AMW tests adhesion of thermal spraying layers

AMW Industry – Antwerpse Motoren Werke – is a mechanical workshop specialised in the manufacturing and repairs of parts for the industry and shipping sectors, as well as hard coatings for metals. This SME manufactures and repairs machine parts and applies coatings for large corporate groups. AMW has an extensive range of equipment, for conventional and digital lathing, milling, drilling, boring, cylindrical and smooth grinding and polishing. The company plays a major role in the niche market of thermal spray coating, used to apply hard wear-resistant protective layers to metals.

Thermal spraying

HVOF (High Velocity Oxygen Fuel) coating is an economically viable procedure to restore a component’s surface and to apply hard metallic and ceramic layers. AMW uses a cold process that does not subject the substrate to thermal treatment. AMW uses tungsten carbide-based RAM® coatings to prolong the life cycle of the surfaces of parts, old and new, subject to wear, in areas with heavy erosion or abrasion. RAM hard coatings were developed in the USA and are among the foremost options in the HVOF segment. AMW is the exclusive supplier of these coatings in Europe.

Surface tests

AMW wished to investigate the effect of the condition of steel cylinder surfaces on coating adhesion, and approached Sirris to do so. Thirty-two test samples made of hardened 42CrMo4 and stainless steel sprayed with two types of coating were used to determine the effect of the surface condition on coating adhesion. The sample included various pre-treatment combinations, such as grinding, sandblasting and ageing by means of oxidation, and was then subjected to a metallography and three adhesive tests: a scratch-and-indentation test performed on cross-sections of the sprayed cylinders and a bending test on small flat sheets.
Most of the tests demonstrated that grinding and blasting do not usually have a positive effect on layer adhesion, given that the treatment increases surface roughness and increases the risk of contamination. The tests also showed that oxidation has no effect on layer adhesion.
The tests demonstrated that pre-spraying surface treatment can be eliminated from the procedure with no adverse effect on adhesion, resulting in a simplified maintenance procedure.