Uptime a powerful case for split roller bearings

Split roller bearings mean that bearing failures can be rectified quickly, saving thousands in downtime costs, says Adrian Menzies of Revolvo.

Britain's plans to build new coal-fired power stations as part of the country's efforts to address its looming energy crisis mean that coal as a fuel is very much back on the agenda; not that it has ever disappeared as a fuel source for some of the UK's largest power stations.

These stations, in common with the nuclear facilities, still provide a substantial amount of the UK's energy requirement.

However, with the generating industry now carrying virtually no spare capacity, plant failures in any of these generating stations could have serious consequences in disrupting supply.

In this climate, the emphasis has to be on reducing unplanned downtime due to equipment failure to the absolute minimum.

Although this can be difficult with some complex power generation equipment, the problem is much easier to address with smaller mechanical components such as bearings.

Housed bearings are employed widely in coal fired stations, for example on coal feed conveyors.

They operate in an environment thick with coal dust, and problems usually start when this dust finds a route past protective seals and enters the bearing, causing it to fail prematurely.

This is a problem that can be difficult to solve with solid roller bearings.

When such a bearing failure occurs, the cost of the replacement bearing itself is small in relation to the cost of the plant downtime.

The solution to this problem could be to use split roller bearings of the type manufactured in the UK by Revolvo, and now used widely in utilities and process industries worldwide.

Experience shows that split roller bearing fitting time is only around 10 to 15% of the time taken to fit an equivalent size solid bearing.

As well as solid bearings being time consuming to fit, they are impossible to inspect whilst in situ, so routine inspection can often be overlooked.

Yet because their initial purchase price is relatively low, no one stops to compare their overall life costs with those of alternative split roller bearings (SRB).

From the technical, economic and pure design point of views, split roller bearings offer a host of advantages compared with solid types.

Basically, the simplicity of fitting a split roller bearing, compared with a solid bearing, is a major factor in its longevity.

Unlike solid bearings, SRB split roller bearings are totally split to the shaft, a design that both simplifies and expedites installation and cuts installation downtime by up to 90%.

SRB split roller bearings can be removed and replaced by simply supporting the shaft.

There is no need to lift the shaft, or obtain access to the shaft ends, therefore expensive and awkward to handle lifting equipment is not required.

This feature is extremely valuable for all applications, and especially regarding large machines, where sheer size and weight is a barrier to fast and cost effective servicing.

In addition, SRB split roller bearings can have a longer life span compared with conventional solid bearings, because they cannot be crosslocated.

In addition to their overall cost advantages, another major reason for replacing solid housed bearings with SRB split roller bearings is their effective sealing systems, where they have inherent advantages compared with conventional solid housed bearing seals.

With the SRB split roller bearing design, the spherical location between the cartridge housing and the pedestal support ensures that under conditions of shaft misalignment, irrespective of whatever type of seal is specified, it will always remain concentric to the shaft.

As a result, SRB split roller bearings can out-perform solid bearings in harsh operating conditions (in some cases operating underwater) even with shaft misalignment, where solid roller bearings can suffer from nonconcentric ineffective seals that will rapidly lead to expensive premature bearing failure.

Revolvo has developed special labyrinth seals to exclude fine, abrasive and hygroscopic dust encountered in industries such as cement and coal, and these specialist sealing solutions are proving to be far more effective in stopping coal dust contamination, providing much improved bearing reliability, longer life, and greatly reduced levels of maintenance.

One solution developed by Revolvo, for screw conveyors moving fine particulates, incorporates split steel labyrinth collars which are clamped onto the coupling journal between the flights of the screw conveyor.

These collars then engage with the labyrinth profile machined into the bearing housing.

Further modifications to the collars also prevent the build up of dust and particulates in the area around the seal.

Following successful trails, this solution has been adopted widely by many industries, leading to a vastly improved bearing life and a large reduction in downtime.

So, despite an initial higher purchase price compared with a conventional solid housed bearing, SRB split roller bearings can be far more cost effective, in terms of whole life costs, once the costs for labour to replace failed bearings, and production losses are taken into account.

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