Argon 4.6 as an inert shielding gas: Everything you need to know about gas cylinders and argon shielding gas

4 months ago

Welders-Handbook

5 minutes

MSG welding processes such as MIG or TIG use inert gases. A gas is inert if it does not react with its environment. Typical inert gases in welding technology are argon and helium. There is also neon, which is not used in welding. In the following, argon is treated as a welding gas or shielding gas. It is a colourless and odourless gas that has established itself as a shielding gas due to its chemical composition. The chem. Symbol is Ar and is used as a pure gas and as a mixture. When referring to argon with the suffix 4.6, the number is intended to describe the degree of purity. See below for more details.

What is argon 4.6 and why is it used as a shielding gas?

Argon is a noble gas with the symbol Ar in the periodic table of elements. As it is relatively inexpensive and can be easily ionised by electric current, it is often used as a shielding gas. Argon is always used when thermal conductivity is of secondary importance.

Periodensystem der Elemente — Image by Elchinator from Pixabay

Ar is ideal for TIG and MIG welding of high-alloy steels (stainless steel), aluminium materials or non-ferrous metals.

Advantages of argon 4.6 compared to other shielding gases

Argon is always used when the weld pool needs to be protected from oxidation or reduction. The situation is different for welding processes such as MAG welding. Here, gas mixtures are used so that they can react with the weld pool. In the case of high-alloy steels, this would have the disadvantage that alloying elements could burn and thus, for example, the rust protection properties would be lost. There are also gas mixtures with nitrogen, oxygen, CO2 or hydrogen. Up to 5% hydrogen is often added, especially when gas-shielded welding with stainless steel.

Mild steel: mixed gas or CO²
Aluminium: Argon or helium
- thinner sheets: Argon
- thicker sheets: helium / argon-helium mixtures
non-ferrous metals Argon, helium or gas mixtures

Differences between argon, helium and other shielding gases

The shielding gas argon is a rather favourable gas compared to helium. It is easy to ionise and heavier than air. The density is relevant here, as larger flow rates are required at lower densities.

Helium, for example, has a lower density and is lighter than air. In this case, the flow regulator must be turned up a little further. As the thermal conductivity of the gas is higher, the arc also burns hotter. Helium is often used as a shielding gas for thicker metal sheets.

What gas cylinder sizes are available?

Argon gas cylinders are usually available in the following sizes:

10 litres (200 bar)
20 litres (200 bar)
50 litres (200 bar)
50 litres (300 bar)

The 10 or 20 litre cylinders are best suited for hobbyists as they are easy to transport. They are also easier to secure in the car.

There are also disposable cylinders. Here is a short video. It doesn’t sound so good, but it is informative on the subject.

How many litres of welding gas does a gas cylinder contain?

To calculate the content at normal pressure, simply multiply the volume by the pressure. For example, a 10-litre cylinder at standard pressure of approx. 1 bar has a capacity of 2000 litres. A 50-litre bottle at 300 bar, on the other hand, contains 15,000 litres. Attention: Special pressure reducers are used for 300 bar cylinders!

gas reductor, gas flow, bar — Image by Mimzy from Pixabay

The relevance of the purity grade of argon shielding gas

The addition 4.6 tells us something about the degree of purity. 4.6 stands for a purity of 99.996%. A purity of at least 99.95% should be maintained for TIG welding. The shielding gas argon 4.8 stands for 99.998% purity and is more suitable for special welding applications or the laboratory. The standard in which these regulations are laid down is ISO 14175.

Here is more information on this wonderful shielding gas in FAQ form:

Why is argon used as a shielding gas?

Argon is used as a shielding gas in arc and plasma welding due to its inertness and its properties as a component of the atmosphere. It prevents the material from reacting with oxygen or nitrogen from the earth’s atmosphere and the weld pool from oxidising or becoming nitrogenous.

How do I recognise the degree of purity of an argon gas cylinder?

The degree of purity of the argon contained in a gas cylinder is expressed by the code number, e.g. 4.6. This stands for an argon content of at least 99.996 per cent by volume, which corresponds to a very high purity. In addition, an argon gas cylinder is labelled in accordance with DIN EN ISO 14175.

What does the DIN EN ISO 14175 labelling on a gas cylinder mean?

The DIN EN ISO 14175 marking on a gas cylinder means that this gas cylinder fulfils the requirements of the standard for shielding gases and guarantees a high degree of purity of the gas, which is required for shielding gas welding.

How do the cylinder sizes differ?

The most common cylinder sizes for argon are 10 litres, 20 litres and 50 litres. The choice of cylinder size depends on the intended use. A 10 litre cylinder is usually sufficient for occasional small jobs.

When is argon used as a shielding gas for welding?

Argon is used as a shielding gas for TIG and MIG welding, as it effectively protects the weld pool from contact with the ambient air. Due to its inertness, argon is particularly suitable for welding easily oxidisable materials such as magnesium, titanium, zirconium and copper.

Why is a pressure reducer needed?

There is a pressure of 200 to 300 bar in the gas cylinder. A pressure reducer is used to reduce this pressure to the working pressure. The working pressure is 1 bar.

What are the advantages of argon for welding compared to other noble gases?

Argon has the advantage over other noble gases that it effectively protects the weld pool from oxidation due to its inertness and at the same time ensures a more stable and efficient welding torch. Argon also produces less smoke and spatter than helium, for example, which improves working conditions.