INVESTIGATION OF VISCOSITY OF LIQUID WELDING SLAGS AND MELTS OF ELECTRODE COATINGS

The article provides data on investigation of viscosity of welding melts of slags and electrode coatings using common technique of rotating electric viscometer operating on the principle of rotating coaxial cylinders. Molybdenum crucible with internal diameter of 20  mm and height of 70  mm, filled with test material had served as an external stationary cylinder. An internal rotating cylinder was molybdenum head 10  mm in diameter and 10  mm in height, mounted on a rotating molybdenum spindle with diameter of 4mm.To study viscosity of melts were used: electrode coatings tempered in advance at 1000  °C for 30  –  45  minutes in order to avoid foaming during melting process, and slags obtained through welding by electrodes at recommended modes. As a result of the investigations of welding electrodes with various types of coatings, viscosity of liquid welding slags (η_s) and electrodes coatings melts (η_c ) were determined. Analysis of the results was carried out on viscosity polytherms of melts of coatings and slags based on experimental data. Calculations of the temperatures of the start and intensive crystallization, of activation energy of viscous flow were performed based on dependence of viscosity logarithm on melt reciprocal temperature. It was revealed that in regard to influence on electrode metal transfer and weld seam formation during welding, the most interesting are physical properties of coatings and slags melts at temperatures of crystallization start and higher. Mineralogical composition and temperature dependences of viscosity of molten welding slags of the basic type play a major role in providing welding from downward with through penetration of the seam root. Basically coated electrodes for downward welding can be characterized by crystallization start in homogeneous area and high activation energy of melts viscous flow. Technological capabilities of electrodes in welding were determined by “manufacturability potential”, understood as difference in physical properties of melts of “primary” and “secondary” slags of the same electrodes. The higher the “manufacturability potential” is in terms of size and the wider range of determining parameters, the easier is downwards welding. In developing new basic electrodes for downward welding, a number of options for increasing “manufacturability potential” are possible through achieving necessary mineralogical composition of welding slags. For that reduction of fluorine content, increase of content of MnO, FeO and Fe₂O₃ oxide, partially replacement of SiO₂ with TiO₂ and K₂O with Na₂O are necessary, definite substitution of CaO for FeO and MnO oxides is appropriate.

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