Grinding Wheels - 6: Grade
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The grade of the wheel describes the strength of the union between grain and bond. It is desirable for the grains that have been worn down to break away, exposing new grains to the work surface.
As this is accomplished, the old grains are released from the wheel. The bond is rated hard grade if the abrasive is released slowly, and the bond is difficult to break. The grade is graded soft if the bond breaks away easily, allowing rapid grain disintegration.
Selecting the proper grade for the wheel is one of the more difficult choices to make in wheel selection.
It is important to remember that all abrasive grains are hard, and that the hardness of the wheel refers to the strength of the bond, not the hardness of the grain.