Home / Resources / Consultant's Corner / Major Causes of Grinding Wheel Breakages

Major Causes of Grinding Wheel Breakages

As we are all aware, grinding wheels are a safe tool when used properly. However, after they have been shipped, they may be subjected to any number of abuses and misuses, such as damage in handling, improper mounting, over- speeding, jamming or been dropped.

According to a recent OSHA fatality report, an employee was operating a pedestal grinder. The grinder had a spindle operating speed of 3,600 rpm and 14 inch diameter by 2-inch width abrasive wheel. The maximum operating speed of the abrasive wheel was 1,773 rpm. While the worker was grinding a 250-lb ductile cast iron part, the grinding wheel broke apart and struck the worker. The housing around the grinding wheel was significantly damaged and not effective in containing the broken grinding wheel parts. As a result, the employee was killed.

According to another OSHA fatality report, an employee was grinding burrs off metal castings. The employee was using a 30 inch resin-bonded silicon carbide grinding wheel. The wheel had been in use for only nine hours. Without warning, the wheel disintegrated and the employee was struck in the neck by one of the flying pieces. The employee died almost immediately, of a severed jugular vein. An investigation revealed that the wheel was rated at 9,500 rpm, but it was used at 12,500 rpm. In addition to the grinding wheel being stressed beyond design limitations, a ring test was never performed prior to installation.

The following are some major causes and examples of grinding wheel breakages:

• Using a grinding wheel damaged during transportation, storage or as a result of careless or improper handling. Inspect and ring test all grinding wheels before mounting them on a machine. Never install a damaged grinding wheel.

CFR 1910.215(d)(1) - 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".

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 bonded wheels do not emit the same clear metallic ring as do vitrified and silicate wheels.

Figure 1
Figure 2

"Tap" wheels about 45 degrees on each side of the vertical centerline and about 1 or 2 inches from the periphery as indicated by the spots in the figure above. Then rotate the wheel 45 deg. and repeat the test. A sound and undamaged wheel will give a clear metallic tone. If the wheel “rings” when tapped at all of the positions, it passes the ring test. If it sounds dead at any of the positions it fails and should be inspected very closely or discarded. Grinding wheels aren’t free but they are way cheaper than an explosion so error on the side of safety.

Figure 3

• Selecting the wrong grinding wheel for the job. Don’t grind material for which the wheel is not designed.

• Operating a grinding wheel on a machine not designed for it. Never mount a grinding wheel on a machine that is not designed and properly guarded for that grinding wheel.

• Operating the wheel at a higher rpm. Never operate a grinder at a higher rpm than the grinding wheel is designed for. Inspect all grinders frequently to ensure the proper grinding wheel is installed in each one of them.

Figure 4

• The improper mounting of grinding wheels. Follow the proper torque requirements for grinder, don’t over-tighten your grinder flanges.

• Over-tightening can damage the mounting flanges, resulting in breaking even the largest/strongest wheels.

• Review all mounting instructions before attempting to mount a grinding wheel.

Figure 5

• Grinding on the wrong surface of a grinding wheel. Never grind on the side of the wheel. The wheel is designed to be used on the front side only.

• Jamming the work into the grinding wheel can cause the wheel to break.

• Force grinding, so that the motor slows noticeably or the work gets hot. Don’t jam or force the work, let the grinding wheel do its job.

Grinding wheels break for a reason! Injuries in the workplace occur for a reason! Follow all safety instructions and rules before mounting and using a grinding wheel. Inspect all grinding equipment frequently. Read the manufacturer’s instructions for the grinder and the grinding wheel. Always follow safe work practices. Make sure the safety program includes frequent power tool safety inspections, as well as frequent safety inspections of the facility. Hazard identification is the basis for hazard correction and prevention. Prevention is essential to maintain a safe workplace. For more information about safety programs, please visit our website at www.usfsafetyflorida.com or call us at (813) 974-9962.