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NTN Bearing Life Estimation Method

Source: FAG bearings  Tags: News

There are two methods for estimating the fatigue life of NTN bearings: calculation method and test.

The fatigue life of the NTN bearing calculated according to the prescribed formula and calculation rules is used as the calculated fatigue life. The calculated total rotation value is specified as the total rotation value when the inner ring or the shaft ring rotates (the outer ring or the seat ring is fixed at this time).

Roll the fatigue life test procedures of NTN bearings in accordance with the prescribed standard test method), use a testing machine that can meet the requirements specified in a method in terms of performance, and perform a sample fatigue life test on a batch of NTN bearings, obtained from the test data processing The actual test life is the fatigue test life of the batch of NTN bearings represented by the tested NTN bearings.

The rolling bearing fatigue life test is a kind of reinforced fatigue life test method that uses sufficient lubrication to limit the wear factors of rolling NTN bearings to a large extent, and uses enhanced load and speed to highlight the fatigue factors of NTN bearings.  NTN 30226 U bearings online , pls click here :



The calculation method of NTN bearing fatigue life and the fatigue life test are complementary, and the results obtained by the two have sufficient correspondence.

In fact, for each specific use occasion, a sufficient number of NTN bearings are selected for life test to verify whether the selected NTN bearing is suitable, which is very vast in economy, time and labor. The test method of NTN bearing life is only used when it is very necessary or important. In most cases, the standard life calculation method is used to estimate the service life of NTN bearings, which has a sufficient degree of dependence. 

NTN bearing lubrication skills

1.Bearing oil lubrication

Oil drip lubrication is suitable for bearing parts that need to be supplied with a fixed amount of lubricating oil. The amount of oil drip is preferably one drop every 3-8 seconds. Excessive oil will cause the bearing temperature to increase.

2.Oil bath lubrication method of cam bearing

Oil bath lubrication is a common lubrication method in cam bearings, suitable for the lubrication of low and medium speed NTN bearings. Part of the bearing is immersed in the groove, the lubricating oil is taken up by the rotating bearing parts, and then flows back to the oil groove. The oil surface should be slightly lower than the center of the low rolling element.

3.Radial lubrication of bearings

Use the oil pump to shoot low-pressure oil into the bearing through the nozzle, and the oil injected into the bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at a high speed, the rolling elements and the retainer also cause the surrounding air to flow at a relatively high rotation speed. It is difficult to send the lubricating oil to the bearing in an individual smooth manner. At this time, the smooth oil must be sprayed by low pressure radiation In the bearing, the position of the nozzle should be placed between the inner ring and the center of the maintenance frame.

4.Circulating lubrication method of bearings

Use the oil pump to send the filtered oil to the cam bearing parts, and then filter and cool the lubricating oil after the bearing and use it. Because the circulating oil can take away certain heat and cool the NTN bearing, this method is practical for bearing parts with higher speed.

5.Spray lubrication of bearings

The dry shrinkage air is mixed with the smooth oil through the sprayer to cause oil mist. In the radial bearing, the airflow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the smoothing of high-speed and low-temperature bearing components.

Although the raceway noise of the bearing is inevitable, high-precision machining of the work surface of the parts can be adopted, and the correct selection of the bearing and the precise use of the bearing can reduce noise and vibration. 

Troubleshooting of NTN bearings

There are many reasons for NTN imported bearing damage. One of the common reasons is that the bearing is dirty and not clean. The typical dirt immersion period is during the initial installation process and during maintenance. Dirt leaks into the NTN bearing housing through the air, or even through the use of dirty lubricant, into the NTN imported bearing. 

For example, hard and rough foreign substances such as rust or other metal materials can cause small depressions. Due to overload failure, the depression caused by acid corrosion or corrosion is obviously different. Blockage of hard objects can cause the seat ring to rotate.  Eric Bearing Ltd have rich stock for NTN bearings :

However, many of the above-mentioned failures can be avoided or postponed with better lubricants. The failure caused by water, acid or other corrosive substances on NTN imported bearings is a red-brown surface layer and very small corrosion holes on the entire exposed surface of the seat ring. 

Generally, due to the rolling motion, the lubricant is pushed away from the ball track and there is no corrosion on the ball or roller track. Corrosive oxides move like abrasives, which cause wear and leave a dark gray color on the balls or rollers and their races, which contrasts with the red-brown residue on the surface of NTN bearings. 

Noise is a sign of failure. If the NTN bearing is working properly, the sound heard should be a soft whine and loose grease. 

Use a screwdriver as a stethoscope to check NTN imported bearings. A short squeal indicates that it is not completely lubricated. A harsh sound indicates that the shaft or NTN housing is obstructed or improperly adjusted. The crunching sound meant that there was dirt in the bearing. The smooth, pure tone indicates that there are traces in the stationary seat ring. Irregular noise indicates that the bearing ball is damaged. 

The difference between NTN bearing vibration and ordinary bearing

1.Swing load and indefinite load

Sometimes the direction and magnitude of the load cannot be determined accurately. For example, in high-speed rotating machinery, in addition to the load with a fixed rotor weight, there is also a rotating load caused by unbalanced mass. If the rotation load is much larger than the fixed load, then the combined load is the swing load. Regardless of the rotating load or swing load, its size and direction are constantly changing. In the variable working state, some ferrules may be subjected to rotating loads, fixed loads, and swing loads. This load is called indefinite load. The swing load and the indefinite load should be treated in the same way as the rotating load. The loose fit will cause damage to the mating surface. The ferrule rotating with respect to the load direction and the shaft or seat hole should choose a transition fit or an interference fit. The size of the interference is based on the principle that when the bearing is working under load, its NTN bearing ring does not produce "creep" on the shaft or the matching surface in the seat hole. However, when the load is very light, or the ferrule rotates at a low speed occasionally under the heavy load, a transition fit can be used. At this time, the shaft surface should have a higher hardness and a smaller surface roughness. For heavy load occasions, it should usually be tighter than the light load and normal load occasions. The heavier the load, the greater the interference fit . 

2.Fixed load

The synthetic radial load acting on the ring is borne by the local area of ​​the ring raceway and transmitted to the opposite area of ​​the shaft or the Wuxi NTN bearing housing. This load is called a fixed load. The characteristic of the fixed load is that the resultant radial load vector is relatively stationary with the ferrule. Both the ferrule and the synthetic radial load do not rotate or rotate at the same speed are fixed loads. The ferrule that bears a fixed load can use a looser fit.

3.Rotating load

The synthetic radial load acting on the ferrule rotates along the circumferential direction of the raceway and is sequentially received by various parts. This load is called a rotating load. The characteristic of the rotating load is that the resultant radial load vector rotates relative to the ferrule. There are three cases of rotating load: the direction of the load is fixed and the ferrule rotates ;

The load vector rotates and the ferrule is stationary ;

The load vector and the ferrule rotate at different speeds. 

First of all, check the vibration of the NTN bearing during work. Peeling, indentation, corrosion, cracks, wear, etc. will be reflected in the vibration measurement of the bearing. The bearing vibration is very sensitive to the damage of the bearing. Therefore, by using a special NTN Bearing vibration measuring devices (frequency analyzers, etc.) can measure the magnitude of vibration, and it is impossible to deduce the specific conditions of abnormality through frequency points. Since the measured values ​​are different depending on the use conditions of NTN imported bearings or the installation positions of the sensors, etc., it is necessary to analyze and compare the measured values ​​of each machine in advance to determine its judgment standard.

Secondly, check the sound of the NTN bearing rolling. Even if the bearing is slightly peeled and damaged, it will produce abnormal sounds and irregular sounds, so it can be distinguished by a sound sensor. The sound sensor is used to detect the running bearings. Check the size and sound quality of the rolling sound to prevent it in advance. 

Finally, it is necessary to check the temperature when the NTN bearing rotates. If the oil hole can be used to directly measure the temperature of the outer ring of the NTN bearing, it is more suitable. Under normal circumstances, the temperature of the NTN bearing can be estimated based on the temperature outside the bearing. If the lubrication and installation parts are appropriate, the bearing temperature will rise sharply and abnormally high temperatures will appear. At this time, the operation must be stopped and necessary precautions must be taken. 

Generally, the temperature of NTN bearings rises slowly as the operation begins, and reaches a steady state after 1-2 hours. The normal temperature of the bearing varies with the heat capacity, heat dissipation, speed and load of the machine.

Whether it is on the shaft or in the bearing housing, rolling bearings are required to fix their positions in three directions: radial, axial and tangential directions. The radial and tangential positioning is achieved by the tight fit of the bearing ring, but the axial positioning is only used in a few cases; the axial limit parts, such as the end cover and the retaining ring, are used The direction position is limited to the clearance range. 

The following four precautions should be emphasized when selecting and matching rolling bearings:

1.The coordination of rolling bearings should make the installation and disassembly of the bearings simple and convenient, as far as possible to save time and labor, and save money on three points.

2.Also, its ferrule cannot slide along the tangent direction in its mating surface, so as not to damage the mating surface.

3.In order to reduce the degree of deformation of the NTN bearing ring, and to give full play to the bearing capacity of the bearing, it is best to have good support and uniform stress on the bearing ring.

4.It must adapt to the axial position and have the ability to swim within a certain range, so the free-end bearing must be able to adapt to the changes in the length of the shaft and the bearing hole of the NTN bearing.