On ring deformation by internal pressure

Abstract

Large-sized rings, manufactured by various methods of metal forming, are used in many industries. For the power industry, it is relevant to manufacture of retaining rings made of non-magnetic austenitic steel in order to strengthen the winding frontal parts of the rotors of turbine-type generators of a large unit capacity. In the process of generator operating, the retaining ring is one of the most loaded elements. As a result, material of retaining rings should have high strength properties, sufficient plasticity and good magnetic inductivity. Deformation of rings by internal pressure is the most promising and effective way of their cold hardening, providing a favorable and uniform stress-strain state of the metal in the manufacture of non-magnetic retaining rings for powerful turbine-type generators. Since the finished ring must acquire specific dimensions and a specified deformation degree in the process of cold hardening, the urgent task is calculation of the billet dimensions. The existing calculation procedure relies heavily on experimental manufacture data and is applicable only to a narrow range of rings, which reduces the accuracy of calculation and, ultimately, leads to an increase in ring allowances and a decrease in the metal utilization factor. In this research work a new technique for calculating the initial dimensions of rings, which is based on the incompressibility condition was developed and proposed. Taking into account the assumed boundary conditions, a system of two equations with three terms is compiled. To solve an incomplete equation system, it was suggested to introduce additional equations –in first version of the technique, the well-known solution of Nadai was used. In the second version –the condition of constancy of relative thickness of the ring wall permissible from the experimental data of deformation of rings of different sizes was used. The results of calculating the rings initial dimensions for both proposed techniques were compared with the experimental data. The maximum deviation from experimental data does not exceed 4% and the deviation average value does not exceed 1%, which indicates a sufficiently high accuracy of the proposed calculation techniques and the possibility of using them in manufacturing practice. © 2019, National University of Science and Technology MISIS. All rights reserved.