Implementation strategies for high accuracy grinding of hydrodynamic seal ring with wavy face for reactor coolant pumps

Abstract

Large size mechanical seals are one of the most important components used in reactor coolant pumps. However, the hydrodynamic seal rings with wavy face are difficult to machine due to their high hardness and high form accuracy demand. In order to solve this difficult problem, a novel four-axis linkage grinding method using a cup wheel to process the hydrodynamic seal rings by line contact was proposed. A preliminary study indicates that the form error of the ground seal ring surface is extremely sensitive to different linkage relations of the four axes. By taking the center height of the cup wheel and the laws of motion along the X-axis, Z-axis, B-axis and C-axis as control variables, their effects on the principle form error of the ground surface are evaluated. Six implementation strategies are proposed to reach lower principle form errors. It is found that the minimal principle form error is only 9.64 nm and hence its influence on the ground seal ring shape can be neglected in designing an ultra-precision grinding machine. In addition, the results indicate that the position accuracy of the X-axis at the microscale is acceptable no matter which implementation strategy is selected. This study is expected to serve as a theoretical basis for design and development of the four-axis ultra-precision grinding machine.