ANALYSIS AND PREDICTING THE ACCURACY OF PIPES AT SINKING

Abstract

Pipes are subjected to free drawing after short-length drawing or rolling on cold rolling mills, that is, pipes that have a certain wall thickness difference. In order to assess the accuracy of pipes after non-dragging, technological routes for the production of pipes from various grades of steels were designed and investigated. Batches of pipes were pulled along the developed routes according to the production technology, samples were taken from each batch, and the wall thickness was measured at equidistant points of the pipe cross-section. Based on the measurement results, a correlation-regression analysis were performed, the factors influencing the change in wall thickness were determined, and regression models were built. The intensity of the correction depends on the coefficient of reduction in diameter, the greater the value of the ratio of the initial diameter to the final diameter of the pipe, the more intensive the correction of the wall thickness. That is, in order to correct the difference in wall thickness during uncorrected drawing, it is necessary to increase the stretch ratio. With a small wall thickness difference of the work piece (less than 3%), the wall thickness difference of the finished pipes increases, with a work piece wall thickness difference of 3 ... 4%, the wall thickness difference of the finished pipes changes little and at δ0 > 4%, the wall thickness difference of the finished pipes decreases.When analyzing the dependences obtained in the work, some conclusions can be drawn: the more ductile the metal, the less the change in wall thickness. Less ductile steels have a greater tendency to change the wall thickness. At low values of the relative wall thickness difference of the work piece, the coefficient of change in wall thickness reaches 3.5, that is, the wall thickness difference increases by 3.5 times, and at large values of the relative wall thickness difference of the work piece, its correction is more intensive. The intensity of the correction depends on the coefficient of reduction in diameter: the larger the value of the reduction, the more intensive the correction of the difference in wall thickness. That is, in order to correct the difference in wall thickness during uncorrected drawing, it is necessary to increase the stretch ratio.