drive shaft and pinion work
To prepare the drive shaft for the pinion gear reversal, the floating bearing was removed from the shaft and the drive shaft was suspended so it could fit vertically into the thrust device. One of the major challenges the team faced was dismantling and reassembling the pinion shaft. A heavy extraction device was fabricated onsite to dismantle the driveshaft. After the shaft was dismantled, additional supporting beams were used to hold the pinion until it cooled off.
Once the driveshaft was fitted into the thrust device, the pinion was heated with a propane burner, and the shaft was pressed out using hydraulic cylinders.
To shrink the pinion, it was placed in a vertical frame and heated. In order to ensure a temperature difference between the pinion and the shaft at high ambient temperatures, the shaft was cooled and then inserted into the pinion.
The drive shaft was then moved to the rotary kiln and lifted onto the drive foundation. To assemble the girth gear, the second half of the girth gear was lifted onto the rotary kiln, together with the spring plates and alignment supports. Both halves of the girth gear were reversed and secured temporarily onto the kiln shell and the spring plates were then preheated before being welded on.
With the spring plates welded into place, the girth gear was within the set values, and the gear’s axial and radial movement were well within the tolerance parameters. After the pinion was positioned and aligned, the contact pattern on the teeth was optimised and the clearance set.
The girth gear impact screws were redesigned to make the threads on both sides more accessible and to make the screws easier to tighten with a torque spanner, ensuring easier maintenance in the future. To complete the project, retaining washers were placed at the lock nuts, fitted with oil seal rings and then the pinion was moved into position. After only 20 days of downtime, the kiln was heated and brought back into operation. With vibrations and noise no longer a problem, the kiln was soon operating at full capacity once more, and the plant’s overall production returned to normal levels.
Gabriele Teutrine, Teutrine, Germany. This is an abridged version of the full article, which appeared in the December 2012 issue of World Cement. Subscribers can view the full article by logging in.
Read the article online at: https://www.worldcement.com/africa-middle-east/28112012/cement_teutrine_girth_gear_saudi_arabia_plant_766/