The difference is bearing and axle size. The standard CEMA C is designed with a 20mm/.788” bearing and shaft; whereas, our Mine Duty CEMA C (MD30) is designed with a 30mm/1.18” bearing and shaft resulting in 4 times greater L10 bearing life. See the comparison, below.
What is L10 life?
The definition of L10 for belt conveyor idlers: The basic rated life (number of operating hours at 500 RPM) based on a 90 percent statistical model which is expressed as the total number of revolutions 90 percent of the bearings in an apparently identical group of bearings subjected to identical operating conditions will attain or exceed before a defined area material fatigue (flaking, spalling) occurs on one of its rings or rolling elements. L10 life is also associated with 90 percent reliability for a single bearing under a certain load.
This means you should expect 10% of your idlers to fail prior to its design life.
CEMA offers mathematical equations to estimate idler life. There are four overlooked equations that drastically affect idler life; one is solving for IML or the forces due to idler height deviation. (Zero IML assumes that the conveyor structure is perfectly aligned, square and parallel and that the idlers are manufactured to an exact height.) Also, according to CEMA, there are three K factors to be considered; the effect of environmental, maintenance, and temperature on potential idler life. The factor for good to fair maintenance is 0.75, dirty/wet environment is .50, and, temperature <120° F is 1.0. Multiplying these factors against calculated L10 life will reduce idler life, considerably.
The result of these factors…a standard CEMA C idler, fully loaded, will be rated for 30,000 hours L10 life. After applying the maintenance and environmental factors, life is now reduced to 11,250 hours with a reliability of 90%. If you were to calculate the same for 99% reliability, 30,000 hours L10 life is reduced to 2,363 hours which is considered 1 year with 1% failure rate. Our MD30 product line is calculated at 9,450 hours L10 life, or, 4 years life with 1% failure rate.
In addition to the difference in bearing size, our MD30, Mine Duty CEMA C, idler has a larger grease capacity (more grease) than a standard CEMA C aiding to longevity, and, our axle size is sufficient to support the same load for all belt widths up to 48” without being de-rated due to shaft deflection.
Improved construction through engineering and materials improves longevity by enhancing the overall quality of our idlers. Our better roll construction introduces less wear and tear on other conveyor components, from conveyor belts and bearings to drive pulleys. Look for conveyor idlers that are designed to bear heavier loads, which means they will not break down when greater volumes of materials are introduced to the system.
Better conveyor idlers last longer, which increases the company's return-on-investment in terms of equipment costs.