Study of pipe ends shape changes under asymmetrical conditions of the reduction process

In the production of seamless pipes, reducing-stretching and reducing-calibrating mills are widely used to reduce metal consumption and increase productivity. One of the most significant defects that occur during reduction is the curvature of the front end of the pipe. This defect is formed as a result of asymmetric rolling conditions and leads to a decrease in the overall quality of the finished product, an increase in rejects and complications of further processing. The aim of this work is a comprehensive and detailed study of the mechanism of defect formation using the example of reduction in the stands of a reducing-calibrating mill. Using the QForm 3D software package, parametric modeling of various rolling scenarios was performed with varying end bevel angle, unevenness of the temperature field and roll diameter. Modeling was carried out using hollow cylindrical blanks, the wall thickness varied from 9 to 15 mm at deformation degrees of 3–7%. The criterion for the defect was the deviation of the generatrix from the rolling axis on a 400 mm base. The obtained curves showed that temperature asymmetry and end bevel cause an almost linear increase in wall thickness δ, while an increase in compression above 3% has only a minor effect. The results allow us to specify the contribution of each factor and thereby better understand the nature of the defect. It was found that the curvature increases with a smaller wall thickness and a larger bevel angle, as well as with cooling of the lower part of the pipe on the feed roller table. It was found that it is possible to compensate for the curvature by selecting rolls of different diameters or by using a falling mode.