Abrasive Wheel Grinders
April Safety Tip
THE “RING TEST” FOR ABRASIVE WHEEL GRINDERS
One of the most common and useful tools used both at work and at home is the bench or pedestal grinder. Everyone should be reminded never to take this tool for granted. People have been killed and hundreds seriously injured when a cracked or defective grinding wheel has “exploded.”
In addition to a visual inspection of grinding wheels, a “ring test” must be performed. OSHA says that you must “ring-test” grinding wheels before mounting them to prevent the inadvertent mounting of a cracked grinding wheel. A disintegrating wheel can cause solid wheel fragments to fly off at speeds exceeding 125 miles an hour. This is capable of causing serious injury or even death. The ring test helps identify defective grinding wheels.
A ring test is conducted by tapping the wheel gently with a light, nonmetallic implement, such as the handle of a screwdriver for light wheels or a wooden mallet for heavier wheels. The wheels should be “tapped” about 45 degrees on each side of the vertical centerline, and about 1or 2 inches from the outer edge of the wheel. Rotate the wheel 45-degrees and repeat the test. An undamaged wheel will give a clear metallic tone. If it is cracked, there will be a hollow, “dead” sound and you will not hear a clear “ring.” In this case do not use the wheel!
Wheels must be dry and free from sawdust when conducting the ring test, otherwise the sound will be deadened. It should also be noted that organic bonded wheels do not emit the same clear metallic ring as do vitrified and silicate wheels.
Always wear your personal protective equipment, adjust the equipment guards properly and work safely while using abrasive wheel grinders. Yet these steps will offer little protection if the abrasive wheel itself is not in good condition. After heavy use and whenever changing the wheel, conduct the ring test. This is an important step that will minimize your exposure to serious injury.
For larger grinders, grinding wheels are laid flat on a vibration-table, with sand evenly spread over the wheel. If the wheel is cracked, the sand moves away from the crack.
To prevent cracking a wheel during the mounting procedure, employees must be very carefully trained in those procedures. This starts with making sure the wheel is properly matched to that particular grinder, using proper blotters and spacers, and knowing exactly how much pressure to exert with a torque-wrench.