ANALYSIS AND DEVELOPMENT OF ROLLS CALIBRATION FOR PRODUCTION OF ASYMMETRICAL RAIL PROFILES AT UNIVERSAL ROLLING MILL

Analysis of the development of railway track facilities revealed a  tendency to constantly improve quality requirements for rail transfers, which have the most wear in the upper part of the rail way. The major causes of quality inconsistency of switch point transfers to requirements of the standards are poor geometry and spread the values of residual stresses in the initial blanks – switch point rails. Asymmetrical profile of switch point rails greatly complicates their manufacturing technology, especially at use of universal rolling mill stands for their rolling. This paper describes theoretical and technological aspects of the development of OR65 switch point rails production at the new universal rolling mill of JSC “EVRAZ ZSMK”. Imperfection of contract calibration of the supplier of rolling mill equipment, which determined the impossibility of its application for mass production of switch point rails, led to the need to develop new and improved rolling pattern. Distinctive features of the new method of stand, reduction switch point rails rolling are an intensified mode of breakdown in the first breakdown of the number of passes in the second breakdown stand and the use of split inclined rail caliber with diagonal connectors instead of closed split rail caliber. At the same time the possibility of intensifying the strain mode is preliminarily justified by calculations of rolling force conducted using a previously developed authors’ technique. The introduction of a new mode of rolling the OR65 rails allowed to increase the mill's productivity by 39.8  t/h and to reduce the rejection of finished rails by 0.5  % of rolling stock. The analysis of metal flow processes and of the formation of finishing profile of switch point rails while rolling in the universal stands has shown that the clearance of width of the rail profile base is due to the free broadening of the metal at the element deformation. As a result of this feature, the execution of the necessary width of the rail profile base depends on many technological parameters and cannot be predicted with a high degree of accuracy. The experience of industrial rolling of switch point rails on the rail mill of JSC  “EVRAZ ZSMK” has shown that the achievable accuracy of the elements dimensions of the rolling profiles is ±1.0  mm. At the same time, according to the current domestic regulatory documentation for the production of switch point rails of the highest and first grades, the maximum tolerances for the width of the short arm of the base are set within ±0.3 and ±0.5  mm, respectively. Thus, the fulfillment of this requirement is impossible.

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