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2020 / 2021 Edition

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NSK Self-Lube bearings for harsh conditions

NSK

Bearings with triple-lip seals and end-cap protectors prove reliable in quarrying and mining applications

NSK Self-Lube bearing units with triple lip-seals and end cap protectors can provide extended service life in harsh operating conditions, such as those prevalent within the quarrying, mining, and construction sectors, where contaminants can easily penetrate poorly specified bearings, bringing machinery and equipment to a halt.

By leveraging state-of-the-art design, material, lubricant, and seals, NSK say their Self-Lube bearings exceed the life of conventional bearings, and that by selecting Self-Lube bearings with triple-lip seals and shaft end protectors, it is possible to reduce the costs associated with downtime and repairs.

NSK recommend their specially developed triple-lip seal for applications with a high degree of contamination. Bonded to a protective outer steel pressing (secured in the outer ring), this one-piece moulded nitrile seal with three lips is said to offer a highly efficient sealing design that protects the bearing in severe operating environments.

Standard Self-Lube bearing inserts also have a locating groove to allow the easy fitting of an optional end cap protector. The cap helps to protect personnel from rotating components and the bearing from external contamination.

NSK Self-Lube bearing units comprise a broad portfolio of inserts and housings, providing a fast, straightforward, and cost-effective solution for mounting bearings without the need for complex housings or special shaft arrangements.

The combination of ease of use, self-lubrication, and long service life means companies in the quarrying, mining and construction sectors can now reduce their costs for replacement bearings, maintenance, and downtime.

One case in point involved a company that was experiencing frequent reliability problems with the bearing units assembled in a vibrating drum. These bearings work in severe environments, where they suffer exposure to sand that often wholly covers the units. In addition, due to the nature of the application and access difficulties, the regularity and increasing cost of maintenance was proving an issue.

Following a comprehensive failed-bearing analysis as part of their AIP Added Value Programme, NSK proposed Self-Lube bearing units with triple-lip seals, which increased the operating life by a factor of 10 compared with the previous solution. In addition, the three high-integrity nitrile seal lips with lubrication traps have provided an effective way of stopping the ingress of contaminants.

In another customer success story, a company supplying ready-mixed concrete and other construction materials invited NSK to perform an application review of its augur screw pump bearings. The augur pumps transfer ash (an abrasive mixture of ash, sand, glass, fibres, and metal grit) into waiting containers. Here, the screws lift the ash at an angle of approximately 40° and the lower bearing units frequently fail.

Upon examination of the failed bearings, NSK were able to identify several issues. For example, after removing the flinger seal, it was evident that no contact seal was running against the inner ring of the bearing. It had likely worn away, and there was now a direct contamination path into the bearing.

Further problems included heavy cage corrosion and the absence of lubrication. The ingress of fine dust and particulates had probably soaked up any grease and created a grinding paste, eroding the rubber seal.

To rectify the situation, NSK again recommended their Self-Lube bearing units. In this case, they also suggested the inclusion of a small disc plate with an additional seal. This minor redesign would help stop most of the contamination and significantly reduce pressure on the bearing seal, as it features a path for the debris to escape.

By further improving the sealing, using the triple-lip sealing solution on the Self-Lube insert bearing, it is likely that reliability will significantly improve. In addition, the use of an end-cap protector for the bottom bearing could also benefit the company as it will help reduce any dust ingress.

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