Determination of technological factors of rolling ability to occurrence of surface defects on pipes

The most productive and modern method is the production of pipes on pipe-rolling machines using continuous rolling mills with a retained mandrel. The production of seamless hot rolled tubes on such aggregates can be accompanied by the appearance of defects on the surface of the pipes, which leads to an increase in the amount of defective products. Taking into account the current state of the art, the process of defect formation in the production of pipes has not been studied sufficiently. Defects occur on the surface of pipes when rolling in the mills of the line of the pipe-rolling unit. Typical types of surface defects are surface cavity, rolling skin on the outer and inner surfaces of the pipes, pigeon hole. In this article, we consider the quality of pipes with an outer diameter in the range of 219÷325 mm with a wall thickness in the range of 8÷24 mm obtained by rolling on aggregates that have continuous rolling mills with 2- and 3-roll stands in the line. The quality is considered from the point of view of the influence of technological factors of rolling (the drawing coefficient, the reduction in the external diameter, the wall thickness, etc.) on the amount of reject for certain types of surface defects. As a universal, previously little studied, the size of which can be judged on the level of defectiveness of technology, we consider the factor of the ratio of deformations in diameter to deformation along the wall thickness in the rolling mill. A number of models have been obtained by statistical methods, guided by which it is possible to predict the expected level of defects in surface defects in the production of seamless pipes, and also to select deformation conditions that minimize the amount of defect.