3 Fundamentals of press design

62 Fundamentals of press design
Pneumatic control systems with safety valves and damping devices are
reasonable in cost and generally comply with requirements. One of the
problems of pneumatic systems, however, is the limited switching frequency
of single-stroke presses and the environmental damage caused
by wear to the clutch and brake. In order to eliminate these drawbacks,
hydraulic systems are being used increasingly in recent years. With the
aid of cooling systems, these permit far higher switching loads per time
unit and are practically immune to wear. In single-stroke presses, separate
units which permit switching frequencies of up to 30/min have
been used to permit more effective control and to avoid overshooting
and undershooting by the clutch and brake. Large-panel transfer presses
use clutch-brake combinations based on sintered disk sets with up to
20 friction surfaces and transmission torque levels of up to 500,000 Nm.
The compact drive system used in smaller mechanical presses, consists
of a flywheel, clutch, brake and planetary gear in a complete unit.
Such a system achieves a particularly high level of efficiency with an
extremely low moment of inertia and small braking angle, coupled
clutch brake
friction blocks
drive shaft
wear indicator
Fig. 3.2.7 Single-disk clutch and brake in a large-panel press
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998