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In the extrusion process, two key properties of nitrogen are used. One is that nitrogen is inert to aluminum and the other is that liquid nitrogen at -320°F has excellent cooling properties. First, the hot section of the profile is surrounded by protective nitrogen gas. Then the die and the extruded product are cooled by liquid nitrogen.
Increased capacity
During extrusion, the temperature of the die is further raised by friction and plastic deformation of the aluminum. Cooling the tool assembly, particularly the die with liquid nitrogen, increases extrusion rates without raising the section temperature above the permissible level. The increase in extrusion speed will depend on the alloy and profile being extruded.
Improved surface quality
In relation to aluminum, nitrogen is an inert gas at extrusion temperatures. The nitrogen is applied either in liquid or gaseous form. It forms an inert atmosphere surrounding the section as it emerges from the die. This decreases the formation of aluminum oxide, as the oxidation is most severe at this point where the profile is hottest. In addition, the profile is cooled by the nitrogen, further decreasing the degree of oxidation.
Prolonged die life
Nitrogen cooling reduces wear on the die, which means that more profiles can be extruded before the die has to be repaired or replaced. |
