Engineering Controls Database
Pulsed Power Welding to Reduce Welding Fumes
|
Welding operations produce gaseous and aerosol by-products composed of a complex array of metals, metal oxides, and other chemical species volatilized from either the base metal, the welding electrode, or the flux material. The effect of welding fumes and gases on a welder’s health can vary depending on such factors as the length and intensity of the exposure, and the specific toxic metals involved. Welding processes involving stainless steel, cadmium – or lead-coated steel, or metals such as nickel, chrome, zinc, and copper are particularly hazardous as the fumes produced are considerably more toxic than those encountered when welding mild steel. Mild steel consists mainly of iron, carbon, and small amounts of manganese, phosphorous, sulfur, and silicon, while stainless steel contains mainly iron, chromium, nickel, titanium, and manganese. The NIOSH criteria document identifies arsenic, beryllium, cadmium, chromium (IV), and nickel as potential human carcinogens that may be present in welding fumes. |
|
| Census data indicates that over 700,000 workers in the United States are involved in welding or allied processes. Animal and epidemiological studies suggest that welding is associated with a wide range of adverse health effects such as metal fume fever (with symptoms resembling the flu), pneumonitis, chronic bronchitis, and decrements in pulmonary function. A large body of evidence suggests that welders have a 40% increase in relative risk of developing lung cancer as a result of their work. Other cancers associated with welding include leukemia, cancer of the stomach, brain, nasal sinus, and pancreas. Welding processes are known to generate aerosols with a significant fraction in the nanometer size range. Recent research also has indicated that particles in the nanometer size range may have adverse health effects. Other health hazards during welding can include vision problems and dermatitis arising from ultraviolet radiation exposures, burns, and musculoskeletal stress from awkward working positions. | |
| Pulsed power welding, or pulsed spray transfer, is an arc welding process variation in which the power is cyclically programmed to pulse so that effective, but short, duration values of power can be utilized. Such short duration values are significantly greater than the average value of power. When pulsed power welding is used with the GMAW process, small metal droplets are transferred directly through the arc to the work piece. The current alternates from a low background current, which begins to melt the wire while maintaining the arc, to a high peak current during which spray transfer occurs. One droplet is formed during each high peak current pulse. As the wire is advanced, the current pulses again and transfers the next droplet. The average arc energy during this pulsed process is significantly lower than during conventional axial spray transfer, thus, reducing the amount of welding wire that is vaporized. With the reduction of weld wire vaporization, welding fume generation is reduced. Some laboratory research indicates that a reduction in welding fume during pulsed arc welding is only attainable for certain ranges of voltages for each wire feed speed. If the pulsed technique is to be an effective engineering control, the voltage parameter must be controlled to an optimum setting for the welding operation. Voltages that are too low may result in spatter, while voltages that are too high will increase the fume generation | |
| 214-11-A; 214-12-A; 214-13-A; 214-15-A; | |
|
arc welding gas metal arc welding metal working metal working pulsed power welding welder |