Abstract: At present, my country has introduced a large number of high-speed, wide-width, and highly automated papermaking machinery and equipment. However, after long-term operation, various types of equipment failures will inevitably occur, affecting the normal operation of the equipment. This paper mainly discusses the diagnosis of main faults of papermaking machinery and proposes corresponding maintenance methods to improve the efficiency of papermaking machinery and equipment operation.
Keywords: papermaking machinery; condition monitoring; fault diagnosis
Introduction
With the continuous advancement of science and technology, the development of the paper industry is no exception. In the production process of the papermaking industry, many machines are used, and mechanical failures will inevitably occur. At this time, timely measures should be taken and the correct method should be selected for maintenance to ensure the normal and safe operation of the papermaking machinery.
1. Typical characteristics of modern mechanical failures
From the perspective of fault diagnosis, modern mechanical faults generally have the following characteristics:
1.1 The complexity of causality
As the functions and structures of modern mechanical systems become increasingly complex, the causes of mechanical failures also become more complex. Symptoms, faults and causes often overlap in various ways, and a single fault is commonly attributable to multiple causes. For example, excessively slow hydraulic actuator motion may result from inadequate lubrication, actuator wear, excessive load, leakage within the system, a faulty pressure-control system, excessive guideway error or a faulty speed-control system.
In addition, a certain fault source can also cause multiple symptoms, and a certain symptom may be caused by the combined action of multiple fault sources.
1.2 The fault point is relatively hidden
Failure and damage of mechanical systems are usually caused by deep internal causes. Since the disassembly and assembly of most mechanical systems are complicated and cumbersome, there are usually no effective detection conditions at the fault site, so it is difficult to determine the source of the fault. At the same time, because symptoms that can be directly observed by the naked eye are effective after all, coupled with the influence of many uncertain factors, it is difficult to analyze mechanical faults.
Uncertainty about factors related to 1.3
During routine operation, many mechanical systems are vulnerable to failures caused by a variety of uncertain factors, such as changes in ambient temperature, fluctuations in grid voltage and the ingress of external contaminants. This uncertainty is also reflected in the nonlinearity, nonstationarity and non-Gaussian distribution of relevant signals. These factors often make the location and development of mechanical system failures difficult to determine. As a result, fault signatures may be weak, making it difficult to accurately identify and analyze the source of a mechanical failure.
2. Vibration monitoring and papermaking machinery fault diagnosis and maintenance
2.1 Introduction to Vibration Monitoring Technology
According to relevant statistics, more than 60% of mechanical equipment failures are caused by mechanical vibration. Vibration is closely related to the operating status of the mechanical system. With the rapid development of my country's papermaking industry in recent years, large, complex, and refined papermaking machinery has also developed rapidly. As a result, the vibration problem of papermaking machinery engineering has become more and more prominent. At present, the daily monitoring and maintenance of many medium and high-speed papermaking machinery increasingly rely on online vibration monitoring technology.
Vibration monitoring and fault diagnosis for papermaking machinery use signal-processing techniques to analyze collected vibration data, followed by pattern recognition to determine whether equipment is operating abnormally, locate faults and identify their causes, or predict failures. These methods help keep papermaking machinery operating normally, provide good real-time performance and are easy to integrate with the equipment. They also reduce maintenance costs and improve economic returns. Analyzing and studying this technology therefore has substantial practical significance.
2.2 Main distribution of vibration monitoring parts of papermaking machinery
State vibration monitoring and fault diagnosis of paper-making machinery are mainly divided into two aspects: detection and diagnosis of paper-making machinery operating performance and paper-making machinery operating status.
(1) Operating-performance monitoring is carried out by measuring vibration, pressure pulses, rotational speed and paper quality. Its main focus is the effects of various rotating machinery components on the paper machine during operation. Measurement points are connected to a computer monitoring station, where the measured signals are processed using time-synchronous averaging. The relevant trend data, measurement data and application calculation results are stored. Trend data allows detailed calculation and analysis of spectra and time-domain signals and is mainly used to analyze the magnitude of changes in different parameters.
Nip vibration, paper quality and headbox pressure fluctuations are the targets to be monitored. Changes in these monitored parameters are reflected and displayed to monitoring personnel in the form of proportions occupied by each monitoring device. The main monitoring points are located at post-screen pressure measurement, drying pulse generator, pump pulse generator, tube bundle pressure measurement, sizing pump pressure measurement, nip roller vibration, nip roller pulse generator, scraper loading pressure vibration, roller vibration, roller pulse generator, etc.
② Operating-condition monitoring uses vibration measurements to monitor papermaking machinery. It can detect mechanical faults early and allow timely maintenance and repair, supporting normal operation and reducing unplanned downtime. Sensors and analysis stations are the main monitoring equipment. Vibration signals are measured systematically and the results used to calculate time-domain signals, envelopes and frequency spectra.
3. Oil analysis technology and papermaking machinery fault diagnosis and maintenance
3.1 Application overview of oil analysis technology in my country
The earliest scientific research in China using oil analysis for equipment condition monitoring began in the late 1970s. In 1982, Guangzhou Mechanical Engineering Research Institute imported a FOXBORO dual ferrograph analyzer from the United States to monitor machinery operating conditions. In 1983, it imported a PC-320 automatic particle counter from another American company to measure contamination in hydraulic and lubricating oils. From 1984 to 1988, it monitored the mechanical operating conditions of Dongfeng diesel locomotives using infrared spectroscopy, ferrography, and particle counting in combination with scanning electron microscopy.
3.2 Oil analysis technology and monitoring equipment operating status system
The lubricating oil used in machinery can reveal substantial information about equipment operating conditions. Monitoring equipment during normal operation and analyzing wear particles and changes in the properties of its in-service lubricating oil provides information about wear debris and lubrication conditions. This allows timely assessment of equipment operation and prediction of failures, identifying the type, causes and precise location of mechanical faults. It provides useful reference information for correct maintenance and allows suitable repairs before a failure occurs. This reduces maintenance costs and lost working time while improving equipment utilization, service life and safety.
3.3 Contents of Oil Analysis Technology
Oil analysis has two main aspects: analysis of the lubricant's own properties and analysis of the wear particles it carries. In-use oil is collected from machinery, then its particles are analyzed qualitatively and quantitatively alongside the oil's properties to assess operation and predict or diagnose faults. Lubricant-condition analysis mainly examines physical and chemical indicators and contamination, particularly oil degradation and the contamination or depletion of additives.
The number of wear particles, particle chemical composition, particle size distribution and geometric shape are the main aspects of lubricating oil wear particle analysis. Through this analysis, the wear type, degree and location of mechanical equipment can be more accurately judged, which will facilitate further exploration of the wear mechanism of mechanical parts.
4. Conclusion
Mechanical fault diagnosis and maintenance technologies continue to develop with scientific and technological progress and social development, becoming increasingly intelligent and diverse. Extensive practical experience in China and abroad shows that vibration monitoring and oil analysis are effective methods for diagnosing faults and maintaining modern papermaking machinery. Papermaking machinery is becoming larger, faster, more complex, and increasingly continuous in operation. Condition monitoring and fault diagnosis centered on online vibration monitoring are therefore an inevitable part of the development of predictive maintenance for this machinery.
At the same time, because there is very little research on oil technology in diagnosing and repairing modern papermaking machinery in my country's papermaking industry, its application is far less common than vibration monitoring technology. However, we must see the potential value and research significance of oil analysis technology and pay more attention to its analysis and research.
References:
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[4] Zhang Hui. Application and development of papermaking machinery condition monitoring and fault diagnosis technology [J]. China Papermaking, 2003 (11): 53-56.
(Source: Internet)