As the world's top bearing SKF bearings, it is widely used. Each industry has different damage characteristics. Today we will look at the damage characteristics of engine sliding bearings.
Sliding bearing mechanical damage refers to the appearance of groove marks on the alloy surface of the bearing pad. In severe cases, metal peeling and large-scale chaotic scratches occur on the contact surface; under normal circumstances, contact surface damage and ablation phenomenon coexist. The main cause of bearing mechanical damage is that it is difficult to form an oil film on the bearing surface or the oil film is severely damaged.
Sliding bearing under the repeated action of cylinder pressure impact load), the surface layer undergoes plastic deformation and cold work hardening, locally loses its deformability, gradually forms lines and continues to expand, and then forms cavities in the loaded surface layer as the abrasive debris falls off . Generally, when pitting corrosion occurs on the bearing bush, pits first appear, and then the pits gradually expand and cause cracks at the interface of the alloy layer. The cracks extend along the parallel direction of the interface until they flake off.
The main reason for the erosion of sliding bearings is that due to the sudden change in the cross-section of structural elements such as oil grooves and oil holes, the oil flow is strongly turbulent, and bubbles are formed in the vacuum area where the oil flow is turbulent, and then the bubbles are destroyed due to the pressure increase eclipse. Cavitation generally occurs in the high-load area of the bearing, such as the lower bearing pad of the crankshaft main bearing.
Bearing fatigue pitting refers to the overheating of the engine and excessive bearing clearance, resulting in fatigue damage, fatigue pitting or fatigue shedding in the middle of the bearing. Most of this damage is caused by overloading, excessive bearing clearance, or unclean lubricating oil, and foreign matter in it.
Therefore, you should pay attention to avoid overloading the bearing and do not run at too low or too high speed; adjust the engine to a stable state when idling; ensure normal bearing clearance to prevent the engine speed from being too high or too low; check and adjust the cooling The working condition of the system ensures that the working temperature of the engine is appropriate.
(4)Bearing alloy corrosion
Bearing alloy corrosion is generally due to impure lubricants. The chemical impurities (acidic oxides, etc.) contained in the lubricant oxidize the bearing alloy to generate acidic substances, causing the bearing alloy to partially fall off, forming irregular tiny cracks or small recesses. pit. The main reasons for bearing alloy corrosion are improper selection of lubricating oil, poor corrosion resistance of bearing materials, or rough working of the engine and excessive temperature.
There is a small convex metal surface directly contacting between the journal and the bearing friction pair, which forms a local high temperature. In the case of insufficient lubrication and poor cooling, the bearing alloy will be blackened or locally melted. This failure is often caused by the over-tightening of the journal and the bearing; the lack of lubricating oil pressure can also easily burn the bearing.
(6)The bearing takes the outer circle
The outer circle of the bearing means that the bearing has relative rotation in the seat hole. After the bearing goes out of the circle, it not only affects the heat dissipation of the bearing, but also easily causes the ablation of the inner surface of the bearing, but also damages the back of the bearing and burns the bearing in severe cases. The main reason is that the bearing is too short, the tenon is damaged, and the processing or installation does not meet the specifications.
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How to check the fault of SKF bearing in operation
1. The first is to identify and check the sound of SKF bearing rolling
We can use a sound meter to check the size and sound quality of the running SKF bearing rolling sound. SKF bearings can produce abnormal sounds and irregular sounds even if there is slight peeling and other damage, so they can be distinguished by a sound meter, which plays a role in preventing them in advance.
2. Secondly, identify and check the vibration of SKF bearings during work
SKF bearing vibration is very sensitive to bearing damage. For example, peeling, indentation, rust, cracks, wear, etc. will be reflected in the vibration measurement of SKF bearings, so by using a special SKF bearing vibration measuring device (frequency analyzer, etc.), the size of the vibration can be measured by frequency The specific circumstances of the abnormality cannot be inferred. The measured value differs depending on the use condition of the bearing or the installation position of the sensor, etc.
Therefore, it is necessary to analyze and compare the measured value of each machine in advance to determine the judgment standard.
3. Finally, check the temperature of the SKF bearing
The temperature of the SKF bearing can generally be inferred based on the temperature outside the SKF bearing. If the oil hole can be used to directly measure the temperature of the outer ring of the bearing, it is more suitable.
Generally, the temperature of SKF bearings slowly rises with the start of operation, and reaches a steady state after 1-2 hours. The normal temperature of SKF bearings varies depending on the heat capacity, heat dissipation, rotation speed and load of the machine. 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. According to a large number of test data, Table 4-1 lists the average value of the outer ring temperature of the bearings in various machines during operation, for reference.
Since the temperature is affected by lubrication, speed, load, and environment, the values in the table only indicate the approximate temperature range. The thermal sensor can be used to monitor the working temperature of the bearing at any time, and to automatically alarm or stop the shaft burning accident when the temperature exceeds the specified value.