(June 10, 2011)

NSK has revealed how its asset improvement programme has solved a recurring problem of large bearing failures in a screw pump conveying system at a major cement works.

Because of dust contamination, 27 bearings in one year were consumed by the screw pump system.

A solution based on Hi-TF bearings from NSK has reduced this number by more than 50 per cent, as well as reducing maintenance costs and improving reliability at the plant.

The screw pump conveying system was experiencing regular failures due to large angular contact bearings experiencing dust contamination.

Hygroscopic dust was entering the bearings, wearing the raceways and increasing clearance to the point that, to avoid catastrophic failures, the bearings had to be changed prematurely and on a regular basis.

The problem became so bad that in just one year, a total of 27 bearings were employed on the conveying system.

This was bad enough in terms of replacement bearing costs alone.

However, once expenditure on maintenance was added, for breaking down the system repeatedly, the total cost made for serious reading and was clearly unsustainable.

NSK recommended bearings made from Hi-TF steel as a solution to the premature failure problem, asserting that the material would manage the problem by offering resistance to contamination.

In addition, the bearings would run more quietly and smoothly and offer shock load protection.

Hi-TF is said to address the problem of premature bearing failures that occur due to arduous and dirty operating conditions when bearing lubricant is easily contaminated with debris.

In comparison with bearings made of ordinary carburised steel, Hi-TF offers up to seven times the life with contaminated lubricant, and up to 1.5 times the life with clean lubricant.

Where the problem is related to insufficient lubrication, the life of Hi-TF is still around 4.7 times that of ordinary carburised steel.

In addition to extending service life under conditions of boundary or contaminated lubrication, Hi-TF bearing steel offers increased resistance to wear and seizure as a result of the dispersion of a large number of fine carbides and nitrides in the bearing material.

In comparative tests with bearings made of conventional materials such as SUJ2 steel, the Hi-TF material structure has shown less than one-third the rate of wear and a 20 per cent increase in seizure resistance.

NSK manufactured replacement angular contact bearings from Hi-TF material for the screw pumping plant.

In addition to superior carburised rings for improved shock resistance, the bearings have brass cages, lube slots on their outer faces and are supplied with P6 accuracy to provide quieter and smoother running.

Since installing the Hi-TF bearings, bearing consumption at the cement plant has reduced by more than 50 per cent.

The plant has since converted other areas of its operations to Hi-TF bearings.

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