1. What is needle roller bearing
The needle roller bearing is one of the rolling bearings with elongated cylindrical rollers (L/D ratio ≥ 4:1), the core feature of which is the high load density achieved with a very small cross-section, designed for compact machines with limited radial space. Needle roller bearings usually consist of an outer ring, needle rollers, a cage and an inner ring, of which the inner ring can be omitted in some models to allow the needle rollers to roll directly on the shaft surface, in order to reduce the overall size of the bearing and improve design flexibility. The roller diameter is usually less than 5mm, the length can be up to 5-10 times of the diameter, through the dense arrangement (each column can contain 30-50 rollers) to maximize the contact area, so that the radial load carrying capacity of the same size ball bearings 3-5 times, especially suitable for low-speed, high-impact working conditions.
According to the different structure and use, needle roller bearings can be divided into stamping outer ring needle roller bearings, solid sleeve needle roller bearings, combined needle roller bearings and other types, in order to adapt to the needs of different working conditions.
2. Types of Needle Roller Bearings
Needle roller bearings can be classified into the following categories according to their structure and different manufacturing processes to meet different needs and working conditions:
(1)Machined Needle Roller Bearings Machined needle roller bearings adopt solid outer rings, which are usually made of high-precision alloy steel or bearing steel, possessing high strength, rigidity and wear resistance. This type of bearings can withstand large radial loads and have a long service life, suitable for high load and high precision requirements, such as machine tool spindles, heavy machinery and equipment.
(2)Drawn Cup Needle Roller Bearings The outer ring of stamped outer ring needle roller bearings is made of thin-walled stamped steel, which is light in weight and compact in structure, and is suitable for working conditions where the installation space is restricted. Due to their lightweight design, they are widely used in automobiles, motorcycle transmissions, agricultural machinery and small motors because they can reduce overall weight while maintaining load carrying capacity.
(3)Needle Roller And Cage Assemblies Needle roller and cage assembly is a kind of bearing form without inner and outer rings, which only consists of needle rollers and cage, and the cage can ensure the even arrangement of needle rollers and prevent mutual friction. These bearings need to be used in conjunction with shaft or housing races, and are suitable for applications requiring light weight, low friction and high speeds, such as aerospace, textile machinery and automation equipment.
3. Needle Roller Bearing Characteristics
(1)High load carrying capacity: Needle roller bearing adopts long and thin needle rollers as rolling bodies, compared with ordinary roller bearings, the needle rollers are in line contact with the raceway, which can disperse the load and improve the load carrying capacity.
(2)Compact structure, space saving: Due to the small diameter of the needle roller, occupies a limited space, so that the needle roller bearing can be applied to the installation of space-restricted equipment.
(3)Low friction, suitable for high-speed operation: Needle roller bearing design optimization, low friction coefficient, in high-speed operation can reduce energy loss, reduce bearing heat, improve operating efficiency and service life.
(4)Different structural forms, adapt to a variety of applications: Needle roller bearings are available in machined type, stamped outer ring type and needle roller cage assembly, etc., which can be selected according to different working conditions and meet the requirements of light weight, high load and low friction.
(5)Inner ring can be omitted to meet different mounting requirements: Some needle roller bearings are designed without inner ring, so that the needle rollers roll directly on the surface of the shaft, which not only reduces the size of the bearings, but also improves the rigidity of the bearings, but the shaft surface needs to be precision machined and hardened.
4.Needle Roller Bearing Application
Needle roller bearings have wide usage in various mechanical equipment due to their compact size, heavy load carrying capacity and low friction characteristics, etc. The principal fields of application of needle roller bearings are as follows:
(1)Automobile: Needle roller bearings are used very widely in automobile engines, gearboxes, steering systems, clutches, valve trains, drive systems and so on.
(2)Machine tools and mechanical euqipment: In CNC machine tools, grinding machines, lathes, drilling machines, etc., needle roller bearings are used in spindle support, feed mechanism and speed change mechanism, which can provide high-precision rotary support to guarantee machining accuracy and operating stability.
(3)Textile and printing machinery: Textile machinery in the spinning machine, weaving machine, winding machine etc. need high-speed rotation and long-term operation, needle roller bearings because of its low friction, high rigidity and long life and become the optimal selection.
(4)Metallurgy and mining equipment: In heavy-duty uses such as rolling mills, crushers and conveyors, needle roller bearings withstand very heavy radial and shock loads, increasing the equipment load carrying capacity and life.
(5)Aerospace: Needle roller bearings are an important contribution in turbine engines, flight control systems, satellite attitude control systems in aerospace uses to deliver high-precision, high-reliability performance.
(6)Power tools and small household appliances: Electric tools such as electric drills, electric saws, angle grinders etc. usually utilize needle roller bearings in order to reduce friction and enhance speed and stability. Further, in the home appliance industry, for instance, washing machines, electric fans, food processors and other machinery, needle roller bearings are used in order to support the load of high-speed operation.
(7)Robotics and automation machinery: In industrial robots, automated manufacturing lines, conveyors, etc., needle roller bearings are utilized in transmission structures and joint configurations to give machinery more flexibility, stability and lifespan. 
