Productivity of extrustion plants can be increased by the use of nitrogen in die cooling and shrouding. The resulting benefits are higher production rates, improved surface finish and increased die life time.
During the extrusion process, two key properties of nitrogen are exploited: Nitrogen is inert to aluminium, and liquid nitrogen has excellent heat removal potential.
First, the hot section of the profile is surrounded by protective nitrogen gas. The die and extruded product are then cooled with liquid nitrogen.
Aluminium extrusion offers many benefits, including:
Increased capacity: During extrusion, the die temperature is further raised by friction and the plastic deformation of the aluminium. By cooling the tool assembly (and particularly the die) with liquid nitrogen, extrusion rates are increased without exceeding permissible section temperatures. (Increases in extrusion speed depend upon the alloy and profile being extruded.)
Improved surface quality: Nitrogen is inert to aluminium at extrusion temperatures. Nitrogen is applied either in liquid or gaseous form, and it forms an inert atmosphere that surrounds the section as it emerges from the die. This reduces the formation of aluminium oxide, which is typically most severe at this point (i.e., where the profile is hottest). The profile is also cooled by the nitrogen, further reducing oxidation.
Prolonged die life: Nitrogen cooling reduces die wear, and so more profiles can be extruded before the die must be repaired or replaced. This reduces costs associated with both wear-and-tear and downtime.
To learn how Linde can help optimise your metallurgy and extrusion operations, be sure to contact us.