| Abstrakt: |
The article presents a study of the accuracy of reproduction of parameters of operational control of flash butt welding of railway rails in order to increase the reliability of evaluating the compliance of the process to the Technical Specifications (TS) and improve the quality of welded joints. For the statistical analysis of protocols of welding rails at rail-welding enterprises the review of existing indices of accuracy and stability of technological processes was made. For the analysis, the coefficient of variation Kv was chosen, which is not related to the tolerance of the deviation of the process parameter. Evaluations of Kv coefficients according to the welding protocols of more than 10 thou joints and more than 100 specimens of a technological test for the stationary machine K1000 showed that the mode parameters set directly by the control system, are reproduced with an error of not more than 1.5 %. The Kv coefficients increase sharply for the rate of flashing, transition from flashing to upsetting and particularly upsetting, which are included in the TS for welding rails and an active electric power, that occurred during flashing at the input of the welding transformer. The studies of Kv coefficients with grouping of welding data by six months showed that the variation of process parameters had no trends and the process was stable over time with a sufficient accuracy. The mean values and the standard deviation of the parameters of the process of welding rails and specimens of a technological test differ within the statistical error, which indicates the possibility of approximating the results of test studies on the rail joints. Evaluation of effect of parameters of the process of rate, tolerance and energy of flashing on the heat-affected zone (HAZ) with the use of linear regression dependence showed an essential dependence of HAZ on variation of electric energy during flashing. For control of active energy, the measuring converter of average active electric power with a pulse output was developed, which is adapted to the control systems of K1000 and K922 machines with input signals of current to 1000 A and voltage to 440 V, a frequency band of these signals to 1 kHz and the resulted error of measurement to 1 %. It is recommended to include active electric power released during flashing at the input of the welding transformer in the list of control parameters to the TS, and to improve the quality of joints not only to control the parameters within tolerance, but to create the conditions of the smallest variation of parameters from obtained data. [ABSTRACT FROM AUTHOR] |
