Gas metal arc welding (GMAW) is one of today’s most popular welding methods in nearly all industrial manufacturing fields. This is a positive development; however, the process has a wide range of risks for the welder. Welders protect themselves from the negative effects of welding by wearing protective gear to protect the body and eyes from burns, electrical shock and bright light and ultraviolet radiation.
Protection from welding fumes is often left out of this equation. Weld fumes contain minute particles of metallic oxides, silicates and fluorides - usually less than 1.0 µm in size. The composition of welding fumes varies with material being used and can be harmful if inhaled.
It is possible to select welding processes and consumables that generate lower levels of welding fumes or lower levels of key harmful fume components such as manganese and chromium. For instance, using a gas mixture with a higher percentage of argon, or switching from ER70S-6 to ER70S-3 which contains less manganese. Some welding power sources also utilize waveforms that reduce fume generation.
Occupational Health and Safety organizations around the world recommend that the removal of these fumes begin at the origin of the weld. This is achievable with a fume extraction welding torch.
Fume extraction welding guns are efficient in removing harmful welding fumes directly at its source without affecting the protective gas shield. In these types of guns a vacuum is integrated at the front nozzle and suctions the fumes through a hose to a filtration system to catch harmful particles.
There are many benefits in using fume extraction MIG torches. First and foremost, the welder’s breathing zone is protected. It also cleans the air for the other workers around. In other processes, the filtration occurs after the welder’s breathing zone thus not protecting the workers that are in contact with the worst air quality. Capturing fume at the source is extremely economical and efficient as the process takes place where the highest concentration of particles is found. As fume extraction is built into the tool, the welder does not have to worry about moving an arm into the proper position; between 6-12 inches of the weld. It also requires less vacuum volume; typically 80-100 CFM compared to 600-900 CFM for large fume extraction arms. When air is evacuated outside, you also have to consider extra Heating or Air conditioning costs.
Every detail is important if you want to achieve excellent results from your fume extraction investment:
Fume Extraction Theory
It is really important to understand the factors in place to properly perform efficient fume extraction. First, the hot welding fume goes up! It seems simple but needs to be understood. Also, the speed of the fume is proportional to the power used to perform the weld; the higher the parameters, the faster the fumes will go up. In order to catch the fumes, you need to be properly positioned and have enough vacuum to remove faster than the speed of the fume going up.
Fume Extraction Guns
Fume extraction guns historically have been heavier than standard GMAW torches. Today, that's not always the case. Choose the most ergonomic and the lightest weight guns possible for the required application. Also make sure that the nozzle and fume shroud are small enough to access your welds. For higher amperage applications, consider using water-cooled guns to keep the weight down. This will ensure the welders' comfort, reduce fatigue, and optimize handling.
Positioning Correctly While Welding
Proper positioning is as vertical as possible to the weld. Flat welds would require a close to 90 degree position. Corner welds between 45 and 60 degrees. Vertical welds are harder to control and need more vacuum pressure, and even sometimes the use of a cone in front of the torch. As this tool is being integrated into production, consider welding in flat position as much as possible.
Shielding Gas
Another factor to control is the welding shielding gas. It needs to be accurately set to properly cover the weld but not in excess as this will push the fume away from the efficient suction zone. It is also critical to control the initial gas surge that can be up to 3 times the set flow for a few seconds, especially when flowmeter is far from the feeder. A portable flowmeter should be used on a regular basis to check the gas flow with the vacuum on.
It is important to keep the front end of the gun free of debris and weld spatter. This will ensure proper gas coverage and vacuum. Ceramic anti-spatter spray works well applied directly on the front end consumables and fume shroud.
High-Vacuum Fume Extraction Systems
Fume extraction guns need a high-vacuum type of system. The latest models will perform properly without causing porosity or weld quality issues at up to 100 CFM. This requires the vacuum system to provide such volume at operating pressure of 85-90 in H2O (-22kPa). The static pressure capacity of the system is irrelevant as it does not inform of the operating pressure at target flow.
Welder Training
As in many other situations, training is an important aspect to consider when integrating new equipment such as fume extraction MIG torches. The welders need to use the recommended best practices like in regular GMAW welding. They also have to understand why some aspects are extremely critical in fume extraction. The proper torch position is easy to implement and the use of video sessions is very helpful for them to see their own position in relation to the fume extraction performance.
The basic maintenance and cleaning of the torch should be part of the initial training.
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This post originally appeared in Shop Metalworking Technology's Tech Tips section.