Thermal processes in electroslag surfacing of rolling rolls in a current-conducting solidification mould

Abstract

Electroslag surfacing in a current-conducting solidification mould is one of the promising methods of reconditioning rolling rolls. The production of highquality metal is determined by the treatment of deposited metal with high-activity and refining slags, by the electromagnetic effect on the liquid metal, and by the accelerated cooling of the solidifying deposited layer. Nevertheless, the final result of surfacing, i.e. production of high-quality bimetallic components, is controlled by the thermal processes taking place in the melting space of the solidification mould. In this work, investigations were carried out into the thermal state of blanks of rolls in long-term surfacing. Surfacing trials were carried out on blanks of rolls of 2000 OAO NLMK rolling mill, with the diameter of 810 mm, the length of the barrel 2000 mm, the total length of approximately 5000 mm, weight approximately 13 t. The temperature changes in the bank in surfacing were estimated for two cases: with the heating of the blanks in the furnace prior to surfacing and in an additional application of heating during surfacing. Measurements were taken of the surface temperature of the barrel and the neck of the roll, and the temperature of the slag pool on the surface and in the depth was measured. Temperature was measured with measuring devices of four types: a contact chromel–alumel thermocouple, a Hefest optical pyrometer with the maximum measured temperature of 600 oC, a Cyclops infrared thermometer with the measurement range 600–1600 oC, and using TPR-91-1200 thermoelectric block with the tungsten–rhenium immersion thermocouples. Surfacing was carried out in a modernized electroslag furnace EShP-10VG. Modernization consisted of organizing the working area carrying a currentconducting solidification mould and devices form supplying surfacing shot (figure 1), and also devices for centring the roll and supplying current to the lower part of the roll. Prior to surfacing, the roll was preheated in a shaft furnished to a temperature of 600 oC, which was reduced during technological operations: extraction of the role from the heating furnace, transport by a shop crane to the surfacing equipment, insertion into the solidification mould, centring and securing in the strictly vertical position. The main task of preheating the roll was to ensure price surfacing (prior to pouring the slag into the solidification mould) of the surface temperature not lower than 250–300 oC. As shown by experience in practice, Thermal processes in electroslag surfacing of rolling rolls in a current-conducting solidification mould