Safety tests of grinding wheels

Superabrasive 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.

In hand-held applications, in addition to the tangential forces acting on the periphery of the abrasive product, there are always also lateral (axial) stresses acting on the grinding wheel. With products approved for side grinding, these stresses are completely normal. However, a slight tilt or a curved cut is enough to cause enormous lateral loads even on cut-off wheels that are only approved for straight cuts.

The EN safety standard for bonded abrasive products (EN 12413) therefore requires that certain abrasive products have sufficient side load capacity in addition to a safety factor against bursting. The side load capacity is determined by the single-point side load and the impact test (working capacity). The requirements generally apply to resin bonded grinding wheels for use on hand-held machines. EN 12413 specifies required values for the single-point side load and the working capacity depending on the type of grinding wheel. The side load capacity is verified by the single-point side load test and the impact test.

The single-point side load test is carried out on both cutting-off and grinding wheels. The abrasive product rotates at maximum operating speed. Then a pressure roll is fed at a constant feed rate vertically to the axis of rotation against the grinding wheel and loads it until rupture or up to the required value. During the test, the force acting on the pressure roll in the feed direction is measured as the single-point side load.

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.