Theoretical and experimental studies of the electrical properties of electrical contact gasket for the graphitizing of electrode preparations in direct heating furnaces

Abstract

The article presents the results of theoretical and experimental studies of specific contact electrical resistance (SCER) and specific electrical resistance (SER) of electrical contact gaskets (ECG) made of thermally expanded graphite (TEG) and intended for their placement on the ends of electrode blanks before their graphitization in direct heating furnaces – furnaces Castner's. The obtained data of SCER “graphite–gasket–graphite” and SER (or electrical conductivity) of the ECG material are needed to minimize the energy consumption of the graphitization process using numerical modeling of the thermoelectric state of Castner's furnaces in order to develop energy-efficient regulations for their operation. The method of two samples was used for the experimental determination of the SCER, and the theoretical-experimental approach was used for the study of the SER, which makes it possible to exclude the influence of the contact resistance between the experimental sample and the electrodes for supplying the electric current on the value of the measured quantity and is based on the solution of the inverse coefficient problem of electrical conductivity (ICPE) using experimental data obtained during the SCER study. A mathematical formulation of the ICPE was formulated, a numerical method and an algorithm for its solution were developed, and a study of the SER of the TEG at different values of temperature and pressure was carried out. Determination of SCER and SER was carried out for ECG material with an initial density of 1000 kg/m3 in the temperature range up to 250 °С under different pressures in the range of up to 1.75 MPa. The results of these studies are presented in the form of two-parameter dependences on pressure and temperature with extrapolation up to 3000 °C. The measurement error of SCER and SER by the specified methods is estimated to be within 4–5% in the intervals of temperature change up to 250 °С and pressure up to 1.75 MPa. The obtained SCER and SER dependences for the ECG material are needed to perform a numerical analysis of the thermoelectric state of Castner's furnaces in order to develop rational graphitization regulations.