Extrusion Defect

A cone-shaped cavity or seam in an extruded shape (ring in a hollow shape or tube) formed due to frictional instabilities and instabilities of the dead zone surface. The seam may be filled with oxide and billet surface contaminants, and is an intrusion of surface matter into the extrudate interior. Other types of de­fects that can be found in extruded insulations include longitudinal die marks, inclusions of burned compound and lumps and neck-downs.