In extrusion, hot plasticised material is forced through a die opening to produce a profile of the desired shape. This extruded profile is left to cool – by exposure to air in room temperature, by passing through a bath held at controlled temperature or by compressed air – before it is cut to length. To ensure the profile retains its finished shape and size, a special calibrator unit is used as cooling is a sensitive process.
Extrusion therefore employs different engineering parts requiring different requisite properties according to its functions. The calibrator units are often made of aluminium for quick cooling, while the die is normally produced in steel. The strength requirements of the steel die are moderate while the demand for corrosion resistance and wear resistance is high. Generally pre-hardened grades possess enough strength for a typical extrusion procedure, although the dies are often nitrided for fibre reinforced products.
ASSAB’s answer for this application includes pre-hardened materials like ASSAB 718, Nimax, Mirrax 40 and through-hardened grades such as Stavax ESR, Mirrax ESR and Corrax depending on plastic material and hardness requirement.