Needle bearings are roller bearings with cylindrical rollers, which are thin and long relative to their diameter. Such rollers are called needle rollers. Despite having a smaller section, the bearing still has a high load bearing capacity.
Needle roller bearings are equipped with thin and long rollers (roller diameter D≤5mm, L/D≥2.5, L is the length of the roller), so The radial structure is compact, and when the inner diameter and load capacity are the same as other types of bearings, the outer diameter is the smallest, especially suitable for the support structure with limited radial installation size.
Depending on the application, a bearing without an inner ring or a needle roller and cage assembly can be selected. At this time, the surface of the journal and the surface of the housing hole matched with the bearing are directly used as the inner and outer rolling surfaces of the bearing.
In order to ensure the load capacity and running performance As with the bearing with ring, the hardness, machining accuracy and surface quality of the raceway surface of the shaft or housing hole should be similar to the raceway of the bearing ring. This type of bearing can only bear radial loads.
Needle bearing type
In addition to those listed in the catalog, bearings that can be used for general engineering, such as: open drawn cup needle roller bearings, closed drawn cup needle roller bearings, inner ring needle roller bearings and needle roller bearings without inner ring/without inner ring Needle roller bearings without cage, with cage and without cage filled needle roller bearings
Needle roller bearing drawn cup
Drawn cup needle roller bearings are needle roller bearings with a thin drawn cup outer ring. Its main feature is that the section height is very low and the load bearing capacity is high. It is mainly used for the bearing configuration with compact structure and low price, and the inner hole of the bearing box cannot be used as the raceway of the needle roller cage assembly. Bearings and bearing housings must be installed with an interference fit.
If the axial positioning functions such as the box shoulder and the stop ring can be omitted, the inner hole of the bearing box can be made extremely simple and economical. The drawn cup needle roller bearings mounted on the shaft end are of double-sided open type and single-sided closed type.
The base end face of the closed drawn outer ring can bear little axial guiding force. Drawn cup needle roller bearings generally do not have an inner ring. Where the journal cannot be hardened and ground, the inner rings listed in the table may be used. The hardened steel outer ring of the drawn cup needle roller bearing is inseparable from the needle roller cage assembly. Free space for lubricant storage allows extended relubrication intervals. Bearings generally use a single-row design.
Except for the wider bearing series 1522, 1622, 2030, 2538 and 3038, which are equipped with two needle roller cage assemblies. There are lubricating oil holes in the outer ring of the bearing. According to user needs, all single row drawn cup needle roller bearings with shaft diameter greater than or equal to 7mm can be equipped with an outer ring with lubricating oil hole (code suffix AS1).
Drawn Cup Needle Roller Bearings with Oil Seals For occasions where oil seals cannot be installed due to space constraints, open-end or closed-end drawn cup needle roller bearings with oil seals (3 to 5) can be provided. These bearings are equipped with friction oil seals of polyurethane or synthetic rubber, which are filled with lithium-based grease with good rust resistance, and are suitable for operating temperatures of -20 to +100 °C.
The inner ring of the bearing with oil seal is 1mm wider than the outer ring, which enables the bearing to ensure that the oil seal works well and avoid contamination of the bearing even when the shaft has a slight displacement relative to the bearing housing. The inner ring of the bearing also has lubrication holes, which can be supplemented by the outer ring or the inner ring according to the needs of the bearing configuration.
Needle roller bearing solid ring
Solid ring needle roller bearings are composed of one or two rings and a needle roller set with a cage. Depending on the application, it can be divided into bearings with an inner ring or without an inner ring.
Therefore, the solid ring needle roller bearing can meet the requirements of light weight, small space occupation and high transmission power. Solid ring needle roller bearings have smaller volume and higher load capacity.
Structural type outer ring double ribs (or double lock ring) with cage needle roller bearings NA, NAV, NKI type can be installed with inner ring and outer ring (with lock ring, full set of needle rollers and cage), high speed, There are two types of single row and double row. Needle roller bearings with inner rings can be used if the shaft cannot be used as a raceway, i.e. if it is impossible or uneconomical to harden the shaft by grinding. [1]
Features NA, NKI type bearings without inner ring are RNA, NK type needle roller bearings. This kind of bearing has no inner ring and is suitable for the support structure with limited radial installation size, and the journal matched with the bearing directly serves as the rolling surface.
As the shaft of the raceway surface, the hardware must be hardened and ground, and only when it is processed to the appropriate size and shape accuracy, the complete set of needle roller bearings can achieve high life and running accuracy. At the same time, since there is no inner ring, the diameter of the shaft can also be appropriately increased, thereby increasing the rigidity.
Needle roller bearing combination type
The combined needle roller bearing is a bearing unit composed of a radial needle roller bearing and a thrust bearing. It has a compact structure, small volume, and high rotation accuracy. It can bear a certain axial load while bearing a high radial load. And the product structure is diverse, adaptable and easy to install. Combined needle roller bearings are widely used in machine tools, metallurgical machinery, textile machinery and printing machinery and other mechanical equipment, and can make the mechanical system design very compact and flexible.
Needle Roller Bearing Thrust Type
Thrust bearings consist of thrust cage assemblies with needle or cylindrical rollers or balls and thrust washers. Needle rollers and cylindrical rollers are held and guided by thrust cages. When used with different series of DF thrust bearing washers, many different combinations of bearing configurations are available.
Due to the selection of high-precision cylindrical rollers (needle rollers) to increase the contact length, this bearing can obtain high load capacity and high rigidity in a small space. Another advantage is that if the surface of the adjacent parts is suitable for the raceway surface, the washer can be omitted, which can make the design compact. The cylindrical surface of the needle roller and cylindrical roller used in the DF thrust needle roller bearing and the thrust cylindrical roller bearing is Contoured surface reduces edge stress and increases service life.
Needle bearing installation
The installation of full complement needle roller bearings is usually carried out with an auxiliary sleeve. At this time, the auxiliary roller or the auxiliary sleeve supports the needle roller to prevent the needle roller from falling out, and the journal lifts the needle roller with its own chamfer. As the needle roller bearing slowly moves inward on the journal, the auxiliary roller Or the auxiliary sleeve is slowly withdrawn until it is installed in the working position.
The outer diameter of the auxiliary roller and auxiliary sleeve should be 0.1-0.3mm smaller than the shaft diameter. When installing, first coat the inner surface of the outer ring of the bearing with grease, place the needle roller against the inner surface (a gap should be left when placing the last needle roller), and then place the auxiliary roller that replaces the journal or the inner ring of the bearing.
Or push the auxiliary sleeve into the outer ring hole, and align its end face with the end face of the installation shaft or the end face of the bearing inner ring that has been installed on the shaft, and then tap with a press or a hand hammer to apply pressure.
Needle roller bearings can also be installed in this way, that is, apply a thin layer of lubricating oil to the outer diameter of the auxiliary sleeve, and set it into the outer ring of the bearing, so that the auxiliary sleeve and the outer ring of the bearing form an annular hole, and then install the needle roller in the annular hole. After the needle roller is installed, the auxiliary sleeve can be pushed out with the working shaft.
For needle roller bearings without inner ring or outer ring, when installing, first apply a thin layer of grease to the rolling surface of the shaft or housing hole, and put the needle rollers against the grease on the installation site in turn. There should be a gap when placing the last needle roller, and the size of the gap should be 0.5mm on the circumference of the needle roller bearing.
The last needle can not be squeezed into it, or one less needle can be installed, because when the bearing is squeezed, the bearing will be stuck and cannot rotate. Twist and break. For needle roller bearings with only stamped outer ring, because the outer ring wall is very thin, non-needle roller bearings should be installed by hammering with a hand hammer, and should be pressed in by a press. Because the pressure is uneven when the hand hammer hits, it is easy to cause local deformation of the outer ring of the needle roller bearing.
Needle roller bearing comparison
1. The friction coefficient of the rolling bearing is smaller than that of the sliding bearing, and the transmission efficiency is high. The friction coefficient of general sliding bearings is 0.08-0.12, while the friction coefficient of rolling bearings is only 0.001-0.005;
2. Rolling bearings have been standardized, serialized and generalized, suitable for mass production and supply, and are very convenient to use and maintain; 2. 3. Rolling bearings are made of bearing steel and have undergone heat treatment. Therefore, rolling bearings not only have high mechanical properties and long service life, but also can save more expensive non-ferrous metals used in the manufacture of sliding bearings;
3. The internal clearance of the rolling bearing is small, and the machining accuracy of each part is high, so the running accuracy is high. At the same time, the rigidity of the bearing can be increased by preloading. This is very important for precision machinery;
4. Some rolling bearings can bear radial load and axial load at the same time, therefore, the structure of bearing support can be simplified;
5. Because the rolling bearing has high transmission efficiency and less heat generation, the consumption of lubricating oil can be reduced, and the lubrication and maintenance are more convenient; Rolling bearings can be easily applied to shafts in any orientation in space.
Needle Roller Bearing Precautions
Needle roller bearings have a large bearing capacity and are suitable for supporting structures with limited installation dimensions. The surface of the journal is hardened as a rolling surface, and the bearing is fitted into the seat hole with a press fit, and there is no need to axially position it. An appropriate amount of grease should be injected into the bearing before installation. Normally, no relubrication is required after assembly. BK type bearings are used in the support of journals without protruding ends. The end face is closed for sealing and can withstand small axial movement.
Causes of damage to needle roller bearings
Generally speaking, 33.3% of needle roller bearing damages are due to fatigue damage, 33.3% are due to poor lubrication, and 33.3% are due to contaminants entering the bearing or improper disposal of equipment. [1]
Fine dust cleans the bearing and the surrounding environment. The fine dust invisible to the naked eye is a powerful killer of the bearing, which can increase the wear, vibration and noise of the bearing. Stamping forms strong stamping when using the equipment, which is very likely to cause damage to the needle bearing, or use a hammer to directly hit the bearing, and transmit pressure through the rolling body.
Effects of non-professional tool installation Using suitable and accurate equipment, the use of cloth and staple fibers can be avoided as much as possible. Needle roller bearings can be clearly seen in laboratory tests or in practical applications. Needle roller bearings with the same appearance under the same operating conditions actually have very different lifespans.
