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Contents of the issue
INFLUENCE OF TECHNOLOGICAL FACTORS IN MANUFACTURE OF LOW-HYDROGEN ELECTRODES ON HYDROGEN CONTENT IN THE DEPOSITED METAL
A.E. MARCHENKO and N.V. SKORINA
E.O. Paton Electric Welding Institute, NASU. 11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: firstname.lastname@example.org
Abstract PWI department of «Physico-chemical processes in the welding arc», led by Prof. I.K. Pokhodnya, academician of NASU, celebrated its 50th anniversary in 2012. Alongside the work on arc welding metallurgy and development of welding consumables, a considerable scope of research conducted by the department staff during this period deals with improvement of the technology of mechanized production of welding electrodes. This work enables clarifying the nature of the phenomena which are the basis for technological processes of manufacturing this kind of mass products, as well as improving the metallurgical, technological and service characteristics of electrodes and their quality. Given below are the results of investigation of the influence of such technological factors of manufacturing low-hydrogen electrodes as composition and amount of water glass in the electrode compound, its interaction with marble in the electrode coating, as well as organic hydrocolloids (carboxylmethyl cellulose and alginates) on dehydration of electrode coating and hydrogen content in the deposited metal. It is found that alkali hydrosilicates remaining in the electrode coating after dehydration of its water glass binder during electrode heat treatment, are a potential source of hydrogen in the deposited metal. There exists a direct relationship between water-retaining capacity of sodium-potassium hydrosilicates, dependent on the module and Na2O:Ka2O ratio, potential hydrogen content in the coating and hydrogen content in the deposited metal. However, at evaluation of the degree of potential hydrogen «assimilation» by the deposited metal, we should take into account the possible influence of potassium and sodium ions contained in the hydrosilicate, on fluorine removal from the reaction of hydrogen fluoride formation and on kinetic conditions of hydrogen sorption and desorption by electrode metal drop. Marble powder, contained in the electrode coating, and water glass which is the coating binder, interact with each other in a heterophase fashion. Calcium ions coming to the water glass binder lower the water-retaining capasity of alkali hydrosilicates. Products of interaction on marble particle surface hinder their thermal dissociation up to higher temperatures, compared to the temperature of pure calcite dissociation. Both promote lowering of hydrogen content in the deposited metal. Organic hydrocolloids such as sodium modifications of carboxylmethyl cellulose (CMC) and sodium or potassium alginates, are sorbed by the surface of marble particles and, blocking water glass access to it, they hinder the heterophase transition of calcium ions into the water glass. This has a favourable effect on the technological properties of electrode compounds, but at the same time improves the water-retaining capacity of alkali hydrosilicates in the electrode coating and hydrogen content in the deposited metal. Calcium ions are capable of moving from calcium-containing CMC modifications and alginates into the water glass binder as they do from calcite particle surface. Therefore, they should be considered as technological additives, which not only increase the plasticity of electrode compounds, but also lower the potential hydrogen content in the coating and hydrogen content in the deposited metal. 15 Ref., 8 Tables, 7 Figures.
Keywords: manual arc welding, welding electrodes, electrode coating, water glass, hydrogen in the deposited metal, cold cracks, technological causes for hydrogen lowering
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