There might be air remained in the aluminum profile in the process of aluminum extrusion, which brings bubbles in the inner and surface of the aluminum profiles and turn the aluminum profiles into waste profiles. To prevent air form entering into the aluminum profiles, we make an analysis on what cause the air remained in the aluminum profiles and conclude the following results:

1 The residual air is caused by hot shearing of long aluminum billets
There can imperfect cut face when the long aluminum billet is cut by the hot shear, which, if with poor shearing performance, can lead to serious bending of aluminum billets, which can further lead to oval cross-section and rounding of aluminum billets and finally result in the air remained in the aluminum profiles.

2. No air emission process is performed in the aluminum extrusion process
The aluminum extrusion press will exert pressure on the aluminum billets in the aluminum extrusion process, which can cause deformation of billets and when the billets expanded to the same size as the internal cylinder of extruder, air in the cylinder should be removed, otherwise, the air in the cylinder will be extruded to form bubbles in the aluminum profiles.

3. Air residue caused by connection of the two aluminum billets
The long aluminum billets will be cut into short pieces in the extrusion process, and when the joint surface of the two aluminum billets is not smooth, there might be air in the joint suface.