Failure analysis on the loose closure of the slipper ball-socket pair in a water hydraulic axial piston pump

The slipper ball-socket pair in the piston-slipper assembly is one of the key friction pairs in a Water Hydraulic Axial Piston Pump (WHAPP). The slipper ball-socket pair usually manufactured using a closing process to ensure its flexible swing and approximate zero axial clearance. Once the closure of the slipper becomes loose during use, resulting in excessive axial clearance, it will lead to pump failure. Similar problems occur on the WHAPP of the steel plate production line. In order to find out the root cause of the loose closure failure of the slipper ball-socket pair, the stress and strain during the closing process of the slipper ball-socket pair, the load during use, the size of the failed parts, and the macroscopic and microscopic morphologies were systematically characterized and analyzed. Through comprehensive failure analysis, the residual stress generated by the crimping and closing processes of the slipper ball-socket pair may be the main cause of its loosening and failure, while wear probable a secondary factor. Based on the conclusions, the direct injection molding method of the slipper ball-socket pair is proposed to solve this problem. The durability test results of the improved slipper ball-socket pair indicate that the countermeasures are effective. The obtained achievements would be helpful to improve the quality of the slipper closure and increase the service life of the WHAPP.