ANSI B7.1 (Safety Requirements for the Use, Care and Protection of Abrasive Wheels) defines segments as abrasive bodies in various standard shapes that, when individually chucked in a suitable holding mechanism, form a grinding unit.
Segments (as shown in the photograph below) are used on surface grinders and mounted in a holding or clamping mechanism. Like most grinding wheels they are very strong, but brittle. Improper mounting and usage can cause them to break. Below are a few of the most common causes of segment breakage.
Failure to Use Segments with Blotters
Use segments with attached blotters. Blotters are used for several reasons. They tend to cushion the pressure of the segment holder against high points or uneven surfaces and distribute the pressure evenly. They prevent damage to the surfaces of the segment holder from the abrasive surface of the segment. They provide a better coefficient of friction, thus aiding in preventing a segment from moving in its holder.
If a segment slips out of its holder, it can strike the work-piece, work chuck or other object and break. Tighten all segment fasteners enough to prevent slippage. Over tightening may cause damage to the segment holding mechanism or the segment itself. If a torque requirement is required, it must come from the machine builder, rebuilder, or other holding mechanism authority.
Bending the Segment
Segments are strong, but brittle. If the segment is bent in the holding or clamping mechanism it may break. Any foreign materials between the segment and the clamping mechanism can cause the segment to break. Worn out or damaged clamping devices can grip a segment unevenly and break it. The segments must be clean and free of any burrs, fully aligned, and centered in the clamping mechanism or breakage may occur.
Any type of impact on the face or side of a segment or segments can cause a breakage. Excessive segment in-feed, work-piece slippage or improper movement, improper alignment, or any type of hard impact can lead to breakage.
The standard speed for resin bonded segments (Organic Bonds) range from 6,500 to 8,500 SFPM and for vitrified bonded (Inorganic Bonds) range from 5,500 to 6,500 SFPM per ANSI B7.1-2010. Excessive speed can cause the segments to break.
It is common practice to “block” or place a spacer above a used segment to extend the life of the segment. There are some important rules you must follow such as: do not “block” a segment until the segment has worn completely down or has become “stubbed out.” Never use a segment down more than 50% the segment’s original height.
Always use a segment machine guard and, when required, retaining bands.
You must always remember to play it safe at the wheel!
For additional information on this topic or if you need any other abrasive safety information, please review ANSI, OSHA and all literature provided by the abrasive wheel and machine manufacturer. You may also contact the Saint-Gobain Product Safety Department at Tel. (508) 795-2317 or Fax. (508) 795-5120 or contact your Saint-Gobain Abrasives, Inc. representative with any safety related questions.