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Plant engineering and maintenance

NSK bearings prove reliable in bucket-wheel excavator

The selection of NSK spherical rolling bearings in one of the world´s largest bucket-wheel excavators has proven to be an astute decision. Despite six years of heavy duty operation at RWE Power´s opencast mine in Hambach, Germany, the bearings are still going strong - without any relubrication.NSK spherical rolling bearings have been operating for six years in Excavator 290 without relubrication.

Every day, ´Excavator 290´ at the Hambach mine moves up to 240,000 tonnes of coal or, using its 130-tonne bucket-wheel, excavates large volumes of overburden which is then transported to a spreader on conveyor belts in its upper structure. The four central conveyor belts located here have to work hard, not only due to the volume of material transported, but because they operate 24/7 in an adverse environment heavy with dust and moisture. This is where two NSK spherical rolling bearings are helping the mine operator maximise the operational uptime of Excavator 290.

The idea of using NSK bearings was driven by the need to reduce maintenance costs on the mine´s largest machines. Excavator 290, which is 240m long, 40m wide, 100m high and 14,000 tonnes in weight, has been in service since the end of the 1970s. With this in mind, the RWE Power product managers responsible for the conveyor belt drums set up a pilot project that involved installing a sealed, dual row NSK spherical roller bearing with tapered bore inside the drive drum of belt 2 on Excavator 290.

Image: Sealed, dual row NSK spherical roller bearing with tapered bores are fitted to RWE Power´s excavator conveyors.

The bearing, which has an external diameter of 500mm and a shaft diameter of 300mm, was then replaced at the scheduled time. Inspection of the removed bearing revealed that it was in excellent condition despite having been subject to continuous, intensive use. This provided RWE Power with the confidence to adopt NSK´s spherical rolling bearing technology, a move that has been rewarded with excellent service - with zero maintenance - for the past six years.

Among the reasons for this high level of performance is the efficiency of the seals, the high quality grease used by NSK, plus the Super-TF (STF) raw material used for the bearing. STF is a carbonitrate steel that is subjected to a specific heat treatment that helps retain optimum levels of austenite content. STF bearings have twice the service life in comparison with conventional roller bearing steels with clean lubricant, and where there are contaminants in the grease, bearing life can be increased as much as ten-fold.

NSK in profile
Established almost 100 years ago, NSK (Nippon Seiko Kabushiki Kaisha) is a Japanese-listed company that has evolved from a regional ball bearing supplier to a roller bearing specialist and automotive supplier with a global market presence. Today, NSK employs more than 30,500 employees in 29 countries. As per March 2014 NSK achieved a turnover of 6,2 billion Euros. This result has been driven by ever-increasing investment in research & development, enabling the company to continuously improve the quality of its products and services. This investment supports NSK's objective of "No. 1 in Total Quality". In addition to a complete rolling bearing portfolio, NSK develops and manufactures precision components and mechatronic products, as well as systems and components for the automotive industry, including wheel bearing units and electric power-steering systems.

In 1963, NSK's first European subsidiary, Düsseldorf, Germany, was opened and in 1976, the first European production facility in Peterlee, England. Today, NSK Europe supports pan-European sales with production locations in England, Poland and Germany, logistics centres in the Netherlands, Germany and England and technology centres in Germany, England and Poland. In 1990, NSK purchased the UPI Group including the renowned European bearing manufacturer RHP, with its factory in Newark (UK). Additionally, NSK has developed a comprehensive network of authorised sales distributors. NSK Europe is divided into application-based business divisions: Industry rolling bearing technologies & linear and precision technology (EIBU) as well as bearing modules and steering systems for the automotive industry (EABU & ESBU). In this organisation, NSK Europe's 3,500 employees achieved a turnover of over 900 million Euros as per March 2014.

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