Measuring System for Monitoring the Microarc Heating Process During Surface Hardening of Steel Products

An accelerated heat treatment technology for hardening steel products has been studied. A possibility of measuring temperature of steel products using thermoelectric platinum/platinum–rhodium converters (thermocouples) under the microarc heating conditions was analyzed. To conduct the experiments, hot junctions of two type S (Pt/Pt–Rh) thermocouples (process and reference) were embedded into the sample surface at the same level. The free ends of the thermocouples were connected to a digital multimeter and a personal computer. It was determined that the measurement results are affected by the following five factors: electric current, fraction of carbon powder burnout, calibration, number of repeated measurement cycles, and actual thermocouple being used. When planning the experiment, a concept of conducting a stepwise nested experiment was used. A statistical treatment of the array of data, consisting of measured temperatures of the steel samples, was performed using the analysis of variance. The following precision characteristics of the measurement method were calculated: repeatability and reproducibility. A linear mathematical model was obtained, which links the reproducibility parameter of the measurement method with the measured temperature value. A measuring system for experimental determination of the steel sample temperature is proposed. The application of such system is justified at different densities of electric current on the sample surface and varying duration of microarc heating. The possibilities of selecting and controlling the microarc heating conditions depending on the required temperature of heat treatment of the steel products are determined.