Hazards – Blog
I am often asked about some
of the hazards I generally found during inspections. These are by far the most
frequent hazard I found while conducting inspections. Most of them are actually very simple to fix.
Description: A bench grinder
in the maintenance shop was not safeguarding to OSHA’s minimum
requirements. OSHA requires the
following items with respect to bench grinders:
- Tool rests (work rests) shall be kept adjusted closely to the wheel with a maximum opening of 1/8” to prevent the work from being jammed between the wheel and the rest.
- Tongue guards shall be kept adjusted to within 1/4” of the outside of the grinding wheel to deflect fragments away from the operator should the wheel shatter.
- As the bench grinder is designed for a fixed location, it must be securely anchored to prevent walking or moving during operation. (1910.212b)
- Immediately before mounting, all abrasive wheels are to be closely inspected and sounded (ring tested) by the user to make sure they have not been damaged in transit, storage, or otherwise.
Condition: Work rests. On offhand
grinding machines, work rests shall be used to support the work. They shall be
of rigid construction and designed to be adjustable to compensate for wheel
wear. Work rests shall be kept adjusted closely to the wheel with a maximum
opening of one-eighth inch to prevent the work from being jammed between the
wheel and the rest, which may cause wheel breakage. The work rest shall be
securely clamped after each adjustment. The adjustment shall not be made with
the wheel in motion. Exposure adjustment. Safety guards of the types
described in Subparagraphs (3) and (4) of this paragraph, where the operator
stands in front of the opening, shall be constructed so that the peripheral
protecting member can be adjusted to the constantly decreasing diameter of the
wheel. The maximum angular exposure above the horizontal plane of the wheel
spindle as specified in paragraphs (b)(3) and (4) of this section shall never
be exceeded, and the distance between the wheel periphery and the adjustable
tongue or the end of the peripheral member at the top shall never exceed
one-fourth inch. (See Figures O-18, O-19, O-20, O-21, O-22, and O-23.) Inspection. Immediately
before mounting, all wheels shall be closely inspected and sounded by the user
(ring test) to make sure they have not been damaged in transit, storage, or
otherwise. The spindle speed of the machine shall be checked before mounting of
the wheel to be certain that it does not exceed the maximum operating speed
marked on the wheel. Wheels should be tapped gently with a light nonmetallic
implement, such as the handle of a screwdriver for light wheels, or a wooden
mallet for heavier wheels. If they sound cracked (dead), they shall not be
used. This is known as the "Ring Test".
Standard: 1910.215(a)(4),
1910.215(b)(9), 1910.215(d)(1)
Potential
Effects: Cuts
to fingers and penetration injuries from contact with or disintegration of the
grinding wheel.
Recommended
Action:
Ensure the grinder is bolted to the bench and adjust the tongue guard and tool
rest to the specifications listed above.
As the wheel is ground down, readjust the guards. This adjustment should be checked routinely
before energizing the wheel, as a standard safe operating procedure. Ring test stones.
Procedures for ring test stone: To conduct the ring test on smaller wheels, they
should be tapped lightly with a light nonmetallic implement, such as the handle
of a screwdriver for light wheels, or a wooden mallet for heavier wheels. Tap
wheels about 45 degrees each side of the vertical centerline and about one or
two inches from the periphery. Then
rotate the wheel 45 degrees and repeat the test. A sound and undamaged wheel will give a clear
metallic tone. If cracked, there will be
a dead sound and not a clear "ring." If they sound cracked (dead)
they must not be used. Wheels must be dry and free from sawdust when applying
the ring test, otherwise the sound will be deadened. It should also be noted that organic bond
wheels do not emit the same clear metallic ring as do vitrified and silicate
wheels.
Larger wheels may be tested by vibration to detect damage. To perform the vibration test, an abrasive
wheel is set on a test fixture in a horizontal position and coated with a thin
layer of fine dry sand. The wheel is
vibrated gently. As the wheel vibrates,
the sand granules respond to the vibration.
The granules will move away from any cracks that may be in the
wheel. Conversely, the granules will be
uniformly distributed over the surface of a sound and undamaged wheel.
Note that the spindle speed of the machine must be checked before
mounting the wheel to be certain that it does not exceed the maximum operating
speed marked on the wheel.
Author: Deborah Grow, Safety Specialist
Author: Deborah Grow, Safety Specialist
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