Nozzle Shape Suitable for Vertical-Type High-Speed Twin-Roll Casting of Al-5%Mg Alloy Strip

A vertical-type high-speed twin-roll caster can cast strips at a speed of 60 m/min. However, ripple marks, which are typical surface defects on strips cast using a twin-roll caster, also appear on strips cast using this caster. In the present study, Al-5%Mg was used because severe ripple marks occur on Al-5%Mg strips. The influences of the molten-metal head (50, 100, and 150 mm), which is a characteristic parameter for this caster, the molten-metal temperature (645, 685, and 735 °C), and the nozzle thickness on ripple marks were investigated. The nozzle thickness was an important factor in eliminating ripple marks, and a nozzle thickness of 3 mm was suitable for eliminating them. No relationship was found between ripple marks and surface cracks. The surface cracks decreased as the roll load decreased, and a roll load of 5 N/mm was suitable. Based on the obtained results, the optimum nozzle shape and casting conditions for casting strips without ripple marks or cracks were clarified.