Preventing wear on coal handling conveyors

Paul Boughton
Split bearing units used on underground coal handling conveyors are preventing premature wear.

The UK's Hatfield Colliery reopened in May 2006, by accessing 27 million tonnes of high quality reserves in the Barnsley seam, and Longwall coal face production has resumed that has created jobs for over 300 mineworkers and a guaranteed coal supply for electricity generators. The mine has known reserves of 100 million tons, and weekly output is around 45,000 tonnes, producing annually over two million tonnes.

Reopening of the mine was a major undertaking, involving substantial investment, which when a clean coal power station is built adjacent to the mine, could exceed £2.6 billion. One of the investments in the first stage of the reopening, were the large conveyor systems for handling in excess of 2 million tonnes of coal per year, supplied by Continental Conveyor of Sunderland.

These conveyors are equipped with Revolvo's SRB split bearings - Heavy Duty 240mm units on the main pulleys, with Medium Series 110 mm units on the tail pulleys. All of these SRB split roller bearings were manufactured with bored pocket precision brass cages as standard; meaning that they can be used underground without any modification.

This high material specification of the standard SRB bearings was a major factor in their specification; equally important were the bearings ease of maintenance - particularly important in the cramped conditions underground - and their superior sealing systems. SRB split roller bearings are much easier to fit and replace than solid bearings: fitting a SRB split roller bearing takes just 10 per cent to 15 per cent of the time required to fit a typical solid bearing. As a result, SRB split roller bearings reduce downtime substantially.

SRB split bearings also offer the benefit that they can be inspected in situ as part of a planned maintenance schedule; and have a longer life span because they cannot be crosslocated.

In addition to being easier to fit, inspect and maintain than solid bearings, Revolvo's SRB split roller bearings are providing Hatfield Colliery with the highest levels of reliability, due to the performance of their sealing systems.

The design of Revolvo's SRB bearings means that they perform exceptionally well in harsh operating conditions, even with shaft misalignment. With SRB split bearings, the spherical location between the housing and pedestal support ensures that even under conditions of shaft misalignment, the seal will always remain concentric to the shaft. In contrast, solid mounted roller bearings under conditions of misalignment can suffer from non-concentric ineffective seals that will rapidly lead to premature and expensive bearing failure.

Revolvo has taken this design advantage forward and developed many designs of high performance seals, which provide effective sealing even in the worst operating environments - even under water. The excellent performance of their labyrinth seals is evidenced by am recent application where Revolvo solved a major problem of premature wear on screw conveyor bearings in the cement industry.

With its many new design features, Revolvo's range of SRB split roller bearings meets and surpasses all the demands of traditional users in process industries, 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 1500mm in outside diameter. It is fully interchangeable with competitive products on the market.

Long life grease

Meanwhile, by employing a programme of material substitution and longer life lubrication technology, a wind turbine manufacturer was able to achieve maintenance cost-savings.

The manufacturer of micro wind turbines had been experiencing problems due to the prohibitive cost of bearings. The manufacturer was facing a stark choice: improve the purchasing and manufacturing costs for the project, or it would not continue.

NSK engineer visited the customer to review the machine design. This highlighted several areas where unit build cost could be reduced substantially. Following the visit, a supporting design justification report, and bearing and grease life calculations were produced.

These not only underpinned the design cost reductions, but also promised benefits such as simplified assembly procedures, and improvements in overall bearing performance, reliability, and bearing life.

The customer acted upon NSK's recommendations; substituting NSK premium brand single row radial ball bearings, where before there had been a selection of mixed brand products, including single row radial ball bearings and angular contact bearings.

The NSK bearings are lubricated by NSK's long life grease, which delivers a grease life of over 200,000 hours compared with a grease life of 22,400 hours for the mixed brand bearing package.

This improvement in grease life has enabled major reductions in maintenance to be achieved, helping to keep the micro turbine in service substantially longer. The quantification of this improvement, in conjunction with the additional improvements gained from the NSK package, has been calculated by the customer to exceed EUR337,000.

Moreover, the manufacturer is also benefiting from extended product life, improved reliability and reduced maintenance, as a result of replacing mixed brand bearing products with NSK's premium brand bearings and longlife grease.

NSK is producing similar cost saving results across all industry sectors. The company's cost saving programme looks at all aspects of bearing systems: design, specific problem applications, lubrication, and even training issues.

The process often starts with a site survey, which is very detailed. NSK engineers visit a customer's premises, talk to them and get to understand what the difficulty is. Data acquired from the visit is subsequently analysed, leading to recommendations for improvements.

These improvements are then quantified in cost terms, demonstrating the level of savings that can be expected by the customer as a result of adopting the solution proposed by NSK

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