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Load Rating and Bearing Life (continued) __________________________________________________________________
| GENERAL
FATIGUE LIFE CORRECTION FACTORS |
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The L10 preload life of a bearing is normally adjusted as follows, according to real-world operating conditions:
a1 = Life correction factor for material and desired statistical reliability, the values for a1 being given below: Values
for Life Correction Factor a1
a2 = Life correction factor for operating conditions. It has been empirically determined to have a value between 2.0 under ideal operating conditions and 0.2 where one or more of the following conditions may apply:
Since there are many factors that determine
observed bearing life, the above figures should be used conservatively. |
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MAXIMUM
STATIC LOAD Co |
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When subjected to an excessive load or shock, rolling bearings may incur a permanent damage to the raceways, called brinelling. This occurs when the elastic limit of the raceway material is exceeded and will permanently effect the smooth rotation of the bearing. The maximum static load
rating of a bearing (Co) is defined as that load which
will produce a contact stress of 609,000 lbf /in2 (428
kgf/mm2) between the rolling element (ball) and the raceway.
The values of Co are listed in the bearing tables for
each individual bearing. Exceeding this value will damage the bearing. |
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In most cases, the actual load applied to a bearing is a combination of fluctuating radial and axial loads which cannot be directly used for fatigue life calculations. Instead, the Equivalent Load (P) is used. This represents the hypothetical load of constant magnitude, passing through the center of the bearing, that would give the actual observed bearing life when used in the fatigue life formula. It is an estimate, dependent on the initial ball contact angle αo and the static capacity of the bearing Co, as well as the actual load applied (F).
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