Method of selecting a preload oil pressure valve for a die cushion pin pressure equalizing system of a press machine

摘要

In a die cushion pin pressure equalizing system wherein a plurality of die cushion pins are vertically movably provided in a bolster of a press machine, pressure equalizing hydraulic cylinders supported by die cushions are respectively provided downwardly of the plurality of die cushion pins and the plurality of pressure equalizing hydraulic cylinders are connected to one another through hydraulic paths, so that oil pressure is applied to the pressure equalizing hydraulic cylinders and the hydraulic paths, preload oil pressure acting on the plurality of pressure equalizing cylinders is raised to thereby prevent the plungers from bottoming.