This paper deals with the development of a coordinate measuring machine for parallel tactile probing of microstructures. The particular challenges due to the parallel probing will be discussed and the concluding results regarding the construction, the control and the simulation environment will be outlined.
Ceramic coatings with high electrical insulation capabilities can be sprayed on to metallic substrates by plasma spraying for insulation purposes, e.g. for corona rolls. However, the electrical and mechanical properties of such coatings severely depend on the spray conditions used during coating. This paper discusses the effects of spray conditions on coating properties and what parameters are essentially to be monitored for achieving high quality coatings. The paper does not confine to the classical machine parameter control techniques, however, it introduces recently developed diagnostic tools for on-line monitoring the spray particle jet and substrate conditions. I INTRODUCTIONThe low value for electrical conductivity and high dielectric strength of oxide ceramic materials such A1,0,, ZrO,, SiO, and TiO, make them popular for applications requiring electrical insulation. Beside the use of these materials for monolithic ceramics the high process temperatures and flexibility of Atmospheric Plasma Spraying allows deposition of these oxides to form a coating on all kind of substrate materials. Coatings, even up to several mm thick can be produced. The formation of A1,0, from it's molten phase shows many modifications. The high cooling rates involved cause formation of metastable phases q, y, 6 and 8, since nucleus activation energy for these phases is comparably low. These phases, Table 1 : Properties of oxide ceramic materials ceramic a-Al,O, TiO, SiO,however, show explicitly inferior electrical properties. The desired a-phase can only be formed for low cooling rates or subsequent heat treatment. A high a-content can be achieved by slow solidification which can be controlled by spraying on substrates with high temperatures and by using bigger particles leading to decreased cooling rates. Of special interest for electrical shielding of components up to very high voltages are thick coatings (1-5 mm). To manipulate phase composition and optimise residual stresses, especially in case of thick coatings, tools to monitor the process are required [1,2,3,4]. An on-line process control approach will be discussed in the following. I1 MONOLYTHIC AND COATED OXIDE CERAMICS FOR ELECTRICAL INSULATION PURPOSESThe low electrical conductivity and high dielectric strength of oxide ceramic materials such as A120,, ZrO,, Cr,O, and TiO, make them popular for insulation purposes (Table 1). For monolithic ceramics the dielectric strength is ca. 20 kV/mm and for plasma sprayed coatings depending on the thickness, the value is only a factor 0,3-0,s. Responsible for the insulation capacity of the plasma sprayed coating is the purity of the spray powder (contaminations are FeO, Si02, ...) and porosity as well as crack density and orientation. The investigations focus on development of thin(ner) coatings, to avoid residual stresses, but with improved dielectric strength.The content of a-and y-phase in the coating is determined by the melting degree of the powder which consequently determines insulative capacity. The high cooling rates involv...
Thermally sprayed coatings of high performance thermoplastics are of interest espacially for the chemical industry for anti-corrosion applications at elevated temperatures. In this paper coatings of polyetherether-keton (PEEK) and polyphenylen-sulphide (PPS) have been produced by simple flamespraying. They have been investigated by optical metallography, FT-IR analysis and DSC-analysis. Among the coating properties also the "in-flight" particles have been studied by wipe-tests and FT-IR analysis in order to assess possible decomposition effects during spraying.
For very large structures and parts in critical environments, a materials solution often cannot be found by using one material. The specific desired properties for those structures, like stiffness, ductility, high temperature stability, corrosion resistance, etc. are difficult to fulfill with only one material. In this case a solution may be found by using coatings and design their specific properties to replenish each other by their combination. The Thermal Spraying processes offer the necessary flexibility of producing thin to thick, ductile, soft to hard coatings while due to the wide range of process temperatures it is possible to process a wide range of materials, both as coating and structure. In this paper the some recent and important developments in Thermal Spraying to produce coatings for technical demanding structures will be described. These developments consist of High Power Plasma Spraying, powder- and process control development. To ensure process consistency during long spraying times and to apply reproducible coating quality a suitable process control is of great importance and the development of temperature control by Pyrometry and Thermography will be presented. The example will be drawn according to the application of a coating on a ball valve for off-shore and ship diesel engine parts (piston and valve).
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