Optimizing the Hydraulic Characteristics and Thermal Performance of a Slabbing Mold for the High-Speed Continuous Casting of Steel

Abstract

The most important component of continuous steel-casting machines is the mold, since it forms the skin of the ingot and removes 20‐25% of the heat of crystallization of the metal. The thermal performance of the mold affects its durability, the productivity of the continuous caster, and the number of surface defects on the slabs. Widespread use is being made of slabbing molds with walls of hot-rolled copper 70‐80 mm thick that contain drilled channels and a loop-type cooling system [1]. Such molds have shown satisfactory results with high-speed ingot withdrawal at 0.8‐1.0 m/min. At speeds greater than 1 m/min, there is an increase in the wear of the walls and a corresponding increase in the number of surface defects on the slabs ‐ defects such as spider-shaped cracks. Hydraulic calculations were performed for molds with a loop-type water supply system. Calculations were also performed to determine the temperature fields in the copper walls of the mold. It was proposed that a mold be designed with thin walls made of a cold-worked copper-silver (CS) alloy containing milled channels, a separate water feed for each surface, and high-speed water flow within the channels. Local water flow velocities and coefficients characterizing heat transfer from the copper wall to the water in each channel for ingot withdrawal speeds up to 1.4 m/min were calculated for a 250 〈 (1020‐1910) mm mold with a length of 1200 mm. The mold had a loop-type water supply system and drilled channels (water discharge 320 m 3 /h, average flow velocity 6 m/sec). Similar calculations were performed for a mold which had the same cross section and length and milled channels (water discharge 700 m 3 /h, average flow velocity 6 m/sec). In the hydraulic calculation, we assumed the existence of a parabolic distribution of water velocity across the water pipe and in the channels of the mold. In using the iteration method to perform calculations for a pipe when the channels are connected in series and parallel, we determined the hydraulic resistance of the system, water discharge, and average water flow velocity in each channel of the mold. The last quantity was subsequently used to calculate convective heat transfer between the copper wall and the water. The calculations showed that the hydraulic resistance of channels used with a loop-type feed system is nonuniform due to a difference in the losses caused by friction and the rotation of the flow. Such nonuniformity leads to a nonuniform distribution of velocity in the channels of the mold (Fig. 1). Nonuniformity of the velocity distribution can also be caused by a difference in geometric pressure in the channels that is related to a difference betwe en the temperatures of the copper walls. These problems do not exist in a scheme in which water is fed separately to the surfaces of the mold. We developed an algorithm to calculate the thermal performance of a mold for different slab withdrawal speeds. The algorithm makes it possible to determine the heat-transfer coefficients along the cooling channels, water temperature in the channels, and the temperature distribution in the wall. An evaluation was made to identify the regions of the working surface of the mold that might be weakened during service.