Analysis of factors affecting fractures of rails welded by aluminothermic welding

The thermic welding of rails is carried out in the following sequence: a mould is placed on the rails to be joined; a crucible is mounted on a special bracket; a portion of thermite is charged; the rail ends are pre-heated and thermite is ignited by a special ignition primer. On Latvian Railway, the use of the thermic welding is widespread using the Elektro-Thermit Company technology. Today it is a basic method for rail joints.The analysis of the metal structure in the thermic welded zone of rails showed that the weld metal had inclusions of iron oxides infused (FeO, Fe2O, and Fe3O4) and small pores. Pores and infused oxides are concentrators of stresses and sources of cracks development. Pores and infused oxides reduce hardness of the weld joint under the action of tensile forces.
To heat metal during the aluminothermic welding process, a powdery mixture of metallic aluminum (Al~22%) and iron scale (Fe3O4~78%) is used as a thermite.
The thermic welding of rails is carried out in the following sequence: a mould is placed on the rails to be joined; a crucible is mounted on a special bracket; a portion of thermite is charged; the rail ends are pre-heated and thermite is ignited by a special ignition primer.
After a thermic reaction has been completed (20-25 s), a crucible plug is open and thermic steel in the liquid state is discharged into the mould. During the process of fused thermic steel casting into the joint gap, the rail ends are penetrated and welded. On completion of steel crystallization (3-5 min), the equipment is removed, the fin is trimmed and the welding joint on the rail head is ground. Because ATW is based on using heat from liquid metal as a result of thermite mixture burning thermochemcal reaction, third Chapter gives a detailed study of ATW technology and its components used on Latvian railroad. (...)

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Źródło: Czasopismo Logistyka

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