The methods and solutions to control the outward folding are as follows.
①Ensure the quality of billets. There should be no subcutaneous bubbles on the surface of the billet, and the cold skin, indentation, and cracks on the surface of the billet should be cleaned up, and the edge of the groove after the removal should be smooth.
②It is required that the notch of the piercer roll cannot be too deep or too steep, and the edges of the notch must be smooth.
③ Reasonably adjust the pass pattern of the piercing machine and rolling mill. If the surface of the roll is severely worn, it should be replaced in time.