Thickness difference of electrode coatings caused by elastic turbulence of electrode compounds under condition of nonisothermal pressure flow

Abstract

Generalized and analyzed are the results of investigations carried at the E.O. Paton Electric Welding Institute on technological properties of electrode compounds, promoting thickness difference of electrode coatings. The investigations were carried out using capillary viscosimeter of fixed flow-rheometer with electric drive, which can be used for simulation of the conditions of compound extrusion application over the electrode rods, typical for commercial electric extrusion presses. Thus, specific pressure on compound under condition of stationary flow achieves 60-75 MPa, average gradient of shear rate is gradually regulated in the ranges from 1 to 5⋅10 3 s-1 , and it makes to 65⋅10 3 s-1 for separate types of compound. The compounds for rutile, low-hydrogen and cellulose electrodes, differing by wide range of consistency indices, were investigated. In addition to shear and longitudinal viscosity, the investigations were carried out on a range of change of their modulus of shear elasticity, period of relaxation, criterion of Reynolds elastic turbulence, elastic potential and reversible (elastic) deformation. The results received were analyzed from point of view of existing phenomenological theory of elastic turbulence of polymer materials, combining viscosity and elasticity properties. It is successfully used in the course of many years in rheology of melts and solutions of high-molecular compounds for solving of technological problems of their extrusion processing. Variants of elastic turbulence, detected in capillary and pre-capillary zones, were analyzed. Quality relation of this phenomenon to appearance and nature of coating thickness difference in course of real extrusion application of compound over the electrode rods was shown. 24 Ref., 4 Tables, 9 Figures.

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

“…Similar to experiments, conducted with application of capillary viscosimeter with working cylinder with D R = 30 mm, the results of which are published in [2][3][4], it was found that the nature of extrusion curves depends on the consistency of coating mixtures and their pressure flow modes. In S2 mixtures with viscous liquid-glass binder, all of them, irrespective of the container section, have a smoothed shape, which is little affected by the flow rate.…”

“…Above-mentioned procedures of measurement and calculation, as well as other rheological indices used in this study, are described in detail in [2,4,5]. Table 1 gives the complete plan and results of experiments.…”

“…It is completed, apparently, in the capillary initial section. This is exactly where pulsation of the coating mixture jet [2] and of polymer melts [8] begins.…”

“…The above instability, as a rule, develops at the transition stage of flow formation, while it, passing through the forming channels in the extruding machine or in the measuring cell of the capillary viscosimeter, after change of its section, direction or rate, reaches the steady-state flow mode. It can develop both in the capillary, and in the zone before it [2][3][4].Experimental study of the causes for or mathematical modeling of the conditions, provoking appearance of instabilities of coating mixture pressure flows, should be performed, as in polymer rheology, with application of stepped channel model of continuous-flow type in the first case. In it the flow section decreases abruptly (step-like) or more seldom, gradually narrowing, at transition from the tank (mixture container) to the die (or capillary).…”

“…The above instability, as a rule, develops at the transition stage of flow formation, while it, passing through the forming channels in the extruding machine or in the measuring cell of the capillary viscosimeter, after change of its section, direction or rate, reaches the steady-state flow mode. It can develop both in the capillary, and in the zone before it [2][3][4].…”