SAFETY TESTS OF GRINDING WHEELS

Super #abrasives / #grindingwheels products: Verification of the strength of the joint between the abrasive layer and the blank

Safe abrasive products must be able to withstand the forces and loads that are to be expected both under normal conditions of use and in the event of misuse. The resistance to deformation and bursting depends on various factors such as material, geometry, type and duration of stress and environmental conditions.

The EN safety standard for superabrasive products containing diamond or cubic boron nitride (EN 13236) therefore requires that, in addition to a safety factor against bursting, abrasive products also have a certain strength of the joint between the abrasive layer and the blank. This applies to abrasive products that consist of a metal blank and an abrasive layer containing diamond or CBN applied by laser welding, brazing or sintering. Typical representatives of this product group are cutting-off wheels (diamond saws) or segmented cup and dish grinding wheels. With diamond saws, we differentiate between segmented cutting-off wheels and those with a continuous rim. The strength of the joint between the abrasive layer and the blank is determined by means of a bending or shear test.

The bending test on cutting-off wheels (diamond saws) is carried out with a regularly calibrated torque wrench or a bending test device. The abrasive segment to be tested is held by a clamping piece. Load is applied to the clamping piece at a lever arm and the applied force is measured. The applied force is steadily increased until breakage. The bending moment is calculated from the force and lever arm. The test devices are described in more detail in EN 13236.

Verification of compliance with the requirements is considered as provided if the minimum bending strength or the minimum bending moment according to EN 13236 is reached. The abrasive products used for the test must be destroyed afterwards.

In the?shear test?for verification of the shear strength, the cup or dish grinding wheel is mounted in the area of the core on a console on which the segment to be tested is subjected to shearing force by means of a hardened pressure stamp. The segment is loaded in a radial outside direction. The applied force is steadily increased until the required shear force or shear strength is reached. Verification of sufficient shear strength is considered as provided if the required minimum values according to EN 13236 are reached, there is no breakage or visible crack and no clearly visible plastic deformation of the core.