Rheological investigations of non-isothermal pressure flows of coating mixtures for welding electrodes

Abstract

Continuous flow capillary viscosimeter, presented in the form of abruptly narrowing stepped channel, and INSTRON 1251 testing machine were used to model the processes of pressure flow of coating mixtures for welding electrodes in extrusion chamber and in die space of production extruding machine. Thermocouple measurements were used to study the thermal conditions in pre-capillary zone, and visualization method was applied to analyze the structure of flow in it. Mathematical apparatus developed for calculation of rheological characteristics of polymer materials in the state of viscoelastic pressure flow was applied to calculate similar characteristics of the two types of coating mixtures for two types of low-hydrogen electrodes made with application of viscous in one and low-viscous liquid glass in another one. Grain composition of their filler is the same. Values of viscoelastic characteristics of the mixtures were calculated, including shear and longitudinal viscosity, elastic potential, first difference and coefficient of first difference of normal stresses and the relaxation period. Their dependencies on geometrical dimensions of stepped channels and values of volume flow of the mixture at capillary measurements were analyzed and commented upon, allowing for suspension nature of the mixtures, as well as resistance of pressure flows formed in them to viscoelastic instability. 12 Ref., 3 Tables, 12 Figures. K e y w o r d s : rheology, welding electrodes, mixtures for coatings of low-hydrogen electrodes, viscoelastic characteristics of mixtures, pressure flow instabilitiesAs the coating mixture passes from the working cylinder of extruding machine into the sizing die, in which the coating mixture envelops the metal rods, its flow cross-section decreases, and its rate rises by tens of times. Here, the mixture properties, which determine the manufacturing properties and working characteristics of welding electrodes, change essentially. For many years it was not known exactly which of these properties change, to what extent and in which way. Essentially, this is why the very physicochemical nature of coating mixtures proper remained unclear. The work [1] published 65 years ago, even though it did not disclose this nature, nonetheless, provided objective evidence of the fact that this cannot be done, proceeding just from the concepts of electrode coating mixture viscosity.Application of colloidal materials science and engineering rheology approaches at PWI for the last 10-15 years allowed establishing that electrode coating mixtures, similar to other kinds of highlyconcentrated suspensions of hard particles in viscous liquid medium, are characterized by elastic properties alongside viscosity. Not only shear and longitudinal viscosity, but a number of elasticity characteristics should be used for complete description of their rheological properties.The elastic component, first of all, essentially improves energy consumption for organizing the mixture pressure flow for their application on electrode rods. Alongside th...

Technological properties of covering masses of electrode coatings

“…The results of experiments, manufacturing experience and their analysis on the basis of the available scientific publications [1][2][3][4] allow stating that molding properties of covering masses are determined by:…”