A. V. Korol

This paper examines the wear of the working tool of a two-high screw rolling mill using QForm, a software package for modeling metal forming (MF) processes. The influence of tool setup factors on wear and, consequently, the quality of the resulting pipe geometry is relevant as the range of seamless pipes with high chromium content expands. The program was used to simulate the piercing process in seamless pipe production. The geometric dimensions of the rolls, guides, and plugs of the MISiS-130D mill were used to model and construct the deformation zone. A 3D model of the deformation zone with a tool was created in SolidWorks and loaded into QForm. The piercing simulation was performed by varying the zone parameters: ovalization coefficient, feed angle, and relative reduction in the pitch point. The resulting pierced shells had identical geometry. The wear study was conducted using simulation modeling with numerical methods for solving problems in metal forming processes. The calculations were performed using the “Wear” subroutine for the tool in the QForm software package. The tool-workpiece contacts were divided into several cross-sections. Wear measurements were taken in these cross-sections for the roll, plug, and guide. Average wear values were calculated. Using a full factorial experiment, mathematical regression models were constructed to describe the relationship between roll, plug, and guide wear during piercing. The influence of model factors on wear magnitude was determined.This work was completed as part of the integrated project “Development and Implementation of Integrated Technologies for the Production of Seamless Pipes from New-Generation Steels with Controlled Corrosion Resistance under Harsh Operating Conditions for the Fuel and Energy Complex of the Russian Federation” under Agreement No. 075-11-2025-017 of February 27, 2025, in accordance with Russian Government Resolution No. 218 of April 9, 2010.

As part of the work performed, an analysis of the unsteady final stage of piercing on a two-high screw rolling mill with guide drive disks was carried out based on numerical methods for studying metal forming processes. The implementation of numerical research methods was carried out using piercing process modeling in the Qform software product based on the finite element method. Using a description of the nature of the shape change of the rear end of the workpiece in the deformation center of the piercing mill, the mechanism of defect formation on the rear end of the sleeve when using a non-centered workpiece is described. The cause of defect formation on the rear end of the sleeves (“skirt”, “penny”, “earring”) is the action of the piercing mandrel on the deformed workpiece and the formation of a sink mark on the rear end of the workpiece in the final stage of deformation. When using rear centering, no metal delamination is formed on the end surface of the sleeves. Therefore, the accuracy of the rear ends of the pipes increases, the durability of the rolling mill mandrels increases, which is very important for piperolling units with a continuous rolling mill operating on a retained or partially retained and movable mandrel. But due to the rear centering on the inner surface of the sleeves, there is a high probability of internal defects. The cause of the defect is two types of destruction: metal peeling due to the formation of internal shrinkage (1) and annular destruction of the metal during the immediate approach of the transforming bottom of the recess to the end of the mandrel (2).The work was carried out within the framework of a comprehensive project on the topic “Development and implementation of integrated technologies for production of seamless pipes from new-generation steels with controlled corrosion resistance under complicated operating conditions for the fuel and energy complex of the Russian Federation” within the framework of Agreement No. 075-11-2023-011 dated 10.02.2023 according to the Decree of the Government of the Russian Federation No. 218 dated 09.04.2010.

Lubrication are widely used in metal forming. The main purpose of lubricant is decreasing the coefficient of friction. The lubricant forms an intermediate layer between the body being deformed and the tool, completely or partially isolating them from each other. Due to high specific pressures, the grease does not always completely isolate the rubbing surfaces, allowing the tool and workpiece surfaces to come into contact, resulting in accelerated wear and increased heat generation. This can cause damage to the tool and workpiece, reduce machining accuracy and shorten equipment life. This paper presents a method for determining the effect of lubrication on friction conditions for the processes of continuous hot rolling of seamless tubes in multilayer rolling mills. The variant of realization of installation for friction research on the basis of laboratory mill DUO-210 is presented. This installation allowed to carry out physical modeling to study friction in conditions as close as possible to the real production process. The results of tests of the process of rolling of shells on a movable mandrel in a two-roll mill with the use of various technological lubricants, as well as the results of experience without the use of lubricants are given. The research with the use of technological lubricants based on graphite showed the difference in the mandrel holding force during the rolling of the sleeve depending on the applied composition. At the same time, the use of grease significantly reduced the holding force.The work was carried out within the framework of a comprehensive project on the topic “Development and implementation of integrated technologies for the production of seamless pipes from new-generation steels with controlled corrosion resistance under complicated operating conditions for the fuel and energy complex of the Russian Federation” within the framework of agreement No. 075-11-2023-011 dated 10.02.2023 according to the RF Government Resolution No. 218 dated 09.04.2010.

One of the key steps in the production of hot-rolled pipes is the helical piercing process, as this process establishes the initial geometry and quality of the resulting pipe. Wear of the working tool surface is one of the factors that lead to deterioration of pipe quality and decrease of equipment productivity. Particular attention is paid to mandrels because it is their condition that influences the quality of inner surface of the produced tubing and the accuracy of geometrical dimensions. Increased wear of piercing mandrels also leads to loss of productivity of industrial units due to necessity of their frequent replacement. The wear of mandrels during piercing of billets of corrosion-resistant steel 20Cr13 into sleeves on an experimental screw-rolling mill MISIS-130D is investigated in the present paper. Experimental piercing of billets of 20Cr13 steel 60 mm in diameter and 400 mm in length was carried out using piercing mandrels of different steel grades to determine the material subjected to less wear. We used mandrels from steel grades 20Cr2Ni4А, 4Cr5MoVSi, 3Cr3W8V, 3Cr3Mo3V, 4Cr4WMoVSi, 5Cr3W3MoVSi. To reproduce the operating conditions of mandrels close to the production, we varied the frequency of rolls rotation, the length of pierced workpieces and the angle of rolls in order to compare the wear resistance of mandrels under different rolling modes. On the basis of the obtained data the conclusion about the durability of the mandrel material when piercing steel 20Cr13 was formed, as well as the effect of several factors of the rolling process on the wear rate of the mandrel was estimated.The work was carried out as part of a comprehensive project on the topic “Development and implementation of integrated technologies for production of seamless pipes from new generation steels with controlled corrosion resistance under difficult operating conditions for the fuel and energy complex of the Russian Federation” within the framework of Agreement No. 075-11-2023-011 dated 10.02. 2023 according to Decree of the Government of the Russian Federation No. 218 of 04.09.2010.