High Precision Ball Bearings - Kraftmek

4. Definition of nominal life rating L 10h
Diagram 1
10 C 3
L 10h = 6
· [hours]
60 · n P
n : Speed (1/min)
C : Dynamic load rating [N]
P : Equivalent dynamic load [N]
The nominal life rating is based on a 10% probability of
failure.
5. Definition of adjusted life rating L nah
L nah =
a 1 · a 23 · f t · L 10h [hours]
a 1 : Factor for probability of failure
a 23 : Factor for material and operating
conditions
f t : Factor for operating temperature
L 10h : Nominal life rating [hours]
Probability 10 5 4 3 2 1
of failure
[%]
Factor a 1 1 0.62 0.53 0.44 0.33 0.21
Maximum 150 200 250 300
operating temperature (°C)
Factor f t 1 0.73 0.42 0.22
6. Definition of factor for material and operating
conditions a 23
Step 1:
The operating viscosity is determined in diagram 1.
For grease lubrication, the viscosity of the base oil is
entered.
Step 2:
The reference viscosity 1 is determined in
diagram 2.
Step 3:
After calculation of the viscosity ratio /1 ,
the a 23 -factor is determined in diagram 3.
Comments on diagram 3:
• Lower line: Normal operating conditions and
cleanliness.
• Middle line: Improvement of a 23 -factor by EP-additives.
• Upper line: Improvement of a 23 -factor by extreme
(highest) cleanliness and optimised spin and slide
conditions.
Operating viscosity [mm 2 /s]
Reference viscosity [mm 2 /s]
1000
500
400
300
200
150
50
40
30
20
15
10
9
8
7
6
5
200
100
50
20
10
5
4
Diagram 2
0 10 20 30 40 50 60 70 80 90 100110120 130
50 000
100 000
20 000
Grease: Isoflex Topas L30
10 000
1000
1500
2000
3000
5000
Speed [1/min]
Oil: Vitam DE 32
Operating temperature t [°C]
500
200
50
100
3
10 20 50 100 200
Mean bearing diameter
d m [mm]
d D + d
m = [mm]
2
... for bearing calculation
35