Three roller bending machine must pass the pre bending on, roll round, round the four process to complete. The hydraulic automatic two roller bending machine, completely changed the three roll rolling method, eliminating the above process, can be a molding. Two rollers of the upper roller of the device for the rigid roller, the lower roller is a flexible roller, the current roller in the upper roller extrusion will have a certain type of radial concave deformation. When the steel plate is fed between the upper and the lower rollers, the two roller is made into a cylinder. From the microscopic point of view, the cylinder is made up of a small circular arc.