Description

Aluminothermic cast welding has its origins in an invention from the end of the 19th century. In around 1895, Professor Hans Goldschmidt succeeded in putting the aluminothermic reaction to use for technical purposes. In the course of this vigorous exothermal reaction, heavy metal oxides are reduced to their metal elements using aluminium powder. The massive amount of energy released in the form of heat during the process soon gave rise to its use in a welding application. Today, this method is still only used in isolated applications in the iron and steel industry; however, it is indispensable in creating a gapless track. It was around 1910 that rails were first continuously welded by tramway companies. On the one hand, paving the rails over their entire length meant they were subject to reduced fluctuations in temperature and thus in voltage, and on the other hand, there was no risk of deformations as a result of embedding the rails. With the improvement in the track in terms of its stability against axial and transverse forces, in the 1920s the first attempts were made to use continuously welded tracks for standard gauge railways. From 1924, Deutsche Reichsbahn implemented continuous welding for rails on bridges and in tunnels. At this time, numerous investigation works were carried out, forming the basis for the very rapid nationwide introduction, from 1950 onwards, of continuously welded tracks. Since 1928, the Thermit ® method has been the regulation welding method used by Deutsche Bahn. From 1955 onwards, the SmW method enabled welding to be executed considerably more quickly, ensuring that by 1964 around 50% of the nation's tracks – totalling a good 70,000 km – had already been continuously welded. This process was continued with the introduction of the SkV method in 1972. Aluminothermic welding is the final link in a long process chain which starts with the manufacture of the rails and includes stationary flash butt welding and the largely automated laying of the rails, finishing with the gapless track. In addition to the requirements in terms of high wear resistance, the best possible resistance to rolling contact fatigue, and minimising the risk of fracture, these welds also have to meet the demands resulting from advances in rail transport technology, the development of new grades of rail, increased speeds for passenger transport and increased loads in goods transport. The technical disadvantages of a Thermit ® weld, resulting on the one hand from the manufacture of a highly stressed cast part under site conditions, and on the other hand from the metallurgical differences between the rolled rail materials and the structures created within the weld metal during casting, no longer play an important role. Although a Thermit ® steel created on site does need to meet the demands on today's railway technology listed above, it does so over the service life of the rail. The disadvantages are accounted for by developments aimed at selectively controlling properties of the weld seam, such as head-hardened welds using a subsequent heat treatment, or HPW welding in which the rail head is selectively alloyed to optimise the mechanical properties of the running surface or the rail head, and improvements to casting technology. Differences between the Thermit ® welding processes Differences between the Thermit ® welding processes The Thermit ® welding processes are essentially differentiated according to their application on the various rail types. Rail Type Thermit ® welding processes Flat bottom rail SkV SkV-Elite SkV-Elite L25 SoW-5 SoWoS SmW-F HPW LSV THR Grooved rail SRZ SRZ-L50, transition grooved/flat bottom SRE Crane rail SKS Thermit ® welding processes are also divided based on central or lateral inlet, and on rising or falling casting system. A further distinguishing criterion is the specified preheating duration, which is defined either on the basis of the time passed or on reaching a particular temperature, depending on the process. In current welding processes, the preheating period ends on the expiry of a specified period of time. The preheat temperature reached is not checked visually by the welder. These processes thus have a higher degree of automation. In contrast, in the SoWos, SmW-F, SRZ, SRE and SKS processes, the welder makes a visual check that the preheat temperature of 1000°C has been reached in the weld gap on both sides. Preheating only ends when this temperature has been reached throughout the cross-section of the rail end. Guidelines are available regarding when this preheat temperature can be expected. A prerequisite here is that all the other process-specific parameters have been fulfilled. Benefits of the Thermit ® welding processes Benefits of the Thermit ® welding processes The Thermit ® welding processes enable simple, safe and robust execution on the track. Owing to the successful use of the Thermit ® welding processes over several decades, their ongoing development, and certifications to EN 14730-1, the welding processes have become a reliable and customer-oriented product for welding on the track. What stands out about the Thermit ® welding processes, and in particular the welding processes for flat bottom rails, is their short implementation time coupled with their high reliability. The Thermit ® welding processes can be used in a wide range of applications. There is a comprehensive offering of moulds and portions for all current profiles and grades of rail. Special solutions can also be created at the customer's request. The SkV welding processes, in particular, have very short preheating times, resulting in high economic efficiency due to reduced gas consumption. Process modifications to the standard welding processes for flat bottom rails make it possible to weld gap widths of 40 - 50 mm (L50) and 65 - 75 mm (L75). With the SRZ welding method, it is only possible to weld L75 gaps. In the SkV-Elite and SkV-Elite L25 welding processes, and also for the SoW-5 process, one size of mould shoes is used for all profiles. This simplifies work on the rail, especially if different profiles often need to be welded. One size of mould shoes is likewise used in the welding processes for welding wide gaps (process modifications for L50 and L75). As a general rule, the welding processes are offered for use both with the single use crucible and with the long life crucible. For individual welding processes, only the single use crucible should be used, in order to ensure that the customer benefits from the best possible properties of the welding process. Welding processes certified in accordance with EN 14730-1 must prove their suitability within a tolerance range for the gap width; for nominal gap widths up to 30 mm, this is ± 2 mm. In order to achieve optimum process reliability during execution on the track, the work instructions limit the tolerances to ± 1 mm. As a general rule, Elektro-Thermit GmbH Co. KG welding processes are provided with 2-part mould shoes. In some cases, 3-part mould shoes can also be provided at the customer's request. Thermit ® welding processes have high economic efficiency owing to: a small investment in equipment a very high level of flexibility and mobility on the construction site robust and rapid execution Differences between the Thermit ® welding processes The Thermit ® welding processes are essentially differentiated according to their application on the various rail types. Rail Type Thermit ® welding processes Flat bottom rail SkV SkV-Elite SkV-Elite L25 SoW-5 SoWoS SmW-F HPW LSV THR Grooved rail SRZ SRZ-L50, transition grooved/flat bottom SRE Crane rail SKS Thermit ® welding processes are also divided based on central or lateral inlet, and on rising or falling casting system. A further distinguishing criterion is the specified preheating duration, which is defined either on the basis of the time passed or on reaching a particular temperature, depending on the process. In current welding processes, the preheating period ends on the expiry of a specified period of time. The preheat temperature reached is not checked visually by the welder. These processes thus have a higher degree of automation. In contrast, in the SoWos, SmW-F, SRZ, SRE and SKS processes, the welder makes a visual check that the preheat temperature of 1000°C has been reached in the weld gap on both sides. Preheating only ends when this temperature has been reached throughout the cross-section of the rail end. Guidelines are available regarding when this preheat temperature can be expected. A prerequisite here is that all the other process-specific parameters have been fulfilled. Differences between the Thermit ® welding processes The Thermit ® welding processes are essentially differentiated according to their application on the various rail types. Rail Type Thermit ® welding processes Flat bottom rail SkV SkV-Elite SkV-Elite L25 SoW-5 SoWoS SmW-F HPW LSV THR Grooved rail SRZ SRZ-L50, transition grooved/flat bottom SRE Crane rail SKS Thermit ® welding processes are also divided based on central or lateral inlet, and on rising or falling casting system. A further distinguishing criterion is the specified preheating duration, which is defined either on the basis of the time passed or on reaching a particular temperature, depending on the process. In current welding processes, the preheating period ends on the expiry of a specified period of time. The preheat temperature reached is not checked visually by the welder. These processes thus have a higher degree of automation. In contrast, in the SoWos, SmW-F, SRZ, SRE and SKS processes, the welder makes a visual check that the preheat temperature of 1000°C has been reached in the weld gap on both sides. Preheating only ends when this temperature has been reached throughout the cross-section of the rail end. Guidelines are available regarding when this preheat temperature can be expected. A prerequisite here is that all the other process-specific parameters have been fulfilled. Benefits of the Thermit ® welding processes The Thermit ® welding processes enable simple, safe and robust execution on the track. Owing to the successful use of the Thermit ® welding processes over several decades, their ongoing development, and certifications to EN 14730-1, the welding processes have become a reliable and customer-oriented product for welding on the track. What stands out about the Thermit ® welding processes, and in particular the welding processes for flat bottom rails, is their short implementation time coupled with their high reliability. The Thermit ® welding processes can be used in a wide range of applications. There is a comprehensive offering of moulds and portions for all current profiles and grades of rail. Special solutions can also be created at the customer's request. The SkV welding processes, in particular, have very short preheating times, resulting in high economic efficiency due to reduced gas consumption. Process modifications to the standard welding processes for flat bottom rails make it possible to weld gap widths of 40 - 50 mm (L50) and 65 - 75 mm (L75). With the SRZ welding method, it is only possible to weld L75 gaps. In the SkV-Elite and SkV-Elite L25 welding processes, and also for the SoW-5 process, one size of mould shoes is used for all profiles. This simplifies work on the rail, especially if different profiles often need to be welded. One size of mould shoes is likewise used in the welding processes for welding wide gaps (process modifications for L50 and L75). As a general rule, the welding processes are offered for use both with the single use crucible and with the long life crucible. For individual welding processes, only the single use crucible should be used, in order to ensure that the customer benefits from the best possible properties of the welding process. Welding processes certified in accordance with EN 14730-1 must prove their suitability within a tolerance range for the gap width; for nominal gap widths up to 30 mm, this is ± 2 mm. In order to achieve optimum process reliability during execution on the track, the work instructions limit the tolerances to ± 1 mm. As a general rule, Elektro-Thermit GmbH Co. KG welding processes are provided with 2-part mould shoes. In some cases, 3-part mould shoes can also be provided at the customer's request. Thermit ® welding processes have high economic efficiency owing to: a small investment in equipment a very high level of flexibility and mobility on the construction site robust and rapid execution Benefits of the Thermit ® welding processes The Thermit ® welding processes enable simple, safe and robust execution on the track. Owing to the successful use of the Thermit ® welding processes over several decades, their ongoing development, and certifications to EN 14730-1, the welding processes have become a reliable and customer-oriented product for welding on the track. What stands out about the Thermit ® welding processes, and in particular the welding processes for flat bottom rails, is their short implementation time coupled with their high reliability. The Thermit ® welding processes can be used in a wide range of applications. There is a comprehensive offering of moulds and portions for all current profiles and grades of rail. Special solutions can also be created at the customer's request. The SkV welding processes, in particular, have very short preheating times, resulting in high economic efficiency due to reduced gas consumption. Process modifications to the standard welding processes for flat bottom rails make it possible to weld gap widths of 40 - 50 mm (L50) and 65 - 75 mm (L75). With the SRZ welding method, it is only possible to weld L75 gaps. In the SkV-Elite and SkV-Elite L25 welding processes, and also for the SoW-5 process, one size of mould shoes is used for all profiles. This simplifies work on the rail, especially if different profiles often need to be welded. One size of mould shoes is likewise used in the welding processes for welding wide gaps (process modifications for L50 and L75). As a general rule, the welding processes are offered for use both with the single use crucible and with the long life crucible. For individual welding processes, only the single use crucible should be used, in order to ensure that the customer benefits from the best possible properties of the welding process. Welding processes certified in accordance with EN 14730-1 must prove their suitability within a tolerance range for the gap width; for nominal gap widths up to 30 mm, this is ± 2 mm. In order to achieve optimum process reliability during execution on the track, the work instructions limit the tolerances to ± 1 mm. As a general rule, Elektro-Thermit GmbH Co. KG welding processes are provided with 2-part mould shoes. In some cases, 3-part mould shoes can also be provided at the customer's request. Thermit ® welding processes have high economic efficiency owing to: a small investment in equipment a very high level of flexibility and mobility on the construction site robust and rapid execution

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