Split Roller Bearings Come of Age

Modern generations of plant and maintenance engineers are under pressure like never before to deliver uninterrupted production and achieve the highest levels of overall equipment efficiency (OEE). In pursuit of this ideal, machines are monitored, lubrication is optimised, and maintenance is planned; however, there is still no legislating for the standard bearing that fails at midnight and requires 8 hours to change. No legislating perhaps, but if the bearing in question was a split roller bearing rather than a solid bearing, then the bearing cartridge could be easily removed from the shaft, and the time for replacement would be around 1 hour. Moreover, the downtime costs would be a mere fraction of what would otherwise be incurred. Split roller bearings (SRB) are not new; they have been around for over 50 years. However, with a new and improved design from Revolvo, the leading specialist bearing manufacturer, the split roller bearing has really come of age and is well equipped to deliver operating benefits and reduced costs, not just in traditional core markets such as Quarrying, Mining, Steel, Power Generation, Cement and Sugar Processing, but also across mainstream industry The major benefit of Revolvo's new and improved split bearing design is that the company started with 'a clean sheet of paper'. This meant that all aspects of traditional designs could be analysed and improved upon. This is exactly what Revolvo has done in just about every area of its product specification, including materials, mechanical design, sealing, and simplifying the inspection and maintenance procedure. Revolvo's first consideration was the material to be used. The objective was to ensure maximum strength and durability of the product. To achieve this the company chose the toughest grey cast iron that could be practically machined: a 250- grade material, to BSEN1561,1997, which meets all design requirements. In addition to the material selection, Revolvo's designers studied the actual shape of the casting making up the pedestal halves. They found that by incorporating two ribs on the pedestal cap casting, it significantly increased rigidity. This is important, because operating conditions are tough in the type of industries where these bearings are used, and any extra robustness that can be provided against knocks can extend the life of the bearing cartridge and pedestal. At the same time as optimising the design of the cast iron pedestal cap, another problem: that of visual inspection, was addressed. Split roller bearings are very convenient and quick - up to 80 percent quicker than solid bearings - to fit and remove from shafts. However, in many industries there is a requirement to inspect bearings at regular intervals, as part of a planned maintenance campaign. Revolvo's design makes this procedure a simple one. Firstly it provides 'Pry' slots to enable disassembly of the cartridge and pedestal, reducing the likelihood of components being broken, especially in applications where the bearing unit has been installed for some time; and/or where the environment is dirty. Secondly, the Revolvo design addresses the serious problem of cage clips falling out during the inspection or replacement process. The design achieves this with a new design of cage clip, which is retained via spiral pins to one half of the cage during assembly and disassembly. The importance of this feature to maintenance engineers cannot be overstated: lost cage clips can halt production as effectively as any breakdown. Moreover, with Revolvo's retained design the maintenance engineer benefits from a 'free hand', which can only speed up the bearing replacement process. Complementing the cage clip design as an additional aid to assembly, SRB bearings are designed to be statically self-aligning. This means that there is no need to accurately realign the bearing housing to the shaft or any other in-line equipment, which might be involved in the installation. SRB split roller bearings are designed to accept up to 3 degrees of shaft misalignment. As a further aid to extend bearing life, Revolvo's split roller bearings use specially profiled rolling elements to minimise damaging edge stresses that can occur under conditions of dynamic misalignment. These are able displace slightly, and so prevent potential damage to the bearing raceway and rolling elements. For the user in high-speed applications such as fans, this may mean all the difference between premature failure and good reliable long-term operation. In addition to the rolling elements optimised profile, another key factor designed to extend the bearings potential life by ensuring the accurate guidance of the rollers is the machined brass cage. Revolvo's cage design has CNC bored pockets that are optimised to give very accurate roller guidance, which prevents skewing, a condition that can lead to edge loading on the bearing and reduced bearing life. In addition to providing excellent roller guidance, the Brass cage also allows operation at higher temperatures up to 140oC without problems, and operating speeds up to 25 percent higher, as long as thrust loads are within design limits. Overall, Brass is one the best cage materials as it absorbs lubricant and performs well in aggressive environments where lubrication is marginal. The ability of SRB split roller bearings to perform reliably in aggressive environments is also due to the performance of the sealing systems available to protect the cartridge bearing units. In this area the SRB product has inherent advantages over traditional solid bearing sealing systems. With SRB, the spherical location between the cartridge and pedestal support ensures that under conditions of shaft mis-alignment 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 number of 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. With its many new design features, Revolvo's range of SRB split roller bearings meets and surpasses all the demands of traditional users, and also those of users in new industries. Manufactured in Dudley, in the West Midlands, in a plant that is benefiting from over £1.5 million of investment in new machinery, the range is available in Light, Medium and Heavy series in sizes from 35mm to 600mm diameter, plus imperial equivalents, and larger non-catalogue sizes up to 1400 mm in outside diameter. It is fully interchangeable with competitive products on the market.