Which problems smallest remainder dirt particles can cause, has recently experienced a German car manufacturer: He had to recall numerous vehicles due to malfunction in the engine. Reason were production residues consisting of hard particles, which lead to a capital engine damage - in the worst case to burning cars.
Hard residual dirt particles usually come from the fine machining of surfaces by glass blasting, vibratory grinding, honing or trowalizing. With these steps, components should be specifically refined and the dimensional and dimensional accuracy improved. As production residues, the particles remain on the surface, unless it is adequately cleaned.
Hard particles have an extremely abrasive effect, ie they break down other materials, damaging functional layers and surfaces. In addition, hard residual dirt particles can get into the sliding surfaces of bearings and raceways, jamming them and thereby lead to the complete destruction of an engine.
Our team was able to assist the manufacturer by providing the hardness and origin of the production residues of various individual parts of the affected engines with an automatic SEM-EDX microscope of FEI-Aspex brand investigated (see figure). Hard residual dirt particles such as corundum and silicon carbides with a Mohs hardness> 8 were determined in the crankshaft, connecting rod and cylinder head. For comparison: diamond has a Moh's hardness of 10.