RESEARCH OF THE INFLUENCE OF TUBE ROLLING CONDITIONS IN THE PLUG MILL ON TECHNOLOGICAL PARAMETERS AND TUBE QUALITY
The purpose is to develop a methodology for studying the influence of the conditions of forming tubes in round calibers in a plug mill on a short mandrel on the technological parameters of the forming process, force parameters, and geometry of produced tubes.
Methods. When conducting the research, the following was used: a mathematical model of the deformation process during two-pass longitudinal rolling of tubes in round calibers on a short mandrel in n plug mill, which allows, with given design parameters of calibers and mandrels and their settings, to determine the change in the wall thickness along tube’s perimeter, the size of the contact surface, and axial forces when rolling.
Results. Studies of the process of rolling tubes in a plug mill, which, as a rule, is carried out in two passes, using the same caliber of rolls with a tube bevelling at 90 degrees between passes, made it possible to establish the following.
Tube rolling in a plug mill, as a rule, is carried out in two passes, using the same caliber of rolls with a 90o pipe canting between passes. If rolling in both passes is carried out on plugs of the same diameter, then theoretically the wall thickness of the finished rough pipe will be constant around its perimeter. If rolling is carried out on plugs of different diameters then, even theoretically, wall thickness of the finished rough pipe will be volatile around its perimeter. Usually, tables of tube rolling in a plug mill are created in such a way that, for part of the assortment, the gap between the rolls adopted during the design of the gauge does not equal the actual gap between the rolls. Existence of this discrepancy leads to the fact that, even while rolling using mandrels of the same diameter, the wall thickness of the finished rough pipe will be volatile around its perimeter.
Based on the analysis of the geometric parameters of the rolling process, an assessment was made of the influence of the values of different parameters on the nature of the change in the thickness of the pipe wall along its perimeter. The power parameters of the pipe rolling process were analyzed for various values of the plug displacement in the rolling direction. It has been identified that the displacement of the plug in the rolling direction to a position at which the plane of the roll centers coincides with the linking plane of the cylindrical and conical sections of the plug slightly reduces the axial force applied to the mandrel and, therefore, improves the conditions for gripping the workpiece by the rolls. Further displacement of the plug in the rolling direction does not improve the gripping conditions, but leads to distortions of the deformation zone, which requires reduction of the gap between the rolls by the certaine value to compensate for them. Reduction of the gap between the rolls, in its turn, increases the axial force applied to the mandrel, which worsens the conditions for gripping the workpiece.
Originality. Using computational methods and mathematical modeling of the deformation process in a plug longitudinal rolling mill on a short mandrel, it is substantiated that the use of mandrels of the same diameter in each of the two passes reduces the transverse wall thickness difference of the tubes. Analytical dependencies are obtained that substantiate the optimal settings of n plug mill for various rolling conditions. For plug mills, the dependences of the distortion of the deformation zone and the force parameters of the process on the position of the mandrel have been determined.
Practical implications. The proposed methods for determining the tuning parameters of a longitudinal tube rolling on a short mandrel can be used in plug mills of the classical type and tandem mills to control the process of wall deformation. It is recommended to carry out rolling in two passes on identical mandrels, setting the mandrel in a position in which the plane of the roll centers coincides with the interface plane of the cylindrical and conical sections of the mandrel.
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