When there is smoke, there's flux.

Ever wondered why welding (especially stick welding) produces smoke? Apart from the heat produced from welding the base metal and filler metal, the smoke coming out of the weld is from the flux coating of the welding electrode called a shielding gas.

AWS D1.1 Structural Code Welding for Steel defines shielding gas as the protective gas used to prevent or reduce atmospheric contamination.

It protects the weld from hydrogen attack that causes embrittlement and porosity.

Apart from the shielding gas, there are other functions of this flux coating in the weld,

1. Shielding – coating decomposes to form a shielding gas. This prevents atmospheric gases from contaminating the welded metal
2. Deoxidation – fluxing action removes impurities
3. Alloying – provides alloying elements for the weld deposit
4. Ionizing – improves electrical characteristics to increase arc stability
5. Insulating  - solidified slag slows down the cooling rate

The electrode is made up of a solid wire with flux coating for shielded metal arc welding as seen in the figure below.

This solid wire is made up of a metal core wire covered with a granular layer of flux held by a bonding agent. When the solid wire gets heated up, it deposits metal and slag into the weld puddle. The covering or flux also forms slag which in turn slows down the cooling rate of the weld. This is important because it reduces the risk of embrittlement due to rapid changes in temperature.

Some flux coating also contains low-alloy steels which help with the alloying properties of the electrode as mentioned above. This is also used for economic purposes as some electrodes used for carbon steel may also be used for low-alloy steels as well.

Characteristics of flux coating for common SMAW electrodes

• Common electrodes - For some SMAW electrodes, the flux covering makes slag removal easier like in E6013 which is why it is regarded as one of the easiest electrodes to use as a beginner welder.
• Low-hydrogen SMAW electrodes - the ones that end with 5, 6, and 8, there is a maximum covering moisture limit of 0.6% or less as required in ASME Section III-C. This is one of the reasons why low-hydrogen electrodes need to be stored properly because if they are exposed to humid conditions, their low hydrogen characteristics will be lost due to considerable moisture in these humid conditions.Moisture itself does not cause cracking in the weld according to ASME Section III-C. What causes cracking is the diffused hydrogen that forms from moisture in the arc that will cause cracking.
• Fast-fill electrodes - such as E6027 and E7028 which are only suitable for horizontal position because of their fast-fill characteristics, have electrode coverings that are much thicker, making 50% of the weight of the electrodes.To know more about SMAW electrodes, you can visit my article elaborating that right here .

Hazards of Flux exposure

Smoke coming from melting metals is generally not good for our health. The smoke coming out of a stick welding process is no different.

Many welding or even cutting processes produce fumes and gases which may be harmful to health. Filler metals, base metals, and the flux produce solid-particle fumes. The composition of these fumes depends upon the composition of the filler metal, base metal, welding process, flux, current level, arc length, and other factors.

Possible effects of overexposure range from irritating of eyes, skin, and respiratory system to severe complications. Effects may occur immediately or may take some time.

Fumes depending upon the flux and base metal composition or any coatings it might have may cause symptoms such as nausea, headache, and metal fume fever (if exposed to zinc compounds).

In confined spaces, the effects of these fumes are magnified because it can displace air for breathing, hence proper PPE must be worn at all times. Sufficient ventilation must be present to prevent the accumulation of these fumes. Appropriate safety personnel must check first the condition before and during the welding activity to ensure that safe levels of oxygen are present.

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