Page 225 - Rollingbearings

Lubrication (step 2)
Bearing size Operating temperature and
speed

The manufacturer’s existing rope sheave design uses two
6207-2RS1 bearings. SKF has replaced the RS1 seal with the RSH
seal. In this example we check the suitability of 6207-2RSH bearings When the load ratio C/P > 10, the operating temperature is below
(page 274). 100 °C (210 °F), the operating speed is below 50% of the limiting
The next step in the selection process is to determine the method, speed, and there is no pronounced external heat input, a detailed
on which to base the size selection. The bearings are running in typ- thermal analysis is not required. In this example:
ical operating conditions and, therefore, rolling contact fatigue is the
probable failure mode. We base the size selection on rating life. • load ratio: C/P = 49 > 10
• operating speed: 2 450 r/min < 0,5 × 6 300 (limiting speed)
Basic rating life • From experience of rope sheaves operating in similar conditions,
the bearing operating temperature is about 90 °C (195 °F).

⎛ 10 6 w ⎛ C w p
= J J J
L 10h ⎝ 60 n⎠ ⎝ P ⎠ So a detailed thermal analysis is not required.

As there is no axial load, the equivalent dynamic bearing load, P, on
Lubrication (step 2)
each bearing is equal to the radial load divided by two.
• P = 0,55 kN
• load ratio C/P = 49

The basic rating life L 10h = 804 800 h. This is much longer than the
required maintenance-free period of 5 years (43 800 h). 1. Grease life MT33
Grease life can be estimated using diagram 1, page 246. Because
Conclusion the bearing outer ring rotates, for grease life estimations, nD is used
instead of nd (table 2, page 115).
m
• With such a high basic rating life at 2 450 r/min, it is recommended Then, using the input values:
to check that the bearing is suficiently loaded to maintain ball roll-
ing and avoid ball sliding. This will be done after the lubrication is • nD = 2 450 × 72 = 176 400
checked, because lubricant viscosity inluences the requisite min- • MT33 grease with a grease performance factor, GPF = 1
imum load. • operating temperature of about 90 °C (195 °F)
• Grease life should be checked to see if the bearing fulils the
end-customer’s requirement. The grease life, L 10h , is about 12 500 hours, which is less than the
required 5-year maintenance-free period.
The SKF rating life, L 10mh , will be calculated after the lubrication is
checked and the operating temperature and speed are checked, 2. Grease life WT
because lubricant viscosity inluences the result. This will be done in The SKF bearing 6207-2RSH is available with the grease WT, which
Bearing size (step 2), page 224. has a GPF = 4. It is a polyurea-type grease with an ester base oil,
table 3, page 245.
From diagram 1, page 246 the grease life, L 10h, is 50 000 hours,
which is greater than 5 years.
Lubrication
Conclusion

The SKF bearing 6207-2RSH with the grease WT fulils the require-
ment in terms of grease life.
C.2 Rope sheave
Bearing 6207-2RSH is illed with MT33 grease (table 2, page 245).
The operating temperature should be deined before continuing.

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