In recent years, with the development of modern industry, the demand for large rotating machinery has been increasing, and this type of machinery itself has continued to develop towards high power, large capacity, high speed, high efficiency and complexity.
How to manage these equipment well, ensure the safety and reliability of the work process, avoid accidents, and maximize the economic benefits of the equipment has become one of the important goals of modern enterprise management.
To this end, it is required to identify minor faults as early as possible through online monitoring of the machine and monitor the development of the fault so that remedial measures can be implemented in a timely manner or a prepared shutdown can be implemented before the entire system is severely damaged.
On the other hand, condition monitoring of large rotating machinery can more effectively guide the maintenance and management of equipment. Developing early post-event maintenance methods and planned maintenance methods into predictive maintenance can allow machines to create maximum value within their limited service life.
Mechanical failure refers to the functional failure of a machine, that is, the deterioration of its dynamic performance and failure to meet technical requirements. For example, the machine runs unstable, produces abnormal vibration and noise, changes in operating speed and output power, and abnormalities in the temperature, pressure, and flow of the medium, etc.
The reasons for machine failure are different, and the information reflected is also different. Based on this unique information, the fault can be diagnosed. However, the cause of machine failure is often not a single factor, but is generally the result of the combined action of multiple factors. Therefore, when performing fault diagnosis on equipment, a comprehensive analysis and study must be conducted.
Due to reasons such as the structure and parts design and processing, installation and commissioning, maintenance and repair of rotating machinery, as well as errors in operation, the machine vibrates during operation. The vibration types can be divided into radial vibration, axial vibration and torsional vibration.
Excessive radial vibration is often the main cause of machine damage. It is also the main parameter for condition monitoring and the main basis for fault diagnosis.
According to the cause of the failure and the different stages leading to the cause of the failure, the causes of failure of rotating machinery can be divided into several aspects:
1. Design reasons
1. Improper design, poor dynamic characteristics, forced vibration or self-excited vibration occurs during operation;
2. The structure is unreasonable and the stress is concentrated;
3. The design operating speed is close to or falls into the critical speed zone;
4. Thermal expansion calculation is inaccurate, resulting in poor thermal alignment.
2. Reasons for manufacturing
1. The parts are poorly processed and manufactured with insufficient precision;
2. The parts have poor material, insufficient strength, and manufacturing defects;
3. The rotor dynamic balance does not meet the technical requirements.
3. Installation and maintenance
1. Improper mechanical installation, misaligned parts, and large preload;
2. Shaft system misalignment;
3. The machine geometric parameters (such as fitting clearance, interference amount and relative position) are improperly adjusted;
4. The pipeline has high stress, and the dynamic characteristics and installation accuracy of the machine have changed under working conditions;
5. The rotor has been placed improperly for a long time, which changes the dynamic balance accuracy;
6. Failure to perform maintenance according to regulations has destroyed the original matching properties and accuracy of the machine.
4. Operation
1. The process parameters (such as the temperature, pressure, flow rate, load of the medium, etc.) deviate from the design values, and the machine operating conditions are abnormal;
2. The machine operates at overspeed and overload, which changes the working characteristics of the machine;
3. The operating point is close to or falls into the critical speed zone;
4. Poor lubrication or cooling;
5. The rotor is partially damaged or scaled;
6. Improper operation during start-up, shutdown or acceleration and deceleration, insufficient warm-up, uneven thermal expansion or staying in the critical zone for too long.
5. Machine deterioration
1. After long-term operation, the rotor deflection increases or the dynamic balance deteriorates;
2. The rotor is partially damaged, detached or cracked;
3. Parts wear, pitting or corrosion, etc.;
4. The force on the mating surface deteriorates, resulting in insufficient interference or looseness, etc., destroying the mating properties and accuracy;
5. The machine foundation settles unevenly and the machine shell is deformed.
(Source: Internet)