Driven Controls for Remote-Controlled and Automatic Operation

The various hand-lever controls for tube and rod extrusion presses are arranged in such a way that the operator can closely watch the ram motions and the charging operations. A drawback to this system is the large space required and the distances between the various hand-levers, on account of which the operator has to change his position frequently 

It is for these reasons that - already many years ago - the controls were installed underground (Fig. 180), that the hand-levers were arranged closely to each other and that these were connected to the control shafts via a mechanical or hydraulic linkage. This development and the demand for automation of the working operations soon led to electric remote drives (Fig. 181) being actuated by pushbuttons or small control levers from a central desk. These drives operate directly or via a servo-motor, as already described, the control shaft. 

The simplest type of eleetrie remote control is the end-position change-over control which shifts the control shaft either to the pressure-or return position, when, however, the main piston cannot be stopped nor is it possible to regulate its speed. Such motions occur in hydraulic shears and saws, die shifting devices, wedge-type locks etc. The control shaft is advantageously driven by a 3-phase a.c. motor through a 

In oil-hydraulic presses which are controlled by balanced piston-valves, there is only a small force required and therefore a solenoid in conjunction with a spring may be used. As a rule, the solenoid is deenergized in the return position of the main piston. Large control slide-valves are moved by a piston, when the solenoid operated piston-valve serves as a pilot control. 

The main control of tube and rod extrusion presses - whether accumulator driven or directly driven by variable-delivery oil-hydraulic i ressure pumps - has to meet much higher demands. They must be able to regulate the working speed of the press at least in steps, and set the plunger motions to advance, stop, and return. This could be attained by arranging a number of intermediate switches on the control shaft, which, however, is not made use of, as there are better and simpler methods. 

---