3 Fundamentals of press design

68 Fundamentals of press design
tional safeguard against downward travel of the slide caused by gravity.
Pneumatic weight compensation guarantees low-noise, vibration-free
operation, smooth loading of the motor and short braking distances.
For counterbalancing weights up to 200 t, at 10 bar air pressure,
cylinder sizes up to a 900 mm diameter are required. Long slide strokes
of up to 1,300 mm and permissible pressure spikes of up to 25% require
substantial surge tanks. The arrangement of cylinders and tanks depends
on the type of press and safety issues. In the case of counterbalance
cylinders which are not externally enclosed, double piston rods
are often required to safeguard against the risk of breakage (Fig. 3.2.11).
Conversely, if the system is integrated in the press crown, this additional
safety feature is not necessary.
With every die change, the weight compensation system must be
automatically adjusted to the new die weights for this purpose.
Individual presses are fitted with special weighing and control functions.
Program-controlled automatic systems used in transfer presses
automatically set the program inherent pressure value when changing
dies in order to reduce set-up times to a minimum.
slide
breakage sensor
piston
cylinder
compressed
air tank
tubular rod
safety rod
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
Fig. 3.2.11
Compensation of slide speed with
double piston rod