Partners: CA Technoloogy Ltd., Comint, S.A., ENEL SpA, Engineering Services International Ltd., Euromat GmbH and Metallisation Ltd.

Funded under the European Brite-Euram Programme

Protective coatings produced by thermal spraying processes comprise an area of great economic importance which cuts across many sectors of the European industry: the power, petrochemical, gas, aerospace and construction industries demand corrosion/erosion resistant coatings.

The Arc Wire Spraying process, which insures the highest deposition rate (up to 40 kg/h) has poor oxide and porosity levels (cumulatively greater than 25%); on the other side the Vacuum Plasma Spray process (VPS) which guarantees coatings with low oxide levels (less than 5%) is very expensive both in terms of the capital (of order 1 MECU) and operating costs (very low production rates). There is a need, therefore, of more cost effective spraying processes able to produce good quality coatings.

This project was aimed at developing modified arc wire and air plasma spraying processes, able to produce higher quality coatings than present processes, with a potential of replacing respectively air plasma and vacuum plasma spraying in most demanding applications.

The scheduled objectives were to obtain:

-coatings with porosity < 5% and oxides < 15% with a modified arc wire technique,

-coatings with porosity < 3% and oxides < 5% by a modified air plasma spray technique.

In order to reach Project objectives innovative shroud devices were designed for the two torches, and an "intelligent" control system was developed. The shroud attached at the face end of spraying torch provides shielding gases which avoid air entrainment and protect the particle stream from oxygen. The final shroud devices were developed starting from prototypes and improving them with the help of the results of computational techniques, modelling the gas flow fluid-dynamics of both the arc-wire and the plasma spraying process.

The control system was developed as a self standing stream monitoring device to provide a tool able to measure the main characteristics of the particle stream and to compare them with those of a reference optimised situation. Using this device before starting to spray the component process parameters can be adjusted in order to reproduce reference spraying conditions.

The quality of the coatings produced with the innovative devices was checked by metallographic techniques, adhesion tests and hardness measurements. On the coatings devoted to the most demanding applications corrosion tests were performed in the environment representative of operating conditions. Very good results were obtained both on FeCrAl coatings sprayed by shrouded arc for the boiler panel protection and on AMDRY 995 coatings sprayed by shrouded plasma for application to gas turbine blades (usually such coatings are produced by the much more expensive VPS technique).

The effectiveness of the innovative devices were finally demonstrated by coating real components such as boiler panel sectors, parts of valves or train and a gas turbine blade.

The final analysis showed the cost effectiveness of the new processes; the degree of development of some Project deliverables let industrial partners to put them on the market immediately after the end of the Project.