"Where most people will put large hoods above a welding bay, we prefer to extract welding fume at source, where the welding is happening, so that no fume goes anywhere near the welders face," begins Hoon. To do this, Nederman offers the most comprehensive rang of fume extraction arms to ensure that the extraction point is always less than 500 mm from the point of welding. "All possibilities are covered. We offer mobile fume extraction systems and fully centralised extraction and filtration solutions, along with on-torch fume extractors that can be supplied with a dedicated torch or as a retrofit that can be fitted to any torch. Nederman produces the full range of hi-vac and low vac systems coupled with a number of dust filtration and collection systems," he says.
Centralised high-vac systems, according to Herteberger, are typically mounted onto the welding torch and involve suction pressures of -20 kPa at high airflow speeds and relatively low volumetric flow. "High-vac would typically be used with 38 mm pipe on the extraction arms," he explains, adding that these systems extract less of the surrounding air but they need to be very close to the source, "typically 50 mm away", hence their suitability for on-torch use.
"These solutions are quite universal and can even be attached to grinders, for example," adds Hoon. "On-torch extraction is an excellent at-source solution that has been proven to have no effect on gas shielding, but people remain sceptical," he reveals. "Low-vac systems, on the other hand, are designed for higher volume flows at lower suction pressures, in the order of 1.5 kPa."
Welding fume is particularly harmful because of the metal vapour and particles in the fume. "Stainless welding, for example, produces chromium-6 or hexavalent chromium, which exists in fume as particle in the 0.01-0.1 µm size range. This means they are easily inhaled deep into the lungs and can penetrate facemasks. Chromium-6 is a known carcinogen and investigations have proved that exposure has very dangerous effect on a person's health," Hoon warns.
Back in 2006, the Occupational Safety and Health Administration (OSHA) in the USA significantly lowered the permissible exposure limit (PEL) of chrome-6 from 50 to 5.0 μg/m3 as an eight-hour time-weighted average (TWA). Fume from manual metal arc (MMA) welding and flux-cored arc welding (FCAW) contain a high proportion of components coming from the electrode coating or the flux-core, while little comes from the filler metal. Fume from metal inert gas (MIG) and metal active gas (MAG) processes, on the over hand, while they may look less 'smoky', contain high concentrations of the metals being deposited, which can make these processes even more dangerous.
"Any particle size less than 0.5 µm in welding fume can reach the lungs, causing health risk including: cancers; asthma; nasal and skin ulcers (chrome holes); allergic and irritant contact dermatitis; lung disease (siderosis); fertility complications; and infarctions (tissue death). Company's can also reduce the number of sick-days taken by welders, simply by removing their exposure to fume," Hoon suggests. "And while respirators are also an option, welders don't like to work an eighth-hour shift breathing through a mask," he adds.
Collected dust, continues Herteberger, can also pose a fire or explosion risk: "We supply FX-rated (explosion proof) hoods and air filtration systems for applications such as aluminium grinding, because aluminium dust poses an explosion risk if ignited. Any dust can, in fact, be dangerous, so it needs to be properly handled and disposed of in a safe and environmentally responsible way," he advises.
Small and mobile fume extraction
While Envirox offers solutions for general industry – including plasma cutting extraction systems, oil-mist filtration on the CNC side, and complete workshop systems that can extract dust off the floor to keep it clean – "our niche focus in South Africa is welding fume. We offer everything from small (0.7 to 2.2 kW) mobile systems for occasional welding, to very large systems extracting 20 000 m3/h or more," says Hoon.
Nederman portable fans are simple and powerful extractor units. They are compact and easy-to-use with multiple inlet and outlet connection options. The smallest is the Fume Eliminator, which is a small, lightweight, portable unit designed to be carried to the working area. These units provide an airflow of 150 m3/h, use disposable cartridge-type filters and are ideal for on-torch extraction. FilterCart is another mobile extraction and filter unit for light welding applications. These come with an arm length of 2.0 or 3.0 m and are suitable for up to 1 050 m3/h over a filter area of 35 m2.
Where a mobile solution for continuous welding and dust extraction is required – for large fabrications on an open shop floor, for example – Nederman has developed the Filterbox, which can be used with more that one extraction arm. "These systems have a self cleaning filter that operates via reverse pulse compressed air, along with a scraper. As with large-scale dust collectors, the dust is dropped into a collector below the unit for safe disposal after use," Hoon tells African Fusion, adding that these Nederman systems are "among the most cost effective small system available" and the range can be "customised to suit almost any workshop application".
Twelve Nederman mobile filtration systems have recently been supplied to Kumba Iron Ore for its welding activities, to overcome the limitation of a 3.0 m radius arm.
Centralised extraction and filtration systems
Nederman centralised systems are available with three dust collection variations, Filtermax, FMC and MJC, and are installed with all of the ducting extraction arms and fans required for each particular application. "At the starting point of the design of a fume extraction system is Nederman's NetQuote design software. Based on a basic specification, this 'app' can produce a 3D drawing of a fume extraction system within 10 minutes, including all of the fan, ducting and extraction arm sizes. The software will also produce system performance curves that show the relationship between pressure, flow and power for different operating points," Hoon says.
Highlighting Envirox's capability, according to Herteberger is the centralised extraction installation at Murray and Robert's Medupi welder training centre in Lephalale. "This is our biggest installation to-date. It consists of two independent 18.5 kW systems, with 30 telescopic arms connected to each system.
"To cater for the variation in the number of welders being trained at any one time, Murray and Roberts chose to use variable speed drives (VSDs) on the fans of both systems. When a welder begins to weld, the damper in the telescopic extraction arm automatically opens to allow the fume to be extracted. On opening, a signal is sent to the VSD to increase the fan speed and accommodate the additional flow. So the fan speed adjusts to the total extraction requirement, speeding up when more welders are busy and slowing down as each welder stops welding. This ensures that the energy use of the system matches the extraction demand and that the fan is never running at an unnecessary speed," Herteberger explains.
"These systems are necessary for welding operations to comply with health and safety regulations – and almost every workshop has a welder on its premises," says Hoon. "The OHS Act specifies that you must create a safe environment for your employees, while ISO 14000 specifies the exact allowable values. All European companies are now tending to adopt these globally accepted standards and even our mines are mindful of the air their workers are breathing.
"We are proud promoters of at-source solutions. Not only is this safer, but it also saves energy, because less airflow is needed. Nederman's at-source solutions range from the most cost effective portable and mobile solutions available through to very large, modern and highly efficient centralised designs," he concludes.