Standard bearing types are costing extraction industries dearly...
22 August 2012
It can take as little as 30 minutes to replace a split roller bearing and even less time to inspect it; whereas solid bearings routinely take many hours, and sometimes days to replace and are notoriously difficult to inspect while in place. Yet overwhelmingly solid bearings comprise the major segment of rolling bearings in use in extraction industries today. Adrian Menzies explains why 'lowest cost' for the OEM is usually the most expensive for the quarry end-user.
Solid roller bearings are difficult to fit & to replace, and usually impossible to visually inspect whilst in service - relying instead on complex and expensive vibration monitoring systems for critical units. But, with the smaller sizes in particular, they are relatively inexpensive to purchase so few companies compare the overall lifetime costs with those of alternatives - such as split roller bearings (SRBs). In an industry that is driven by cost down pressures rectifying this situation could potentially lead to large savings in maintenance and plant downtime.
Companies are increasingly embracing the fact that to achieve performance gains they must first achieve improved production efficiencies. To achieve these longer term efficiencies it may be more cost effective to specify components that initially cost a little more, but will reduce maintenance and repair costs during their service life, therefore offering the customer a lower ‘whole life cost’ and reducing the total cost of ownership (TCO). It is the classic case where the component with the lowest initial price, often does not offer the customer the lowest lifetime cost.
This is particularly true of bearings and is one of the major reasons why companies in all industries are increasingly turning to Revolvo’s SRB split roller bearings as a means of reducing downtime. So why bear the additional initial purchase cost? The answer is threefold: initial installation time can be reduced by up to 90%; bearings can be inspected in situ; and the ease and speed with which SRB split roller bearings and housings can be replaced if there is a maintenance issue.
Unlike solid bearings, SRB split roller bearings are totally split to the shaft; a design that both simplifies and expedites installation and cuts downtime when compared to replacing solid bearings of the same size. SRB split bearings allow the shaft to be supported by the lower section of the bearing; while the top section can be removed, making bearing inspection simple, without the need to remove drives or the shaft itself. This intrinsic feature is especially valuable with regards to large machines, where sheer weight and size can be a barrier to fast and effective servicing.
The relative price differential which can be significant for smaller bearing sizes starts to narrow for larger sized bearings, with sizes above a 220mm shaft diameter being more comparable in price, and very large bespoke sizes over 400mm shaft diameter often similar in cost, especially when availability also starts to become an issue. With large split bearings available on relatively short lead times they fair well in comparison to some large made-to-order sizes of solid bearings from the global manufacturers which are far more susceptible to changing market conditions and have sometimes quoted lead times that have varied from months to even years.
The additional cost of purchasing a SRB split bearing comparable in size to a solid bearing is often no more than the additional maintenance cost for one replacement unit, and a fraction of the cost of any unplanned downtime. Should a solid bearing fail on a crucial piece of quarry equipment it may take days to replace, requiring not only the bearing replacement, but the dismantling of the machine and specialist tools and sometimes lifting equipment to remove it, which also creates the possibility for more damage to be caused during the machine disassembly and shaft handling process.
With SRB split bearings the spherical location between the housing and the support pedestal ensures that under conditions of shaft misalignment, and irrespective of the type of seal used, the seal always remains concentric to the shaft. As a result, SRB split roller bearings perform exceptionally well in harsh operating conditions (in some cases underwater) even with serious shaft misalignment, whereas solid mounted roller bearings can suffer from non-concentric ineffective seals that will rapidly lead to expensive premature bearing failure.
Revolvo has taken this advantage forward and developed high performance labyrinth, and Kevlar Packing Seals, which provide effective sealing even in the worst operating environments. This has been evidenced in many applications; including many worldwide cement plants where the Revolvo labyrinth seal overcame a long term problem of premature failures of hanger bearings on cement screw conveyors.
From the technical, economic and pure design points of view, SRB split roller bearings offer a host of advantages and cut downtime significantly for the end user. The simplicity of fitting a split roller bearing and its design, compared to a solid bearing, are major factors in its longevity.
It is understandable why during the specification stages of a new project an OEM may choose to make short term savings by specifying the most inexpensive bearing for the job. However it is important that the end user considers whole life costs, specifically downtime implications for maintenance and repairs. Talking to Revolvo, the split roller bearing specialist will help you to understand the long term savings that are possible with most applications, and ensure that OEM machinery manufacturers fit bearings that won’t cost dearly in the long run.
Adrian Menzies is sales director of Revolvo Ltd
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