Four Deadly Myths About Overhead Cranes
As a crane operator, maintaining a safe operating environment for yourself and fellow workers is absolutely paramount. Unfortunately, there are plenty of deadly rumors and unsafe myths lurking about that could trip up even the most veteran of operators. It's important to recognize these dangerous myths and the plain, unvarnished truth that counters these myths.
You Can Always Rely on a Secondary Brake in the Event of a Power Failure
It's a common assumption that the secondary brake on a typical overhead crane is designed to prevent the load from crashing down onto the ground in the event of a power failure or mechanical breakdown. Unfortunately, the purpose of a secondary brake is quite different from what many expect.
Most modern overhead cranes use a regenerative secondary brake that not only controls the descent of the load, but much of the energy that is otherwise wasted as heat is instead converted into electricity and fed back into the crane's power system.
In the event of a power failure, the secondary brake will not hold the load. Instead, it will lower the load at its normal "controlled" rate of speed. However, that speed could be downright fatal to anyone unfortunate enough to be underneath when it happens.
Hitting the Upper Limit Switch Is Necessary When You Lift
Instead of lifting a load high enough to maintain proper clearance around various obstacles, many overhead crane operators assume that they must gain as much height as possible. This often means hitting the crane's upper limit switch, a device designed to keep the hook assembly from coming into contact with the drum. However, there are a few problems with this approach:
- The upper limit switch is intended as a safety function and not as an operational function. The upper limit switch should only be used to prevent accidents.
- Hitting the upper limit switch on most hoists will actually shut the machine down, leaving it stuck in the up position. If it fails, it could cause the rope to fail and the load to drop.
Under proper operating conditions and guidelines, the upper limit switch should never be triggered. For special situations where an operational upper limit switch is needed, a secondary switch wired in fail-safe mode can be installed. It'll help you recognize when the upper lift limit has been reached, but without triggering a hoist shutdown.
There's No Need to Check the Crane Every Single Day
Daily inspections are the cornerstone of overhead crane safety. Sadly, too many operators assume that a crane that worked safely yesterday will work safely today and, as a result, inspections are unnecessary. As a result, operators and other personnel can easily be injured or even lose their lives due to a malfunction or flaw that was never checked because a daily inspection was never performed.
OSHA regulations require daily inspections of all lifting equipment prior to use, preferably at the beginning of each shift. Daily inspections are essential for ensuring the structural and operational integrity of the overhead crane and to ensure its safe use throughout the day.
Side Pulls Are Okay as Long as the Load Is Well under Capacity
Your overhead crane was designed solely to lift loads vertically. Asking it to lift loads in any orientation other than "up" and "down" is asking for trouble.
For starters, side pulling a load can cause the wire rope to damage itself through contact with the drum and/or remaining rope. The rope can even jump out of the drum and tangle itself around the shaft during a side pull. Side pull also adds unintended stress on the bridge beam and other parts of the overhead crane.
Even with loads that are well under the overhead crane's lift capacity, the unpredictable stresses placed on it during a side pull could cause it to fail in unexpected ways. For this reason, you should always avoid side pulls and always lift vertically. You can find more info here on cranes.