Blotter Size vs. Flange Size- What’s the Rule?

The 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. These blotters are more than just cardboard or paper, but are designed to strict standards for material type, thickness, coefficient of friction, and compressibility. Use only 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 tend to 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.

http://industryrailway.com/blotter-size-vs-flange-size-whats...

Blotters
Blotters are made of flexible and compressible material, e.g. cardboard or plastic, and are placed between the flange and the grinding wheel (see Fig.)
The blotters should be between 0.2 and 1.0 mm thick and their diameter must be at least that of the flan¬ge. The purpose of the blotters is to:
take up any distortion between the flange and the wheel, within the area of flange pressure
reduce the risk of slippage between the wheel and the flanges
distribute, equally, the axial clamping force when the nut is tightened, over the entire contact area between the flanges and grinding wheels

http://www.andreabrasive.com/technical-description/safety-in...

http://www.gardei.net/products/