Discussion on condition monitoring and fault diagn

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Discussion on condition monitoring and fault diagnosis of large grinding equipment

1 preface

in recent years, the emergence and improvement of grinding equipment such as vertical mill, roller press and barrel roller mill have promoted the rapid development of energy-saving grinding equipment and process in cement industry. The new grinding process greatly improves the output of the grinding system and reduces the power consumption of the system. The safe, stable, reliable and trouble free operation of grinding equipment is the key condition for modern cement plants to improve economic benefits. These equipment have the characteristics of large-scale, low-speed, heavy load, high grinding pressure and so on. The working environment is relatively poor, and they also bear serious impact loads. The relevant physical characteristics of materials and changes in production process parameters have a great impact on the working conditions of the equipment. These factors will cause the equipment failure rate to rise

modern cement plants have widely adopted the distributed control system DCS with decentralized control and centralized management to obtain the process and equipment parameters of the production process, the number of ECG sensors, judge the process working conditions, and implement appropriate operation control based on this, so as to ensure the stable operation of production and excellent product quality. Among them, the monitoring positions and parameters of grinding equipment vary slightly with the type of equipment, but it is nothing more than motor current, equipment vibration, bearing and lubricating oil temperature, etc. For example, for the vertical mill, it mainly includes the vibration on the reducer input shaft base or the base, as well as the oil temperature and oil pressure of the high and low pressure lubrication circuit, the oil level at the bottom of the reducer box, the grinding roller pressure, bearing temperature, etc; The roller press mainly includes main frame vibration, main bearing temperature, reducer oil temperature, oil level, hydraulic cylinder pressure, etc. However, the existing monitoring parameters can not effectively predict the wear or fracture of gears and bearings in reducers and spindles and the degree of damage

2 deficiency of monitoring temperature and vibration parameters

the existing detection of bearing temperature is mainly to monitor the lubrication state of bearings and the damage of components. However, there are many reasons for bearing temperature rise, such as low bearing accuracy, bent spindle or non concentric box hole, low assembly quality, poor lubrication, bearing inner shell race, bearing damage, etc. The practice shows that when the bearing is well lubricated, unless the bearing is pulled down, generally speaking, the components have obvious wear or initial fracture, and the bearing temperature rise is not significant. In addition, the temperature of some bearings of grinding equipment is difficult to detect, such as the temperature of the planetary gear bearing in the vertical mill planetary reducer

detecting vibration signal is the most effective method to monitor bearing and gear faults. The relevant technology has been quite mature and has been successfully applied. However, for grinding equipment, under normal working conditions, high-pressure crushing materials produce strong continuous vibration shock signals, which are enough to submerge the vibration characteristic signals of faulty bearings and gears. Moreover, in the vertical mill planetary reducer, the bearings and gears are installed in a solid cylindrical box, and the upper part is a compact floating planetary transmission gear train. It is difficult to detect meaningful fault vibration signals from the outside. The internal structure and working environment decide that it is extremely difficult to install the vibration sensor. Whether the sensor can work reliably needs to be seriously considered in the reducer design stage. Therefore, vibration signals are rarely used to monitor and diagnose bearing and gear faults in grinding equipment. At present, measuring the vibration speed or displacement value on the reducer input shaft base or the main engine base and interlocking with the main engine motor is to prevent strong vibration from damaging the main engine and key parts during operation. In fact, equipment maintenance personnel often feel unsure about the operation status of key components of the host machine, such as vertical mill reducer and roller press spindle bearings. This is unfavorable for preventing sudden accidents, ensuring equipment safety, reducing downtime, preventing shutdown losses, improving equipment reliability, extending equipment service life, optimizing maintenance decisions, and reasonably arranging maintenance

3 actively adopt oil analysis technology

lubrication system is an important part of grinding equipment, such as reducer, main bearing, grinding roller bearing lubrication oil circuit, etc. Obviously, oil analysis technology (such as ferrography analysis) can be used to make up for the deficiencies of temperature and vibration parameters in monitoring the wear and fatigue failure of the above key components. The so-called oil analysis Bayer materials technology is one of the largest polymer production companies in the world. It refers to the technical process of obtaining the macro or micro physical state characteristic information about the changes of equipment in-service lubricating oil performance indicators, wear products in oil, pollution and deterioration products through the detection and analysis of representative lubricating oil samples obtained from operating equipment, so as to evaluate the lubrication and wear status of equipment or diagnose related faults. Oil analysis mainly includes the analysis of lubricating oil condition? Acupoint nature? Analysis of snow and wear particles in oil

in the process of using the lubricating oil in the equipment, affected by the changes of equipment working conditions, the company's deeds will be further enhanced by the role of building and environmental factors, and a series of changes are also taking place in composition, structure and performance. The research shows that the high temperature effect and relative moving surface during the operation of the equipment? Holes like gears? The high shear effect of snow on lubricating oil can lead to oxidative deterioration of lubricating oil and produce corresponding deterioration products. The oxidation of the lubricating oil in use not only reduces its ability to maintain the inherent characteristics of the lubricating oil film, but also significantly changes the viscosity of the oil with the increase of oxidation deterioration products, which eventually worsens the lubrication condition of the friction pair and greatly increases the probability of damage to the parts; When the water leaked from the environment or the cooling system is mixed into the lubricating oil to a certain extent, the lubricating oil will emulsify, thus losing the original lubricating efficiency. The appearance of other pollutants in the oil products, such as dust, sand, metal particles, sludge, fiber and some harmful gases, will also have a bad impact on the mechanical system, or directly intervene in the friction surface to cause abrasive wear, or block the oil circuit to make the lubrication of the friction pair lack oil, or cause the performance of the oil products to change, affect the normal lubrication of the friction pair, or cause the chemical changes of the oil products and serious deterioration. Obviously, the dynamic monitoring of oil performance and the form and quantity of pollutants is of great significance for timely mastering the occurrence of bad working conditions in the equipment, discovering the leakage faults of relevant subsystems and possible changes in lubrication efficiency, and eliminating possible hidden troubles as soon as possible

on the other hand, in-service lubricating oil is also the main carrier of wear products of key friction pairs in machinery. During the operation of the machine, a large number of particles produced by the wear of friction pairs will enter the lubrication system, and these particles will circulate in the oil. By collecting representative oil samples in the oil circuit of the equipment lubrication system, separating the wear particles and analyzing them, we can find very important information about the potential or ongoing failures and faults of mechanical equipment. Previous studies have confirmed that there are significant differences in the morphological characteristics of wear particles produced by machines in different wear periods, running in wear period, normal wear period and abnormal wear period; Different wear mechanisms? Cavity adhesion wear, abrasive wear, surface contact fatigue wear, corrosion wear, etc? Characteristics of wear particles produced by snow? There are also great differences in the shape, size, surface morphology, quantity and distribution of holes; The wear particles produced by friction elements with different motion forms and materials are also significantly different in morphology and material composition. Therefore, through the morphology of wear particles? Acupoints include macro and micro? The analysis of the characteristics of snow, quantity, size distribution and composition can find out the mode and degree of machine lubrication and wear failure and the state of the machine where we are absorbing advanced technology at home and abroad, and determine the cause of the failure, so as to provide basis for further equipment maintenance decisions. Because the collection of lubricating oil samples can be carried out conveniently without shutdown and disassembly, the analysis of wear particles in the oil can be carried out dynamically while the machine is running. Practice has proved that as long as the method is appropriate, the analysis of wear particles in oil can find potential or emerging problems in the early stage of failure, which is of special significance for preventive maintenance of equipment. It goes without saying that it is of great significance to improve the early warning level of actual equipment faults, formulate a more scientific oil change cycle and equipment maintenance plan by organically combining the monitoring of the quality and pollution indicators of the lubricating oil used by the equipment with the analysis of wear particles in the oil to form an equipment tribological condition monitoring system that is mutually causal to a certain extent. For the contents and methods of oil analysis (such as routine physical and chemical indicators, Ferrography and spectral analysis), sampling frequency, methods and rules, please refer to relevant books and literatures

in the process of using oil analysis as equipment condition monitoring and fault diagnosis, modern cement production enterprises can first cooperate with colleges and universities and professional oil testing institutions, starting with sending oil samples for testing and analysis, training specialized personnel to accumulate experience, and purchasing necessary instruments to carry out on-site monitoring. It is necessary to determine the unit, period, instrument and personnel. Only by perseverance can we achieve good results

4 conclusion

for modern cement grinding equipment, oil monitoring, ferrography analysis and diagnosis technology has its irreplaceable position and advantages. With the application of computer technology, image analysis technology and pattern recognition technology in oil monitoring and wear particle automatic recognition, the factors that depend on human knowledge and experience in its application have been overcome, which has laid a foundation for cement enterprises to apply this technology and improve equipment management level

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