luminium extrusions are made from solid aluminium cylinders called billets, which are continuously cast from molten aluminium. Billets are available in a wide variety of alloys, pretreatments and dimensions, depending upon the requirements of the manufacturer.

The extrusion process involves aluminium metal being forced through a die with a shaped opening. This is made possible by preheating the billet to 450-500°C and then applying a pressure of between 500 and 700 MPa (equivalent to the pressure found at the bottom of a 60km high water tank!). The heated and softened metal is forced against the container walls and the die by a hydraulic ram, the only exit is the geometric cross-section of the die opening, and the metal is squeezed out.

The extrusion leaves the die at a temperature of around 500°C and the exit temperature is carefully controlled in order to achieve specified mechanical properties, a high quality surface finish and good productivity.

The Press

The press supplies the force necessary to squeeze the billet through the extrusion die. It consists of:

• The container where the billet is put under pressure.
• The main cylinder with the ram for pushing the billet into the container and through the die.
• The front platen giving counter support to the die package.
• The main columns fixing the front platen and the cylinder together.

The die is supported by a series of back dies or backers and bolsters for transferring the main press load to the front platen.

The principle of an extrusion press can be seen in the schematic diagram below:

Applications

Aluminium extrusions are used throughout the construction industry, particularly in window and door frame systems, prefabricated houses/building structures, roofing and exterior cladding and curtain walling. Extrusions are also used in road and rail vehicles, airframes and marine applications.