Split bearings speed major steel plant overhaul
09 June 2013
Schaeffler UK was part of a team that successfully completed the replacement of the main trunnion bearings on a basic oxygen steelmaking plant at Tata Steel's Port Talbot site.
With a steel making capacity of 330 tonnes, any loss of operation of a basic oxygen steelmaking (BOS) vessel inevitably results in significant lost revenues. By replacing the drive-side trunnion bearings with split rolling bearings, Schaeffler helped to save its customer five extra days of work. If solid rather than split bearings had been used, the customer would have had to disassemble the bull gear unit, which is the main drive unit for the basic BOS plant vessel.
Tata Steel Port Talbot operates two BOS vessels: V1 and V2. The original vessel was installed in the late 1960s by UK firm, Ashmore, Benson, Pease & Co and was subsequently upgraded in 1991/1992 by Mannesmann Demag, an overhaul that included trunnion bearing replacements.
Sudden bearing failure on V2
In July 2011, Schaeffler UK received a telephone call from an area works engineer at the BOS plant, advising of a sudden bearing failure on the non-drive side (NDS) of the V2 vessel. The BOS plant engineers arranged a meeting and a request was made for two engineers from Schaeffler Germany to be on site at Port Talbot soon afterwards.
A meeting subsequently took place at Port Talbot to discuss action plans and how to the bearings were to be replaced. Schaeffler UK senior applications engineer, Dave Wall takes up the story:
“A method statement document was drawn up by Schaeffler UK, which specified the sequence and method to replace the bearings and to outline Tata’s requirements. Included in this document were a detailed tooling list and a step-by-step procedure for the dismounting and mounting of the drive-side [DS] and non drive-side [NDS] bearings.
“The standard ‘solid’ bearing on the DS was replaced by a special FAG split spherical roller bearing [SSRB], as this reduces the amount of downtime when installing a replacement. The NDS bearing was to be replaced with a similar solid bearing. In addition, various surrounding components also required replacing, once the secondary damage caused by the bearing failure had been identified.”
Removing the DS bearing - The cutting away of the existing bearing took a total of 36 hours. The distance between the trunnion spacers (bearing seating width) was measured in order to determine the thickness required for two special, Tata designed, split ‘dovetail’ spacers. These were required to ensure that the new split bearing would be correctly secured in place. The new split SRB inner ring halves with clamping rings, outer ring half and bottom roller cage halves, were fitted without any problems.
Removing the NDS bearing - The original bearing on the NDS had failed during operation, which had caused the BOS converter to drop down. It was now resting on the bearing housing and the housing covers. After lifting, parts of the damaged bearings were removed, including cage pieces; outer and inner ring fragments and rolling elements. All recovered fragments were sent for forensic examination to Tata’s Central Engineering Metallurgy & Inspection Department.
The housing back cover, bearing pressure plate and sleeve spacer were found to be seriously damaged. New ones had to be urgently manufactured by Tata Steel’s Central Engineering Shops (CES). The bearing inner ring had disintegrated and the sleeve had to be cut off due to its deformed shape. After removing the damaged bearing, it was also discovered that the trunnion back spacer was in need of repair. Again, machining work was urgently carried out by CES.
With the bearing housing also damaged as a result of this catastrophic failure, Schaeffler was instructed to manually repair this surface and restore it back to an acceptable condition.
During the dismounting process the NDS ladder expansion bearing rollers had to be replaced. To facilitate the ladder roller replacement and installation of a Tata manufactured solid inner bearing housing cover, the bottom half of the housing had to be moved away from the journal using specially manufactured crossbeams.
Mounting the new NDS bearing - The new bearing was first pre-mounted to determine the correct sleeve spacer width. The bottom half of the housing was then moved back into position and the crossbeam construction removed. Mounting the new bearing proved challenging, as the collapse of the original bearing had caused the vessel to move out of alignment.
The lowering of the converter was also a challenge as the vessel had to be moved sideways by 40mm to achieve the correct installation position. Side shifting was initially a problem for the vessel lifting contractor but this problem was successfully overcome.
For the DS bearing, the remaining roller cage and outer ring halves were installed. For both bearings, the housing caps were fitted and each bearing was 100 percent filled with grease, including the surrounding free space.
The housing covers were bolted in position and new seals with their tensioning devices were fitted. After having successfully completed the work in under two weeks, Schaeffler engineers were pleased to be leaving behind a very happy customer. But with the bearings successfully installed, the work didn’t finish there.
Schaeffler UK prepared a recommended practical maintenance schedule list and forwarded this to the BOS engineering team, among whom it was well received. In addition, customer ‘as built’ cross-sectional drawings were updated to show the actual parts (with measurements) now in place at V2. Schaeffler UK participated in, and contributed to, the Bearing Failure Review meetings with Tata Steel that followed the bearing replacement for the BOS vessels. Dave Wall again:
“Since replacing the trunnion bearings, Schaeffler UK engineers have also supervised two further BOS vessel bearing changes in a very short timeframe of just two months: Converter C at SSI UK/Teesside and Converter 1 at Tata Steel Port Talbot. Schaeffler has now been selected as the preferred supplier of main trunnion bearings for the two BOS plant vessels at Tata Steel Port Talbot.
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