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Surface preparation for thermal spraying


Before applying coatings by means of thermal spraying the metallic surfaces are roughened and activated, usually by grit blasting either with alumina or chilled iron grit. This procedure causes problems: As proved by surface analysis finely dispersed residues of grit blasting material cannot be removed completely by subsequent blasting with compressed air. Investigations of damaged parts revealed that these surface contamination hinders the adhesion between the coating and the substrate. Even when self - fluxing alloys are remelted diffusion to the substrate may be detrimentally affected. For safe mechanical interlocking between coating and substrate the roughness should be as high as possible. Consequently a minimum thickness of the coating becomes necessary with a high surface roughness. This excludes many potential applications and needs a considerable effort for post treatment. Therefore it is the aim of this cooperative research project to develop a new technique for surface pretreatment or to adopt from other surface technologies well known methods in order to clean grit blasted surfaces and thus to ensure good coating adherence in spite of low substrate roughness. The following processes shall be investigated for their suitability to improve the adhesion of sprayed coatings and their applicability by SMEs: Cleaning by blasting with CO2 - grit Plasmaetching / vacuum anealing Using transferred arc in atmosphere or under shielding gas


KVT Kurlbaum GmbH.
71-73,Use Akschen
28237 Bremen

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SLM Sociedads Lisponense da Metalicaçao Lda
Catujal Apartado 3
2686 Sacavem Codex