Bearings are components that fix and reduce the friction coefficient of the load during mechanical transmission. It plays a decisive role in contemporary machinery and equipment. Its
main function is to support the mechanical rotating body to reduce the
mechanical load friction coefficient of the equipment during the
transmission process. Bearings can be divided into two types of rolling bearings and plain bearings. Today we will talk about rolling bearings in detail.
Rolling
bearings are precision mechanical components that reduce the frictional
losses by converting the sliding friction between the rotating shaft
and the shaft seat to rolling friction. Rolling
bearings are generally composed of four parts: inner ring, outer ring,
rolling element and cage. The function of the inner ring is to cooperate
with the shaft and rotate together with the shaft; the outer ring
function is to cooperate with the bearing seat to play a supporting
role; the rolling element is to help The
cage distributes the rolling elements evenly between the inner ring and
the outer ring. The shape and quantity of the rolling elements directly
affect the performance and life of the rolling bearing. The cage can
evenly distribute the rolling elements, preventing the rolling elements
from coming off and guiding the rolling elements. Rotate from lubrication.
Rolling bearing characteristics
1. Specialization
Bearing parts processing, a large number of bearing special equipment. Such as ball processing using ball machines, grinding machines and other equipment. The characteristics of specialization are also reflected in the
production of bearing parts, such as steel ball companies specializing
in the production of steel balls and micro bearing factories
specializing in the production of miniature bearings.
2. Advanced
Due
to the large-scale requirements of the bearing production, it is
possible to use advanced machine tools, tooling and processes. Such as CNC machine tools, three-jaw floating chuck and protection atmosphere heat treatment.
3. Automation
The specialization of bearing production provides the conditions for its production automation. In
the production of a large number of automatic, semi-automatic special
and non-specific machine tools, and gradually promote the application of
production lines. Such as heat treatment automatic line and assembly automatic line.
Classification by structure type
According to the structure of rolling elements and ferrules can be divided into:
Deep
groove ball bearings, needle roller bearings, angular contact bearings,
self-aligning ball bearings, spherical roller bearings, thrust ball
bearings, thrust spherical roller bearings, cylindrical roller bearings,
tapered roller bearings, spherical ball bearings with a seat Bearings and so on.
Rolling bearings can be divided into:
Deep groove ball bearings
Deep
groove ball bearing is simple in structure and easy to use. It is the
largest production batch and the most widely used type of bearing. It mainly uses a radial load, but also can withstand a certain axial load. When
the radial clearance of the bearing is increased, it has the function
of an angular contact bearing and can withstand a large axial load. Used in automobiles, tractors, machine tools, motors, pumps, agricultural machinery, textile machinery, etc.
Needle roller bearing
Needle
roller bearings are equipped with long, thin rollers (3 to 10 times the
diameter of the rollers and generally no larger than 5 mm in diameter),
so they have a compact radial structure and have the same internal
diameter and load capacity as other types of bearings. The smallest diameter, especially suitable for support structures with limited radial mounting dimensions. According
to different occasions, the inner ring bearing or needle roller and
cage assembly can be used. The journal bearing surface and the housing
hole surface matched with the bearing directly serve as the inner and
outer rolling surfaces of the bearing to maintain the load capacity and
running performance. As
with a bearing with a ring, the hardness of the raceway surface of the
shaft or housing bore. The machining accuracy and the surface and
surface quality should be similar to the raceways of the bearing ring. This type of bearing can only withstand radial loads. For example: universal joint shafts, hydraulic pumps, sheet rolling
mills, rock drills, gear boxes for machines, gearboxes for automobiles
and tractors, etc.
Angular contact bearing
Angular
contact ball bearings have higher limiting speeds and can withstand
both meridional and axial loads as well as pure axial loads. The axial
load capacity is determined by the contact angle and increases with the
contact angle. Used for: oil pumps, air compressors, various types of transmissions, fuel injection pumps, and printing machinery.
4. Self-aligning ball bearings
Self-aligning
ball bearings have two rows of steel balls, two raceways in the inner
ring, and outer ring raceways with inner spherical shape, with
self-aligning performance. It
can automatically compensate for concentricity errors due to shaft
bending and shell deformation, and is suitable for parts where the
support hole does not guarantee tight concentricity. The
bearings are mainly subjected to radial loads, and they can also bear a
small amount of axial load while they are subjected to radial loads.
Usually, they are not used for bearing pure axial loads. For example,
they are subjected to pure axial loads and only one ball is subjected to
force. Mainly used in agricultural machinery such as combine harvesters,
blowers, paper machines, textile machinery, woodworking machinery,
bridge crane wheels and drive shafts.
5. Self-aligning roller bearings
Spherical
roller bearings have two rows of rollers, which are mainly used to
withstand radial loads and can also withstand axial loads in either
direction. This
kind of bearing has high radial load capacity and is especially
suitable for working under heavy load or vibration load, but it can not
bear pure axial load. It has good aligning performance and can
compensate the same bearing error. Main applications: papermaking machinery, deceleration devices, axles
for railway vehicles, gear box seats for rolling mills, crushers, and
various types of industrial speed reducers.
6. Thrust ball bearing
Thrust
ball bearing is a type of separate bearing. The bearing ring of the
shaft ring can be separated from the assembly of the cage steel ball. The
shaft ring is a ferrule matched with the shaft, the seat ring is a
ferrule matched with the bearing seat hole, and there is a gap between
the shaft and the shaft. Thrust
ball bearings can only handle the axial load, one-way thrust ball
bearings can only withstand the axial load of a room, two-way thrust
ball bearings can withstand axial load in both directions. The thrust ball can't restrain the longitudinal direction of the shaft to move, and the limit speed is very low. One-way
thrust ball bearings can limit the axial displacement of the shaft and
the housing in one direction. Bidirectional bearings can limit the axial
displacement in both directions. Mainly used in automobile steering mechanism, machine tool spindle.
7. Thrust roller bearing
Thrust
roller bearings are used to withstand the axial load of the main shaft.
Longitudinal joint load, but the radial load must not exceed 55% of the
axial load. Compared
with other thrust roller bearings, this type of bearing has a lower
friction coefficient, a higher rotational speed, and a self-aligning
ability. The
roller type 29000 bearing is an asymmetrical spherical roller, which
can reduce the relative sliding of the stick and the raceway during
operation. The roller is long. The diameter is large, the number of
rollers is large, and the load capacity is large. Usually, oil
lubrication is used. Low speed grease lubrication. In the design selection, should be preferred. Mainly used in hydraulic generators, crane hooks, and so on.
8. Cylindrical roller bearings
Cylindrical
roller bearing rollers are usually guided by two ribs of a bearing
ring. The cage, roller, and guide ring form an assembly that can be
separated from another bearing ring and is a detachable bearing. This
kind of bearing installation and disassembly is more convenient,
especially when the inner ring, the outer ring and the shaft are
required to show the advantages. This
kind of bearing is generally only used to bear radial load. Only single
row bearings with ribs on the inner and outer rings can withstand small
constant axial loads or large intermittent axial loads. Mainly used for large motors, machine tool spindles, axle shaft boxes, diesel engine crankshafts, and automobiles.
9. Tapered roller bearings
Tapered
roller bearings are mainly used to withstand the radial and axial
combined load mainly radial load, while the large cone angle tapered
roller bearings can be used to withstand the axial load-oriented radial,
axial joint load. This
type of bearing is a separate type bearing. Its inner ring (including
tapered roller and cage) and outer ring can be installed separately. In
the process of installation and use, the bearing's radial clearance and
axial clearance can be adjusted. It can also be used to pre-install the
wheel used for rear axle of automobile, large-scale machine tool
spindle, high-power reducer, axle bearing box and conveying device. .
10. Outer spherical ball bearing
Spherical
spherical ball bearings are composed of double-faced sealed spherical
ball bearings and cast (or steel stamped) bearing blocks. The
external structure of the spherical ball bearing is the same as that of
a deep groove ball bearing. However, the inner ring of this type of
bearing is wider than the outer ring. The outer ring has a spherical
outer surface that matches the concave spherical surface of the bearing
housing and can be self-aligning. Usually
there is a gap between the inner bore of this type of bearing and the
shaft. The inner ring of the bearing is fixed on the shaft with a top
wire, an eccentric sleeve or an adapter sleeve, and rotates with the
shaft. Seat-mounted bearings are compact in structure, easy to load and
unload, and perfectly sealed. They are suitable for simple support and
are often used in mining, metallurgy, agriculture, chemicals, textiles,
printing and dyeing, transportation machinery, etc.
Sort by size
Bearing according to its outer diameter size
(1) Miniature bearings - Bearings with a nominal outside diameter of 26mm or less.
(2) Small bearings - Bearings with a nominal outside diameter range of 28-55mm.
(3) Small and medium-sized bearings - Bearings with a nominal outer diameter range of 60-115mm.
(4) Medium-to-large-sized bearings: Bearings with a nominal diameter range of 120-190mm.
(5) Large bearings - bearings with a nominal outside diameter range of 200-430mm.
(6) Extra Large Bearings - Bearings with a nominal outside diameter range of 440-2000mm.
(7) Major bearings - bearings with a nominal diameter range of over 2000mm.
Advantages
1. Small frictional resistance, low power consumption, high mechanical efficiency, easy to start;
2, the standardization of size, interchangeability, easy to install and remove, easy maintenance;
3, compact structure, light weight, smaller axial size;
4, high precision, large load, small wear, long service life;
5, some bearings have self-aligning performance;
6, suitable for mass production, stable and reliable quality, high production efficiency;
7. The drive friction torque is much lower than the hydrodynamic
bearing, so the frictional temperature rise and power consumption are
low;
8, starting friction torque is only slightly higher than the rotating friction torque;
9. Bearing deformation is less sensitive to load changes than fluid dynamic pressure bearings;
10, only need a small amount of lubricant to be able to run normally, can provide lubricant for a long time when running;
11, the axial size is smaller than the traditional fluid dynamic pressure bearing;
12, can simultaneously withstand radial and thrust combination load;
13, in a large load-speed range, the unique design can obtain excellent performance;
14. Bearing performance is relatively insensitive to fluctuations in load, speed, and operating speed.
Shortcomings
1, noisy.
2, the bearing seat structure is more complex.
3, the cost is higher.
4. Even if the bearings are well lubricated, properly installed, tight
in dust and moisture, and functioning properly, they will eventually
fail due to fatigue on the rolling contact surfaces.
Routine maintenance
First, the installation surface and installation site requirements?
Yes. If
there are foreign materials such as iron filings, burrs, and dust in
the bearing, the bearing will cause noise and vibration during
operation, and even damage the raceways and rolling elements. Therefore, before installing the bearings, you must ensure that the
installation surface and the installation environment are clean.
Second, the bearing must be cleaned before installation?
The
surface of the bearing is coated with anti-rust oil. You must clean it
carefully with clean gasoline or kerosene and then apply it with clean,
high-quality or high-speed and high-temperature grease before
installation. The impact of cleanliness on bearing life and vibration noise is very large. However, we must remind you that the sealed bearings do not need to be cleaned and refueled.
Third, how to choose grease?
Lubrication
has a very important influence on the operation and life of the
bearing. Here you will briefly introduce the general principles of
selecting a grease. Grease
is made of base oil, thickener and additives. The performance of
greases of different types and the same type of different brands varies
greatly, and the allowable rotation limit is different. Be careful when
selecting. The
performance of grease is mainly determined by the base oil. Generally
low viscosity base oil is suitable for low temperature, high speed, and
high viscosity suitable for high temperature and high load. Thickeners
are also responsible for the lubricating properties, and the water
resistance of the thickeners determines the water resistance of the
grease. In principle, brands of different greases cannot be mixed, and even
greases of the same thickener will have bad effects on each other due to
different additives.
Fourth, when lubricating bearings, the more grease the better?
When lubricating bearings, the more grease the better, which is a common misconception. Excessive
grease in the bearing and bearing chambers will cause excessive
agitation of the grease, resulting in extremely high temperatures. The number of bearings filled with lubricant should be 1/2 to 1/3 full
of the internal space of the bearing and should be reduced to 1/3 at
high speed.
Fifth, how to install and remove?
When
installing, do not directly hammer the bearing end surface and the
non-force bearing surface. Use a pressure block, sleeve or other
installation tool (tooling) to make the bearing evenly stressed. Do not
install it through the rolling element transmission force. If the mounting surface is lubricated, the installation will be smoother. If
the interference is large, the bearing should be put into mineral oil
and heated to 80~90°C and installed as soon as possible. Strictly
control the oil temperature to not exceed 100°C to prevent the hardness
of the tempering effect from decreasing and affecting the dimensional
recovery. When it is difficult to disassemble, it is recommended that you use
the disassembly tool to pull out the inner ring while carefully pouring
hot oil, and the heat will make the inner ring of the bearing expand,
which makes it easier to fall off.
Sixth, the smaller the radial clearance of the bearing, the better?
Not all bearings require minimum working clearance. You must choose the proper clearance according to the conditions. In
GB 4604-93, the radial clearance of rolling bearings is divided into
five groups of -2 groups, 0 groups, 3 groups, 4 groups and 5 groups. The
clearance values are from small to big, among which group 0 is the
standard clearance. The
basic radial clearance group is suitable for general operating
conditions, conventional temperature, and commonly used interference
fit; bearings that work in special conditions such as high temperature,
high speed, low noise, low friction, etc. should use large radial
clearance; For
precision spindles and bearings for machine tool spindles, smaller
radial clearances should be used; for roller bearings, a small amount of
working clearance can be maintained. In
addition, there is no clearance for the separate type bearing; finally,
the working clearance after the bearing is installed is smaller than
the original clearance before the installation, because the bearing is
subject to a certain load rotation, as well as bearing fit and load Elastic deformation.
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