Fume and debris are unavoidable in a facility where robotic welding takes place. Certain approaches are more effective than others in reducing haze and improving overall air quality on the plant floor when robotic welding applications exist in the same building.
“Most welding processes spread out light to medium fumes over a large area,” says Greg Schreier, metalworking market manager at Camfil Air Pollution Control. “Robotic welding, however, creates a column of dense smoke that creates a unique capture problem. Also, because robots are typically used in high-volume production, the level of smoke generation is very high, making smoke and fume capture even more challenging.”
Cartridge-style dust and fume collectors handle robotic welding fume capture with the required high level of filtration efficiency, explains Schreier, who offers five factors to consider when designing such a system.
- Materials being welded. The EPA National Emission Standard for Hazardous Air Pollutants (NESHAP), Rule 6X, imposes strict environmental monitoring of outdoor air exhausted from many metalworking processes. OSHA indoor air regulations must also be satisfied, especially where toxic dusts are generated during welding of stainless or galvanized steel. Whatever the application, the dust collection system must be designed with high enough capture efficiency to meet local, state, and federal regulations and ensure worker safety.
- Type of robot. A typical setup may use one or two wire robots. Two produce a much higher level of smoke, which will have an impact on dust collector sizing and other components.
- Hours of operation. Robot operation may vary from eight hours a day to 24/7. The ability to handle dust loading over an extended period of time needs to be considered in the system design.
- Hood design. Because robots occupy a small space, overhead hoods provide an efficient way to capture weld fumes. A hood might be quite small or as large as 16 ft by 16 ft. The horizontal area under the hood needs enough vertical velocity to capture and contain the smoke. At the same time, the vertical area where the operator stands needs to have enough horizontal velocity to protect the operator’s breathing zone.
- Fire protection. Robotic welding produces lots of sparks that can ignite a fire, and mild steel operations generate an oil mist that settles on the collector and filter cartridges and becomes a potential fuel source. The system must be protected against fire risks. A variety of technologies can be applied, from sprinkler systems to spark arresting devices to flame-resistant filter media, explains Schreier.
Reduced maintenance, increased safety
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“Source collection is your best bang for the buck,” says Bill Thumme, president of Environmental Solutions, which sells equipment from Donaldson Torit. “You catch the greatest amount of particulate with the least amount of airflow while the smoke is concentrated. Enclose the robotic cell. Put dust collection above the enclosure. Seal it up as best as you can on all four sides and the top. Use the natural rising heat of the welding smoke to make an updraft.”
Typically, it’s normal to cover work areas that produce the fume and particulate with extraction hoods, suggests Mark Oxlade, arc welding manager, ABB Robotics. “Dependent on the type, location, and amount of particulate or fume being produced, these can be locally placed hoods or larger hoods over the complete area including load/unload stations,” he says. “It’s quite normal for welded components to continue to produce gases and particulate long after they’ve been removed from the immediate welding area.”
The amount of air movement requires close scrutiny so it’s enough to remove the fume and particulate without disturbing the gas shielding required for the process, continues Oxlade. “If the components to be welded or cut are particularly oily or corroded, then the increase of material to be removed may be best served with a downdraft approach,” he says. “Some materials and coatings can produce particularly harmful byproducts and require very specific removal procedures. Local health and safety regulations will dictate whether the gases and particulate can be removed straight to atmosphere or any preconditioning is required. Cleanliness and good upkeep of the fixturing will also complement the quality of the local environment.”
In another approach, some torch manufacturers have added the extraction directly at the weld torch. “The upside is it has the ability to remove the gas and particulate directly at the source as it’s generated,” says Oxlade. “The downside is the torch can become larger in size and may restrict weld access. All robots move relatively quickly, and so they have the tendency to depart from the just-welded joint onto the next weld, leaving behind gas and particulate requiring removal.”
Capturing and containing the fume locally at the robotic weld cell is essential to prevent migration of the fume, reminds Travis Haynam, director of business development and technical sales, United Air Specialists. “Local fume capture, also known as source capture, is the most effective method and requires the least amount of energy and initial investment to accomplish,” he says. “To achieve local containment, utilize the thermal rise of the weld fume to your advantage by using a tapered, fixed hood across the top of the welding cell to collect the fumes. Size the airflow of the fume extraction system to achieve an average minimum transport velocity — 150-200 ft/min — across all openings of the weld cell. Maintaining these velocities will keep the weld cell under a negative ingress that will contain the fume locally to be extracted and filtered. Protecting the containment area from external airflow patterns that would disrupt the ingress velocities is an important aspect of successful fume extraction system operation. Cooling fans, HVAC systems, or automated machinery are common sources of disruption. Translucent, arc flash curtaining is a good way to achieve containment and block external airflow patterns while still providing access and visibility to the work being completed in the cell.”
Figure 1. Implementing the recommended method of capturing weld fumes at the source helps to ensure that the harmful fumes don’t migrate into the workers breathing zone and also results in a decrease in maintenance and housekeeping costs. (Source: UAS)
Implementing the recommended method of capturing weld fumes at the source helps to ensure that the harmful fumes don’t migrate into the workers breathing zone and also results in a decrease in maintenance and housekeeping costs by reducing the amount of pollutants circulating in the air and depositing on other equipment, as well as on floors and exposed surfaces throughout the facility, says Haynam (Figure 1).
Substitution, isolation, and ventilation are three considerations to make, according to Jason Lange, environmental technical sales at Lincoln Electric. “Is it feasible or practical to substitute a different gas or welding consumable for a process?,” asks Lange. “Different welding consumables and mixed gases produce different fume generation rates (FGRs). By reducing the FGR, the amount of welding particulate that rises in a facility will be reduced. When welding with a robotics or hard automation system, we like to isolate the welding fumes from the operators, which in turn helps to protect the breathing zone of the worker present. Isolation can be done by placing a barrier between the process and the worker. Typically, a hood with curtains allows you to create the barrier. We divide ventilation into three areas. First is source capture, second is local capture, and third is general ventilation. Source capture is the process of capturing the fumes as close as possible to the welding arc. This is done using fume extraction guns, backdraft tables, arms, or nozzles. Local capture is done using a hood over the needed collection area. Typically curtains are then used off the hood to create an enclosure or barrier between the operator and work zone. General ventilation is the next area of cover. General ventilation allows the capture of the welding fume as it is suspended in the air.”
Users and employers have the sole responsibility for and control over workplace conditions, including the manner in which work is performed and the safety measures are taken, says Lange. Always read and follow applicable OSHA regulations, as well as all information on product labeling and material safety datasheets. “The operation of welding fume control equipment is affected by various factors, including proper use and positioning of such equipment, maintenance of the equipment, and the specific welding procedure and application involved,” cautions Lange. “Users and employers should have an industrial hygienist check worker exposure levels to be certain that they are within applicable OSHA PEL and ACGIH TLV limits.”
|Mike Bacidore is chief editor of Plant Services and has been an integral part of the Putman Media editorial team since 2007, when he was managing editor of Control Design magazine. Previously, he was editorial director at Hughes Communications and a portfolio manager of the human resources and labor law areas at Wolters Kluwer. Bacidore holds a BA from the University of Illinois and an MBA from Lake Forest Graduate School of Management. He is an award-winning columnist, earning a Gold Regional Award and a Silver National Award from the American Society of Business Publication Editors. He may be reached at 630-467-1300 ext. 444 or firstname.lastname@example.org or check out his Google+ profile.|
To reduce haze and improve overall air quality on the plant floor, several factors should be considered for a robotic welding application, recommends John Woolever, product manager, Donaldson Torit. “Proper initial containment and capture of generated robotic weld fume is critical,” he says. “To achieve this objective, robotic welding fabricators typically enclose their welding areas in a booth to limit fume from escaping from the immediate manufacturing zone. With the fume contained inside the booth enclosure, the next step is to properly convey the fume to the dust collector. It is best to consult a professional who will follow good industrial ventilation practices for weld fume control and conveying. When full enclosure is not possible, source fume collection with a smaller extraction hood located close to the weld location is an alternative.”
The dust collector must have the airflow capacity to support the welding application, booth volume, and hood design, explains Woolever. “Consult a professional for proper equipment sizing,” he recommends. “The collector should also have high efficiency filtration media filter elements to capture and contain the weld fume. A filtration media with a nanofiber efficiency layer and a minimum efficiency rating value (MERV) of 15 is currently the best available filtration technology. If the filtered air is deemed acceptable for recirculation back into the plant floor, a secondary filter may be recommended.”
A combination two methods, source capture of the weld fume directly from the weld gun, and ambient air cleaning and filtration, has proved to be very effective in maintaining low levels of smoke and haze in the air even in intensive manufacturing operations and, when set up and maintained correctly, can be run virtually side by side with sensitive operations like powder coating and paint finishing, explains Mike Hattingh, marketing and product development at RoboVent. “The latest state-of-the-art high-vacuum collectors can capture the bulk of generated fume and particulate from right at the source, the weld gun itself, before it escapes into the general plant environment,” he says. “The remaining fugitive particles can be captured by general ambient air dust collectors, which must be situated correctly to create an air circulation or exchange pattern. All this combines to create a very open, flexible work environment that leaves material handling and overhead crane access unrestricted.”