Part Revolution Clutch
How do you determine if a press has a part revolution clutch for compliance purposes?
Classification depends on the physical clutch type, not how the press is operated. Inspect for an air line to the clutch; if present, it is typically a part revolution clutch press. Check for an operating rod mechanically linking the flywheel to the crankshaft; its presence with no air system often indicates a full revolution clutch. Confirm against manufacturer data plate and diagrams. Once identified as part revolution, the press must comply with all OSHA 1910.217(b)(7) and (c) requirements for part revolution clutches.
Why are two-hand controls restricted to part revolution clutch presses?
Two-hand controls rely on the ability to stop the slide immediately when hands leave the controls. On a part revolution clutch press, the ram stops on the downstroke when controls are released, as the clutch disengages and brake applies. On a full revolution clutch press, the slide cannot be stopped mid-stroke, so releasing controls would not prevent the hazardous portion of the stroke. Thus, two-hand controls are used only on part revolution presses and require control reliability and brake monitoring where needed.
What additional safeguarding is required when using presence-sensing devices on a part revolution press?
When a presence-sensing device, Type B gate, or movable barrier is used, the press must have a brake monitor that prevents activation of a successive stroke if stopping time or braking distance deteriorates beyond the safety distance. It must also detect top-stop overrun beyond established limits when used with Type B gates or movable barriers. The control system must be control-reliable, meaning a failure cannot prevent normal stopping but does prevent initiation of a successive stroke until detected.
A part revolution clutch on a mechanical power press is a type of clutch that can be disengaged at any point before the crankshaft completes a full revolution and the press slide completes a full stroke, allowing the slide to be started and stopped anywhere in its stroke. This contrasts with a full revolution clutch, which cannot be disengaged until a full crank revolution and full slide stroke are completed.
On the shop floor, a part revolution clutch press typically uses an air-operated friction clutch and brake. Compressed air engages the clutch and releases the brake, transmitting flywheel energy to start the slide stroke. Removing or losing the clutch-engaging signal causes the clutch to release and the brake to apply, stopping the slide at any point. This allows for top-stop adjustments, inch operations, and integration with two-hand controls or presence-sensing devices. OSHA requires automatic clutch release and brake application when the engaging means is removed, a red stop control at each operator station, and a stroking selector for off, inch, single-stroke, and continuous modes. Inch mode is for setup only and must be safeguarded.
Misclassification and misapplication of safeguarding: Treating a part revolution clutch press as a full revolution press, or vice versa, leads to incorrect controls and guarding. For example, using two-hand controls on a full revolution press (which cannot stop mid-stroke) defeats protective intent, while failing to install control reliability and brake monitoring on part revolution presses using presence-sensing devices violates OSHA requirements.
Failure of clutch/brake and brake monitoring systems: Degraded stopping performance due to missing, defeated, or poorly maintained brake monitors and control-reliable circuitry. This includes bypassing brake monitoring on presses using presence-sensing devices, lack of periodic testing of stopping performance, and inadequate preventive maintenance on air clutch and brake systems, compromising the ability to stop mid-stroke.
Control/stop devices and mode selection not compliant or misused: Improper design, placement, or use of stop controls and stroking selectors. Common issues include missing or non-functional red emergency stop buttons, using inch mode for production tasks, and modifying or defeating stroking selector supervision, leading to unintended continuous cycling and increased injury risk.