Makina performansının titreşim analizi metodları yardımıyla belirlenmesi ve rulmanlarda titreşim analizi ile hasar tesbiti

Abstract

Bu çalışmada öncelikle mevcut bakım sistemleri tanıtılmış, bu bakım sistemlerinin avantaj-dezavantajlarından bahsedilmiş, en yaygın olarak kullanılmakta olan "Makina Perfonmansının İzlenmesine Dayalı Bakım Tekniği" uygulamalarına yer verilmiştir. Saha verilerinin toplanmasında kullanılan transduser tipleri ve montaj şekilleri tanıtıldıktan sonra, titreşim analizi teknikleri ile rulman hasarlarının tesbit edilmesi ve rulmanlarda titreşim iletimi esasları üzerinde durulmuştur. Rulman hasarının rulmanı meydana getiren parçalardan (iç bilezik-yuvarlanma elemanı-dış bilezik) hangisinde olduğunu belirlemede kullanılan formüller deneysel çalışma ile gerçeklenmeye çalışılmıştır. Önerilen formüllerin deneysel sonuçlar ile uyumunu gözlemlemek amacıyla bir deney tesisatı kurulmuş ve tek hasara sahip rulman dış bileziği, yuvarlanma eleman üzerinden alman titreşim genliği ölçümleri, hasarsız referans rulman titreşim genlikleri ile karşılaştırılmıştır. Deneyler öncelikle yüksüz olarak dört farklı devirde dış bileziği hasarlı, yuvarlanma eleman hasarlı ve hasarsız referans rulman üzerinde tekrarlanmış ve rulmanlara ait titreşim spektrumlar alınmıştır. Daha sonra 100 Newtonf luk eksenel yönde uygulanan kuvvet ile üç farklı devirde, dış bileziği hasarlı, yuvarlanma elemanı hasarlı ve hasarsız referans rulman üzerinden yüklü titreşim spektrumlar ölçülmüştür. Önerilen formüller ile teorik olarak hesaplanan hasar frekanslarına ait harmoniklerde pik değer gözlenmekle birlikte titreşim analiz cihazında 1*RPM, 2*RPM, 3*RPM ve 50 Hz gibi farklı kusurlara ait olabilecek frekans harmonikleri elimine edilemediği için, rulman hasar frekansına ait pik titreşim genliği değerleri kimi ölçümlerde çok net olarak gözlenememiştir. Uygulamalar sırasında uzun çalışmalara rağmen giderilemeyen yüksek sürtünme kuvvetlerinden kaynaklanan tahrik mili sıkışması nedeniyle eksenel ve radyal yükleme tertibatlarının eflektif olarak kullanılması mümkün olmamıştır. Deneyler sadece 100 Newtonfluk eksenel kuvvetin uygulanması ile sınırlı kalmıştır.

Have you ever heard someone say, "Something is wrong with this machine; it's making a funny noise! ", or," It's running rough-I can feel it." ?. It is natural to associate the condition of a machine with the level of noise or vibration it makes. And if it shakes or rattles more than usual, you begin to suspect mechanical trouble. This idea of relating a machine's condition with its level of vibration is not a new one. Since the mid-1950's, the measurement and the analysis of vibration has become an increasingly useful technique for controlling machinery condition. This technique is called MECHANALYSIS. MECHANALYSIS is the contraction of two terms: MECHanical and ANALYSIS. This word applies to machinery vibration, shaft movement, temperature and any other condition that permits us to determine a machine's condition during normal operation. Mechanalysis techniques do work and the reasons are fairly simple: First, it is natural for machines to vibrate. Even machines in the best of operating conditions will have some vibration because of minor defects as a result of manufacturing tolerances. Therefore, each machine- whether it's a 10.000 RPM compressor, a steam-turbine generator, a lathe or a vacuum cleaner- will have a level of vibration which may be regarded as normal or inherent. Second, when machinery vibration increases or becomes excessive, some mechanical trouble is usually the reason. Machinery vibration levels just do not increase or become excessive for no reason at all. Something couses it unbalance, worn gears or bearings,looseness, etc. Finally, each mechanical defect generates vibration in its own unique way. This makes it possible to positively identify a mechanical problem by simply measuring and noting its vibration characteristics. If you are participating in a carefully conducted mechanalysis program, you can learn to recognise small increases in vibration and read the machine's vibration "signature" long before the defective component will actually fail. A good mechanalysis program makes it possible for you to detect an impending program, analyze its cause and take appropriate corrective action before the failure actually occours. The success of a company often depends on the continued, safe and productive operation of rotating machinery. An effective maintenance program is vital to this kind of success. The quality of maintenance program determines how long the machines will run, how safe they are for the people working around them, and how productive the machine will be. You can bear these things in your mind while considering the following benefits of a mechanalysis program in greater detail. 1. Prolongs Machinery Life Xlll Expensive production machinery and plant support equipment can be maintained at a level where it will meet or even exceed its expected service life. This means you can reduce its long-term capital investment in new machinery, while maintaining the same level and quality of production. 2. Minimizes Unscheduled Downtime Unexpected breakdowns play havoc with production schedules and dramatically increase production costs. An effective mechanalysis program lets you defect a problem before it becomes critical. You can then schedule a maintenance shutdown at a time better suited for production and operating schedules. 3. Eliminates Unnecessary Overhauls Annual inspections and routine overhauls cost time and money. In order to prevent unexpected breakdown, machines are often taken off line and disassembled when there is actually nothing wrong with them. Mechanalysis allows a machine to run continuously until you detect the earliest stages of a problem. This often means you can run the machine for much longer periods of time than a preventive maintenance schedule would allow. 4. Eliminates Standby Equipment Idle standby equipment is no longer a prudent investment for new or expanding facilities. Standby, or redundant, machinery is intended to maintain operations in the event of unexpected breakdown. A good mechanalysis program can prevent unexpected breakdown, allowing you to schedule a maintenance shutdown at a time when it will have minimal effect on normal operations. 5. Provides More Efficient Operation Undesirable vibration and associated noise degrade working environments, cousing needless employee fatigue, raising the potential for accidents, and generally lowering worker productivity. Although a certain amount of noise is inherent in the operation of machinery, a good mechanalysis program can held keep machines running at minimum inherent noise levels. 6. Increases Machinery Safety Certain class of machinery defects pose serious safety hazards. The risk to personnel in the area rises as the defect reaches a critical point, and in some instances, the obvious signs of trouble appear only moments before a dangerous catastrophic breakdown occours. A good mechanalysis program lets you see the "signatures" of breakdown conditions long before the situation gets out of hand. 7. Improves Quality Perfonmance Quiet, smooth-running machinery is a vital element in the production of high quality products and reliable services. By maintaining a low level of machinery vibration, a good XIV mechanalysis program helps to assure a high level of product quality, and minimizes the occourrenge of reject parts. 8. Improves Customer Satisfaction Satisfied customers are the basis for profitable repeat business. Companies that produce rotating equipment can use the techniques of mechanalysis to deliver well-balanced and alighned equipment. This assures customer satisfaction during start-up in the field. Here, if we consider the three ways that machines can be maintained: 1. Breakdown Maintenance With breakdown maintenance, a machine is allowed to run until complete failure, inefficiency or product spoilage forces a shutdown. Although many machines are maintained in this way, breakdown maintenance has several disadvantages. First, failures can be most untimely and, there is little one can do beforehand to anticipate tool, manpower and replacement part requirements. Secondly, machines allowed to run until failure often require more extensive repair than would have been required if the problem had been detected and corrected early. Some failures can be catastropic, requiring total replacement of the machine. This also suggests a safety problem to operators and other personnel. In addition, the added cost of lost production while the unit is down can be staggering. 2. Scheduled Maintenance Compared to breakdown maintenance, a program of periodic disassembly and inspection has the distinct advantages of lessening the frequency of breakdown repairs and permitting scheduled shutdown. Under this program each critical machine is shut down after a specified period of operation and partially or completely dismantled for a through inspection and replacement of worn parts-if any. This approach to machinery maintenance, too, has disadvantages. First, to periodically dismantle every critical piece of equipment in the plant is expensive and time consuming. Second, the interval between periodic inspections is difficult to predict. If the program is so successful! that no machinery failures occour, it may be that the interval is too short and the money is being wasted. Third, a machine is operating satisfactorily may actually be degraded by frequent disassebly. There is always a chance that a gasket or seal will be improperly installed, bolts not tightened properly, or the original alignment or balance of the machine disturbed during reassembly. In addition, some machinery problems such as unbalance are evident only during operation. 3. Predictive Maintenance-Mechanalysis On line detection and diagnosis of machinery problems is obviously the most desirable way to maintain machinery. If a problem can be detected early, when defects are minor and do XV not affect machine operation, and if we can diagnose the nature of the problem as the machine runs:... Shutdown for repairs can be scheduled for a convenient time. A work schedule, together with the requirements for manpower, tools and replacement parts can be prepared before the scheduled shutdown. Extensive damage to the machine resulting from forced failure can be minimized. Repair time can be kept to a minimum, resulting in less machinery downtime. Of course, machines in good operating condition can continue to run as long as no problems develop. Time and money are not wasted dismantling machines which are already operating smoothly. Importance Of Detecting Bearing Faults With Mechanalysis: The continuous progress of some significant branches in technology (the manufacture of flight vehicles, instruments and machine tools, automative, electric machine engineering, and other industries) is linked with the use of numerous rolling contact and sliding bearings. In many cases, perfonmance of the instruments and devices is highly dependent on dynamic phenomena taking place in bearings. This is why the question of technical diagnosis of the bearing assembly, which by itself represents an autonomous rotary system which is the basic source of all undesirable disturbances in the machine or instrument as a whole. This can be exemplified by gyroscopic instruments in which the friction torque in the bearings causes appreciable deterioration of the dynamic characteristics of the whole setup due to vibrations. In tape recorders, oscillations in the speed of tape movement measured by the coefficient of detonation are caused by defects in the geometric sizes, accuracy of rotation, and variation in friction torques in the ball bearings used as the rolling contact support of all the rotating components (tone shaft, guide rollers, etc.). In recent years, extensive studies aimed at determining dynamic characteristics of the bearings and rotor systems working under different conditions have been carried out. All phenomena taking place in the bearing assemblies are to greater or lesser extent related to vibrations. Consequently, a change in the friction torque, varying parameters of a lubricating film in bearings, oscillations of rings, and other processes may be treated as vibrational changes. Methods of analysis and data processing for these prosesses are identical and thus all the processes in this study are considered under the common headline of vibratory process. In this study we tried to verify the common formulas which are used to find out the real damages location exactly. By the help of these formulas it is possible to find out which component of the bearing has the damage that causes vibration. We built up a test stand to make measurements in different shaft speeds and under different bearing loads. To make our diagnostic ability more efficient necessitates first studying the processes which take place in bearings and bearing assemblies. XVI The tasks posed to the industry may successfully be solved by improving the quality and expanding the capabilities of technical means for the control and measurement of parameters of bearings and rotor systems. Registration of the parameters, however, has only an auxiliary character, because the basic goal of measurements is to facilitate the diagnosis of the object being tested by taking into account its dynamic characteristics.