It is reliable that the water content in electrode coating (i.e., free water, combined water and chemical water) has much influences upon the partial pressure of hydrogen in arc atmosphere during metallic arc welding.
Van den Blink advocated the next formula as a quantitative relation between them;
F=1-
PH2·(
PH2O) (1/
PH2+1/
PH2O+1/
PCO+1/PCO2) (1)
When
F>1, partial pressure of hydrogen increases in accordance with increase of the water content, but when
F<1, the former decreases in spite of increase of the latter.
Our experiments on this problem are as follow:(1) We calculated
F in (1) theoretically at various compositions of arc atmosphere using water gas reaction at 1400°C, 1530°C, 1600°C and 1700°C, and determined the diagram of
F=0.
(2) Electrodes experimentaly used were three kinds of cellulose types, three limestone types, three deoxide types and four kinds of cellulose-limestone types. They were mixed with same base mixing.
(3) The free water and other types of water in electrode coatings were separatly measured at 110°C and 1100°C. Arc atmosphere generated from drying and non-drying (as wet) electrodes were collected and analized.
(4) The principal conclusions obtained were as follow:(a) When cellulose type electrodes were used, the partial pressure of hydrogen was very little affected by drying or non-drying of the electrode coatings.
(b) When other type electrodes, particularly limestone types, were used, the partial pressure of hydrogen from non-drying electrode showed remarkable increase than that from drying electrode.Therefore, electrodes, except cellulose types, must be dried sufficiently before they are used in welding.
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