New Technologies and Processes Applied in Steel Rolling Production and Welded Pipe Mill in Recent Years – Automation Technology (2)

The key to developing from traditional continuous hot strip rolling to endless rolling is to weld the head and tail of adjacent intermediate billets, continuously supplying intermediate billets to the finishing mill. Therefore, the following technical difficulties must be solved:

• (1) How to ensure the required time for welding with the next intermediate billet under the condition of finishing rolling the previous intermediate billet.

• (2) How to prevent the temperature drop of the intermediate billet and ensure that the microstructure and strength of the weld seam are close to that of the base material.

• (3) How to cut and roll the welded strip after being rolled by the finishing mill at high speed and before coiling, respectively.

Semi endless rolling is mainly used in thin slab continuous casting and rolling production lines, mainly designed for producing thin gauge hot rolled strip steel. The basic equipment configuration of this production line is generally the same as traditional thin slab continuous casting and rolling, but there are significant technological changes, which is called semi endless rolling technology in terms of technology.

For example, the thin slab of CSP continuous casting has a thickness of 63mm when it comes out of the mold, and a thickness of 48mm when it leaves the continuous rolling mill after being pressed by the liquid core. At this point, the billet is not cut and enters the tunnel heating furnace (traditional CSP technology cuts the billet to over 40 meters). The heating furnace can reach over 300 meters, and the billet is homogenized and then rolled into a 7-stand continuous rolling mill.

The semi endless rolling technology utilizes the feature that continuous casting billets can be longer, reducing the problems of reduced strip temperature, difficult thickness control, and unstable production during the threading process. Therefore, it is very beneficial for rolling thin specifications.