Attacking welding fume at the source

A user’s guide to fume extraction guns

PRACTICAL WELDING TODAY® MARCH/APRIL 2014

March 24, 2014

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Fume extraction guns are a viable alternative for collecting harmful welding fumes and particulate right at the source. They can be used in tandem with another source-capture device or with a localized filtration system. Knowing how they work and how to use them will help yield the best results.

Fume extraction guns can help companies maintain compliance with safety regulations and create a cleaner, more comfortable welding environment. Obtaining optimal results depends on properly using and maintaining the equipment.

The Occupational Safety and Health Administration (OSHA) and other safety regulatory bodies set the allowable exposure limits for weld fumes and other particulates, including hexavalent chromium, with the aim of protecting employees against potential health hazards in the workplace. Providing welders with proper ventilation during the welding process is an important step to help meet these standards—and to help provide a safe and comfortable work environment for everyone.

Companies may opt to invest in centralized fume extraction systems, which are designed to protect the entire shop area. These systems involve installing new ductwork and fans to remove fumes and are highly effective, but they are also more expensive than other options. A viable alternative for some companies is a fume extraction gun used in conjunction with a fume extraction device or localized filtration system.

Fume extraction guns are available in a variety of amperages—typically 300 to 600—cable styles, and handle designs. As with any welding equipment, they have their best applications, advantages, and limitations, as well as recommended techniques for achieving the best results.

Fume Extraction Gun Basics

Fume extraction guns capture fumes generated by the welding process right at the source, over and around the weld pool. The weld fumes these guns remove are composed of a combination of the filler metal and base material.

Various manufacturers have proprietary means of constructing guns to perform this action, but at a basic level they all operate similarly: by mass flow, or the movement of material. A vacuum chamber suctions the fumes through the handle of the gun, into the gun’s hose, and through to a port on the filtration system, sometimes informally referred to as a vacuum box.

Typically, fume extraction guns are larger than regular welding guns because they include the vacuum and hose that are necessary to extract the fumes. Some manufacturers offer fume extraction guns with a vacuum hose swivel on the rear of the handle to make them easier to maneuver. Also, design advancements have minimized the handle weight and size to make the guns as light as possible for operator comfort, while still offering consistent fume extraction benefits.

Fume extraction guns are especially well-suited for applications using solid welding wire or those in confined spaces, where the goal is to capture fumes immediately at the source, in a welder’s breathing zone.

Industries where these applications often occur include shipbuilding and heavy equipment manufacturing, as well as general manufacturing and fabrication applications that use mild or carbon steel. Petrochemical and other applications where stainless steel welding and hexavalent chromium levels are prominent may also present the opportunity to use a fume extraction gun. The guns work well on high-amperage and high-deposition-rate applications.

For the best results, fume extraction guns should be used for in-position welding, such as on flat butt welds, because they can most effectively capture fume particles as they rise from the weld pool in this position. It’s more difficult for a fume extraction gun to draw fume particles downward and through the vacuum hose in out-of-position welds, because the fume particles rise quickly in those cases.

Techniques for High Performance

Operating a fume extraction gun is similar to operating a standard gas metal arc welding (GMAW) gun, with many of the same recommended best practices. However, there are some techniques that you can follow to help get the best performance from a fume extraction gun.

Fume extraction guns operate by capturing the fume generated by the welding process right at the source, over and around the weld pool.

  • Watch Your Gun Angle. Perhaps the most important tip for maximizing performance is your gun angle. With solid wire—the most common filler metal used with fume extraction guns—use a push technique and a 0- to 15-degree gun angle, which provides the best means for capturing the fume generated. For flux-cored wire (which generates more fume), use a drag technique with a 0- to 15-degree angle. If the parts are set up at a 0- to 30-degree angle and you keep your gun straight (vertical) during the welding process, the fume rises, which maximizes the gun’s extraction capabilities. The travel speed you use during either of these welding processes will typically depend on the base metal and the wire size.
  • Adjust Your Vacuum Level During FCAW. Flux-cored wire generates more weld fume because it produces a slag. To address this, increase the vacuum level of the gun by closing off all the vents and extend the shroud as far as possible. This maximizes the vacuum at the front end of the gun without disturbing the shielding gas, since there is none with self-shielded flux-cored wire. If you use a gas-shielded flux-cored wire, be sure to hold your gun at a 0- to 15-degree angle.
  • Pause at the End. At the end of the weld pass, pause for 10 to 15 seconds, holding the fume extraction gun in place without depositing weld metal. This allows the gun to capture residual fumes as the weld bead cools.
  • Let the Wire Type Determine Stickout. You can extend your contact tip-to-work distance—about ½ to ¾ in.—when welding with flux-cored wire and a fume extraction gun. With solid wire, try to keep the stickout to about ½ in. or less to maximize fume capture. These lengths are comparable to the stickout lengths used with standard GMAW guns.
  • Experiment With the Air Control Regulator. Some fume extraction guns feature adjustable extraction control regulators at the front of the gun handle, while other guns include this function internally. These regulators give you the ability to increase suction as needed without disrupting shielding gas coverage.

The ability to balance between the downward flow of shielding gas and the upward flow of the suctioned air is important. Fume extraction guns need to provide the appropriate amount of shielding gas to protect the weld from defects such as porosity without sacrificing the ability to suction fumes efficiently enough to protect you. Adjusting the air control regulator to the appropriate level can be a matter of trial and error, so you may want to test it on scrap material to optimize the suction rate before welding on a product.

Maintenance and Consumables

Just like any piece of welding equipment, fume extraction guns benefit from good preventive maintenance practices. Caring for them is similar to caring for a standard GMAW gun. Also note that using flux-cored wire with these guns requires more frequent gun maintenance than solid wire because of the slag and fumes it generates. Regular maintenance is important to help prevent a clog or spatter buildup, which can limit the fume capture rate.

Inspecting and maintaining the front end of the gun is key to optimizing fume extraction. Frequently inspect the nozzle and contact tip for signs of spatter buildup, which, along with blocking the fume extraction, can also obstruct shielding gas flow and cause weld defects. Spatter buildup also can cause consumables to fail prematurely.

Replace the consumables if spatter buildup appears, or clean them according to the manufacturer’s recommendations. Also inspect the vacuum hose regularly for damage such as cuts or kinks, which can lead to loss of suction. Replace a damaged vacuum hose as necessary. Be sure to use the manufacturer’s recommended consumables package. Guns are engineered to get the best results with specific consumables. When in doubt about maintenance or any other aspect of using a fume extraction gun, consider working with a trusted welding distributor, certified industrial hygienist, or the gun manufacturer to address any questions or concerns.

In combination with many other variables in the welding operation—wire, transfer method and welding process, welder technique, and base material—fume extraction guns can help companies maintain compliance with safety regulations and create a cleaner, more comfortable welding environment. Proper use and maintenance of the equipment are important to get optimal results.



Dan Weimer

Engineering Lab Technician
Bernard
449 W. Corning Road
Beecher, IL 60401
Phone: 708-946-2281

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