[166] Exercise: Embossing press (activation of a single acting cylinder)
Additional hydraulic
components are to be added to an embossing press to eject the
finished workpieces. A single acting cylinder (1A) is to be
fitted for this purpose. A proposed solution in the form of a
circuit diagram with a 2/2-way valve is to be examined to see if
it is suitable for this control problem. Following this, a
circuit diagram with a 3/2-way valve as final control element is
to be developed and a parts list prepared. A comparison is to be
made of the behavior of these two circuits during the advance and
return strokes.
When a 2/2-way valve is used to activate a single acting cylinder, the final control element must be reversed and the hydraulic power unit switched off in order to retract the piston rod. The load acting on the piston rod must be larger than the resistance of the directional control valve. This solution cannot be used due to the presence of the second control chain (embossing cylinder). If a 3/2-way valve is used, a direct switch-over can be made from the advance stroke to the return stroke without switching off the hydraulic power unit. Halting at overlap positions, on the other hand (which are not required here), would be possible only by switching off the hydraulic power unit.
The non-return valve fitted in each case protects the pump against oil back-pressure. This is necessary in case the hydraulic power unit is switched off with the cylinder advanced and under load.