熔接衛生に関する研究 (その3) : 電弧熔接時の発塵の原因と予防

Abstract

Coating materials of four types electrodes (low hydrogen type, high iron oxide type high titania type and ilmenite type) and quartz, as a raw material for the coating, were examined by a thermobalance in order to recognize the temperature and state of solid dusts which were produced. Causes and the prevention of dust development during arc-welding were considered by both the present results and those already reported. 1) Temperatures at which dusts were produced from the electrodes. The coating materials of the low hydrogen type electrode produced abruptly a large quantity of solid dusts at both 600 and 1, 000°C. In the high iron oxide type, solid dusts were slowly produced in a wide range of temperatures, however somewhat abruptly at 100, 450, and 1, 000°C. In the high titania type, solid dusts were also slowly produced in a wide range of temperatures and somewhat abruptly at 250 and 680°C. In the ilmenite type, solid dusts were abruptly produced at 100 and 680°C. These temperatures, at which a large quantity of solid dusts were produced, are generally in accordance with temperatures at which minerals contained in the coating materials react severely turning the thermal stress to the thermal shock. 2) Scattering or fine quartz particles. When quartz, a raw material of the coating of the electrode, was heated at temperatures continuously from the room temperature to 900°C, it did not show a constant weight even at 900°C because it contains a little alkali salts as impurities. Thermobalancecurve of the quartz is composed of two factors, i.e. the weight decrease shown as a straight line, which means dehydration of the bound water, and the weight decrease shown as steps, which means giving out fine quartz particles by extrication of liquid inclusions. The more conspicuous the latter, the thinner the layer of the sample. 3) The cause and the prevention of dust production during arc-welding. Causes of dust production are classified into three groups: a) partial pressures of the gases, b) changes of the thermal expansion of minerals contained in the coating materials, c) lacking glutinosity. As to the prevention for a), it is necessary to use dried electrodes, to give grinding, and to give heat treatment to the raw materials of the electrode. For b), to heat beforehand the electrode, and for c), to use contractibitity-bond instead of water glass.