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Rolling Bearing Basic Knowledge Summary - Comprehensive Guide

We are committed to providing the best service and quality to our customers. This guide assists in selecting the correct bearing for your application. It includes content to help you determine:

  • The right type of bearing

  • The type of construction of the rolling bearing

  • Dimensions of rolling bearings

  • Characteristics of rolling bearings

  • Disadvantages of rolling bearings

  • Designation of rolling bearings

  • Common problems with bearings


Rolling bearing is the operation of the shaft and the shaft seat between the sliding and rolling friction, thereby reducing the friction loss of precision mechanical components. Rolling bearing generally by the inner ring, outer ring, rolling body and cage four parts; the role of the inner circle is to match with the shaft and rotate with the post; the outer ring's position is to check with the bearing seat, play a supporting role; rolling body is with the help of the cage will be evenly distributed rolling body between the inner circle and the outer ring, the shape size and number of directly affect the use of rolling bearings performance and life; cage can make the rolling body evenly distributed, prevent rolling body falling off, guide the rolling body rotation to play a precision mechanical components to reduce the friction loss. The shape, size and quantity of the rolling element can directly affect the performance and life of the rolling bearing.

Characteristics of Rolling Bearings

  • Specialization - Bearing parts processing, a large number of bearing special equipment. Such as steel ball processing using a ball grinding machine and other equipment. Discipline is also reflected in the production of bearing parts, such as in the production of a steel ball company specializing in producing miniature bearings in a small bearing factory.

  • Advanced - Due to the large-scale requirements of large quantities bearing production, it is possible to use advanced machine tools, tooling and technology, such as CNC machine tools, three-jaw floating chuck and protective atmosphere heat treatment.

  • Automation - Bearing production specialization for production automation provides the conditions. The production of many fully automated, semi-automated, special and non-specialized machine tools and the output of automatic lines gradually promote the application, such as heat treatment and assembly of automatic lines and automatic lines.

Types of Rolling Bearings-Classified by Structural Type

Rolling bearings, according to the structure, can be divided into deep groove ball bearings, needle roller bearings, angular contact bearings, self-aligning ball bearings, self-aligning roller bearings, thrust ball bearings, thrust self-aligning roller bearings, cylindrical roller bearings, tapered roller bearings, spherical ball bearings with seats.

Deep groove ball bearings.png

Deep groove ball bearings - The deep groove ball bearing structure is simple, easy to use, and produces the largest batch, the widest range of applications of a class of approaches. It is mainly used to bear a radial load and can take a certain amount of axial load. When the radial clearance of the bearing is increased, it has the function of an angular contact bearing and can bear a larger axial burden. Used in automobiles, tractors, machine tools, motors, pumps, agricultural machinery, and textile machinery.


Needle roller bearings - Needle roller bearings are equipped with thin and long rollers (roller length for the diameter of 3 ~ 10 times, the diameter is generally not greater than 5mm), so the radial structure of the compact, the size of its inner diameter and load capacity and other types of bearings with the same, the smallest outside diameter, especially suitable for radial mounting dimensions of the support structure is limited. According to the use of different occasions, you can choose no inner ring bearings or needle roller and keep frame assembly, at this time and bearing with the journal surface and shell hole surface directly as the inner bearing. Outside the rolling surface, to maintain the load capacity and running performance and have the same ring bearing, shaft or shell hole raceway surface hardness. Machining accuracy and surface and surface quality should be similar to the bearing collar raceway. This kind of bearing can only bear radial load. Examples: universal joint shafts, hydraulic pumps, thin plate mills, rock drills, machine tool gearboxes, automobile and tractor machine gearboxes, etc.

Angular contact ball bearings.png

Angular contact bearings - Angular contact ball bearings limit speed is higher, can simultaneously withstand the longitudinal load and axial load, can also withstand pure axial load, its axial load capacity by the contact angle decision, and with the contact angle increases and increases. It is mostly used in oil pumps, air compressors, transmission, fuel injection pumps, and printing machinery.


Self-aligning ball bearings - Self-aligning ball bearings have two rows of steel balls, the inner ring has two raceways, and the outer ring raceway has an internal spherical shape with automatic self-aligning performance. It can automatically compensate for the coaxiality error due to the winding of the shaft and shell deformation, and it is suitable for the parts in which the supporting seat hole can not guarantee strict coaxiality. The bearing mainly bears radial load but can also take a small amount of axial load, usually not used to take pure axial load, such as bearing pure axial only a row of steel ball force. It is mainly used in combine harvesters and other agricultural machinery, blowers, paper machines, textile machinery, woodworking machinery, bridge crane wheels and drive shafts.


Spherical roller bearing - The spherical roller bearing sentence has two rows of rollers, mainly used to carry a radial load, but can also withstand any axial load direction. This kind of taking radial load capacity is high, especially suitable for heavy or vibration load work, but can not withstand pure axial load. Spherical performance is good and can compensate for the same bearing error. Main applications: paper-making machinery, deceleration devices, railroad vehicle axles, rolling mill gearbox seats, crushers, all kinds of industrial reducers and so on.


Thrust ball bearings - Thrust ball bearings are a kind of separated bearing; the shaft ring or "seat ring can be separated from the cage" steel ball assembly. The shaft circle is with the post with the collar; the sitting circle is with the bearing seat hole with the collar and the clearance between the shaft. A thrust ball bearing can only draw hand axial load, a one-way thrust ball bearing can only withstand a room axial load, and a two-way thrust ball bearing can withstand two directions of axial load. Thrust ball bearings can not limit the axis of the warp direction for a shift; the limit speed is very low. One-way thrust ball bearing can limit the axial displacement of one direction of the shaft and shell; two-way bearing can limit the axial displacement of two approaches. Mainly used in automobile steering mechanisms, machine tool spindle.


Thrust roller bearings - Thrust roller bearings bear axial load, mainly shaft. Warp direction combined load, but the warp direction load shall not exceed 55% of the axial load. Compared with other thrust roller bearings, this kind of bearing friction factor is lower, has higher speed, and can self-align. 29000 type bearing roller for asymmetric type spherical roller can reduce the stick and raceway in the work of the relative sliding, and the roller long. Large diameter, the number of rollers load capacity, usually oil lubrication, individual low-speed cases can be grease lubrication. In the design selection, it should be preferred. It is mainly used in hydroelectric generators, crane hooks, etc.


Cylindrical roller bearings - Cylindrical roller bearings rollers are usually guided by a bearing collar of two retaining edges, a cage. The roller and guide ring form a combination of parts, can be separated from another bearing ring, and belongs to the separable bearing. In this kind of bearing, installation disassembly is relatively convenient, especially when the requirements of the inner. Outer ring and shaft. Shell interference fits more and shows the advantages. These bearings are generally only used to bear radial load, only the inner. With the edge of the single-row bearing, the outer ring can withstand a small fixed axial load or a larger intermittent axial load. It is mainly used for large motors, machine tool spindles, axle shaft boxes, diesel engine crankshafts and automobiles, keeping in mind the gearbox and so on.


Tapered roller bearings- Tapered roller bearings are mainly suitable for bearing to radial load-based radial and axial joint load, and large cone angle tapered roller bearings can be used to take to an axial load-based radial-axial common load. This kind of bearing is separate; its inner ring (including tapered roller and cage) and outer ring can be installed separately. In the process of installation and use, it can adjust the bearing's longitudinal clearance, and axial clearance can also be pre-surplus installation for automobile rear axle hubs, large machine tool spindles, high-power reducers, axle bearing boxes, and conveyor rollers.


Housed external spherical ball bearings - Housed external spherical ball bearings are made up of sealed external spherical ball bearings on both sides and cast (or stamped steel) housings. The internal structure of outer spherical ball bearings and deep groove ball bearings are the same, but the inner ring of such approaches is wider than the outer ring. The outer ring has a truncated spherical outer surface, and the concave spherical surface of the bearing housing can be automatically centred. Usually, there is a gap between the inner hole and the shaft of this kind of bearing, and the inner ring of the bearing is fixed on the post with the top wire, eccentric sleeve or tight sleeve, and rotates together with the shaft. Compact structure, easy loading and unloading, perfect sealing, suitable for simple support, commonly used in mining. Metallurgy. Agricultural. Chemical industry. Textile. Printing and dyeing. Conveying machinery and so on.

Types of Rolling Bearings-Classified by Size

Bearings are categorized according to their outer diameter size:

  • Miniature bearings - bearings with a nominal outside diameter size range of 26mm or less. For example, 689zz.

  • Small bearings - bearings with a nominal outside diameter size range of 28-55mm. For example, 4200 ATN9.

  • Small and medium - sized bearings - bearings with a nominal outside diameter in the range of 60-115 mm. For example, 4309 ATN9.

  • Medium and large bearings - bearings with a nominal outside diameter range of 120-190 mm. For example, B7218-E-T-P4S-UL.

  • Large bearings - bearings with a nominal outside diameter range of 200-430mm. For example, QJ 328 N2MA.

  • Extra large bearings - bearings with a nominal outside diameter range of 440-2000mm. For example, QJ 1296 N2MA.

Features of Rolling Bearings

  • Low friction resistance, low power consumption, high mechanical efficiency, easy to start;

  • Size standardization, interchangeability, easy to install and dismantle, easy maintenance;

  • Compact structure, lightweight, axial size is more reduced;

  • High precision, high load, low wear and long service life;

  • Part of the bearing has the performance of automatic centring;

  • Suitable for mass production, stable and reliable quality, and high production efficiency;

  • Transmission friction torque is much lower than the fluid dynamic pressure bearing, so the friction temperature rise and power consumption are lower;

  • The starting friction torque is only slightly higher than the rotating friction torque;

  • The sensitivity of bearing deformation to load changes is less than that of hydrodynamic bearings;

  • require only a small amount of lubricant for proper operation and can be supplied with oil for long periods during the process;

  • smaller axial dimensions than conventional hydrodynamic bearings;

  • can withstand combined radial and thrust loads simultaneously;

  • Unique design for excellent performance over a wide load-speed range;

  • Bearing performance is relatively insensitive to fluctuations in load, speed and operating speed.

Drawbacks of Rolling Bearings

Rolling bearing capacity to bear the load is much smaller than the same volume of plain bearings; therefore, the radial size of rolling bearings. Thus, in the occasion of bearing large loads and the requirements of small radial size, compact structure requirements of the event (such as internal combustion engine crankshaft bearings) are more than plain bearings.

Rolling bearing vibration and noise are bigger, especially in the use of late; therefore, the precision requirements are very high, and not allowed to have the pulse of the occasion; rolling bearings are difficult to perform, so choosing the sliding bearing effect is better;

Rolling bearings are particularly sensitive to metal shavings and other foreign matter; once the bearing enters the foreign value, it will produce intermittent larger vibration and noise, which also will cause early damage. In addition, rolling bearings are also susceptible to early damage due to metal impurities. Even if the early damage does not occur, the life of rolling bearings is also limited. In short, the life of rolling bearings is faster than that of plain bearings.

Rolling Bearing Designation

Rolling bearing designation consists of basic designation, front designation and rear designation.

Table 1 Composition of rolling bearing designations

Front DesignatorBasic  Rear Designator
letterType Designator Size Series Designator  Inside Diameter DesignatorLetters (or plus numbers)
Numbers or lettersWidth Series DesignatorsDiameter Series DesignatorTwo-Digit

For example, rolling bearing code N2210/P5 in the basic code: N - type code; 22 - size series code; 10 - inner diameter code, after the code: / P5 - accuracy level code.

1、Basic code (except needle roller bearings)

The basic code indicates the bearing's type, structure and size, which is the basis of the bearing code. The basic principle comprises three parts: bearing type, size series, and inner diameter code.

(1) Type code

A party expressed in numbers or letters.

Table 2 General rolling bearing type designation

Code NameBearing Type
0Double Row Angular Contact Ball Bearings
1Spherical ball bearings
2Spherical Roller Bearings and Thrust Spherical Roller Bearings
3Tapered roller bearings
4Double Row Deep Groove Ball Bearings
5Thrust Ball Bearings
6Deep Groove Ball Bearings
7Angular contact ball bearings
8Cylindrical Roller Thrust Bearings
NCylindrical Roller Bearings
NNDouble or Multi-row Cylindrical Roller Bearings
USpherical Ball Bearings
QJFour-point contact ball bearings
(2) Size series code

Size series code by the bearing width (thrust bearing refers to high) degree and diameter series code. Each has a digital representation.

The bearing width series code refers to the same inner diameter as the centripetal bearing, with a different width size series. Bearing width series code 8, 0, 1, 2, 3, 4, 5, 6, width size in ascending order. There are different height dimensions for thrust bearings with designations 7, 9, 1, and 2 in ascending order of height dimensions.

Bearing diameter series designation means bearings with the same inner diameter are equipped with different outer diameter size series. Its code has 7, 8, 9, 0, 1, 2, 3, 4, 5, the external diameter size in ascending order. The following figure compares different diameter series codes of deep groove ball bearings.


(3) Bore diameter code

The bearing bore diameter is expressed in two digits of the method.

Table 3 Bearing Bore Designators

Bore Code012304~99
Bearing Inner Diameter d (㎜)10121517Number x 5

2、Front code

The front code of the bearing is expressed in letters. For example, with L being separated, the bearing can be separated from the inner or outer ring, code example LN207.

3、Rear code

The rear code of the bearing is expressed in letters (or numbers). The content of the back code is many, the following is introduced several commonly used rear code.

(1) The internal structure code with letters immediately after the basic code. Such as contact angle α = 15 °, 25 ° and 40 ° angular contact ball bearing with C, AC and B, respectively, said the internal structure of different. Code example 7210C, 7210AC and 7210B.

(2) Seal, dustproof and external shape change code. For example, "-Z" means that one side of the bearing has a dust cover; "N" indicates a stop groove on the outer ring of the bearing. Code example 6210-Z, 6210N.

(3) The bearing tolerance level is divided into 2, 4, 5, 6, 6X and 0 levels, a total of 6 levels, and precision is reduced. Its code were / P2, / P4, / P5, / P6X, / P6 and / P0. The tolerance level, 6X level, only applies to tapered roller bearings; 0 levels for the general level, omitted in the bearing code, does not indicate. Code example 6203, 6203/P6, 30210/P6X.

(4) Bearing clearance is divided into 1, 2, 0, 3, 4 and 5 groups, a total of 6 clearance groups, support from small to large. The commonly used clearance group is 0 clearance group, omitted in the bearing code does not indicate the rest of the clearance group in the bearing code with symbols / C1, / C2, / C3, / C4, / C5 said. Code example 6210, 6210/C4.

The actual application of rolling bearing type is a lot; the corresponding bearing code is also more complex. The above code is the most basic and commonly used part of the bearing code; if you are familiar with this part, you can identify and check the widely used bearings.

Routine Maintenance of Rolling Bearings

1. Requirements for mounting surface and mounting place?

Yes. If there are iron chips, burrs, dust, and other foreign objects entering the bearings, it will make the approaches produce noise and vibration when running and even damage the raceways and rolling elements. Therefore, you must ensure the mounting surface and environment are clean before mounting the bearings.

2. Must bearings be cleaned before mounting?

The bearing surface is coated with anti-rust oil; clean gasoline or kerosene is used to clean carefully, and then coated with clean high-quality or high-speed and high-temperature lubricating grease before installation and use. Cleanliness has a great impact on bearing life and vibration noise. We want to remind you that fully enclosed bearings do not need to be cleaned and refuelled.

3. How to choose grease?

Lubrication is extremely important to the operation and life of the bearings; here to briefly introduce you to the general principles of selecting grease. Grease is made of base oil, thickener and additives. The performance of different kinds of fat and various grades of the same type of grease varies greatly, and the permissible rotational limits are other, which must be noted when selecting a lubricant. The base oil mainly determines the performance of fat. Generally, low-viscosity base oil is suitable for low temperature and high speed, while high-viscosity is suitable for high temperature and high load. Thickeners are also related to lubrication performance. The water resistance of the thickener determines the water resistance of the grease. In principle, different oil brands can not be mixed, even if the same kind of thickener grease, but also due to various additives to bring each other bad influence.

4. When lubricating bearings, is it better to apply more grease?

When lubricating bearings, it is a common misconception that the more grease you apply, the better. Excessive fat in the bearing and bearing chamber will cause extreme oil agitation, producing extremely high temperatures. The amount of bearing filling lubricant to fill the internal space of the bearing 1/2 to 1/3 is appropriate and should be reduced to 1/3 at high speed.

5. How to install and disassemble?

Do not hammer the bearing end face and non-stressed surface directly when installing. Should use a pressure block, sleeve or other installation tools (tooling) to make the bearing uniform force; do not install through the rolling body power transmission. If the mounting surface is coated with lubricant, it will make the mounting smoother. If the fit interference is large, the bearing should be put into mineral oil, heated to 80~90℃, and mounted as soon as possible. The oil temperature should be strictly controlled not to exceed 100℃ to prevent the hardness of the tempering effect from decreasing and affecting the size recovery. In the dismantling encountered difficulties, it is recommended that you use the dismantling tool to pull outward simultaneously to the inner ring on the careful pouring of hot oil; the heat will make the bearing internal ring expand, making it easier to fall off.

6. The smaller the radial clearance of the bearing, the better.

Not all bearings require the smallest working clearance; you must choose the appropriate support according to the conditions. National standard 4604-93, rolling bearing radial clearance is divided into five groups - 2 groups, 0 groups, 3 groups, 4 groups, 5 groups, the clearance value from small to large, of which 0 groups for the standard clearance. The basic radial clearance group applies to general operating conditions, conventional temperature and commonly used interference fit; in high temperature, high speed, low noise, low friction and other special needs under the work of the bearing, it is appropriate to choose a large radial clearance; on the precision spindle, machine tool spindle bearings and different proper selection of smaller radial clearance; for roller bearings can maintain a small amount of work clearance. In addition, the separation of the bearing is no matter clearance. Finally, the bearing after the installation of the working license, than the original clearance before installation of small, because the bearing to withstand a certain load rotation, and bearing with the load generated by the amount of elastic deformation.

7. The assembly process of rolling bearing.

Rolling bearing parts such as the inner ring, outer ring, rolling element and cage, etc., after qualified inspection, into the assembly workshop for assembly, the process is as follows.

Parts demagnetization, cleaning → internal and external rolling (groove) channel size group selection → combined set → check clearance → riveted cage → final inspection → demagnetization, cleaning → rust prevention, packaging → into the finished product library (box, shipping).

Bearing Failure Analysis and Solutions

At TFL, our extensive experience speaks for itself, making us the first choice for bearing failure analysis in various industries and applications. We serve diverse customers in industrial sectors such as machine building and power plants, machine tools and agricultural machinery. We provide our users with comprehensive knowledge and expertise on failure modes and access to our state-of-the-art testing facilities and specialized equipment. By working with us, customers can avoid the inconvenience, unnecessary costs and even more serious consequences of bearing failure downtime.

Bearing common problem analysis is mainly divided into 9 categories:

  • Peeling burns 

  • Crack defects 

  • Cage breakage 

  • Abrasion cord injury 

  • Rust and corrosion

  • Abrasion 

  • Electrical corrosion 

  • Indentation bruise 

  • Creep

PeelingThe running surface peeled off after peeling with obvious convexity and concavity.- Excessive load MisuseRevisiting the conditions of use
- Poor mounting- Reselect the bearings
- Poor accuracy of shaft or bearing box- Reconsider clearance.
- Small clearance- Check shaft and housing machining accuracy.
- Foreign object intrusion- Study the design of the bearing surroundings
- Rust occurs- Check mounting methods
- Loss of hardness due to abnormally high temperatures- Check lubricants and lubrication methods
Burn (injury)Bearings become hot and discoloured, and then burned and cannot rotate
- Excessive clearance (including excessive clearance in deformed parts)- Set proper clearance (increase clearance)
- Insufficient or improper lubrication- Check the type of lubricant to ensure the amount injected
- Excessive load (excessive preload)- Check conditions of use
- Roller deflection- Prevent positioning errors

- Check the design around the bearing (including bearing heat)

- Improvement of bearing assembly methods
Crack defectsPartially chipped and cracked- Excessive shock load- Check the operating conditions
- Excessive interference- Setting proper interference and checking material
- Large stripping- Improvement of mounting and use methods
- Friction cracks- Prevent friction cracking (check lubricant)
- Poor accuracy on the mounting side (corner rounding too large)- Check the design around the bearings
- Poor use (use of a brass hammer, jamming of large foreign objects)
Broken cageLoose or broken rivets, cracked cages- Excessive torque load- Checking the conditions of use
- High-speed rotation or frequent speed changes- Check lubrication conditions
- Poor lubrication- Revisit cage selection
- Foreign objects stuck in the machine.- Pay attention to bearing use
- High vibration- Studying shaft and housing rigidity
- Poor mounting (mounting at an angle)
- Abnormal temperature rise (resin cage)
Scratch and snagSurface roughness, accompanied by small dissolution, ring gear edge and the roller end face of the abrasion, is called jamming- Poor lubricationRe-examine lubricants and lubrication methods
- Foreign object intrusion- Check the operating conditions.
- Roller deflection due to bearing tilt- Setting the appropriate pre-pressure
- Oil breakage on retaining surface due to high axial load.- Enhance sealing performance.
- Large surface roughness- Normal use of bearings
- Roller sliding
Rusty and corrodedPartial or total surface rusting, rolling body tooth pitch rusting- Poor storage condition- Prevents rust in storage
- Improper packaging- Enhancement of sealing performance
- Insufficient rust inhibitor- Check the lubricant regularly.
- Moisture, acid solution, etc.- Pay attention to the use of bearings.
- Direct manual handling of bearings
ErosionReddish-rust-colored wear particles on mating surfaces- Insufficient interference- Checking of interference and lubricant application
- Small bearing rocking angle- Separate inner and outer rings for transportation or apply preload if they cannot be separated.
- Insufficient lubrication (or no lubrication)Re-selecting the lubricant
- Insufficient lubrication (or non-lubricated condition)- Reselect the bearing
- Vibration during transportation
Wear and tearSurface wear, resulting in dimensional changes, mostly accompanied by abrasions, wear marks- Foreign matter in the lubricant- Check lubricant and lubrication method
- Poor lubrication- Reinforcement of sealing performance
- Roller deflection- Prevent positioning errors
Galvanic corrosionSpit-like craters on rolling surfaces further developed as corrugated plates- Rolling surfaces energized- Make current bypass valves
- Insulation to prevent electric current from passing through the inside of the bearing
Indentation bruiseStuck solid foreign objects, or impact-induced surface craters and scuffs on the mounting.- Solid foreign body intrusion- Improvement of mounting and use methods
- Snagging on the stripper- Prevent foreign objects from entering the bearing.
- Impacts, dislodging due to poor mounting- If caused by a metal plate, check other parts of the bearing.
- Installation at an angle
CreepSlippage on the inside diameter surface or outside diameter, resulting in mirroring or discolouration, sometimes jammed- Insufficient interference at the mating pointRe-examining the excess
- Inadequate tightening of sleeves- Study the conditions of use
- Abnormal temperature rise- Check shaft and housing accuracy
- Excessive loads

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