Study On Lubrication Mechanism For Continuous Casting Mold Based On Experimental Oscillation

During continuous casting of steel, the mold powder in the free surface of molten steel which melts to form liquid flux and flows into the gap between the mold and the cast metal with the mold oscillation. The surface quality of the cast slab and casting stability are mainly governed by heat-transfer and lubrication behavior of mold flux. In this study, a new experimental apparatus for simulating mold oscillation of continuous casting was developed and a hydrodynamic lubrication model in continuous casting mold with high casting speed was established on the basis of elastohydrodynamic lubrication law in combination to physicochemical properties of liquid flux. A mechanism of hydrodynamic lubrication was proposed to explain the interface phenomena in mold channel and estimate the surface defects of continuous casting steel. The main conclusions are obtained as follows:(1) The flux channel has a profile that it becomes wider along casting direction based on the oscillating experiment in which flux infiltration is simulated. The variation of pressure in the channel results from the periodical movement of the oil in the downward and upward caused by the oscillating motion of the plate. The dynamic change in the pressure and liquid friction of the oil are similar to the oscillation mode and shortly lag behind the cyclic variation in the steel plate velocity, because of the inertia of the oil. The lag time is strongly dependent on the flux viscosity and oscillation frequency. The liquid film thickness of flux has a significant influence on the infiltration behavior compared with the oscillating motion of the mold.(2) A hydrodynamic lubrication model in continuous casting mold was established on the basis of elastohydrodynamic lubrication law by combining physicochemical properties of mold slag. The temperature-dependent and pressure-dependent viscosity exponent are chosen to be 1.25 and 2.2×10 m2·N-1 respectively. The effect of temperature is more apparent than pressure, and the maximum viscosity of slag increases 63% at the bottom of meniscus in flux channel. Both channel pressure and liquid friction increase with the increasing of n and m.(3) The oscillation marks are generated at the bottom of meniscus in the negative strip time.The surface cracks on the slab are formed during the positive strip time and healed within the cumulative negative strip time. The liquid flux infiltrates down from the end of positive strip time to the beginning of next positive strip time, and the infiltration is largely dependent on the negative strip time in between.(4) The increase of viscosity of flux, casting speed and oscillation frequency, enhances the liquid friction due to the reduction of the mold flux consumption. On the contrary, the higher non-sinusoidal oscillation factor improves the infiltration and decreases the frictional force. The oscillation amplitude increases the consumption and liquid friction slightly.