Page 19 - needle bearings

Load Rating and Life
NTN

Table 2.1 Operating conditions and requisite lifetime
Operating conditions Lifetime L10h
Tools and devices requiring no all-time running
Ex) Door switcher, etc. 500
Machines which are operated for a short time or intermittently and do not cause comparatively great affect on others
even if they shut down incidentally due to trouble.
Ex.) Hand tools, heavy material handling hoist in a machining shop, general hand-operated machines, agricultural machines, 4 000 ʙ 8 000
crane in a casting shop, material automatic feeder, home appliances, etc.
Machines which are not put in continuous running but required to run very precisely
Ex.) Auxiliary machines in a power station, conveyor in a flow process, elevator, general cargo handling crane, 8 000 ʙ 14 000
machine tool of low frequency in use, etc.
Machines which are operated for 8 hours per day but not put in all-time continuous running
Ex.) Power generator in a factory, general geared unit, etc. 14 000 ʙ 20 000
Machines which are operated for 8 hours per day
Ex.) General machines in a machining shop, crane in all-time operation. 20 000 ʙ 30 000
Machines which are put in 24-hour continuous running
Ex.) Separator, compressor, pump, main shaft, table roller of rolling mill, conveyor roller, winding engine in a mine, 50 000 ʙ 60 000
driving motor in a factory, etc.
Machines which are put in 24-hour continuous running and, in addition, are not allowed absolutely trouble shutdown.
Ex.) Cellulose manufacturing machine, paper making machine, power station, drainage pump in a mine, 100 000 ʙ 200 000
urban city water related equipment, etc.

2.4 Bearing life using the adjusted life rating factor Table 2.2 Values of reliability adjustment factor a1
The basic bearing life rating (90% reliability) can be Reliability % Ln Reliability adjustment factor a1
calculated using the formulas prescribed in Subsection
90 L10 1.00
2.2, but on occasion the bearing life of over-90% reliability
95 L5 0.62
must be determined on application. Also, the bearing life
96 L4 0.53
can be further extended by using a specially improved
bearing material and special manufacturing 97 L3 0.44
process/technique. Furthermore, it was clarified by the 98 L2 0.33
elastohydrodynamic lubrication theory that the bearing life 99 L1 0.21
would be influenced by bearing operating conditions
(lubrication, temperature, speed, etc.) materials and manufacturing processes / techniques
The bearing life considering the above factors can be being used in NTN, and usually a2=1 rating is used.
determined by formula (2.7) using "Life Adjustment Furthermore, a2>1 is eventually applied to the bearings
Factor" specified in ISO 281. manufactured using the specially improved material and
manufacturing process / technique. In such a case, feel
p
Lna ʹ a1ɾa2ɾa3ʢCʗPʣ ʜʜʜʜʜʜʜʜ(2.7) free to contact NTN for further instruction.
Where bearings made of high carbon chrome bearing
where, steel are used at 120˚C and over throughout a long term,
6
Lna : Adjusted life rating 10 revolutions the dimension of the normal heat-treated bearing varies
a1 : Reliability adjustment factor significantly and, therefore, dimension-stabilizing heat-
a2 : Bearing material adjustment factor treatment (TS treatment) must be done to the bearings
a3 : Operating condition adjustment factor according to the maximum operating temperature.
However, this dimension-stabilizing treatment causes the
bearing hardness to reduce, finally an inverse affect on
2.4.1 Reliability adjustment factor a1
The values of reliability adjustment factor a1for 90% the bearing life. To avoid it, the bearing life is adjusted
and higher reliability are as shown in Table 2.2. (compensated) by multiplying the life rating by the life
adjustment factor for bearing material a2 shown in Table
2.3.
2.4.2 Life adjustment factor for bearing material a2
Where bearing material used is special type and quality
and manufactured in the special process, the life-related
Table 2.3 Values of life adjustment factor for bearing material a2 for
bearing characteristics are inevitably variable depending dimension-stabilizing heat-treated (TS-treated) bearings
on the specialties of the material. In such a case, the
Code Maximum operating Life adjustment factor
bearing life is adjusted using the life adjustment factor for temperature for bearing material a2
bearing material a2. TS2- 160˚C 1.00
The basic dynamic load ratings described in "Bearing TS3- 200˚C 0.73
Dimensions Table" are subject to use of the standard TS4- 250˚C 0.48

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