As important basic rotating machinery parts in various industrial fields, rolling bearings are widely used. According to statistics, about 30% of the mechanical failures in our country are caused by bearing damage, so its operating state has a huge impact on the normal operation of the equipment. During the operation of the rolling bearing, the temperature of the bearing increases due to lack of oil, lack of oil or collision, friction, etc., and the phenomenon of "burning shaft" will occur; the bearing is damaged due to fatigue wear, indentation, cracks, surface peeling, adhesion and impurities. , resulting in impact vibration, which will cause the foundation anchor bolts to vibrate and break, the bearings to burn out, and the bearing bushes to fly out.
Once a failure occurs, it will not only seriously affect the normal operation of the entire machine, but also may cause personal injury and bring huge economic losses to the enterprise. Therefore, it is necessary to monitor the running state of rolling bearings to avoid sudden failures. Let's take a look at the forms of bearing failure and the commonly used condition monitoring methods.
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Common failure forms of rolling bearings
Rolling bearings may fail due to various reasons during operation, such as improper assembly, poor lubrication, stress corrosion and overloading, which may lead to premature bearing failure. There are many failure forms of rolling bearing failures, which may generally be classified into four types: wear failure, fatigue failure, fracture failure, and glue failure.
1. Wear failure.
Poor lubrication conditions of rolling bearings or the presence of dust or deterioration in the lubricant causes direct contact between the rotating parts of the bearing, resulting in mechanical friction or wear of tiny particles. Continuous bearing wear increases bearing clearance and equipment vibration.
2. Fatigue failure.
The main cause of fatigue failure of rolling bearings is the alternating stress caused by the load. When the shaft rotates at high speed, due to the repeated impact of the huge alternating contact stress of the bearing, fatigue pitting corrosion occurs on the metal surface of the bearing element, spalling occurs, and small pits are formed.
3. Fracture failure.
When the bearing load is too large, stress concentration occurs in a certain part of the bearing when it is impacted, and pitting corrosion causes cracks, which in turn causes the bearing components to break.
4. The gluing fails.
Gluing refers to the bearing failure caused by the partial fusion of the raceway and the rolling element surface due to overheating. It is often caused by high speed, high temperature, heavy load and poor lubrication.
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Main Condition Monitoring Methods of Rolling Bearings
The condition monitoring technology for rolling bearings mainly includes vibration signal analysis, bearing lubrication condition monitoring, oil analysis, temperature monitoring, etc.
1. Vibration signal analysis and diagnosis method
Among the condition monitoring and fault diagnosis methods of various rolling bearings, the vibration signal analysis and diagnosis method has the strongest coverage for different failure modes (fault locations) of the bearing, and is also the most widely used.
When there is local damage on the surface of the rolling bearing element, the bearing will generate periodic pulse excitation during operation, and the pulse is a broadband signal. Below), mid-band spectrum (1~20KHz), high-band spectrum (above 20KHz).
2. Bearing lubrication state monitoring and diagnosis method
When the lubrication state of the bearing rolling surface changes, such as from complete liquid lubrication to dry friction, the proportion of time in direct metal-to-metal contact increases, the shock pulse value also increases, and the oil film resistance decreases. In view of this phenomenon, two monitoring methods are commonly used in practical work: the oil film thickness method and the oil film resistance diagnosis method.
3. Oil analysis and diagnosis method
The main ways of rolling bearing failure are wear, fracture and corrosion, etc. The main reason is improper lubrication. Therefore, by systematically analyzing the lubricating oil used during operation, and testing the content of various abrasive particles in the oil, you can understand the lubrication and lubrication of the bearing. Wear state, make early forecasts for various hidden troubles, find out the causes and locations of failures, and take timely measures to prevent the occurrence of malignant accidents.
4. Temperature monitoring and diagnosis method
As a rotating machine, the rolling bearing will generate heat on its surface during operation. If some kind of damage occurs, its temperature changes, so bearing temperature can be monitored to diagnose bearing failure.
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