Demiryollarında ray birleştirme yöntemlerinin incelenmesi, alüminotermit ve yakma alın kaynak yöntemlerinin karşılaştırılması
Investigation of rail joining methods, comparison of aluminothermic and flash-butt welding methods in railways
Yazar: FATİH ÖZKUL
Danışman: PROF. DR. ZÜBEYDE ÖZTÜRK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Ulaştırma Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Günümüz dünyasında demiryolu taşımacılığı çok yaygın olarak kullanılmakta, özellikle hızlı tren projeleri birbiri ardına hizmete girmektedir. Dünya ile paralel olarak ülkemizde de, demiryolu taşımacılığına önem verilmeye başlanmış ve yüksek hızlı tren hatları inşa edilmiş ve edilmeye devam etmektedir. Demiryollarına yapılan yatırımlar, ülkemizde taşımacılık alanında yeni bir devrin başlangıcı kabul edilebilmektedir. Demiryollarının kapasitesinin yüksek olması, düşük arazi kullanımı, çevreci olması ve ekonomik avantajları sebebiyle, demiryolu taşımacılığı her geçen yıl önemini daha da artırmaktadır.
Demiryolu taşımacılığında konfor ve emniyete etki eden faktörler arasında ray birleşim bölgeleri önemli bir yer tutmaktadır. Ray birleşim bölgeleri, hatların en zayıf bölgelerinden biridir. Konfor, emniyet ve maliyet açısından önemine bağlı olarak bu bölgelerin imalatına özen gösterilmesi gerekir. Ayrıca demiryolu bakımlarında en önemli kesimlerinden biri ray birleşim bölgeleridir.
Demiryolu rayları günümüzde genellikle sürekli kaynaklıdır. Kaynaklı ray birleşim bölgeleri, cebireli birleşimlere göre çok daha az bakım gerektirmektedir. Ayrıca araç tekerleklerine çok daha az zarar verdiği için, son yıllarda artan araç hızlarına uygun ray birleşimini sağlar. Ancak, zamana bağlı yorgunluk, daha yüksek tren hızları, yüksek aks yükü ve artan trafik yoğunluğu nedeni ile kaynakların hasar görmesi muhtemeldir.
Dünya genelinde, demiryolu hatlarının imalatında 4 tip ray birleştirme kaynağı uygulanmaktadır. Bunlardan en yaygın olarak kullanılanları, alüminotermit ve yakma alın kaynağı yöntemleridir.
Bu çalışmanın amacı; öncelikle ray birleştirme yöntemlerinin incelenerek çalışma prensiplerinin ve yöntemlerinin tespitidir. Ayrıca en yaygın olarak kullanılan ray birleştirme yöntemi olan ray kaynak yöntemlerinden alüminotermit ve yakma alın kaynak yöntemlerinin incelenmesi ve bu iki yöntemi maliyet ve teknik açıdan karşılaştırarak en avantajlı yöntemi tespit etmektir.
Çalışmada öncelikle bir demiryolu hattının üstyapısı ve üstyapının görevleri hakkında genel bilgiler verilmiştir. Bunun yanı sıra, demiryolu hatlarının en önemli elemanı olarak kabul edilen raylar hakkında bilgi verilmiş; rayın yapısı, kimyasal ve mekanik özellikleri ve görevleri genel hatlarıyla incelenmiştir.
Çalışmanın devamında cebireli ray birleştirme yöntemi, cebirelerin teşkili ve düzenleme şekilleri genel hatlarıyla incelenmiştir. Cebire düzenleme şekillerinin demiryolu üstyapısına ve araçlarına yapacağı etkilere değinilmiştir.
Ardından uzun kaynaklı raylar konusu incelenmiştir. Öncelikle rayların kaynak kullanılarak birleştirilmesinin, cebire ile birleşime göre meydana getirdiği avantajlar, devamında uzun kaynaklı ray yapım koşulları, uzun kaynaklı ray uygulanacak
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hatlarda yolda alınacak önlemler ve ray gerilimlerinin alınması hakkında bilgiler verilmiştir.
Çalışma, yaygın olarak kullanılan kaynaklı ray birleştirme yöntemleri olan alüminotermit ve yakma alın kaynağının incelenmesiyle devam etmiştir. Öncelikle alüminotermit kaynak yöntemi incelenmiş; kaynak uygulamasında kullanılan ekipmanlar, kaynak uygulama aşamaları ve dikkat edilecek hususlar ayrıntısıyla incelenmiştir. Benzer şekilde yakma alın kaynağı incelenmiş; avantajları, uygulama aşamaları ve kaynak uygulamasında dikkat edilecek hususlar hakkında ayrıntılı bilgiler verilmiştir.
Daha sonra ray kaynaklarına uygulanan tahribatlı ve tahribatsız test yöntemlerinden bazıları hakkında genel bilgiler verilmiş ve bu yöntemler genel hatlarıyla incelenmiştir.
Çalışmanın sonunda, çalışmanın hedefi olan alüminotermit ve yakma alın kaynak yöntemleri, maliyet ve teknik yönleriyle incelenerek karşılaştırılmıştır. Maliyet olarak incelemede; her iki yöntemin amortisman, malzeme, işçilik ve diğer maliyetleri, güncel fiyatlar kullanılarak incelenmiş ve karşılaştırılmıştır. İnceleme sonucunda yakma alın kaynağının alüminotermit kaynak yöntemine göre çok daha avantajlı olduğu sonucuna varılmıştır. Teknik incelemede; Aksaray-Havalimanı hafif metro hattında yapılan ray ultrasonik ölçüm sonuçlarından yararlanılmıştır. Yapılan ölçümlerin sonuçları incelendiğinde; yakma alın kaynaklarında meydana gelen ray kusuru sayısının, alüminotermit kaynaklarda oluşan kusur sayısına göre oldukça az olduğu tespit edilmiştir. Ayrıca, her iki yöntemin sertlikleri, dayanımları ve kaynak yapım süreleri karşılaştırılmış ve yakma alın kaynak yönteminin tüm bu karşılaştırmalarda avantajlı olduğu belirlenmiştir.
Sonuçların tamamı incelendiğinde; yakma alın kaynağının, alüminotermit kaynağa göre tüm yönleriyle avantajlı olduğu ve günümüzde uygulanabilecek en güvenilir ray birleştirme yöntemi olduğu sonucuna varılmıştır.

Abstract:
Railway transportations such as high-speed train lines become widely used in recent years. The railway transportation is an area of growing interest for Turkey too. The high-speed train lines has been built since last years. Economic investments for this type of transportation are accepted as the beginning of a new era in that area.
The railway transportation has been becoming more crucial lately because of its high capacity, effective land use, being enviromentally friendly and economical advantages.
Rail junction zones has an important place among the factors effected the safety and the comfort in railway transportation. The superstructure of railways should be mentioned at first.
The elements and materials which are furnished on infrastructure for providing to course vehicle safely, comfortably and economically is called superstructure. It can be understood from the definition that, superstructure not consist only the rails. Superstructure is the group name consisted of rails, ballast layer of concrete beams under-rail, rail fasteners and sleepers. The rails act as a guide to vehicle wheel and provide to wheels a certain contact surface. Rail fasteners provide connection between the rails and sleepers or under rail concrete. Rail fasteners and sleepers, protect the gauge and transfer the loads from the rails. Ballast is the name of the tough and rugged stones which was broken in size of 30-60 mm. Ballast layer transmitted the load from sleepers to infrastructure.
Providing a uniform and smooth rolling surface for rail vehicle along the way, transmitting static and dynamic loads from rail vehicle to infrastructure safely and partly reducing without causing changing in the shape, having sufficient elasticity, it can be easily restored when it becomes distorted, having ability to drain the water on its surface and having long service life and being economically.
Rail junction zones are one of the weakest points of the tracks and depending on the importance of comfort, safety and cost, these areas must be produced carefully. Moreover, rail junction zones are one of the most important parts in railway maintenance.
Nowadays, the railway tracks are usually welded continously. Welded rail joints require less maintenance than the joinings with fishplate. Also, because of less damage to car wheel, it provides suitable rail junction for the increasing train speed recently years. However, the time dependent fatigue, higher train speeds, high axle load and increased traffic density, cause damages to rail weldings. The role of rail welding should be mentioned at this point. Some of these are; the welding of rails increases the life of rails due to decrease in wear at ends, results in decrease in the maintenance cost to the extent of about %25, it results in comfort of passengers due to smooth working of the track (if welded rails are used), the creep is considerably reduced, if welded rails are used in the track, for track circuited and electrified tracks,the welding of rails affords better results, the welded rails are helpful on large bridges as rails of length equal to each span give better performance and reduce the effect of impact, the welding of rails decreases construction cost due to less number of rail joints, the tractive effort is reduced due to the elimination of the loss of strain energy and impact energy at rail joints and hence it increases effective fuel use, the risks of sabotages and the accidents are considerably decreased because of long length of rails and absence of many joints, the use of long welded rails affords more lateral, longitudinal and vertical stability to the track and the rail coaches and vagons with reduced weights can be used on the welded track.
Welding technologies for railway lines setting are still in progress. There are wide range of welding processes with strong stress on productivity and safety. Inspection of rail welds is important issue due to there are a lot of risks at railway lines transport. Contemporary technologies are very important in that global traffic.
Aluminothermic welding and flash-butt welding processes are used in construction and maintenance of railway lines. They are cost effective and reliable if they are performed under strict conditions and welding parameters in workshop as well as on site. Beside short fundamentals of those welding processes, experimental results of microstructure examinations of individual zones in welded joint (weld metal and heat affected zone) and hardness distribution in welded joints.
In railways there are four types of welding methods, the most commonly used methods are aluminothermic and flash-butt welding methods.
The main aim of this study is; to investigate the rail joining methods, to determinate the working principles and methods, to investigate the most widely used rail joining methods aluminothermic and flash-butt welding, and to compare the two methods economically and technically and to determine the most advantageous methods. Creating a guiding resource for individuals and institutions, who are interested with the railways superstructure, is within the scope of this work. In the study firstly, general informations are given about the railway superstructure and the tasks of railway superstructure. In addition to this, informations are given about the rails, which are considered the most important element of railway superstructure, and rail structure, rail chemical and mechanical properties and their tasks are examined in general terms.
Afterwards, rail junction method with fishplate, the constitute and arrangement of fishplate are examinated in general terms. Relating to the structure of the railroad, continuousness of bearing surface of the rail is essential. There are points which damages the continuousness of bearing surface of the rail and which requries certain qualifies.
One of the most important of these points is fishplates. If fishplates are according to mitre difference of rail head on two mutual strings, they are arranged with two ways as both sides. If the fishplates are installed upon the traverse in accordance with the rails, they are applied as supported, cantilever and unmoving fishplate. Because negative effects of supported and unmoving fishplates do not occur in the cantilever fishplate system, the cantilever fishplate is usually applied at the rail system. Disability of the cantilever fishplate is to occur breakings at vehicle and superstructure. It is mentioned in this study to the effects of fishplates to railway superstructure and trains.
After that, long welded rails are examined. Combining the rails of various size and obtaining long length rails are called long welded rails. The increasing of the train weight and speed continously and the progress in the production of rail and switch, required a development in the instructions of construction and maintenance of the railways. Because of this necessaries, the welding technologies should be developed.Firstly, general information are given about, the advantages of using welding methods than using fishplate in the rail joining, long welded rail construction conditions, precautions will be taken in the tracks for construction long welded rail and receiving rail tension.
The study continues with the investigation of the commonly used rail joining methods, aluminothermic and flash-butt welding. Firstly, aluminothermic welding method, the equipment used in welding applications, application stages in weldings and the points to be considered are examinated in detail.
Aluminothermic welding is a process which produces coalescence of metals by heating them with superheated liquid metal from a chemical reaction between ametal oxide and aluminium with or without the application of pressure. The heat for welding is obtained from an exothermic reaction between iron oxide and aluminium by the following formula:
Fe2O3+2Al → 2Fe+Al2O3+850 kJ
Maximum temperature released as a result of aforementioned reaction is approximately 3000°C. The preheating by gas flame is applied before railway lines welding by aluminothermic welding process. The effective time of chemical reaction and welding is less than a few minute but whole procedure with preparing time and post processing time is over 1 hour.
Similarly the advantages, application stages, and the points to be considered in flash-butt welding are examinated in detail.
Flash-butt welding is resistance welding process which produce coalescence simultaneously over the entire area of abutting surfaces or progressively along a joint, by the heating obtained from resistance to electric current through the area where those surfaces are in contact.
Next, general information are given about some of the destructive and nondestructive test methods and these test methods are examinated generally. These tests are hardness test, fatigue test, static bending test, ultrasonic testing, micro structure test and chemical analysis test.
At the end of the study, aluminothermic and flash-butt welding methods are examinated and compared with their technical and cost aspects as the objective of the study. As the cost examination; the depreciation, materials, labor and other costs of both methods are examinated and compared using current prices. As the result of examination, it is concluded that flash-butt welding has more advantages over the aluminothermic welding method.
At the technical examination, rail ultrasonic measuring results of the Aksaray-Havalimanı light metro line, where aluminothermic and flash-butt welding methods are both applied in the track, are utilized. It is observed with analyzing the results of the measurements that the defects occurring at the flash-butt welding are very few than aluminothermic welding. Also, the hardness of both processes, strength and welding time are compared and it is found that, flash-butt welding is advantageous in all comparison.
Considering all of the results, it is determined that flash-butt welding is advantageous in all comparison over aluminothermic weldings and it is concluded that flash-butt welding can be applied today to be the most reliable rail joining method.
The results are base for further investigations relating to reliability and safety of welded joint at railway lines as well as investigations of repair procedure influence on quality of these weldments.