Comair Rotron conducts a continuous and comprehensive life test program for development purposes as well as for continuous monitoring of production units. The results of the life testing are reflected in continuous improvements in Comair Rotron's products in such critical areas as bearings, lubricants, materials and insulation systems. The continuous monitoring of production units provides a means of evaluating the adequacy of production methods and quality assurance programs.

Because the primary mode of an air moving device is bearing failure caused by eventual degradation of the lubricant, Comair Rotron has adopted the method of statistical analysis widely used by the bearing industry, known as the Weibull function analysis. The Weibull function analysis method permits statistically accurate determination of the failure distribution from a small representative sample of air moving devices. Comair Rotron's practice is to accelerate the life testing operating its products at several elevated temperatures until enough failures of each sample group have been obtained to establish these statistical distributions. These data are then extrapolated to predict the time at which, in a large population, 90% of the air moving devices will still be operative. This time is referred to as the "L-10" life, or the time at which 10% of the sample could be expected to fail.

Based upon the results obtained at each of the relevant temperatures, (usually 40° C , 55° C and 72° C) a curve may be drawn which will permit the life to be expected at lower temperatures. The curves presented in this catalog have been determined from tests conducted in the manner described here.

Every model fan, regardless of manufacturer, will exhibit different life characteristics depending on the combination of voltage, frequency, ambient temperature, mounting attitude, environment and restriction to airflow conditions it encounters in an individual application. The normal failure mode is in the bearing system and it is usually related to the total temperature the bearing system sees, although other factors may apply.

Generally speaking, there is not much of a life difference between a sleeve bearing system and its equivalent ball bearing system when the total temperature the bearing system sees is relatively low, but as this total temperature increases, ball bearings give progressively longer life than sleeve bearings.

For normal computer type environments we recommend our sleeve bearing units since they will meet the life requirements, are quieter, are less expensive and can be used in any mounting attitude. For high ambient temperatures, or other operating conditions which result in the bearing system seeing very high total temperatures, or hostile environments, ball bearings should be considered. If a sleeve bearing model will do the job, we suggest i be used instead of a more expensive, less quiet ball bearing model.

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