Bearings perform the splits on ice
18 December 2012
Split roller bearings (SRBs) have been specified for a refurbished icebreaker’s diesel electric propulsion system, recently refitted in the Ukraine. The SRBs – supplied by UK manufacturer, Revolvo – were chosen because they are quickly and easily changed in-situ, preventing unplanned layovers or dry docking, should a bearing need replacing when the vessel is in service.
The move to diesel-electric propulsion has accelerated as its benefits have been proven in service, with estimates of its adoption doubling over the past three years alone. These benefits include a reduction in the overall size of the drive system; smaller engine rooms are made possible by the replacement of large, slow-speed engines with multiple smaller generators.
Noise and vibration are also reduced, and power can be more easily shared among devices other than the main propellers, such as bow thrusters and pumps. Not least, diesel-electric propulsion systems are more efficient, consuming less fuel and achieving a reduction in carbon emissions.
The Revolvo SRBs in this particular application provide support for an intermediate shaft connecting the icebreaker’s diesel engines and generator units. Unlike conventional vessels with fore or amidships mounted main engines, and long propulsion shafts connected via couplings to propellers, the diesel-electric propulsion system uses several medium-speed diesel engines to drive generator units providing electrical power to the motors that drive the ship’s propellers.
The SRB design, which is totally split to the shaft, allows simple and fast installation and easy replacement. Revolvo claims this task can be up to 90% faster than is the case with solid roller bearings, typically found on marine drive propulsion systems. Additionally, it is possible to inspect the bearing in situ without any major disassembly, and sealing systems are available to protect the bearing surfaces from contamination when operated in aggressive environments.
The bearing design allows the shaft to be supported by its lower section while the upper section can be removed, allowing inspection or servicing to be carried out with the shaft remaining in place. This feature is advantageous whatever the application, but it is especially so in the case of large machines, where sheer weight and size can be a barrier to fast and effective servicing.
Revolvo manufactures its SRB split bearing housings, and support pedestals in tough 250-grade grey cast iron to ensure maximum strength and durability. And when greater corrosion resistance is required, the company also offers alternative stainless steel housings.
A recent example was supplied for an underwater application, where the split roller bearings have to operate totally submerged in clean water without any risk of corrosion contamination. This design combines a stainless steel housing with specialised sealing, the latter being achieved with Revolvo’s split and sprung garter seal, which has been proven over many years in submerged applications.
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