Special Issue; Products for Industrial Machinery - NTN

Technical Trends in Bearings for Office Equipment
can be seen in Fig. 6, EF-7 Grease boasts hightemperature
life that is more than three times as long
as that of EF-5 Grease. Therefore, NTN will employ
EF-7 Grease as a standard conductive grease for
fuser roller support bearings.
Test bearing
Resistance value k
Table 4 Test condition of bearing resistance
Running speed (min -1 )
Radial load (N)
Ambient temperature (˚C)
Control resistance (k)
40
35
30
25
20
15
10
5
Operating conditions
0
0 100 200 300 400 500 600 700
Test duration h
EF-5
EF-7
Fig. 5 Results of bearing resistance test
Test conditions
2TS3-SC05B98ZZ 25mm32mm7mm
130
220
200 Room temperature
300
4.2 Bearing technologies for chemical attack
resistance
Many resin components (mainly those made of
aromatic resins) are used in color copying machines
and color LBPs. The bearings used in these machines
are prefilled with grease as lubricant, and their outer
faces are coated with rust-preventive oil. With
particular combinations of oil and resin, cracking
and/or crazing can occur on resin components.
4.2.1 Mechanism of chemical attack
Chemical attack (stress corrosion cracking) is a
phenomenon where corrosion and static stress lead to
cracking and embrittlement. Static stress is a stress
occurring on an object when a given static load is
applied to it. Corrosion occurs when compatibility
between the resin and the solvent is high, as the
solvent dissolves the resin or enters molecules in the
resin and slackens its polymer chains and crystal
structures, leading to the occurrence of cracking
and/or crazing.
4.2.2 Chemical attack evaluation
As shown in Fig. 7, a resin test piece was bent by a
particular amount, and the sample oil was applied to a
face of the test piece where tensile stress was
applied. The test piece was then left to stand under
the test conditions summarized in Table 6.
Table 5 Test condition of high temperature grease life
Test bearing
Test conditions
2TS3-SC05B98ZZ 25mm32mm7mm
Ambient temperature (˚C)
200
Running speed (min -1 )
130
Radial load (N)
220
1) Temperature increase on the bearing (+15°C)
Grease life
judgment criteria
2) Torque increase on the motor (1.5 times
higher than that at the beginning of the test)
Table 6 Test condition of solvent crack
Resin test piece (mm) 150193(length x width x thickness)
Deflection ratio (%)
5
Standing temperature (˚C)
70
Standing time (h)
72
(Deflection ratio = deflection/distance between supporting points)
Resin
(test piece)
EF-5
EF-7
0 100 200 300 400 500 600
Test duration h
Application of oil
100mm
(Distance between
supporting points)
Fig. 6 Results of high temperature grease life test
Fig. 7 Test rig of solvent crack
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