What is it?
This defect appears as a longitudinal crease or hump on the coil. It is also known as a ridge, a hump, or a knuckle. The defect can be caused by plugged spray nozzles on rolling-mill rolls. This crease is created due to non-uniform deformation. In addition, the defect can be created in the hot-mill finishing stands, or in the cold-reduction unit like a reversing mill, tandem mill, or z-mill.