اهمیت تشخیص زود هنگام مشکلات نگهداری در ماشین آلات دوار در مدیریت کارخانه ها: مطالعات موردی از کارخانه های سیم و تایر

In this article, importance of application of predictive maintenance concept with vibration measurement has been discussed. Appreciation of the subject was performed with the help of data collected cases related to maintenance problems from Plants A and B. The first case was examined in aerial conductor manufacturing Plant A. The company does not apply predictive maintenance (PM) in management of the manufacturing activities. The machines used in conductor and similar wire processing plants have very big rotors and their loads on rotors continuously change. Therefore, these types of machines are good examples in checking the health of the machine regularly. The second case was analysed in vehicle tyre plant named as Plant B and it has perfect usage ability of vibration technique of PM methods. The importance of the regular collection of vibration signatures in evaluation of conditions of rotating machines has been analysed in details to indicate the power of the predictive maintenance technique in prevention of losses, which are caused by unbalanced forces, misalignments, improper lubrication of ball bearings, metal fatigue and cracks occurred in welding of constructed parts and locking of the ball bearings due to excessive heating. The second case observed in Plant B is an example to show detection of a ball bearing failure just in time. Evaluation of second case has been performed using measurements of vibration signatures of the machines with the help of fault indicator graphics. Results from the cases have been summarised to give useful ideas in management of the plants to the persons responsible with production and maintenance subjects. Gadget timed out while loading

Maintenance strategies are very important in management of the manufacturing process. In the organisation plan of the factories, manufacturing and sales departments are prime importance. Maintenance department is considered as consumer of income of company. It is thought generally that they present always a plan to stop production machines for maintenance aims. To decrease maintenance cost yearly, several strategies have been developed. However, most of them require huge budget to keep the machine in good condition. That is why; companies seek a maintenance technique to spend money just in time. The technique accepted by the most companies is the PM (predictive maintenance). In our case studies, two companies have been considered. One of them is the “manufacturing plant of aluminium conductor and power cable” indicated here as Plant A. The other one is the “Automobile Tyre Production Plant” indicated here as Plant B. Plant A do not use predictive maintenance technique in the management of the process but Plant B uses it to follow the condition of machines regularly by collecting vibration data from the whole machines run in the production. The predictive maintenance by vibration analysis is the best tool for checking of the conditions of the machines regularly in the production activities. The vibration analysis is a technique, which is being used to track machine operating condition and trend deterioration in order to reduce maintenance cost and downtime simultaneously. This technique consists of vibration measurement and its interpretation. Firstly, vibration signal are collected by means of vibration analyser equipped with 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 forces outages, to maximize utilisation of available assets, to increase the life of the machinery, and to reduce maintenance costs related to health of machinery. The vibration measurements are taken periodically one time per month in general. Then, vibration signatures are monitored and compared previous measurements. The vibration monitoring is based on 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 is also changes. 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. 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 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 [1]. Al-Najjar observed many bearing vibration in paper mills for many years to predict remaining bearing life accurately. He also investigated effectiveness of vibration-based maintenance and proposed some findings [2]. Plants established to manufacture aerial or underground cables, telephone cables, bare conductors and fiber optic cables, steel rope manufacturing, pre-stressed steel ropes plants, etc. have similar wire drawing and stranding machines. All stranding machine includes a rotor loaded with bobbins (spools) loaded with drawn wires to strand required construction of conductor. Thus, unbalanced loads force machine bearings in all manufacturing time continuously. This type working conditions may reason failures of ball bearings early and unexpected accidents due to collapse of whole system. Some parts broken from the rotor body with high kinetic energy can destroy every thing by impacting.

Maintenance concepts of the two companies in management of manufacturing process have been analysed by considering man machine and production safety. Results have been determined as below: (a) The machines used in conductor and similar wire product processing plants such as steel rope, pre-stressed steel rope, tyre steel wires, telephone cable, etc. are forced dynamically by unbalanced loadings due to construction requirements of the wires (see Fig. 2). A typical rigid type wire-stranding machine for manufacturing of conductor or steel rope has been shown in Fig. 10b and Fig. 11. These machines, which can be considered as constructed several rotors with the weight of the spools changing related to processing time, have potential for catastrophically failures owing to locking of the ball bearings under insufficient maintenance service conditions. Thus, safety situations of workers, machines and products depend on the maintenance level applied in the plant. Supports constructed by ball bearings as a most critical part of rotating machines must be observed regularly by persons of production and maintenance departments to detect the abnormalities with the machines. In prevention of the accident analysed here, vibration signature of the machines should be checked up according to a software program regularly. Data collected from the machines must be evaluated systematically by that program and by experienced persons to find out failures before occurrence as indicated in the analysis of case study-2 from Plant B. (b) It has been shown that predictive maintenance eliminates two main problems in the industry simultaneously. Using PM technique, conditions of the machines are observed regularly. However, this is not a unique problem of the manufacturing companies. Companies are also responsible from the safety working conditions of all workers and staffs in the plant. Perhaps the most important problem in the manufacturing areas is the guarding of the workers from the threats, which are created by rotating big masses with high centrifugal forces. If vibration signatures of rotating machines show smoothness, the failure potential of the machine will be in minimum level. Thus, when the rotating stranding machines run without vibration, men–machine and production will be in safety. Because in the running stage of the machines, some of the workers are available between of them for maintenance or production aims. Thus it must be learnt from the case that predictive maintenance PM is not only a technique that is used to detect failure conditions of the manufacturing machines but it also guards the workers and staffs from the potential hazards in the manufacturing areas. (c) It is obvious that organisation of the predictive maintenances may result in increase of the number of the staff and fixed cost of the company. In addition to them, initial investment cost for implementation of the PM to the company is also high. These cause some disadvantages in getting permission from the top management for the technical staff that requires adopting this technique into company. However, maintenance and production departments know very well the power of the PM in management of the manufacturing process. So, they can tell them clearly the importance of the regular controlling of the machine conditions to save the money and ways in getting rid of possible risks summarised in the article.