Wear of diamond-coated cutting tool inserts upon machining of Al-12% Si and glass fiber/polyester resin composites

Results of the wear resistance of the diamond-coated cutting tool inserts upon machining Al-12% Si alloy and glass fiber/polyester resin composites are presented in this paper. The aim of this paper was to demonstrate the advantages of application of cutting tool inserts with the diamond coating over the conventional tungsten-carbide (WC) tools, and to obtain the cheaper serial production (shorter machining time) and satisfactory lifetime of the diamond cutting tool inserts. Surface roughness of the machined samples was measured for both as-received and diamond coated inserts. The diamond microstructure of undamaged part of inserts as well as the appearance of microstructure of diamond coated inserts after machining has been investigated. Results of the behavior of two regimes of preparation of diamond-coated inserts were compared and analyzed. Generally, the wear resistance of the diamond-coated cutting tool is superior over the conventional tool

Chemical vapour deposition of diamond using low pressure flat combustion flame

Diamond coatings were deposited onto Mo and WC-Co Substrates using a low pressure premixed acetylene-oxygen flat flame by means of a special apparatus operating at 50 mbar. Uniform diamond coatings containing significant amounts of non-diamond carbon were deposited over areas of approximate to 7 cm(2) onto Mo substrates, the coating thickness after 1 h deposition amounted to approximate to 1 mu m. Upon machining an Al-12 % Si alloy under identical conditions, the diamond coated WC-Co cutting tool inserts showed 30 % less wear than the as-receivcd inserts

Microstructural and sliding wear behaviour of a heat-treated zinc-based alloy

The effect of heat treatment on microstructure, hardness, tensile properties, fracture mode and wear behaviour during lubricated and dry sliding of the zinc-based alloy with 25 wt.% Al was studied. Microstructural investigation and chemical analysis of as-cast and heat-treated specimens, the fracture and worn surfaces, as well as wear debris were performed by scanning electron microscopy and energy dispersive spectroscopy. Wear tests were carried out using a disc-on block-type wear machine. By a relatively simple heat treating consisting of a short-term annealing in the single-phase region followed by water-quenching, the elongation has been markedly improved, while the strength was maintained high. The results indicate that the wear rate strongly depends on the microstructure, applied load and sliding conditions. The wear rate increases with load, and under dry sliding conditions the wear rate is approximately two orders of a magnitude higher than under lubricated conditions. During dry sliding the best wear behaviour was displayed by the water-quenched specimens, whereas slowly cooled specimens showed the higher wear rate. Lubrication strongly affects the wear behaviour. Contrary to dry sliding, slowly cooled specimens exhibit the best wear properties under lubricated conditions. The wear mechanisms were proposed for dry and lubricated sliding

Economizer water-wall damages initiated by feedwater impurities

The main causes of efficiency loss in thermal power plants are boiler tube failures that diminish unit reliability and availability, and raise the cost of the electric energy. For that reason, the regular examination of boiler tubes is indispensable measure for prevention of future malfunctions of power units. The microscopic examination of economizer's inner wall microstructure, the analysis of chemical composition of deposit using X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) have been performed in a subcritical power plant. Stress corrosion cracking, pitting corrosion, destroyed protective magnetite layer, presence of magnetite and hematite in deposit and corrosive impurities within the cracks have indicated the effect of inadequate quality of feedwater that cannot entirely ensure reliable operation of the boiler. It may be stated that maintenance of present boiler does not provide its reliable operation. The extensive chemical control of water/steam cycle was recommended

Extensive feedwater quality control and monitoring concept for preventing chemistry-related failures of boiler tubes in a subcritical thermal power plant

Prevention and minimizing corrosion processes on steam generating equipment is highly important in the thermal power industry. The maintenance of feedwater quality at a level corresponding to the standards of technological designing, followed by timely respond to the fluctuation of measured parameters, has a decisive role in corrosion prevention. In this study, the comprehensive chemical control of feedwater quality in 210 MW Thermal Power Plant (TPP) was carried out in order to evaluate its potentiality to assure reliable function of the boiler and discover possible irregularity that might be responsible for frequent boiler tube failures. Sensitive on-line and off-line analytical instruments were used for measuring key and diagnostic parameters considered to be crucial for boiler safety and performances. Obtained results provided evidences for exceeded levels of oxygen, silica, sodium, chloride, sulfate, copper, and conductivity what distinctly demonstrated necessity of feedwater control improvement. Consequently, more effective feedwater quality monitoring concept was recommended. In this paper, the explanation of presumable root causes of corrosive contaminants was given including basic directions for their maintenance in proscribed limits