Hardness & Structure


Hardness (or grade) is determined by how well abrasive materials are held in place.

The hardness of an abrasive stone is largely determined by the amount of bond used to manufacture the product. Since most applications have narrow acceptance ranges for stock removal, finish requirements and cycle times, the production of fine grit, bonded abrasive products must be tightly controlled. Utilizing a proprietary tight tolerance grading methodology, Darmann ensures that stone and wheel production is consistent. The following table provides some factors to be considered when selecting a product grade.

  • Harder Grades
  • Light Stock Removal
  • Better Stone Life
  • Better Finish
  • Small Contact Areas
  • Finish Positions
  • More Stone Pressure
  • Used on Softer Materials
  • Softer Grades
  • Heavy Stock Removal
  • More Free Cutting
  • "Rougher" Finishes
  • Larger Contact Areas
  • "Rougher" Positions
  • Less Stone Pressure
  • Used on Harder Materials

Structure is determined by the volume and arrangement of abrasive grains within a stone or wheel. Abrasive tool performance is determined by the interaction of the abrasive grain, bond and porosity. The spacing of abrasive grains and pores should be evenly distributed to assure performance consistency. "Open" structured products provide better chip clearance, and are less subject to loading than a closed abrasive tool. "Closed" structure products are preferred for low stock removal and fine finisher applications.

Open Structure Closed Structure