Once cooled, extrusions are stretched. This is done on all extruded profiles in order to straighten the crookedness incurred during the pressing and cooling steps.
It also reduces the thermal stresses that are always present.
Stretching is done by gripping the ends of the entire runout extrusion length and stretching it by around 1% using a hydraulic piston.
This operation establishes the final profile dimension after pressing. Stretching affects profile shape, particularly for flange angles and gap openings in semi-open profiles.
In certain instances, these dimensions may be calibrated in conjunction with the stretching operation.