Avalie a vida útil do rolamento com base na carga dinâmica

Evaluate bearing life based on dynamic load

When considering a bearing for their application, an end-user engineer will generally choose a bearing based on the basic dynamic load rating, speed limit, dynamic/static alignment, bearing axial load and, of course, price.
One of the predominant characteristics in the purchasing decision is the basic dynamic load rating of the bearing. The higher the rating, the longer the expected bearing life for any given shaft size; however, not all bearings are created equal. When calculating roller bearing life, the following equation is generally used by ABMA and ISO:

l 10 = a 1 to 2 to 3 (C 1 /Physical Education) 3/10 * 1,000,000 / N 60 = h.
l 10 = Statistical life where 90% of the time, 10% of the bearings in a given population of bearings operating under the same application conditions will fail due to raceway spalling.

Legend:
to 1 = Reliability factor (typically normalized to equal 1)
to 2 = Material factor (normally normalized to equal 1)
to 3 = Environmental factor (normally calculated between 0.2 and 3, considering lubrication and contamination)
Pe = Normal equivalent load to the bearing races
N = Shaft Speed ​​– RPM When using this equation to calculate bearing life, it is relatively easy to compare competitive bearings. That said, this equation has a downside. The standardized approach to calculating the basic dynamic coefficient of a bearing considers the size, length and number of rollers around a pitch diameter with a contact angle. The above-mentioned duration equation L 10 Standard assumes a stress condition in the bearing races with a given rating C 1 and an applied load of Pe.

The following ABMA and ISO standardized equation is used to determine the basic dynamic load rating of a roller bearing:

C 1 =f cm (l le Cos(α)) 7/9 Z 3/4 D 29/27 = pounds.

Legend:
f cm = material x design factor and manufacturing quality
i = number of roller lines
le = effective length of the rollers = in
α = bearing contact angle = °
Z = number of rolls
D = roller diameter = inThe service life of the bearing is directly proportional to its tension condition under load. For any load applied to a bearing, its expected service life is determined by the stress condition exerted on the bearing races. This means it is critical to consider a bearing's design when determining its potential service life in any application.

As a rule, manufacturers use the f cm factor provided in the rating standards to calculate the basic dynamic rating of any bearing. If a catalog rating is higher than the standardized rating for a bearing's geometry, the manufacturer increases the f cm factor compared to what is considered standard.

Although this practice may be consistent with laboratory testing, its f-factor is often found to be overestimated in relation to bearing race stress over bearing life.

As shown in the tables below, the PT Select P2B207 bearing ranked third in cataloged ratings, but ranked first in load handling, with the lowest overall stress condition under load compared to six other manufacturers.

With this information, the question becomes: “Which bearing would you buy: competitor brand or Rexnord PT Select?”

Bearing Description Table 1

Bearing Description Table 2 and 3

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