6608ZZ bearing used by a company appears abnormal phenomenon of noise
and vibration value exceeding the standard after one month of storage,
which affects the motor performance.Sample
bearings are shown in Table 1, in which the new bearing is the bearing
without storage, and the old bearing is the bearing after storage for a
period of time.
1. Test analysis
1.1 Preliminary analysis and testing
The phenomenon of abnormal sound and vibration exceedance of low noise bearing is common and the reason is complicated.In
view of the phenomenon that the vibration value of this batch of
bearings increases after being stored (stationary) for a certain time,
the preliminary analysis may be related to the instability of the
original grease in the bearings.Lubricating
grease is the most commonly used lubricant for sealed bearings. It is a
thickening agent and various functional additives dispersed in the base
grease has a certain vibration and noise reduction function, which can
meet the low noise requirements of bearings. However, if the properties
of grease change with the extension of time (that is, grease
denaturation), it will affect the vibration and noise of bearings.
is difficult to extract grease directly from the bearing because the
bearing has a small amount of grease and is double-sealed.Therefore,
direct testing method is adopted, that is, the vibration value of the
bearing is measured to obtain basic data for further analysis.
The test conditions are as follows:
Vibrator: S0910-1 (acceleration type)
Speed: 1480 r/min
Lubricating mode: original grease (origin type unknown)
Axial load: 40N
The test results are shown in Table 2.The
data show that the vibration value of the new bearing in the sample
bearing is slightly lower, while the vibration value of the old bearing
is higher, and the vibration value of C is the highest.
Note: 1) After heating.2) After standing for a period of time (16 days for the new bearing, 13 days for the old bearing).
1.2 Processing and testing
normal circumstances, high quality grease can provide long-term
effective lubrication for bearings, and play the role of vibration and
the grease is deformed, it will affect the normal lubrication state of
the bearing, thus increasing the vibration noise of the bearing and
decreasing the service life significantly.The
reason of grease denaturation is more complex, and there are many
forms. During the storage period, there are mainly oil separation,
hardening (dry cracking), oxidation metamorphism, additive
crystallization precipitation and other denaturation forms.From
the reflected situation and the vibration measurement process, the
original grease of these bearings may appear crystalline precipitation,
that is, solid granular substances are produced inside the grease.These
particles have a certain size and hardness, destroy the elastic
lubrication film provided by the grease for the bearing, resulting in
the increase of bearing vibration value and abnormal sound.
research results and experience show that some crystalline precipitates
produced in grease will gradually become smaller, melt and re-disperse
into grease at a certain temperature.In
order to verify this statement, the old bearings (including the
original grease) were treated with restorative technology. The old
bearings were put into the oven and kept at 85℃ for 2h. After cooling to
room temperature, the vibration values of the bearings were measured
that, the heated bearing is left standing at room temperature for a
period of time (16 days for the new bearing, 13 days for the old
bearing), and then the vibration value is measured to further verify the
phenomenon of grease denaturation.Table 2 lists the changes of bearing vibration values before and after treatment and after standing for a period of time.The test results show that:
(1) After heating, the mean value, maximum value and minimum value of vibration of the old bearing are significantly reduced.Among
them, the average vibration of A and C bearings decreases by 1.1dB, and
the average vibration of B bearings decreases by 2.5dB.
After standing for a period of time, the average value, maximum value
and minimum value of vibration of all bearings are significantly
them, the vibration average value of the old bearing B recovered the
most, which increased by 3.4dB compared with that after heating
1.3 Microscopic observation
out the grease in the bearing, observe its aggregation state with a
microscope, it is found that there are more translucent crystals inside
the grease, the shape is irregular round, the largest diameter of
particles is about 40μm, most of the diameter is about 10μm.These
particles due to large size, large number, and a certain hardness, as
mechanical impurities lead to the increase of bearing vibration value.
2, the conclusion
The denaturation of grease and crystal precipitation in the bearing is
the main reason for the increase of bearing noise and vibration value.After
the restorative heating treatment, the vibration and noise of the
bearing are significantly reduced, but the vibration value of the
bearing increases significantly after more than ten days of standing,
indicating that the storage stability of the grease is poor.
(2) the denaturation process of the grease is reversible.
(3) The formation reason and composition of crystalline precipitates in grease need to be further analyzed.