Based on the physical interpretation of the results obtained, the QCS allows the sprayer to maintain the final quality of the coatings in the highest possible level by controlling the whole process: selection of the best suited powder/s for each specific gun, checking the parameters of the powder and adjusting the spraying parameters accordingly.
The guns participating in the project have been classified into three groups accordingly with their transfer of heat and momentum to the powder granules. The powders have also been classified into six groups following their specific characteristics that influence the heat and momentum transfer from the HVOF jet. The parameters responsible for the final properties of the coatings (wear and corrosion resistance) have been identified and the influence of the spraying parameters on the characteristics of the powder granules assessed.
The absence of reliable methods for selection of spray powders and optimum HVOF thermal spray conditions causes serious problems in assurance of the coating quality and leads to economic losses of SMEs. One of a highly effective approaches used in this proposal to overcome this is to provide research on evaluation of the sprayed thick coatings including characterisation of the coatings, assessment of the coating properties, physical interpretation of the coating formation, testing of the HVOF sprayed coatings in the working conditions on the industrial components and development of the optimum conditions of the spray process giving high quality coatings. In this proposal the system WC-Ni(Co)Cr has been chosen since the industrial partners need a powder material which gives at a reasonable cost the coatings with higher corrosion and oxidation resistance and wear resistance comparable with that of the WC-Co coatings. The main industrial objective of this project is to develop the recommendations enabling formation of a reliable and practice oriented quality control system (QCS) giving high quality and reproducible coatings by HVOF spraying of WC-Ni(Co)Cr powders. The QCS will also allow the optimum spraying conditions for given combinations of above powders and substrates in relation to the operational parameters of the HVOF spray equipment being used (gun design, combustion gases, etc.). Some specific guns will be considered (Diamond Jet, DJ-2700, Jet Kote, Top Gun, CDS Gun, OSU and D-Gun). Propane, propylene, acetylene and hydrogen will be tested as fuel gases and a fuel gas with a minimal oxidation power will be outlined. Through the development of a data bank industrial partners will have ready access to results which have been obtained to meet their needs. The final result of the project (QCS) immediately after finishing this project can be used for commercial purposes. Then also a reduction in working time and costs will be achieved for the production of a suitable quality of the coatings. The principles and inherent characteristics of the QCS developed for the specific combinations of powder system (WC-Ni(Co)Cr) and substrates (mild steel, stainless steel, Al-4%Cu alloy and copper) in HVOF spraying with different guns and fuel gases will enable similar systems to be developed for the other cermet powders and substrates under different spray conditions. The main economic objective is to produce at a reasonable cost and within a period of two years the quality control system. Another economic objective is to reduce the energy consumption and the time for spraying which in turn will lead to an increase in spray productivity. It is expected also that the cermet powder chosen widen the scope of use of HVOF spraying to produce wear, corrosion and oxidation resistant coatings. The main social objective of the project is to increase the life of industrial components. The project has an important environmental objective in decreasing corrosion and hence decreasing the deposits of scrap and waste materials and making HVOF spraying a cleaner technology.
Funding SchemeCRS - Cooperative research contracts