Tech Tips
Check Overhead Crane Brakes
How and
when does an overhead crane operator test the hoist brakes?
Federal
regulation OSHA 29CFR 1910.179(n)(3)(vii) states:
“The operator shall test the brakes each time a load
approaching the rated load is handled. The brakes shall be
tested by raising the load a few inches and applying the
brakes.”
So how
exactly does one apply the brakes on an overhead crane?
Overhead crane brakes are applied automatically when
hoisting motion stops. This braking action, referred to as
holding brakes, requires specific brake torque settings.
According to OSHA 29CFR 1910.179:
“Holding brakes for hoist
motors shall have not less than the following percentage of
the full load hoisting torque at the point where the brake
is applied.
125 percent when used
with a control braking means other than mechanical.
100 percent when used in
conjunction with a mechanical control braking means.
100 percent each if two
holding brakes are provided.”
To test
the brakes we simply raise the load a few inches and stop
hoisting. Holding brakes set automatically, and we’re now
ready to proceed, right?
Wrong!
At this point we have only tested the holding brakes. What
about the control brakes? Control brakes are designed to
prevent the load from accelerating in the lowering
direction. If mechanical load control brakes fail when you
attempt to stop during load lowering, will the holding
brakes still be able to stop the load safely? Probably not.
And, if the control brakes are not working properly you can
lose control of the load.
Now that
we understand how an overhead crane’s holding brakes and
control brakes combine to provide safe load handling, the
process for checking control brakes is simple.
After checking to ensure
that the holding brakes are functioning properly, hoist the
load a little higher, maybe a foot or so more. Allow the
holding brakes to stop and hold the load. Next, lower the
load about halfway and again stop the load. For a crane
equipped with mechanical load control brakes, this
procedure tests both the holding brakes and the control
brakes. If mechanical load control brakes are working
properly the load should stop and hold. If an overhead
crane’s brakes are going to fail, they’re more likely to
fail in the lowering direction.
This
procedure should be followed with the first load of the
shift, and anytime a substantially heavier load is handled
later in the shift. Remember to always keep the load close
to the ground and never perform this test in a location that
cannot support the weight of the descending load.
You can
now see why holding brakes, when used in conjunction with
control braking means
other than mechanical,
must be set to 125% of maximum hoist motor torque.
Non-mechanical control brakes (eddy current) only control
descent speed while the hoist is moving, and are unable to
assist with load holding. If the crane is equipped with eddy current type load control brakes, and the load continues
to drift down during this test, the brakes are either not
set correctly or may be excessively worn.
In either
case, remove any crane from service when the load continues
to drift down during this test. Report the condition to
supervision immediately and do not use the crane until load
control safety is assured.
Operators
are the first line of defense in accident prevention.
Understanding how overhead crane brakes function, and
conducting a meaningful test goes a long way toward ensuring
a safer and more reliable operation. Other standards that
overhead crane users should be familiar include the ASME
B30.2, ASME B30.11, ASME B30.16, and ASME B30.17.
This Tech
Tip is not intended to replace specific instructions
provided by your crane manufacturer. So read and be
thoroughly familiar with each crane's user manual.
Tests are an attempt at
a controlled failure. Operators must follow all safe work
practices and ensure their body is never in a position to be
contacted or struck by the load or rigging.
If you have
questions or comments about this or other Tech Tips you can
email us at
newsstaff@cranetech.com.
