This series is composed of many models. Clamping of flange and web adopts hydraulic automatic centering. Compared with the products with the same specifications, Z20B has larger suitable ranges and better performance to price ratio. There are four groups of web clamping roller front and back arranged and adopts up and down two layer combinable structure. It can rectily the web bending. Better positioning accuracy by means of multi-groups of guiding roller and eliminate the fishtailing phenomenon.