Bearing Performance Factors
Key bearing performance factors during operation are bearing noise, vibration, temperature, and lubricant state. Please
refer to Table 2.2 if any operation irregularities are detected.
4.1 Bearing Noise
During operation, sound detection instruments (stethoscope, NSK Bearing Monitor, etc.) can be used to investigate
the volume and characteristics of the bearing rotation noise. It
is possible to distinguish bearing damage such as small flaking by means of its unusual yet characteristic noise.
4.2 Bearing Vibration
Bearing irregularities can be analyzed by measuring the
vibrations of an operating machine. A frequency spectrum
analyzer is used to measure the magnitude of vibration and
the distribution of the frequencies. Test results enable the determination of the likely cause of the bearing irregularity. The
measured data varies depending on the operating conditions
of the bearing and the location of the vibration pick-up. Therefore, the method requires the determination of evaluation standards for each measured machine.
It is useful to be able to detect irregularities from the bearing vibration pattern during operation. Please refer to the NSK
pamphlet CAT. No. E410 (Bearing Monitor) for more information about such a device.
4.3 Bearing Temperature
Generally, the bearing temperature can be estimated from
the temperature of the housing outside surface, but a preferable way is to obtain direct measurements from the bearing
outer ring by a probe going through an oil hole.
Usually, the bearing temperature gradually increases after
the start of operation until reaching a steady state condition
about 1 or 2 hours later. The bearing steady state temperature
depends on load, rotational speed and heat transfer properties
of the machine. Insufficient lubrication or improper mounting
might cause the bearing temperature to rise rapidly. In such a
case, suspend the machine operation and adopt an appropriate countermeasure.
4.4 Effects of Lubrication
The two main purposes of lubrication are to minimize friction
and reduce wear inside bearings that might otherwise fail prematurely. Lubrication provides the following advantages:
(1) Reduction of Friction and Wear
Direct metallic contact between the bearing rings, rolling
elements and cage, which are the basic components of a
bearing, is prevented by an oil film which reduces the friction
and wear in the contact areas.
(2) Extension of Fatigue Life
The rolling fatigue life of bearings depends greatly upon the
viscosity and film thickness between the rolling contact surfaces. A heavy film thickness prolongs the fatigue life, but it is
shortened if the viscosity of the oil is too low so that the film
thickness is insufficient.
(3) Dissipation of Frictional Heat and Cooling
Circulation lubrication may be used to carry away either frictional heat or heat transferred from the outside to prevent the
bearing from overheating and the oil from deteriorating.
(4) Sealing and Rust Prevention
Adequate lubrication also helps to prevent foreign material
from entering the bearings and guards against corrosion or
rusting.
4.5 Selection of Lubrication
Bearing lubrication methods are divided into two main categories: grease lubrication and oil lubrication. A lubrication
method is adopted that matches the application conditions
and application purpose in order to attain best performance
from the bearing.
refer to Table 2.2 if any operation irregularities are detected.
4.1 Bearing Noise
During operation, sound detection instruments (stethoscope, NSK Bearing Monitor, etc.) can be used to investigate
the volume and characteristics of the bearing rotation noise. It
is possible to distinguish bearing damage such as small flaking by means of its unusual yet characteristic noise.
4.2 Bearing Vibration
Bearing irregularities can be analyzed by measuring the
vibrations of an operating machine. A frequency spectrum
analyzer is used to measure the magnitude of vibration and
the distribution of the frequencies. Test results enable the determination of the likely cause of the bearing irregularity. The
measured data varies depending on the operating conditions
of the bearing and the location of the vibration pick-up. Therefore, the method requires the determination of evaluation standards for each measured machine.
It is useful to be able to detect irregularities from the bearing vibration pattern during operation. Please refer to the NSK
pamphlet CAT. No. E410 (Bearing Monitor) for more information about such a device.
4.3 Bearing Temperature
Generally, the bearing temperature can be estimated from
the temperature of the housing outside surface, but a preferable way is to obtain direct measurements from the bearing
outer ring by a probe going through an oil hole.
Usually, the bearing temperature gradually increases after
the start of operation until reaching a steady state condition
about 1 or 2 hours later. The bearing steady state temperature
depends on load, rotational speed and heat transfer properties
of the machine. Insufficient lubrication or improper mounting
might cause the bearing temperature to rise rapidly. In such a
case, suspend the machine operation and adopt an appropriate countermeasure.
4.4 Effects of Lubrication
The two main purposes of lubrication are to minimize friction
and reduce wear inside bearings that might otherwise fail prematurely. Lubrication provides the following advantages:
(1) Reduction of Friction and Wear
Direct metallic contact between the bearing rings, rolling
elements and cage, which are the basic components of a
bearing, is prevented by an oil film which reduces the friction
and wear in the contact areas.
(2) Extension of Fatigue Life
The rolling fatigue life of bearings depends greatly upon the
viscosity and film thickness between the rolling contact surfaces. A heavy film thickness prolongs the fatigue life, but it is
shortened if the viscosity of the oil is too low so that the film
thickness is insufficient.
(3) Dissipation of Frictional Heat and Cooling
Circulation lubrication may be used to carry away either frictional heat or heat transferred from the outside to prevent the
bearing from overheating and the oil from deteriorating.
(4) Sealing and Rust Prevention
Adequate lubrication also helps to prevent foreign material
from entering the bearings and guards against corrosion or
rusting.
4.5 Selection of Lubrication
Bearing lubrication methods are divided into two main categories: grease lubrication and oil lubrication. A lubrication
method is adopted that matches the application conditions
and application purpose in order to attain best performance
from the bearing.