Posted at 02-Jul-2018

How to Arrange Your Bearings

Paul Skade
By David Oliver
Channel and Platform Development Manager, Bearings and Units at SKF

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The high-volume, all-weather, 24/7 production of the mining and quarrying sector – all conducted in an extremely hostile environment – can cause even the most rugged mechanical components to struggle. And for precision engineering parts such as rolling bearings, it’s one of the toughest tests. But correctly specify the bearing and seal arrangement, and bearings can have a long and trouble-free service life despite the conditions.

 

The recently upgraded SKF Explorer spherical roller bearings now combine high-quality steel with an improved heat treatment process, for even better performance. The result is longer service life, even under difficult operating conditions and where contamination or poor lubrication are a fact of life.

Sealed SKF Explorer spherical roller bearings are ready-to-use units, factory-filled with the correct amount of grease. The high-performance lubricant is then protected by integrated double-lipped seals on either side of the bearing.

The bearings are designed to accommodate high radial and axial loads in applications prone to misalignment or shaft deflections. They’re also vibration tolerant, surface hardened, and have stamped steel cages that withstand much faster accelerations than standard bearings. This combination makes them particularly suited to a tough life in aggregate processing machinery.

 

When three’s better than two

Bearings are typically fitted in grease-filled housings with an open bearing. This creates two barriers to contaminants: the external L- or S-seals within the housing, and the grease.

In contaminated working environments, contaminants are usually forced out of this bearing arrangement by purging the bearing cavity with large quantities of grease. But using the SKF three-barrier solution eliminates that process.

With the open bearing replaced by a sealed SKF Explorer spherical roller bearing, an extra layer of sealing protection is added. At the same time, the barrier grease (for filling the housing) and the housing seals are effectively independent of the bearing lubricant. This can help to extend bearing life, reduce maintenance and – if appropriate – allow the use of biodegradable greases.

 

    

     

Ultra-protection

In quarries where ultra-fine dusts such as taconite abrasive iron ore are released, an even higher level of bearing protection is required. The SKF three-barrier solution can be made even more effective by replacing the housing’s external seals with SKF Taconite seals.

Suitable for protecting bearings in SKF split plummer block housings, these are essentially a labyrinth seal, with three to four labyrinth stages arranged axially.

The additional labyrinth stages include an internal low-friction rotating V-ring facing the bearing, to deflect water. Together, these barriers provide extremely effective and reliable bearing protection, against moisture and fine particle ingress. They also prevent contaminants from penetrating the bearing when the seal is purged for re-lubrication.

Quick-ety split

Another bearing type frequently found in quarrying applications is the split roller bearing, in pillow block or flange housings. These split-to-the-shaft bearings save time and money for quarry operators, because they can be removed more quickly and easily than ordinary bearings, from difficult-to-access locations in machinery. Often an ordinary bearing couldn’t be taken out from the same location without dismantling large components.

SKF Cooper is a leading manufacturer of these bearings – some of which have bores as large as 1,500mm – and is a key supplier to the quarrying industry.

In addition to split roller bearings, the company supplies split tapered roller bearings. These feature two opposed rows of tapered rollers, to take axial loads in either direction. Both bearing types are housed and sealed in special swivel cartridges, suitable for mounting in pedestal or flange outer housings. The spherical outer surface of the cartridge fits into a conforming surface in the mounting unit, so that any shaft misalignment tends to move the cartridge, seal and bearing together – maintaining the seal on an axis parallel to the shaft.

This maintains extremely close tolerances between the housing and shaft, and provides a sealing performance recognised as one of the best in the anti-friction bearing industry. 

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