低水素型熔接棒による金属熱の発生機転について (その1)

Abstract

With a view to determining the role played by the use of low hydrogen type electrodes as a cause of metal fume fever, laboratory experiments were performed with 4 types of electrodes, including low hydrogen type electrodes, and the following results were obtained. 1) The mineralogical composition of coating materials was determined by microscopical examinations. One of the notable properties of low hydrogen type electrodes are the presence of such unusual minerals as CaF2, ferrosilicon, a large amount of CaCO3, MgCO3 (in the form of dolomite) and water glass. 2) After experimental welding which was performed with different electrodes, on evidence of melting was found at the end of low hydrogen type electrodes, while the end of another type showed the evidence of melting by the heat of arc. 3) By the thermobalance method the author measured the change in weight during continuous heating and examined the timeweight loss curve at different firing temperature. The heating behavior of low hydrogen type electrodes was found to be quite different from another type. The heating curves of the former indicate (i) the maximum decrease of weight at 600°C (as a result of the decomposition of carbonates), (ii) a marked increase of weight (as a result of oxidation) by heating above 600°C, (iii) the definite loss of weight as a result of a high porosity above 800°C of the furnace temperature. The time-weight loss curve of the former also indicates high sensitiveness to the sudden change of temperature. 4) Definite heat absorptions at 500°C and 750°C and heat evolution at 600°C were observed in the differential thermal analysis of the low hydrogen type electrods. These properties were especially important as a cause of rapid destruction of the material. 5) The study of the microscopical structure of fired material by the low hydrogen type electrode was useful for ascertaining its high porosity after heating above 800°C. The principal features after firing are a marked decrease of the number of MgCO3 particles, signs of dehydration of the water glass, and production of new round crystaline formation from the ferrosilicon particles which had originally irregular contours. 6) From the facts above mentioned the causative agents for metal fever might be attributable to the high emission of MgO particles in the dusts from the low hydrogen type electrode during the welding process.