**6.4. Contraction of roll gap**

For the continuous caster #2 in Maanshan Iron and Steel Co. Ltd, the ultimate thickness of a produced slab is 230 mm, and the bottom thickness of the mold is 237.5 mm. With a casting speed of 1.1 m/min, the molten steel completely solidifies at the start of the 11th sector where the thickness of the slab is 234.3 mm and the roll gap contraction is 3.2 mm. In this zone, the linear shrinkage ratio is 0.5%~0.7% (1.2~1.7 mm) due to the drop of temperature. Without the contribution of the temperature drop, the roll gap contraction is 1.5~2.0 mm. This amount of shrinkage equals soft reduction of medium or light scale. The roll gap contraction is uniformly distributed. The roll gap contraction acts on the slab and affects the fluctuation of the liquid level of molten steel. However, the slab broadening is far less than that induced by soft reduction. So roll gap contraction is not the main cause of broadening.
