Control system for the level of the molten metal in continuous casting moulds

摘要

In the abovementioned control system, a PD controller (24) is used as the correcting variable generator for the servovalve (14), the hydraulic correcting variable of which is continuously applied to the hydraulic feed lines to correct the displacement travel of the actuating cylinder (11). As a result, the operating point of the PD controller (24) cannot drift. The servovalve (14) has a nonlinear, shallow throughflow characteristic in the operating range, making it possible to convert very small electrical signals directly into hydraulic actuating signals and thus to displace the plug in accordance with the controller output. By inserting a bypass valve (19) into the hydraulic feed lines (13, 13a) of the actuating cylinder (11), the said cylinder can be switched to manual operation. In this arrangement, the servovalve (14) controls the actuating cylinder (11) in accordance with a predetermined throughflow characteristic with a gently rising central portion (I) in the region of the origin and steep flanks (II) at the sides. The servovalve (14) and the bypass valve (19) are rigidly connected as a constructional unit to the actuating cylinder (11). The actuating cylinder (11) is designed as a differential cylinder. IMAGE