Radio frequency thermal plasmas have been used for material processing and waste treatments. Sophisticated modeling considering chemical reactions has been required for industrial application. Therefore, the thermofluid and concentration fields of oxygen radio frequency thermal plasmas were obtained by solving of 2-D modeling. This formulation was presented using higher-order approximation of the Chapman-Enskog method for the estimation of transport properties. The numerical results indicate that RF oxygen plasmas are more concentrated the center with higher energy efficiency than argon plasmas. The present modeling would give the guidance for the rational design of new material processing using thermal plasmas.
On the WT-3 tokamak, stationary m=2 tearing mode was observed on magnetic probe signals in an ohmic heating (OH) plasma. Soft x-ray measurement showed that the m=1 mode and the sawtooth oscillation coexisted with the m=2 mode in this plasma. The frequency of the m=1 mode was the same as that of the m=2 mode. The effect of electron cyclotron heating (ECH) on the m=2 mode was investigated. We have found that both m=1 and m=2 modes were suppressed by applying ECH at the q=1 surface as well as at the q=2 surface. The amplitude of the m=1 and m=2 modes decreased as the power of ECH increased and both m=1 and m=2 modes were completely suppressed when the power of ECH was nearly equal to that of the target OH plasma. The experimental results showed that the m=1 and m=2 modes were tightly coupled to each other. In the case of the application of ECH at the q=1 surface, the central electron temperature increased significantly, suggesting that the confinement characteristics of the plasma was improved probably due to the suppression of the overlapping of the m=1 and m=2 modes by ECH.
Temperatures of metal drop in GMA short-circuiting welding process were in-situ measured using newly developed instrument designed on the basis of two-color pyrometry, which consisted of optical lenses, interference filters for two colors and two sets of high sensitive CCD cameras with fast shutter. In order to avoid radiation from arc plasma, temperature measurement was carried out immediately after molten drop at electrode wire tip was contacted with weld pool and arc was extinguished. Welding current in arcing period was adjusted from 50 A to 250 A using experimental power source in Ar + 20%CO2 mixture gas shielded GMA welding with mild steel wire of 1.2 mm in diameter. It is shown through in-situ measurement that average temperature of metal drop ranges from 2200 K to 2700 K, depending on level and period of arc current governing electrode wire melting.
Full penetration laser welding has been carried out on 11, 15 and 20 mm thick steel plates. Dynamic keyhole behaviour has been observed using a micro-focused x-ray transmission imaging system to elucidate the formation mechanism of the hot cracking. Back shielding by inert gas is effective to prevent the porosity caused by supersaturation of nitrogen in the molten pool. However, the indissoluble inert gas entered from the back surface significantly perturbs the keyhole, and then forms the hot cracking susceptible convex shaped weld section. Increase in the plate thickness raises the hot cracking susceptibility due to promoting the keyhole perturbation. A small amount of aluminium addition is effective in preventing the porosity caused by nitrogen even if the back surface is not shielded by the inert gas. Hot cracking is also prevented by stabilizing the keyhole.
A shot coating process for metalizing at the surface of ceramics has been newly developed as the shot peening treatment. However, microstructure and residual stress of shot coatings, which have an important effect on the adherent strength of coatings and the strength of ceramic substrates, have not always been clarified. An experimental investigation on the microstructure and residual stress was carried out for the shot coating of aluminum on zinc-oxide substrate by comparison with the atmospheric plasma sprayed aluminum coatings. As a result, low porosity, low oxide content and flat surface could be obtained from the aluminum coatings formed by shot coating process in comparison with the atmospheric plasma sprayed aluminum coatings. Also, it was confirmed by the X-ray diffraction technique that the residual stress of shot coated aluminum over zinc-oxide substrate was high compressive in comparison with the atmospheric plasma spraying process.
This paper describes a study result on pot fabrication by the forging cast process of stainless steel with aluminum. Rice cooked with the new bowl-shaped pot for the induction heater type rice cookers is better tasting than rice cooked with the conventional cylindrical one, due to the achievement of better heat conduction and convection. The conventional pot is made of the clad sheet, consisting of stainless steel and aluminum. However, it is rather difficult to form a bowl shape from the clad sheet, primarily due to the problem of a material spring back. The fabrication of a new type of a pot was made possible by means of the adoption of a forging cast process instead of the clad sheet. In this process, iron powder is inserted between stainless steel and aluminum in order to alleviate the large difference on the coefficient of expansion between each material. It was made clear that the application of two kinds of iron particle, namely 10 μm size powder on the stainless steel side and 44 μm on the aluminum side, enables the joints to become strong enough. The joint strength of the new pot by this fabrication process was confirmed by the tests of the shear strength and the fatigue tests together with the stress analysis.
The exhaust amount of the waste dry batteries in our country tends to increase every year. However, most of the recycled calcinations powder gained from the disposal process of these waste dry batteries is still unutilized. ZnO and MnO are the main consists of the calcinations powder, they are expected to be used as thermal spraying materials. This paper describes a study result of the hydrophilicity on the sprayed coating formatted by the calcinations powder. When a water drop spread on the coating surface, the diameter of the droplet is considered as an indicator to evaluate the hydrophilicity in this study. The influences of the coating thickness, temperature and existence of grinding on the droplet diameter are clarified. Furthermore, the infiltration speed of the water drop in the capillary of coating, and the ionic property of combination between the elements, which constitute the coating are discussed. From the results of these general investigations, it is clarified that the sprayed coating formatted by the calcinations powder has a remarkable hydrophilicity. It is shown that the application to a heat exchanger, etc. is expectable.