Defects in Extrusion

Extrusion can result in defects in the surface of the extruded objects.  The components produced will have to be further smoothened. 

Some of the common defects of the extrusion process are

Surface Cracks
These are formed when excessive tensile stress is applied.  The cracks, usually, occur at the ends.  In many cases, they can be found along the length of the product.  Surface cracks can occur if the temperature of the billet is very high.  They can also occur if the billet is pushed through the die too fast.

Surface cracks can be prevented by extruding the material at the optimum temperature and speed.

Surface Lines
These are formed when foreign and unwanted material is present in the surface of the die.  These lines occur in dies which are not maintained properly.  Dies have to be properly maintained and cleaned at regular intervals. 

Internal Cracks
Internal cracks occur when the extrusion rate is very low or if the die has a very high angle.  The cracks are caused by excessive tensile stress in the centre of the material. Cracks can also occcur if the material used is not of good quality.