By the two "arch" composition to install the roller bearing and roll adjustment device, need to have sufficient strength and rigidity to withstand the rolling force. Mainly in the form of a closed frame and open two. Closed frame is a whole frame, with high strength and rigidity, mainly used for rolling force larger rolling mill and strip mill and so on. Open frame consists of two parts of the frame body and the upper cover, easy to change the roll, mainly for the cross-section profile mill.