Hydraulic actuator for an electrode support arm of an arc furnace

In an arc furnace, each of the electrodes (4) is held by an electrode support arm (2) mounted on a plunger cylinder (1). The plunger cylinder can be moved upwards and downwards with the aid of a hydraulic actuator and held in a desired position. The actuator comprises a hydraulic accumulator (6) and a hydraulic pump (8) which is connected to the plunger cylinder (1) or the hydraulic accumulator (6) in a predetermined manner via a 4/3-way valve (5). For raising the electrode support arm, the 4/3-way valve connects the pressure side of the pump (8) to the plunger cylinder (1) and the suction side of the pump to the hydraulic accumulator (6). During the downward movement of the electrode support arm, a reversed connection takes place. When the electrode support arm (2) is to be held, pressure side and suction side of the pump (8) are short-circuited with the aid of the 4/3-way valve. In relation to known actuators with a number of hydraulic accumulators and/or a number of cylinders in the electrode lifting mechanism, considerable energy saving is achieved by the invention (Fig. 1).