Peculiarities of metal work in the defect formation zone of a monoblock crossing

Introduction. The paper analyses the causes of appearance and development of defects of the solid block with wing rails and welded rail ends (monoblock crossing) operating under heavy and intensive traffic conditions. Failure of such crossings is caused by crack initiation and development processes, as well as by metal pitting on the tread surface. One of the effective methods to increase the life of crossings is to harden their tread surface with blast wave energy.

Materials and methods. The metal microstructure of the prototype crossings was investigated using metallographic equipment based on Zeiss Axiovert 25 microscope with Thixomet Pro software. Chemical etching of the surface of the samples used a reagent of 4% nitric acid solution in distilled water. Hardness of the hardened layer was determined by the Brinell method as per GOST 9012–59 on a TSh-2M hardness tester.

Results. The author found that DS.30G.2 defects (Classifier of Defects and Damages of Turnout Elements) could be caused not only by oxide spots and cast seams in the metal but also by insufficient strength characteristics of the crossing structure, which should be eliminated when putting the product into production; increased dynamic loads not foreseen for the respective product. Microcracks formed in further operation in the overmoulded metal layer at the tread surface (without removing the defective layer) result in metal delamination and pitting. Thus, the turning of crossings should include the removal of the entire defective layer in addition to the removal of the swells. The research has shown that the most effective technology is explosive hardening of the crossing tread surface.

Discussion and conclusion. The results show that crossing life could be improved by pre-hardening of the tread surface.

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