Eckart Uhlmann; Mykola Bobyr; Yuriy Borodiy; Pavlo Lypovka; Pavel Protsenko; Janis Thalau
Abstract
As societies have a rising demand regarding mobility as well as an increasing ecological awareness, the energy efficiency, noise emissions and availability of transportation in urban environments become essential for growing cities. In this context, the role of rail-bound traffic in urban environments ...
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As societies have a rising demand regarding mobility as well as an increasing ecological awareness, the energy efficiency, noise emissions and availability of transportation in urban environments become essential for growing cities. In this context, the role of rail-bound traffic in urban environments as well as in intercity-connections is of rising importance. To guarantee travelling comfort and safety, shorter downtimes as well as power efficiency, the condition of the railway network is subject to rising quality requirements. Therefore, the maintenance, repair and overhaul as well as the material quality of railway-tracks is faced with new challenges. An important part of track maintenance is track grinding. To ensure an economically reasonable track life cycle and to prolong the time period between repair tasks, grinding processes should not induce damage such as cracks and hardening. On the other side, high productivity of track grinding, which tends to induce damage, is crucial to reduce disruptions and delays from repair. Research work presented in this paper aims at reducing the lack of knowledge concerning interactions between the track grinding parameters, grinding tool specifications and the topology of the track’s surface and damage of the track’s sub surface. Industrial track grinding processes were tested under laboratory conditions with a variation of the grinding wheel circumferential speed and depth of cut. Afterwards the ground tracks specimens were evaluated with regard to the achieved surface roughness as well as the micro-hardening, induced cracks and residual stresses in the sub surface zone. Furthermore, the influence of different external factors such as environmental conditions on the results of track grinding is analysed by evaluating the influence of the track’s initial temperature on the process results. As a result, the main influencing factors on the surface quality and the sub surface damage in track grinding were identified and their influence on the tribological behaviour of the ground tracks in contact with an opposing steel disc was analysed. Based on these considerations, recommendations on eligible track grinding strategies, which lead to highly productive yet low-damage track repair, are derived.
Eckart Uhlmann; Patrick John
Abstract
The main advantages of cutting with liquid jets are the flexibility and consistently sharpness of the tool, which allows the machining of a variety of materials and complex shapes. Unfortunately, the humidification of the components can be a problem for certain applications and inhibits the spread of ...
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The main advantages of cutting with liquid jets are the flexibility and consistently sharpness of the tool, which allows the machining of a variety of materials and complex shapes. Unfortunately, the humidification of the components can be a problem for certain applications and inhibits the spread of jet technology. Besides, the dry and residue-free cutting of materials is an important topic of today’s research in manufacturing engineering. Due to these advantages, high-pressure liquid CO2 jet cutting has the potential to open new fields of applications in which water jet cutting is not suitable. The liquid CO2 jet with a pressure of up to 300 MPa can be used to machine various materials and functional surfaces before it expands to gas and atmospheric pressure. However, the transition from liquid to gaseous phase implicates density differences which change the cutting performance. As a result, the knowledge about waterjets cannot be adapted to CO2 jets and further investigations are necessary. A new test stand was put into operation and a feed line with abrasives was added. Technological investigations concerning the formation of kerfs with high-pressure liquid CO2 and water jets were performed with and without abrasives as well as subsequently analyzed. The cutting tests were carried out on parts of various metals and technical plastics. The influence of the fluid on the attained cutting surfaces and kerfs produced by the jet was investigated. The experiments indicate that the performance of the CO2 jet as well as of the waterjet depends mainly on pressure and nozzle diameter but show different separation behavior. Especially the impact of the working distance will be discussed. The investigations reveal that high-pressure liquid CO2 jet cutting has a high potential in the field of dry and residue-free cutting of metals, technical plastics and CFRP. Furthermore, no temperature influence was observed and the potential for jet cutting in 3D-applications and for hollow profiles was proven.
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