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Types of bearings and their pros and cons

wallpapers Tech 2020-10-28
What is the purpose of the bearing?
The main purpose of the bearing is to prevent direct metal contact between two elements in relative motion. This can prevent friction, heat generation, and ultimately prevent wear of the parts. When replacing sliding motion with low friction rolling, it also reduces energy consumption.
 
They also transfer the load of the rotating element to the housing. The load can be radial, axial or a combination of both. As mentioned above, the bearing also restricts the freedom of movement of the moving parts in a predetermined direction.
 
Rolling bearing
Rolling bearings contain spherical or cylindrical rolling elements. We know that rolling a wheel is easier than sliding on the ground because the amplitude of rolling friction is smaller than sliding friction. The same principle works here. Rolling bearings are used to promote the free movement of parts in rotational motion.
 
Even when linear motion is required in the bearings application, it is easy to convert motion into sliding motion. Consider an escalator or conveyor belt. Even if the motion is linear, it is driven by rollers driven by motors.
 
Another example is a reciprocating pump, which can convert rotational energy from an electric motor into translational motion by means of a connecting rod. In each of the above applications, ball bearings are used to support the shaft of the motor and other rollers in the assembly.
 
The load carried by the rolling elements does not have much friction, because sliding friction is replaced by rolling friction. Rolling bearings can be divided into two main types: ball bearings and roller bearings.
 
Jack joint
Ball bearings are one of the most commonly used bearing categories. It consists of a volley ball as the rolling element. They are trapped between two annular metal sheets. These metal pieces are called races. The inner ring rotates freely, while the outer ring is stationary.
 
Ball bearings have very little friction during the rolling process, but their load-bearing capacity is limited. This is because the contact area between the ball and the game is very small. In addition to radial loads, they can also support axial loads in two directions.
 
Ball bearings are used to control oscillation and rotational movement. For example, in a motor where the shaft is free to rotate but the motor housing is not free to rotate, a ball bearing is used to connect the shaft to the motor housing.
 
Depending on the application, different types of ball bearings can be selected.
 
Advantages of ball bearings:
 
Good wear resistance
Does not require much lubrication
Provides low friction, so energy loss is small
long lasting
Easy to replace
Small overall size
cheaper
Can bear thrust load
Disadvantages of ball bearings:
May break due to vibration
May be very loud
Cannot bear heavy weight
Deep groove ball bearing
This is the most widely used type of ball bearing. The ball ring enclosed between the two races transfers the load and allows rotational movement between the two races. The ball is fixed in place by the holder.
 
They have very low rolling friction and are optimized for low noise and low vibration. This makes them ideal for high-speed applications.
 
They are relatively easy to install and require minimal maintenance. Care must be taken during installation to prevent the seat ring from sinking, as they must be pushed into the shaft.
 
Angular contact ball bearings
In this type of ball bearing, the inner race and the outer race move relative to each other along the bearing axis. This type of bearing can withstand greater axial loads in two directions other than radial loads.
 
Due to the movement of the inner and outer rings, the axial load can be transmitted to the bearing seat through the bearing. This bearing is suitable for applications requiring rigid axial guidance.
 
Angular contact bearings are widely used in agricultural equipment, automobiles, gearboxes, pumps and other high-speed applications.
 
Self-aligning ball bearing
This type of ball bearing can avoid misalignment between the shaft and the bearing seat due to shaft deflection or installation errors.
 
The inner ring has a deep groove similar to a deep groove ball bearing, followed by two rows of balls and the outer ring. The outer ring has a concave shape, which gives the inner ring a certain degree of freedom and can rearrange itself according to misalignment.
 
Thrust ball bearing
Thrust ball bearing is a special type of ball bearing specially designed for axial load. They simply cannot withstand radial loads.
 
Thrust ball bearings show low noise, smooth running and can be used in high-speed applications.
 
They can be used as one-way or two-way bearings, and the choice depends on whether the load is one-way or two-way.
 
Roller bearing
Roller bearings contain cylindrical rollers instead of balls as the load-bearing element between the raceways. If the length of the element is greater than the diameter (even if only small), it is considered a roller. Because they are in line contact with the inner and outer rings (rather than point contact like ball bearings), they can withstand greater loads.
 
There are also various types of roller bearings. After considering the type and size of the load, the conditions of use and other factors that may be misaligned, the appropriate type can be selected.
 
Advantages of roller bearings:
 
Easy to maintain
Low friction
May bear high radial loads
Tapered roller bearings can withstand higher axial loads
High precision
Used to adjust the axial displacement
Low vibration
Disadvantages of roller bearings:
 
noisy
Quite expensive
Cylindrical Roller Bearings
Cylindrical Roller Bearings
These are the simplest in the rolling bearing family. These bearings may face heavy radial loads and high speed challenges. They also have excellent stiffness, axial load transfer, low friction and long service life.
 
By avoiding the use of cages or cages commonly used to fix cylindrical rollers, the load capacity can be further improved. This allows more rollers to be installed to carry the load.
 
They have single row, double row and four row types. They are also available in split type and sealed type.
 
The split variant is used in hard-to-reach areas such as the engine crankshaft. In the sealed type, it prevents contamination of the bearing and retains lubricant, making it maintenance-free.
 
Spherical roller bearing
When shafts are prone to misalignment, larger radial and axial loads can be a greater challenge.
 
Spherical roller bearings can handle this situation well. They have a high load carrying capacity and can handle misalignment between the shaft and the housing. This can reduce maintenance costs and extend service life.
 
The raceway of the spherical roller bearing is inclined at a certain angle with the bearing axis. The spherical surface of the roller is not a straight edge, but a spherical surface installed on the spherical raceway, and can adapt to smaller deviations.
 
Spherical roller bearings have a wide range of use cases. They are used for heavy loads, medium to high speeds, and applications where misalignment may occur. Some example uses are off-road vehicles, pumps, mechanical fans, marine propulsion units, wind turbines and gearboxes.
 
Tapered Roller Bearings
The tapered roller bearing contains a conical part as a load-bearing element. These rollers are installed between two races, which are also part of the hollow cone. If the axis of the race and the roller are extended, they will all meet at a common point.
 
Tapered roller bearings are designed to withstand higher axial loads in addition to radial loads. The larger the half angle of the common cone, the greater the axial load it can bear. Therefore, they can be used as thrust bearings as well as radial load bearings.
 
Needle bearing
Needle roller bearings are a special kind of roller bearings, whose cylindrical rollers are similar to needle rollers due to their small diameter.
 
Generally, the length of the roller in a roller bearing is only slightly larger than its diameter. The length of the needle bearing is at least four times its diameter.
 
Due to the smaller diameter of needle roller bearings, more rollers can be installed in the same space, thereby increasing the surface area in contact with the rollers. Therefore, they can handle high loads. The small size can also prove useful in space-constrained applications, as they require a small gap between the shaft and the housing.
 
Needle bearings are used in automotive parts such as gearboxes and rocker arm pivots. They are also used in compressors and pumps.
 
Sliding bearing
Plain bearings are the simplest type of bearings. It usually consists of only one bearing surface. There are no scroll elements.
 
The bearing is basically a sleeve mounted on the shaft and fitted into the hole. Sliding bearings are cheap, compact and light. They have high carrying capacity.
 
Sliding bearings are used for rotating, sliding, reciprocating or oscillating motion. When the journal slides on the inner surface of the bearing, the bearing remains fixed. In order to promote smooth movement, a material pair with a low coefficient of friction is selected. For example, different types of copper alloys are common.
 
The bearing can adapt to some misalignment, multi-directional movement, and is suitable for static and dynamic loads. It is widely used in agriculture, automobile, ship and construction industries.
 
In diesel engines, the fixed pins that connect the piston to the connecting rod are connected by sliding bearings.
 
Radial joint bearing
A spherical bearing is also a sliding bearing, although it consists of two parts-an inner ring and an outer ring. Although it looks similar to ball and roller bearings from the beginning, they have no rolling elements between the two rings.
 
Fluid bearing
Fluid bearing is a special type of bearing that relies on pressurized gas or liquid to bear the load and eliminate friction. These bearings are used to replace metal bearings. In these applications, in addition to high noise and high vibration levels, their service life is also very short.
 
They are also increasingly used to cut costs. Fluid bearings are used in high-speed and high-load machines. Although the initial cost is higher, the longer service life under severe conditions can make up for the longer service life.
 
When the machine is running, the contact between the two components is zero (except during start and stop), so the use of fluid bearings can achieve close to zero wear.
 
Fluid bearings are divided into two types: hydrostatic bearings and hydrodynamic bearings.
 
Hydrostatic bearing
In this type, the externally pressurized fluid is forced between two elements in relative motion. The pressurized fluid forms a wedge between the moving parts and separates them. The fluid layer may be very thin, but as long as there is no direct contact, there will be no wear.
 
The fluid circulates through the pump. The diameter of the outlet hole can be adjusted to ensure that the fluid is always under pressure at all shaft speeds and loads. Therefore, precise gap control is possible.
 
Hydrodynamic bearing
This type of bearing uses the movement of the journal to force fluid to flow between the shaft and the housing. The movement of the journal draws the lubricating oil between the moving parts to form a constant wedge.
 
However, this means that during start and stop and at low loads and low speeds, the wedge may not be good enough to prevent wear. Only at the designed speed can the system run exactly as needed.
 
Electromagnetic bearing
Magnetic bearings use the concept of magnetic levitation to keep the shaft in the air. Since there is no physical contact, electromagnetic bearings are zero-wear bearings. There is also no limit to the maximum relative speed it can handle.
 
Magnetic bearings can also adapt to some irregularities in the shaft design, because the position of the shaft will automatically adjust according to its center of mass. Therefore, it can be sideways but still works satisfactorily.
 
They are roughly divided into two types: active and passive magnetic bearings.
 
Active Magnetic Bearing
Active magnetic bearings use electromagnets around the shaft to maintain their position. If the sensor detects a change in position, the system will adjust the amount of current fed into the system and return the rotor to its original position.
 
Passive magnetic bearing
Passive magnetic bearings use permanent magnets to maintain the magnetic field around the shaft. This means that no power input is required. However, due to limitations, the system is difficult to design because the technology is still in its early stages.
 
In many cases, two types of magnetic bearings can be used at the same time, in which permanent magnets handle static loads and electromagnets are used to maintain high accuracy in position.

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