In part I, the effect of the electrode tip angle on the arc properties was investigated. In part II, a mathematical model for the weld pool is developed in order to study the effect of the electrode tip angle on the weld pool properties. The information required to simulate the flow in the weld pool including the heat flux to the workpiece, the input current density and the gas shear stress, was derived from the arc model. By individually examining the various driving forces in the weld pool, it is found that the buoyancy and electromagnetic forces do not play major roles in determining the flow pattern in the weld pool for a 200 A arc. Instead, the relative magnitude of the gas shear stress and the surface tension and also the sign of the surface tension determine the flow pattern in the weld pool. The electrode tip angle which alters the gas shear stress and especially the heat flux to the workpiece can produce a significant change in the overall shape and size of the weld pool. With a very sharp tungsten electrode, the heat-flux distribution over the weld pool tends to be flatter. In addition, there is a very strong shear stress due to gas flow at the top of the workpiece. The overall result of these two effects is a wider and shallower weld pool.

No abstract

Electric Arc Furnace (EAF) dust, defined as special industrial waste in Japan, is treated through pyrometallurgical processes in which crude ZnO powder is recovered. An on-site type process, however, is desired to reduce treatment cost and cost of transportation of the dust. A hydrometallurgical process is considered to be suitable for such an on-site treatment. Although many EAF dust treatment processes by hydrometallurgical method have been proposed, most of them have not been commercialized in Japan. A short review of hydrometallurgical processes for EAF dust was done and a new hydrometallurgical process for EAF dust was proposed in this study. Nitric acid solution is used for the extraction of ZnO from the dust. Some characteristics of the process are as follows:(1) Recovery of Zn from zinc ferrite in EAF dust is the target, while the dissolution of Fe is limited by controlling the pH of the solution. (2) Zn is recovered as metallic Zn by electrowinning from the solution and nitric acid is regenerated in the anode.

The thermodynamic properties of the Ni-Co-S ternary system were determined by equilibrating the system with a known sulfur pressure established by using a gas mixture of H 2 S/H 2 at 1373, 1473, and 1573 K. The isoactivity contours for Ni and Co were determined by application of the GibbsDuhem equation using Schuhmann's method for ternary systems. For this purpose, a computer program was developed to calculate the activities of nickel and cobalt. The cobalt activity coefficients in dilute solutions of cobalt in the nickel-cobalt-sulfur system were evaluated and found to be 0.33, 0.50, and 0.55 at 1373, 1473, and 1573 K, respectively.

The larger part of the molten fly ash which is generated when municipal solid waste (MSW) is treated using gasifying and melting furnaces is handled as a specially-controlled waste in the same manner as incineration fly ash (fly ash from stoker-type incinerators), and is disposed of by landfill burial after stabilization treatment by methods designated by the national government, such as chelate treatment or cement fixation. Basically, however, these are not methods which separate out harmful substances. On the other hand, a shortage of landfill disposal sites has also become a major social problem. Therefore, theestablishment of a technology which separates harmful substances such as lead, cadmium, etc. in fly ash as completely as possible, stabilizes the residual trace amounts of heavy metals, and enables recycling of the residue has been desired.In research on a process of this type, the authors constructed a pilot plant (45kg/h) for treatment of molten fly ash and conducted tests of detoxification and conversion to aggregate using several kinds of molten fly ash as raw materials, and carried out technical development of a new roasting treatment technology which enables advanced detoxification of molten fly ash and effective utilization of the residue. The results confirmed that this roasting process possesses sufficient potential for practical application as a treatment for molten fly ash. In the course of this research, (1) the mechanism of chlorination-volatilization of lead (Pb) was clarified, (2) a 99.5% Pb volatilization rate was achieved, and (3) 99.5% volatilization was possible with lead oxide-containing glass (lead glass from end-of-life televisions and computer monitors) by adequately crushing the lead glass and performing mixed roasting treatment with fly ash.