Both circular duct Yaokou Festival in the seams, duct tube, the pressure hoop, but also in the plate on the inside of the pipe pressure hoop. Size seams and duct wall thickness can be directly under the flexible adjustment, seven sets of forming rolls, four rolls of them round elbow seams for processing, and the other three sets of laminated roll hoop for metal protection, processing only need to switch to a different roll processing can achieve the required shape.