Blotters - Their Function and Proper Use
he proper use of blotters can aid in preventing wheel breakages. Blotters, by definition, are compressible washers that must be placed between an abrasive wheel and a mounting flange. They are important for wheel safety and are required by the safety code ANSI B7.1. These blotters are more than just cardboard or paper; they are designed to strict standards for material type, thickness, coefficient of friction, and compressibility. Only use blotters that are supplied or recommended by the abrasive wheel manufacturer.
Blotters help to assure that the flange clamping pressure is evenly distributed on the wheel. They cushion the pressure of flanges against any high points or uneven surfaces. They also prevent damage to the surfaces of the flanges from the coarser abrasive surfaces of the wheel. You must therefore use one clean new blotter for each mounting flange.
Additionally, blotters provide a better coefficient of friction than would be obtained between the flanges and the wheel without blotters, thereby providing better transmission of the driving power to the wheel.
Blotters must be the correct size to be effective. The blotter must be equal to or greater than the machine’s mounting flanges.
In other words, wheel blotters should NEVER be smaller than the machine’s mounting flanges. The grinding wheel is driven by the machine flanges. The forces that drive the wheel are transmitted through the bearing surface of the flanges. The surface that drives the wheel (bearing surface) must always be in contact with the side of the wheel. A flange that is larger than the wheel’s blotter will hang over the blotter and not make full contact with the side of the grinding wheel. This lack of contact (overhang) could lead to wheel slippage, uneven or increased side pressure, and breakage.
Blotters are also useful for checking the condition of grinding wheel flanges. For more on the importance of flange condition, see the article, Flanges: A Critical Link in Grinding Wheel Safety.
Since blotters are compressible by design, when mounted, they take on impressions from the surfaces of the wheel and flanges. These impressions provide insights into the flange condition and mounting procedures. So next time you perform a wheel change, check for the following:
The blotter should display NO signs of slipping or other movement of the grinding wheel inside its flanges.
Scratches, tears, or other wear marks (as seen in Figure 1) may indicate that there has been movement.
The blotter impressions should be even and NOT indicate concentrated flange pressure.
Figure 2 shows a segment blotter with a sharp indentation on the bottom side. This condition caused the segment to crack.
The blotter should show evidence of complete flange contact over the entire bearing surface.
Figure 3 is an example of partial flange contact; notice the top section where no flange impressions are visible.
Regularly examining blotters after use is an easy and valuable way to check for potential mounting problems. Add it to your preventive safety plan alongside periodic flange inspections and good mounting procedures.
For additional information on this topic or if you need any other abrasive safety information, please review the Norton Product Safety page, ANSI, OSHA and all literature provided by the abrasive wheel and machine manufacturer. You may contact the Saint-Gobain Product Safety Department at (508) 795-2317, fax: (508) 795-5120, or contact your Saint-Gobain Abrasives representative with any safety related questions.