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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Silicates – Your question answered

Silicates

Question from Tom Monaghan on LinkedIn

In response to the Welding Word of the Week “Silicates” Tom had the following question: 

“Am I correct in believing that the very same silicates are present in a Tig/Soft Plasma welding pool, and when the weight of the silicate can no longer be supported by the weld pool it drops below the surface and if it remains trapped, shows on a Radiograph as a solid inclusion. The advantages in the use of silicates for their wetting properties has proven to be invaluable in reducing the lack of sidewall and inter pass fusion, but requires close monitoring.”

Our answer

During MAG welding there are small, or sometimes larger, slags on the weld. With MIG welding, this does not or hardly happen. The reason for this is that MAG welding uses an active gas. An active gas means that another gas is added to the main component Argon that reacts with the puddle during welding. These gases are carbon dioxide (Co2), oxygen (O2) (sometimes both) and hydrogen (H2). Carbon dioxide reacts in the welding arc on the workpiece side and provides extra heat by disintegrating into carbon monoxide and oxygen. The oxygen will try to bind with alloying elements in the weld pool, which can have a negative effect on the strength of the weld. To prevent this, extra deoxidants are added to the wires used for MAG welding. Especially Silicon, but also Manganese. The oxygen will bind to these elements and take the contaminants from the weld pool upwards. These are the brown silicates that remain on the weld. Hydrogen (H2), on the other hand, is a deoxidant that does not produce silicates. Hydrogen disintegrates into atomic hydrogen (H1 and H1), which is accompanied by a lot of heat. This extra heat causes the contaminants to evaporate, creating a clean weld metal and a clean weld surface. Hydrogen is almost exclusively used for MAG, TIG and Plasma welding of stainless steel. But can also offer limited advantages when welding steel.

Silicates are not produced in MIG, TIG or plasma welding. These processes are carried out with an inert gas. This means that there is no reaction with the puddle and no silicon-oxygen compounds and therefore no silicates are formed. If these silicates do exist, it can mean that the work is very impure. In almost all cases the gas cover was not good and somehow oxygen entered the inert gas. In TIG and plasma welding, this can be seen quite quickly on the tungsten electrode, which is quickly contaminated and discoloured, and shows dendrite formation at the tip. During MIG welding, the weld appearance will look oxidized and dark. In aluminium welding, the weld becomes brown or even black.

Inclusions in TIG and plasma welding are often caused by not properly cleaned seam edges, especially when cut with plasma. Plasma cutting with air creates oxides with a very high melting temperature on the seam edges that can cause a lot of annoyance, including silicate-like inclusions. These oxides mix with the puddle and are visible on X-rays as solid inclusions. It is therefore necessary to clean the seam edges thoroughly.

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