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Analysis of the failure cause of NTN bearing
Source: China Bearing Network Time: 2013-05-27
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.1) The effect of the outer surface of the oxide layer on the appearance of oxygen in the steel and the oxygen in the air; the thin layer of iron oxide which is raised to the pole of 20 to 30 nm. It is worth noting that the thickness of the oxide layer and the total thickness of the enthalpy layer of the external grinding The test results are in a corresponding relationship. This indicates that the thickness of the oxide layer is directly related to the grinding process; it is an important mark of the grinding quality.
.2) Amorphous arrangement of the instantaneous high temperature of the grinding zone to cause the workpiece to reach the molten state; the molten metal molecular flow is evenly applied to the work surface; and is cooled by the base metal at a very fast rate; Very thin layer of amorphous arrangement. It has high hardness and resistance; but it only needs about 10nm; it is very simple to be removed in fine grinding.
.3) The instantaneous high temperature in the grinding zone of the high temperature tempering layer can be heated to a temperature higher than the tempering heating temperature of the workpiece at a certain depth (10 to 100 nm). Under the condition that the austenitizing temperature is not reached; The improvement of the heating temperature; the appearance of layer-by-layer will occur with the re-tempering or high-temperature tempering corresponding to the heating temperature; the hardness will also decrease. The higher the heating temperature, the more fierce the hardness is.
.4) Two-layer quenching layer When the instantaneous high temperature of the grinding zone heats the outer surface of the workpiece to above the austenitizing temperature (Ac1); then the austenitizing of the layer is arranged in the subsequent cooling process; Quenching into martensite arrangement. However, any workpiece with secondary quenching burn; under the secondary quenching layer must be a very high temperature tempering layer.
.5) Grinding cracks Secondary quenching burns will change the stress on the outer surface of the workpiece. The secondary quenching zone is under pressure; the maximum tensile stress exists in the high temperature tempering zone below; here is the most likely crack center The local crack is most simply conveyed along the original austenite grain boundary. Severe burns will cause the entire surface of the grinding to show cracks (more cracks) to form the workpiece.
1) The quality of NTN bearing. Crash bearing box time, firstly, check whether the smooth grease can have any abnormal conditions such as enthalpy change, agglomeration, impurities, etc. This is an important basis for judging the cause of bearing damage. Secondly, check whether the bearing has bite and wear. View the inner and outer rings of the bearing, the rolling element, the appearance of the cage, and whether there are any defects such as cracks, rust, peeling, pits, overheating and discoloration, etc., whether the NTN bearing clearance can be overrun; see if the bushing is worn or not, and the pit , peeling, if the above conditions should replace the new NTN bearing.
2) Cooperation of NTN bearings. The cooperation between the bearing inner diameter and the shaft, outer diameter and outer casing is very important. When the cooperation is too loose, the relative sliding of the cooperation surface will be called creep. Once the creep occurs, the wear cooperation surface will be Damage to the shaft or casing, and the wear powder will invade the inside of the bearing, causing heat, oscillation and damage. If the interference is too large, the outer diameter of the outer ring will become smaller or the inner diameter of the inner ring will become larger, and the internal clearance of the NTN bearing will be reduced. To select the appropriate use of cooperation, we must consider the nature of the bearing load, the size, temperature conditions, the rotation of the inner ring outer ring of various conditions.
3) Adjustment of cooperation gaps between NTN bearings. NTN bearing clearance is too small, because the shear force conflict in the gap is too large, and the bearing will heat up. Together, when the gap is too small, the amount of oil will decrease, and it is too late to take the conflict. The heat generated will further improve the temperature rise of the NTN bearing. However, if the gap is too large, the dynamic characteristics of the bearing will be changed, resulting in unstable rotor operation. Therefore, it is necessary to align the equipment and the operating conditions to select the verified bearing clearance. Huatai warehouse #8 unit B induced fan has a problem of high bearing temperature for a long time in operation. In the C-level maintenance of the unit in 2008, the main points of this problem are checked. See the smoothness of the NTN bearing, the static balance of the impeller, and the coupling Normally normal, é‚ will be placed on the gaps of the NTN bearing parts. After measuring the bearing thrust gap as long as 0. 07mm, the analysis of the thrust gap is too small for the bearing temperature is too high. Using the grinding machine to grind the thrust bearing septum ring 0. 07 ~0.08mm, extended thrust gap, the bearing thrust gap is extended to 0. 14~0. 15mm, the NTN bearing temperature is normal during operation, completely eliminating the shortcomings of long-term transmission, ensuring the safe and stable operation of the equipment. Yunnan Phosphorus #1 unit induced draft fan bearing temperature is too high for 80~90 °C, the bearing life is greatly shortened, and the replacement of NTN bearings has not solved the problem. In the 2008 C-level maintenance, the view was found The gap between the end cap shaft seals is too small, the bearing temperature is normal during the cold test run, and the shaft is thermally expanded during hot operation, which conflicts with the end cover shaft seal. This is the reason why the NTN bearing temperature is too high for a long time. The end cover hole is turned by 0. 5mm, so that the shaft and end cover shaft seal gap is extended by 0. 25mm, which prevents the shaft from being in thermal expansion after running and collides with the end cover. Through the disposal, the problem of excessive temperature of the NTN bearing is improved. In the cold state and hot state, the bearing temperature is normal, and the bearing box does not exhibit the leakage oil appearance, which ensures the outstanding operating conditions of the bearing, reduces the replacement frequency of the NTN bearing, and saves the maintenance cost.
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