Raising productivity of aluminium extrusion with nitrogen

Abstract

Nitrogen has been used for cooling and/or inerting aluminium extrusion dies for more than 35 years. Although it has not been widely investigated, the process is reported to improve quality and extrusion speed. Several techniques exist to apply the process in practice. Some of these techniques inert only the die exit. Others additionally use liquid nitrogen to cool the die and the exiting product simultaneously, and it is results from these techniques that are reported in the present paper. Although the gains to be made are very dependent on the profile being extruded and the design of the die set, the use of these techniques significantly improves all the measured parameters. In some cases increases in extrusion speed of over 100% are reported and in one case die life increased by 200%. Several methods of introducing the liquid nitrogen are described. Results are presented for each and the advantages of each technique are discussed. It is shown that liquid nitrogen injection via the bolster is particularly efficient when long runs can be extruded and when the peripheral conditions such as the section shapes, dimensional stability, die design and the plant as a whole, permit the extrusion speed to be increased substantially.