For arc continuous caster, solidification begins on the meniscus of the mould. The mould vibrates and pulls down the billet.
For horizontal continuous caster, because the tundish is sealed with the mould, the steel supply is perpendicular to the direction of billet drawing, so the way of billet drawing cannot follow the method of arc continuous caster.
The solidification of molten steel in horizontal continuous casting begins at the separating ring connected with the mould. The molten steel flows into the mould from the tundish nozzle. First, it contacts the separating ring. Because the heat conduction of the separating ring forms a solidifying shell. If continuous billet drawing is carried out, the solidifying shell thickness gradually decreases from the separating ring along the direction of billet drawing and is broken. In order to make the solidified shell thick enough to pull away from the solidified shell contacted with the separating ring, the drawing speed must be limited to only 20 mm/min, which is meaningless in industrial production.
In order to improve the drawing speed, the intermittent drawing method must be adopted, that is, there is the action of pulling, stopping, pushing and stopping in a drawing cycle: after pulling, the purpose of stopping is to make the shell continue to thicken and have enough strength to pull the whole new solidified shell away from the separation ring. The purpose of backstepping is to make the solidified shell compressed mechanically to compensate the shrinkage of the solidified shell and to improve the drawing speed.
The casting speed mainly depends on steel grade, slab section, molten steel superheat and billet drawing cycle (i.e. the length of billet drawing, pause and back-stepping time in a billet drawing cycle). If the cold barrier on the slab surface is too deep, the drawing stroke can be reduced and the pause time can be shortened. The parameters of billet drawing have an important influence on the welding of the cold barrier on the surface of billet, which should be adjusted in time.
