Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia

М. V. Chukin, Chief Researcher of the Nanosteel Research Institute, Doctor of Technical Sciences, Professor, e-mail: m.chukin@mail.ru
N. V. Koptseva, Professor of the Department of Foundry Production and Material Science, Doctor of Technical Sciences, Professor, e-mail: kopceva1948@mail.ru
Yu. Yu. Efimova, Associate Professor of the Department of Foundry Production and Material Science, Candidate of Technical Sciences, Associate Professor, e-mail: jefimova78@mail.ru
S. А. Linkov, Associate Professor of the Department of Automated Electric Drive and Mechatronics, Candidate of Technical Sciences, Associate Professor, e-mail: xx_linkov@rambler.ru

Studies have been conducted to identify patterns of changes in the thermal EMF values of platinum-rhodium type B thermocouples made of PR30 (30% Rh) and PR6 (6% Rh) alloys from different manufacturers. They were studied at the stages of heating to a temperature of 1300 ^oC and cooling to 300 ^оC, as well as during repeated cycles of thermal exposure at high heating and cooling rates of 10 ^оC/s, in order to determine the possible causes of the discrepancy between the thermocouple parameters and the required measurement accuracy. The effects of thermal EMF hysteresis are revealed, consisting in the discrepancy of thermocouple parameters during heating and cooling, as well as a narrowing of the thermal EMF hysteresis loop during repeated heating and cooling cycles. No impurity elements were detected in the wires of PR30 (30% Rh) and PR6 (6% Rh) compositions from different manufacturers, and there are no significant changes in the chemical composition after thermal exposure when heated to a temperature of 1300 ^оC. It has been established that there is no discrepancy between the thermocouple parameters and the actual temperatures of the technological conditions due to deviations in the regulated requirements for the chemical composition of the wire making up the thermocouple or incorrectly selected welding modes. It is shown that the degree of penetration of the welded joint of the elements of the studied products does not affect the value of thermal EMF. It was found that during the assembly of thermocouples, there are traces of deformation effects from the rollers feeding the wire into the welding unit. It is determined that this may be the reason for the incomplete course of the recrystallization process and the occurrence of temperature discrepancies in thermocouples.

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