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Aluminum Extrusion: Staying Cool with Nitrogen

  • By : PureAire Monitoring Systems
  • Posted on : March 14, 2018

Aluminum is a highly malleable material, which is readily shaped for any number of purposes. The aluminum extrusion process is key to shaping aluminum, and it must be completed in an inert environment to reduce the formation of oxides. Learn why this is important and how facilities can reduce the risks of health hazards in an inert environment.

How Aluminum Extrusion Works

Billets of aluminum are first heated to above 800 degrees Fahrenheit to become malleable, then coated with a lubricant so the molten metal will not stick to the extruding ram.

The ram presses the aluminum billet through a die, which is cast in a given shape. As the aluminum passes through the die, liquid nitrogen flows over the metal to prevent oxides from adhering to the aluminum. This also extends the lifespan of the die by cooling it. In some operations, nitrogen gas is used instead of liquid. While the overall purpose is the same — to keep out oxides, which can cause the extruded aluminum to crack — the gas does not cool the die.

The shaped aluminum passes through the die, then exits the press where its temperature is taken. Temperature records help maintain press speeds, for plant efficiency. The extruded aluminum pieces are then transferred to a leadout table and a puller, where the metal is cooled using fans. Some mixtures of aluminum are cooled with water as well as air.

The cooled and cut aluminum is then stretched via a stretcher, a step that increases the hardness and strength of the finished piece. Finally, extruded aluminum pieces are cut for precision and aged under controlled temperatures via heat treatment.

The entire process resembles a play-doh modeling kit, where the dough is squeezed through a press and comes out in a tube or a star shape, for instance.

Extruded aluminum pieces are used in a variety of industries, including railway cars, lightweight automobiles, bridge decking, solar panels, and coaxial cables.

Whether liquid or gaseous nitrogen is used, there is a risk of a nitrogen leak causing an oxygen deficient atmosphere. Nitrogen is naturally heavier than oxygen, so it displaces the oxygen molecules in the atmosphere. Since nitrogen has no color, odor, or scent, employees are unable to tell there’s a leak. A leak poses health hazards in addition to work disruption and revenue losses. Fortunately, there’s an easy way to protect facility staff.

Why Oxygen Sensors Should Be Used With Aluminum Extrusion 

When nitrogen displaces oxygen, oxygen levels start to fall unbeknownst to anyone present. Eventually, oxygen levels will grow dangerously low. In an oxygen deficient environment, employees may start to feel dizzy or confused. Some may sweat, start to cough, or experience rapid breathing and increased heart rate. Death via asphyxiation is a real risk.

An oxygen sensor provides assurance that there is no leak, since it tracks levels of oxygen in the room 24/7. As long as oxygen levels are above the OSHA threshold of 19.5, the monitor will be silent. If liquid or gas nitrogen starts to leak, leading oxygen levels to fall, the monitor will sound an air horn and flash lights. Staff will understand there is a problem and will have time to evacuate to safety. Staff can also check the monitor face at any time to see oxygen levels at a glance.

PureAire offers oxygen monitors that feature zirconium sensors, which last long and withstand shifts in barometric pressure and temperature. These monitors can operate for over 10 years with no annual maintenance or calibration. PureAire’s monitors work in temperatures from -40 Celsius to 55 Celsius and even function in confined spaces, such as basements or freezers.