The majority of part-revolution presses have an air-applied clutch and an air-released brake. They are designed to trap air in a chamber or tube. When compressed air is put into these chambers or tubes, the clutch is engaged and the brake is released. The press then starts a cycle. To stop the press, the opposite takes place. A part-revolution-clutch press can be engaged and disengaged at any position of crankshaft rotation or revolution.
Occasionally older mechanical-friction-clutch presses are found in plants and are still being used. Sometimes press brakes with mechanical-friction clutches are used as power presses. These press brakes and the older mechanical-friction-clutch presses can be updated by adding a properly sized air cylinder to the part-revolution control packages that are offered.
Due to the many detailed OSHA requirements on part-revolution-clutch presses, most existing clutch/brake control systems on presses do not meet safety standards and regulations if they were installed prior to 1971. Most of these presses do not have control reliability and brake monitoring.
The part-revolution-clutch/brake control-reliable systems in this catalog are designed to stop the press and render it inoperable if there is a single component failure in the control system. This is done by minimizing the use of static-condition components and using critical, redundant components that are checked. Microprocessors or relays of special construction are used in this type of reliable control system. The clutch/brake control systems offered here are furnished with a built-in, two-hand control safeguarding device.
In addition to the clutch/brake control meeting the requirements of the safety standards, all part-revolution presses require a safeguarding device or guard (barrier) to protect people that operate, set up, and maintain these machines.
The following are OSHA- and ANSI-recognized methods for safeguarding the point of operation on part-revolution-clutch mechanical power presses:
1. Barrier guard (EX-AL catalog)
2. Presence-sensing device (Safeguarding Devices catalog)
3. Two-hand control (Refer to this section)
4. Pullback (Not offered by Rockford Systems)
5. Restraint (Safeguarding Devices catalog)
6. Type A or B gate (Safeguarding Devices catalog)
When safeguarding, please keep in mind that the sides and back of the point of operation must also be safeguarded to protect the operator and other employees.