نظارت بر لرزش برای تشخیص نقص و یاطاقان های عنصر نورد به عنوان یک ابزار نگهداری پیشگویانه: مطالعات موردی جامع

Vibration monitoring and analysis in rotating machineries offer very important information about anamolies formed internal structure of the machinery. The information gained by vibration analysis enable to plan a maintenance action. In this study, the vibration monitoring and analysis case studies were presented and examined in machineries that were running in real operating conditions. Failures formed on the machineries in the course of time were determined in its early stage by the spectral analysis. It was shown that the vibration analysis gets much advantage in factories as a predictive maintenance technique.

The failures of rotating machineries can be very critical because these lead to machinery damage, production losses and personnel injury. So, a very important duty of the maintenance department is to prevent these failures when they are in its initial stage. The predictive maintenance by vibration analysis is the best tool for this purpose. The vibration analysis is a technique, which is being used to track machine operating conditions and trend deteriorations in order to reduce maintenance costs and downtime simultaneously [1]. The vibration analysis technique consists of vibration measurement and its interpretation. Firstly, vibration signals are collected by means of the vibration analyzer equipped with a sensor in the time domain then, these signals are converted into frequency domain by processing FFT, and the information gained from the vibration signals can be used to predict catastrophic failures, to reduce forced outages, to maximize utilization of available assets, to increase the life of machinery, and to reduce maintenance costs related to health of machinery [2]. The vibration measurements are taken periodically, one time per month in general and vibration is monitored by comparing previous measurements to new ones. The vibration monitoring is based on the principle that all systems produce vibration. When a machine is operating properly, vibration is small and constant; however, when faults develop and some of the dynamic processes in the machine change, the vibration spectrum also changes [2]. There are many studies on the vibration monitoring of the rotating machinery. Great amount of them concentrate on ball or cylindrical element bearing vibration monitoring [3], [4], [5] and [6]. In these studies a test rig, includes ball or cylindrical roller bearing, is used and either an artificial defect is formed on bearing parts or the test rig is running until a desired defect arise on the bearing in laboratory conditions. These studies were partly realized by ideal condition assumption. However, under conditions of real environment there are many factors that affect the actual running state of the machinery. Thus, these factors must be taken into consideration. Studies related to real operating conditions of machineries were quite few. Gluzman [7] monitored vibration of motor-generator system supported by ball and cylindrical roller bearings to predict impending bearing failures. He successfully identified impending failures of the bearing outer and inner races. Al-Najjar [8] observed many bearing vibrations in paper mills for many years to predict remaining bearing life accurately. He also investigated effectiveness of vibration-based maintenance and proposed some findings. In this study, the application of vibration monitoring and analysis was carried out on the machineries in a petroleum refinery. The vibrations of the machineries were monitored for a certain period and diagnosing of defects arised on the bearings of the machineries during this period was aimed. The study includes three different case studies that were obtained from the machineries, which run under real operating conditions.

In this study, diagnosing techniques of the ball and cylindrical roller element bearing defects were investigated by vibration monitoring and spectral analysis as a predictive maintenance tool. Ball bearing looseness, a ball bearing outer race defect and a cylindrical bearing outer race defect were successfully diagnosed. It was shown that ball and cylindrical roller bearing defects were progressed in identical manner without depending on rolling element type. Furthermore, it was experienced that when a bearing defect reaches an advanced stage, high frequency amplitude levels often decrease due to ‘self-peening’ of the bearing flaws. Remaining life of the bearings can be estimated using vibrational behaviour and running time of the bearings. Diagnosing of defects on multiple parts of the bearing may also be investigated in a real running condition. Also, it can be concluded that if vibration monitoring is applied within regular selected periods, capable instrumentation and if vibration analysis is performed by experienced personnel, impending failures can be easily detected.