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Mould heat transfer in the high speed continuous casting of steel slabs

University of British Columbia

This investigation studies mould heat removal in operational slab casters. These include both the conventional (or thick slab) as well as thin slab (of the CSP type) casters. Mould wall temperatures and other data measured in-plant were analysed using mathematical models developed by other researchers, in addition to new models and commercial finite element software. The primary objective was the calculation of mould heat fluxes, and how this related to aspects of caster operation and slab surface quality. Firstly, the mechanism of heat transfer in slab caster moulds postulated by previous researchers was validated. Heat fluxes calculated for a billet caster using powder lubrication showed that reducing cooling water velocities resulted in an increase in heat transfer. This is due to higher mould hot face temperatures causing the formation of a smaller slag rim, and a hotter, more fluid liquid flux. This mechanism of mould heat transfer was used to resolve transverse corner cracking in a newly commissioned conventional slab caster which had commenced high speed casting. The problem was traced to inadequate mould lubrication and heat transfer, caused by inordinately high water velocities. The incidences of cracking fell drastically after a reduction in cooling water velocities. Secondly, heat fluxes were calculated for the CSP caster. A big dip in heat fluxes was seen in the central portion of the fixed broad face. It was postulated that this could be due to a combination of water flow differential between the two broad faces, and a squeezing in of the mould pocket bulge in the strand. Additionally, the two broad faces, as well the narrow faces, were found to have unequal heat extraction rates. Finally, the effect of the mould hot face temperature on the mould heat transfer was used to develop a procedure of water velocity variation into the working life of CSP caster moulds. Models were used to calculate water velocities which maintained a constant hot face temperature, while the wall thickness reduced. It was found that the current operational practice grossly over-estimated the water flows required in the latter stages of the mould life.

Thesis/Dissertation

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2009-05-26

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http://hdl.handle.net/2429/8265

Metals and Materials Engineering

University of British Columbia

UBCV

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