Advances in powder coating of metal components: A case study for wire die springs

Abstract

The subject of the present paper deals with the description of an innovative coating process, based on polymer powder fluidized bed technology, applied in combination with an adhesive silicone primer. This study aims to overcome the problems of traditional coating systems for mechanical complex-geometry components, for applications where high precision in thin film deposition and high coating uniformity, at a micrometer level, are required. In this context, the case study of wire die spring coating is here proposed, carrying out a validation of the proposed technical solution, compared to the traditional process based on electrostatic coating, through an aesthetic, morphological and mechanical experimental characterization. The results showed that the innovative deposition system ensures excellent aesthetic performance, depositing a homogeneous coating, with a constant thickness of ~15–20 μm, on the surface of the complex geometry component analyzed, as opposed to ~25–90 μm for the traditional process. The proposed technique also ensures an excellent coating uniformity both inside the coils and on the external surfaces, as well as a complete protective coverage of the springs and their uniform coloring, with significantly lower consumption of coating powder, thus verifying the full technological feasibility of the fluidized bed deposition process, which is applicable also on non-conductive surfaces. Finally, the surface morphology of the specimens coated with the advanced system showed a memory effect of the substrate, while the analysis of the mechanical behavior remarked a higher fragility in terms of scratch test resistance, typical of thin films, compared to the reference.