Fume Extraction Guns: Understanding the Basics

New industry standards from the Occupational Safety and Health Administration (OSHA) and other safety regulatory bodies have been developed in recent years with one specific objective in mind: to help protect employees against potential health hazards in the workplace. These regulations, which dictate allowable exposure limits of welding fumes and other particulates (including hexavalent chromium), have led many companies to invest in fume extraction equipment. An increased desire to maintain optimal welding operator safety and to attract new skilled welding operators to the field is also a consideration in investing in this equipment — companies want to create the most comfortable and healthy work environment possible.

Some companies may opt for centralized fume extraction systems, which are designed to protect the entire shop area. These systems involve the installation of new ductwork

A fume extraction gun, as shown here, operates by capturing the fume generated by the welding process right at the source, over and around the weld pool.
 

Fume extraction guns are available in a variety of amperages, cable styles and handle designs. As with any welding equipment, they have their advantages and limitations, best applications, maintenance requirements and more. In combination with many other variables in the welding operation — welding wire selection, specific transfer methods and welding processes, welding operator behavior and base material selection — fume extraction guns can help companies maintain compliance with safety regulations and create a cleaner, more comfortable welding environment. 


The basics of fume extraction guns
Fume extraction guns operate by capturing the fume generated by the welding process right at the source, over and around the weld pool. Various manufacturers have proprietary means of constructing guns to conduct this action, but at a basic level they all operate similarly: by mass flow, or the movement of material. This movement occurs by way of a vacuum chamber that suctions the fumes through the handle of the gun, into the gun’s hose through to a port on the filtration system (sometimes informally referred to as a vacuum box). The welding fumes that these guns remove are composed of a combination of the filler metal and base material.

Some fume extraction guns feature adjustable extraction control regulators at the front of the gun handle, which allow welding operators to increase suction as needed (without affecting shielding gas coverage), while others provide this function internally. Regardless of the manner, the ability to balance between the downward flow of shielding gas and the upward flow of the suctioned air is critical. The fume extraction gun needs 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 the welding operator. The balance allows the weld pool time to react and solidify, and gives the fume particles time to decelerate so they are easier to extract.

Typically, fume extraction guns are larger than regular welding guns and tend to be bulky due to the vacuum and hose necessary to extract the fumes. For that reason, some manufacturers create fume extraction guns with a vacuum hose swivel on the rear of the handle to make them easier to maneuver. Manufacturers have also, since fume extraction guns were first introduced (in the late 1960s and early 1970s), found ways to engineer internal components to minimize the handle weight in order to reduce operator fatigue.

Applications, advantages and limitations
Fume extraction guns are well-suited for applications using solid welding wire and those in confined spaces. These include, but are not limited to applications in the shipbuilding and heavy equipment manufacturing industries, as well as general manufacturing and fabrication. They are also ideal for welding on stainless steel applications, as this material generates greater levels of hexavalent chromium, and on mild and carbon steel applications. The guns also work well on high amperage and high deposition rate applications and are available, typically, in 300 to 600 amp ranges.

Fume extraction guns attach to a localized filtration system, as shown here. Fume removal occurs by way of a vacuum chamber in the fume extraction gun that suctions the fumes through the handle of the gun, into the gun’s hose through to a port on the filtration system.

For the best results, fume extraction guns should be used for in-position welding, such as on flat butt welds. In this position, they can most effectively capture fume particles as they rise from the weld pool. In out-of-position welds, the energy of the fume particles causes them to rise at a high rate, making it more difficult for the fume extraction gun to draw them downward and through the vacuum hose. 

One distinct advantage to fume extraction guns is that they remove the fumes at the source, minimizing the amount that enters the welding operator’s immediate breathing zone. However, because welding operators typically move the gun away from the weld pool after completing a pass, the fume extraction gun is not as able to control residual fume as well as a fume extraction hood can.

Maintenance tips
As with any piece of welding equipment, fume extraction guns benefit from preventive maintenance. Caring for them is similar to caring for a standard GMAW gun. Regularly check for tight connections throughout the length of the fume extraction gun to ensure good electrical flow. Minimizing electrical resistance helps ensure consistent weld quality and prevent premature failure of the front-end consumables — contact tip, nozzle and diffuser.    

Frequently inspect the nozzle and contact tip for signs of spatter build-up, too, as such build-up can obstruct shielding gas flow and cause weld defects that ultimately will need to be reworked. Spatter build-up can also cause consumables to fail prematurely. Replace the consumables if spatter build-up appears or clean them according to the manufacturer’s recommendation. In some cases the shroud that surrounds the nozzle may also have to be replaced or cleaned free of spatter.

To ensure optimal fume extraction capabilities, inspect the vacuum hose regularly for damage, including cuts or kinks that could lead to loss of suction. Replace a damaged vacuum hose as necessary and dispose of it according to the manufacturer’s and/or an industrial hygienist’s directions.

Visually inspect the handle for cracks or missing screws, and also check that the gun’s trigger is not sticking or otherwise malfunctioning. Replace or repair these components as necessary. 

Finally, maintenance on the liner is also important. As with the vacuum hose, use compressed air to clear out any potential blockages during welding wire changeovers or when removing the wire from the gun. Spending an extra few minutes clearing out any debris from the liner can save considerably more time than troubleshooting the weld defects and equipment problems that can result from blockages. Also, track the amount of time that it takes for a liner to wear during the course of the welding operation. Replace the liner prior to that in the future to prevent downtime for replacement during shifts or problems with wire feeding or quality.

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 and/or the fume extraction gun manufacturer to address any questions or concerns. Proper use of this equipment can help provide optimal results, and improve the safety and comfort of the welding environment.