Operating underwater, in an abrasive solution, and at ambient temperatures up to 400°C, Revolvo’s split roller bearings (SRBs) are providing a reliable solution to the problem of support for the twin 11m long Archimedes ascender screws that deliver water to the Zambezi Rapid Water ride in the Gold Reef City theme park in Johannesburg. They were installed to replace plain bearings that proved inefficient under operating conditions of complete submersion in an environment of abrasive sand and silt resulting from the constant churning action of the screw in the water. Meanwhile, other Revolvo SRB bearings have been installed to operate in dry conditions on this application, but have to accommodate a hefty 16 tonnes of axial load.
The 2.7m diameter ascender screws are angled at 30 degrees and rotate at 27.5rpm. Together, they are capable of supplying 7m³ of water per second or 25,200 tonnes per hour. The lower, submerged bearings on the ascender shafts are 200mm units from the SRB Light Series range. These bearings are equipped with a special sealing arrangement that allows them to operate completely submerged, excluding water and other contaminants from the bearing enclosure. This is achieved by means of an arrangement that comprises two lip seals with garter springs, plus centralised positive grease feed. The positive action of the grease purge between the two seals, combined with the efficiency of the sealing arrangement delivers consistently reliable long-term operation.
The upper bearings on the ascender screws are 250mm diameter SRB Medium Series units, designed to accommodate large axial loads. The bearing load is carried between the inner race shoulder on one side and the outer race lip on the other. Both shoulders and lips are specially designed to facilitate the generation of an oil film between the sliding surfaces of roller ends and lips, thereby reducing wear and limiting heat generation.
“This application demonstrates how SRB can design and manufacture units to accept conditions completely outside of the normal perceived split bearing capabilities,” said SRB Sales & Marketing Director Adrian Menzies. “Our SRB split roller bearings perform exceptionally well in harsh operating conditions even with shaft misalignment, whereas solid mounted roller bearings can suffer from non-concentric ineffective seals that will rapidly lead to expensive premature bearing failure. Moreover the number of standard sealing solutions with SRB is far greater, which extends the range of applications for our bearings.”
With SRB split roller bearings, the spherical location between the cartridge and pedestal support ensures that under conditions of shaft misalignment, and whatever type of seal is used, it will always remain concentric to the shaft. As a result, SRB split roller bearings perform exceptionally well in harsh operating conditions even with shaft misalignment, whereas solid mounted roller bearings can suffer from non-concentric ineffective seals that will rapidly lead to expensive premature bearing failure.
The second major advantage provide by SRB in the area of sealing systems is the diverse range of standard options available: eight in total, including Viton high-temperature seals, aluminium triple labyrinth seals for high speeds with high contamination, and high-performance Kevlar packing seals for extremely aggressive environments of the type encountered in quarries, mines and steelmaking plants. Also adding to the versatility of the SRB range are seals for use in very wet environments and laminar seal rings that are highly effective in denying ingress to fine particles such as cement or ash.