Advanced seals: boosting bearing life
15 July 2015
Contamination of bearing oil can be eliminated through the use of modern labyrinth design bearing protection seals, as Dr Chris Carmody, special products manager at AESSEAL explains
The reliability of rotating equipment is almost inevitably linked directly to bearing life, and it is estimated bearing failure is responsible for almost 21% of these equipment failures (Bloch, 2011). Research into bearing failures shows that just over half of these are a result of contamination of the bearing oil (Fig 1). Clearly it is essential to ensure that contamination of the bearing lubricant is minimised and, if possible, eliminated if optimum bearing life is to be achieved thereby improving the equipment reliability (MTBF).
A significant contributor to bearing oil contamination is the bearing enclosure breathing process required by rotating equipment. When equipment rotates, the bearing housing heats up and the oil/air mixture inside expands and is forced through the seal. The problem arises when the equipment cools; the oil/air mixture cools and contracts, sucking air from the external atmosphere through the bearing seal and back into the housing. If bearing seals are to work effectively, they must facilitate this 'breathing cycle' in order to extend bearing life.
Advanced labyrinth bearing protection seals have been developed that offer dust tight protection against both solids and liquids and are also non-contacting in operation. LabTecta 66, for example, prevents bearing oil contamination because it incorporates patented dynamic lift technology to protect against the ‘breathing’ issues that contribute to 52% of all bearing failures. This technology uses the centrifugal force of rotating equipment to open a temporary micro gap allowing expansion of the oil air mixture in the bearing housing, which consequently allows the equipment to breathe.
Rated to IP66, LabTecta 66 is capable of reducing water contamination of the bearing oil from 83% to just 0.0003% compared to lip seals, even when exposed to high pressure water jets. The range is ATEX certified for use in explosive environments and special designs make it suitable for a wide range of applications.
A recent research paper produced by AESSEAL showed through an accelerated life test – with a stop start cycle of four times a day – that the average LabTecta 66 life expectancy was more than 10.5 years. The paper also showed that by using an established statistical (WeiBayes) technique, the average life expectancy was also in excess of 10.5 years. However, because such statistical data can only be modelled with failure data, and as no LabTecta 66 has ever failed, the results have to be viewed as conservative.
Figure 2 shows the effect of water contamination on a continuous digester that was fitted with inadequate bearing protection. The moisture contained in the atmosphere was able to penetrate into the bearing housing. This was enough to destroy the bearings. Independent research has shown that water contamination as low as 0.002% (20ppm) in some oils can reduce bearing life by as much as 48%. The challenge for maintenance and engineering professionals is to reduce this contamination and provide an effective method of sealing the space between the bearing housing and the drive shaft.
An increasing number of engineers are upgrading to modern labyrinth bearing protectors because they eliminate bearing oil contamination from both dust and moisture.