In 1996, Conveyor Equipment Manufacturers Association (C.E.M.A.) changed its conveyor idler specifications. This change enabled manufacturers to build idlers with inadequately sized "sealed for life" ball bearings when comparing it to the pre-1996 tapered roller bearing idler.
Since the early 1900's, US manufacturers have manufactured idlers with tapered roller bearings. The tapered roller bearing has at least 2.5 times greater load carrying capacity than a ball bearing of equal shaft diameter. Furthermore, when comparing similar sized tapered roller bearings to ball bearings under the same load, the bearing life of a tapered roller bearing is exponentially greater than a ball bearing.
Unfortunately, tapered roller bearings must be re-lubricated, regularly. In addition, tapered roller bearings have very little misalignment capability and must be de-rated when misalignment occurs, (Misalignment occurs during the manufacturing process, as well as the operational process due to shaft deflection.)
"Sealed for Life" ball bearings are exceptional alternatives to the tapered roller bearing as long as the ball bearing is correctly sized. The ball bearing advantage is it has greater misalignment capability and does not have to be re-lubricated.
The chart below represents the load ratings of CEMA C idlers as published in CEMA Standard 502-2004.
This chart is no different to the chart published prior to 1996 with exception to idler life in hours. Prior to 1996, idlers were rated 90,000BU (useful life) hours and today 30,000 L10 hours life.
Careful consideration should be taken when specifying CEMA classes. The post 1996 6204 (20mm/.788) ball bearing used in CEMA C idlers has a dynamic load rating of 2113 lbs. whereas the pre-1996 CEMA C L44643/L44610 (3/4"/.750) tapered rolled bearing has a dynamic load rating of 6407 lbs. Not including misalignment adjustments, this tapered roller bearing has 3X the load capacity.
The result of this change is a reduction in bearing life and idler life.
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