Hypothesis of the nature of cross-sectional shape distortion of the cold-pilgering mill die groove during dry pipe rolling

Abstract

The paper provides results on the further development of a method for calculating heat emissions during plastic strain in its instantaneous deformation zone in the course of cold pilgering of pipes, such as the ones that affect the working tool deflection in coldpilgering mills and mechanical properties of wrought pipe metal. It was determined that a decrease in the cross-sectional depth of the coldpilgering mill die groove due to thermal distortions (thermal effect) caused by plastic strain of a pipe in the instantaneous deformation zone is in direct proportion to the distance of the die groove longitudinal section considered to the roll barrel edge. It was found that sections located closer to the roll barrel receive thermal distortion of a lesser degree. A method is proposed for thermal distortion compensation in roll-pass design calculation. Experiments on applying marks on the roll barrel surface near the groove taper showed that the maximum galling of marks takes place directly near tapers. This indicates the local nature of thermal expansion. Dependencies are presented to determine the value of tool geometry variation depending on the heating temperature. The presented dependencies were tested experimentally and were introduced as a basis for developing the method of calculating the transversal die groove parameters for the cold-pilgering mill taking into account local thermal expansion in the instantaneous deformation zone. The inferred law allows taking into account the influence of cold pilgering peculiarities on the variation of the die groove cross-section geometry in the cold-pilgering mill, pipe dimensions and performance parameters.