Spherical Roller Bearings - TIMKEN - (Version JPG) - Page n° 29 - PDF Catalogue | Technical Documentation

ENGINEERING

IAD RATINGS, EQUIVALENT LOADS AND BEARING LIFE- continued

RELIABILITY LIFE FACTOR (A,)

The equation for the life adjustment factor for reliability is:

DEBRIS LIFE FACTOR (a_3d)

Debris in a lubrication system reduces the life of a roller bearing by creating indentations on the contacting surfaces, leading to stress risers. The Timken life rating equations were developed based on test data obtained with 40 urn oil filtration and measured ISO cleanliness levels of approximately 15/12, which is typical of cleanliness levels found in normal industrial machinery. When more or less debris is present within the system, the fatigue life predictions can be adjusted according to the measured or expected lubricant cleanliness level to more accurately reflect the expected bearing performance.

As opposed to determining the debris life factor based on filtration and cleanliness levels, a Debris Signature Analysis ™ can be performed for more accurate bearing performance predictions. The Debris Signature Analysis is a process for determining the effects of the actual debris present in your system on the bearing performance. The typical way this occurs is through measurements of dented/bruised surfaces on actual bearings run in a given application. This type of analysis can be beneficial because different types of debris cause differing levels of performance, even when they are of the same size and amount in the lubricant. Soft, ductile particles can cause less performance degradation than hard, brittle particles. Hard, ductile particles are typically most detrimental to bearing life. Brittle particles can break down, thus not affecting performance to as large a degree as hard, ductile particles. For more information on Debris Signature Analysis or the availability of debris resistant bearings for your application, consult your Timken representative.

a, = 4. 2 6 I l n

100 I ^2/3 + 0.05

In = natural logarithm (base e)

To adjust the calculated L₁₀ life for reliability, multiply by the a, factor. If 90 (90 percent reliability) is substituted for R in the above equation, a₁ = 1. For R = 99 (99 percent reliability), a₁ = 0.25. Table 6 lists the reliability factor for commonly used reliability values.


R (percent)	L_n	a₁
90	L,o	1.00
95	^L5	0.64
96	^L4	0.55
97	L,	0.47
98	L,	0.37
99	L,	0.25
99.5		0.175
99.9		0.093

Table 6. Reliability life factor.

Note that the equation for reliability adjustment assumes there is a short minimum life below which the probability of bearing damage is minimal (e.g., zero probability of bearing damage producing a short life). Extensive bearing fatigue life testing has shown the minimum life, below which the probability of bearing damage is negligible, can be larger than shown above. For a more accurate prediction of bearing lives at high levels of reliability, consult your Timken representative.

MATERIAL LIFE FACTOR (a₂)

The life adjustment factor for bearing material (a₂) for standard Timken bearings manufactured from bearing quality steel is 1.0. Bearings also are manufactured from premium steels, containing fewer and smaller inclusion impurities than standard steels and providing the benefit of extending bearing fatigue life (e.g., Duraspexx™). Application of the material life factor requires that fatigue life is limited by nonmetallic inclusions, contact stresses are approximately less than 2400 Mpa (350 ksi), and adequate lubrication is provided. It is important to note that improvements in material cannot offset poor lubrication in an operating bearing system. Consult your Timken representative for applicability of the material factor.

ISOMETRIC VIEW

I Pits & Valleys

Core Structure

0-5% Bearing Area

5-10% Bearing Area

Fig. 14. Surface map of a debris dented bearing raceway.

SPHERICAL ROLLER BEARING CATALOG

Spherical Roller Bearings - TIMKEN - #29

Rotary encoder, Roller bearing, Bearing unit, Seal, Bearing puller