Piet van der Horst

Piet van der Horst

In 1970 Piet made welding his trade en since then he never stopped learning about that trade. By now he is well past his retirement age, but not welding is still not an option for him. It is not just work, it is a passion.

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Gases for welding processes

Inert and active gases

Classification according to the standard In NEN-EN-ISO 14175 standard, gases are divided into main and subgroups. In this article we discuss four main groups of

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The role of gas in welding processes

This article is about the role that gas plays in gas arc welding processes. We focus on the electrical welding processes. The oxy-fuel welding processes are not considered in this article. 

There are three different electric arc welding processes in which gas plays an important role:

Why do we need a welding gas in these processes?

There are several reasons for using gases during welding. The most obvious reason is to protect the weld pool. But there is more than that. 

The gas used has an influence on the weld quality, the current transfer, the droplet transfer and, last but not least, the welding speed. The gases can be inert or active and they are supplied in different compositions. This makes it worthwhile to take a closer look at the function of welding gases.

Protection of the weld pool

When we start welding MIG or MAG, a weld pool is created to join two metal parts together. Without welding gas, the tip of the welding wire, the melting droplet and the weld pool are affected by oxygen and nitrogen from the air. Both of these gases have properties that we prefer not to experience when making a welded joint. 

Oxygen has a strong oxidising effect on the liquid material of the melting wire and the very hot melting bath. This will cause the material to burn, which can be seen by the black colour of the weld. Nitrogen will cause the melting material and the welded joint to become porous. The result is a weld of very poor quality. The mechanical properties of this joint will leave much to be desired and also the appearance of the weld will not be good. A well chosen welding gas, hence also called shielding gas, will prevent this problem.

The electric welding arc

In the case of an electric arc, the electrical energy must be transferred from the tip of the electrode or wire to the workpiece to be welded. Here, too, the shielding gas has a function. Ionization of the shielding gas creates a very hot and highly conductive arc plasma in which the electrons and ions can easily move and thus transfer the current to the wire. Current flows from minus to plus and because in MIG/MAG welding the wire is connected to the plus pole, it is heated. With TIG and Plasma welding, this is the other way around; the plus is on the workpiece and the workpiece will therefore be heated.

Protective gases are usually inert, i.e. non-active, or inert with an addition of active gases. These can create a very stable welding arc that causes little spatter and ensures a good flux. A good choice of shielding gas therefore contributes to an optimal welding result.

The importance of the right gas

The shielding gas affects various facets of the welding process. The most important are:

  • The droplet separation, the so-called pinch effect. It determines the size of the melting droplet and how viscous or liquid it is.
  • The size of the weld pool.
  • The shape and depth of the penetration.
  • The welding speed.
  • The heat transfer. The heat from the welding arc must be transferred to the workpiece as efficiently as possible. The thermal conductivity of the various gases can vary considerably. A gas with a high thermal conductivity will therefore transfer the heat  to the workpiece very effectively and will also provide a more stable arc.

If all these effects are taken into account, it is clear that the choice of gas can have a positive or negative influence on the economics of a process. 

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