Can improved bearing life be achieved by providing a better bearing cage?
Ball bearings operating in harsh or abrasive conditions may have reduced operating times between failures due to the dirt and abrasive materials that enter the bearings, necessitating frequent bearing replacement.
Not particularly well understood in the reduced lifetime of these bearings is the role played by bearing
If bearing cages are made from materials that
- exhibit low wear rates, and
- are not badly impacted by dirt and abrasives,
can bearing life be significantly extended?
The role played by bearing cage wear was investigated by Chris Venter at South African chemical company African Explosives and Chemical Industries’ (AECI) plant in Sasolburg. In an effort to increase bearing wear life, Venter investigated and tested bearing cages made from three materials, namely steel, heat treated Monel and Vesconite Standard.
Frequent ball bearing replacements were required on a polyethylene reactor stirrer motor due to the excessive wear of a critical ball bearing. This resulted in significant downtime, since the reactor had to be shut down and cleaned out before the bearing could be replaced.
The original bearing had a cage manufactured from a steel grade, and was replaced after 400 hours of operation. The cage holes had worn from an original diameter of 22.5 mm to 27.2 mm, that is 4.7 mm. See table 1 and figure 1.
A new bearing was installed with a heat treated Monel steel cage. After 2,000 hours of operation (a life improvement of five times), the cage holes had worn 1.4 mm from 22.5 to 23.9 mm, a reduction in wear of 70%.
Seeking to improve the bearing lifetime even further, Venter then tested replacing the bearing cage with Vesconite, a self-lubricating bearing material.
This proved to be an excellent substitution, with the Vesconite bearing cage running 9,500 hours without any problems. This was a bearing life increase of 24 times compared to 400 hours of the initial bearing with a steel cage.
Upon dismantling and inspection, the Vesconite bearing cage showed negligible wear with only 0.07 mm of wear and was in excellent working condition. This represented a reduction in bearing cage wear of 98.5%, even though the bearing had operated for 24 times longer.
Expressing the improvement in operating life and cage wear reduction as a wear factor index compared to the original steel, the Monel cage represented a 17 times wear factor improvement, and the Vesconite cage a wear factor improvement of 1,670 times.
Venter wrote at the time (1988): “The Vesconite cage performed far above expectations and since the first Vesconite cage was installed not one motor had to be changed due to a bearing failure. This contributes to a saving of about R200,000 per annum.”
Calculating this saving in today’s terms (June 2021), a R200,000 annual saving is equivalent to a saving of R1.7 million, about US$123,000 per year.
These carefully recorded observations of performance in a tough real world application, combined with significant financial savings, highlight the value of further investigating the potential Vesconite Standard can play in dramatically extending anti-friction bearing life through improved cage materials.
New, advanced Vesconite grades, developed over the past 30 years, namely Vesconite Hilube, Vesconite Superlube and Hitemp 160, create further opportunities for reducing wear and potentially even greater saving.
|Bearing cage material||Hours in Operation||Bearing cage nominal hole diameter (mm)||Bearing cage worn hole diameter (mm)||Estimated Wear (mm)||Wear as percentage of ball diameter||Wear factor|
|Heat-treated Monel steel||2,000||22.5||23.92||1.42||6.3||17|