Aluminum profile extrusion production, will appear in the cut head, tail half of the finished part of the alkali erosion inspection will appear commonly known as  shrinkage cavity defects in tail of extruded aluminium alloy , containing the organization s aluminum profile mechanical properties can not meet the requirements, there are safety hazards.

At the same time, the production of aluminum alloy profiles to surface treatment or turning processing, because of the existence of the defect to undermine the continuity of the material internal, will affect the subsequent surface and finishing, serious will cause dark-print scrap or damage to the knife and other hazard.

1) Hollow shrinkage cavity defects in tail: in the squeeze type, the center of the end of the bar to form a hollow, cross-section presented as a edge not smooth hole or edge filled with other impurities of the hole, vertical is a funnel -shaped (conical), funnel tip toward the direction of the outflow of gold, mainly in the single-hole plane mold extrusion, especially in the squeeze coefficient is small, the product diameter is large.The tail of a thick wall or a profile that is squeezed with oily extrusion gaskets is more noticeable. 

2) Ring-shaped shrinkage cavity defects in tail: in the squeeze shunt mold products at both ends (especially the head) is discontinuous ring or arc shape, in the welding line on both sides of the crescent shape is more obvious, the ring-shaped shrinkage cavity defects in tail of each hole product symmetrical. The reason for the formation of the shrinkage cavity defects in tail: the mechanical condition of the shrinkage cavity defects in tail formation is that when the stratosmy phase is over, the extrusion gasket gradually approaches the mold, the squeeze increases and produces a dN cylinder of surface pressure on the side of the squeeze cylinder.This force, together with the friction al-t cylinder, when the balance condition of the force (dN barrel dT barrel) is broken, the metal located around the squeeze gasket area flows backward into the center of the blank along the edge, forming a shrinking tail.