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Extraction of Fumes Using Plenum Boxes when Mig Welding Furniture Components

Flextraction Ltd, supplier and manufacturer of Local Exhaust Ventilation (LEV) products was recently asked to come up with a solution for the extraction of welding fumes for a steel furniture manufacturer supplying schools and colleges.

The company concerned was MIG spot welding components using static hoods in seven jig welding fabrication bays extracting from above, which was not taking all the fumes away from the welders’ faces. The Company is fabricating tubular steel seating and tables, but the range, type and demand for their products meant that they did not have long production runs and therefore the use of LEV type fume extraction equipment was impractical and not very economic. The welders were not only welding small production runs but also had only spot welds to complete and if using LEV equipment they would have to reposition the welding hood each time they started a different weld on an individual component.

Flextraction were asked to come up with a solution that met the company’s requirement for the welding fumes to be drawn away from the faces of their welders, so that welding was carried out in a clean environment and that they could carry out intricate welding operations without having to adjust any extraction system.

The solution proposed by Flextraction’s design engineers and ordered by the company was to fit rear plenum boxes with six louvered grills on the back wall of each welding booth in close proximity to the worktable, which would draw any welding fumes away from the face of the operator and into a new spiral galvanised sheet steel ductwork system with inspection/access doors and sized to provide good conveying velocity throughout its length.

A 3-phase centrifugal single inlet medium pressure extraction fan running at 2895rev/min and fitted with an impeller having backward facing blades is located on the floor outside the building with the fumes being vented into the atmosphere at a high level. Another modification recommended by Flextraction and taken up by the company was that each welding booth should be fitted with side curtains to contain the fumes and help direct the airflow to the back wall and into the louvered grills.

Flextraction also fitted electronic airflow monitors to each welding bay to confirm to the operators that the system was working to specification. An LED (red-green) and audible alarm confirms that the airflow, monitored by differential pressure, is reflecting a true movement of air.

Lee Darton, Managing Director at Flextraction commented: “We were asked to come up with a fume extraction solution to meet the customer’s specifications. The canopy system they had in operation was not recommended by the HSE and PPE equipment was a last resort. The rear plenum boxes gave the customer what they wanted in that the fumes were drawn away from the welder’s face rather than through the face.”

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