The term inert comes from the Latin language and means lethargic. The inertness of these gases refers to their ability to react with other elements. Inert gases undergo no or hardly any chemical reactions.
Inert gases have a double effect
- Due to their inertness they do not react with metals.
- Shielding gases displace the air we breathe from the machining area and prevent the oxygen from reacting with the metal.
Which inert gases are there?
Of the 118 known elements, only 8 gases are so inert that they could be used as shielding gases. From these gases, only nitrogen, helium, neon, argon, krypton and xenon can be used as inert gases without restrictions.
Radon is also an inert gas, but is not used in industry because of its radioactivity. Carbon dioxide can also be used as a shielding gas at lower temperatures. There is one thing to be considered with this gas though.
Carbon dioxide - An inert gas becomes active
Carbon dioxide is often used as a shielding gas and protects our food, among other things. During welding, CO2 can be used in combination with argon or helium. But it is very important to note that carbon dioxide loses its shielding gas character at higher temperatures and becomes an (partially) active gas. This means that 2 carbon dioxide molecules (CO2) can break into 2 molecules of carbon monoxide (CO) and 1 molecule of oxygen (O2). The oxygen reacts with the weld pool and carbon accumulates in the molten metal. This accumulation can certainly be desirable with the welding process, as it allows the hardness to be increased. The downside can be a more brittle weld. The degree of this effect can be controlled by the amount of CO2 in the shielding gas.
The problem with oxygen
With a volume share of 20%, oxygen is the second most common gas in our atmosphere and by far the most common element on our planet. This gas is very reactive and forms chemical compounds with most of the other elements. However, oxygen only develops its corrosive effect on iron and steel in combination with water. By diffusion processes, water removes ions from the iron, which enables the oxygen to attack the iron effectively.
The situation is different for welding, laser cutting or other thermal processing methods. Due to the enormously high temperatures, the oxygen can react with the metal even without the help of water. For this reason, the area where molten metal is located must be shielded from the air by inert gases.
Nitrogen during laser cutting
Fusion laser cutting is used for Rime. The used nitrogen is very suitable for oxidation-free cutting of metal sheets. In theory, an argon-helium mixture could also be used, but the price of nitrogen is about 40% lower than that of noble gases. The decision to use nitrogen is also economic in order to be able to offer laser cutting at reasonable prices.
Because nitrogen, like noble gases, does not form chemical compounds with the metal, the edges of the work piece are very clean and rarely need to be refinished. This fact makes laser processing an economical sheet metal processing method despite the high nitrogen consumption.
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