Depending on actual conditions for casting steel, the preheat type and non-preheat type can be selected for long shround(LS), and stopper can be different in material and structures, according to different kind of steel  and duration of casting steel  .Submerged entry nozzles(SEN) of different shapes, different materials and different structures can be selected according to different types of continuous casting machines, different  cross-section of billets and slabs and different  duration of casting steel. The total purpose is to increase service life and ensure quality of liquid steel.