Gates
The gate is a moveable barrier that protects the operator at the point of operation before the machine cycle can be started. Type "A" and "B" Gates (See below) are commonly used with presses and, in many instances, designed to be operated with each machine cycle.
To be effective, the gate must be interlocked so that the machine will not begin a cycle unless the gate is in place. It must be in the closed position before the machine can function. If the gate is not permitted to descend to the fully closed position, the press will not function. Operators must be prevented from placing their hands or any other body parts in the point of operation during the die-closing portion of the press stroke.
Another potential application of this type of guard is where the gate is a component of a perimeter safeguarding system. Here the gate may provide protection not only to the operator but to pedestrian traffic as well.
| Safeguarding Action | Advantages | Limitations |
|
Concurrent use of two hands on separate controls prevents hands from being in the danger area when machine cycle starts |
Operator's hands are away from danger area Can be adapted to multiple operations No obstruction to hand feeding Does not require adjustment for each operation |
Operator may try to reach into danger area after tripping machine Some trips can be rendered unsafe by holding with arm or blocking, thereby permitting one-hand operation Protects only the operator May require special fixtures |
"A" Gate Sequence of Operation. Type "A" Gates protect the operator during the entire machine stroke. This means the gate will not open until after the crankshaft rotation is complete (360°) and the machine is stopped at top dead center. Although Type "A" Gates can be used on either part or full revolution clutch presses, best safety practice is the "A" gate should be used only on full revolution clutch presses.
The "A" gate is designed to enclose the point of operation before the press stroke can be started, and it must remain enclosed until all slide motion has stopped. The following is a typical sequence of operation of a complete cycle on a press which uses an "A" gate.
- Initiate the cycle. As long as there are no obstructions, the gate closes by gravity.
- The machine makes one complete cycle and returns to "top of stroke" and stops.
- The gate opens, after the cycle has stopped.
"B" Gate Sequence of Operation. Type "B" Gates protect the operator during the downstroke only. The gate starts to open before the crankshaft rotation is complete (generally after 180° crankshaft rotation). The gates must open on the upstroke of the machine cycle before the crankshaft rotation is complete.
The "B" gate only protects the operator on the down-stroke of the press slide. The following is a typical sequence of operation of a complete cycle on a press which uses a "B" gate.
- Initiate the cycle. As long as there are no obstructions, the gate closes by gravity.
- Once the machine reaches the portion of the stroke where the pinch point has been eliminated and before the stroke has stopped, the "B" gate and the slide go up at the same time.
Knowledge Check Choose the best answer for the question.
3-7. Which of the following is a moveable barrier that protects the operator at the point of operation before the machine cycle can be started?
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