Practical Welding Today - March/April 2009

The Show Low facility is 5,000 sq. ft. and has 20 weld booths, a fabrication area, and testing facility. Each booth is designed for flat plate work, and half are equipped for advanced pipe welding.

With more students came more welding, which in turn generated large amounts of submicron fume from the weld cells that needed to be properly collected. The existing ventilation system consisted of exhaust fans that pushed some of the contaminated air outdoors, but was unable to recirculate cleaned air indoors. This resulted in heated air also exiting the facility and high energy costs. This became expensive in the winter, as northern Arizona can be very cold.

“We had a homemade rig when we first started about 10 years ago and it didn’t work very well. We were on a shoestring budget,” Casey said.

NAVIT staff became familiar with United Air Specialists’ air pollution control equipment while discussing their challenge with NPC. The college had purchased a UAS downward-flow cartridge collector for its Holbrook welding facility in 2004, and was very satisfied with its performance. NPC/NAVIT needed a more effective solution to efficiently clean each weld cell, as well as save costs associated with external venting in both its Show Low and St. Johns locations. With a safe student work environment as the top priority, and energy costs also part of their challenge, NPC/NAVIT staff knew they needed to take immediate action to find a better solution to fit their specific welding facilities.

The bulk of weld fumes are submicron in size, with average diameters of 0.3 to 0.7 micron (µ). Particles ranging from 0.5 to 8 microns are retained in the lungs. Normally, lung retention in the 0.3- to 0.7-micron range is minimal. However, thermal effects can cause agglomeration, in which particles grow larger and can be retained in the lungs.

Average Particle Size Distribution by Percentag Aerodynamic FCAW Globular Diameter (µm) GMAW

< 0.4 75.1 0.4 – 0.7 15.2 0.7 – 1.1 8. 30

1.1 - 5. 8 0.61 > 5. 8 0.77

47.7

23. 3

19. 9

3.04

6.01

Spray GMAW

86.2

8.31

4.74

0.35

0.44

ss Fume Collected
Pulsed
GMAW

86.0 6. 21 5. 19 0.60 1.99

For the Kids

The process to install new fume extraction equipment for the two NPC/NAVIT welding locations started with a visit from UAS manufacturer’s representative Shawn Valandra of Total Filtration Services (TFS), Phoenix, who evaluated NPC/NAVIT’s Show Low welding facility by collecting measurements, taking pictures, and discussing the school’s expectations for air pollution control. He also consulted with a UAS application engineer to generate drawings for an SFC downward-flow cartridge dust collector with customized ducting to 20 weld cells. Valandra recommended this

Source: Jenkins, N. T., Pierce, M.G., and Edgar, T. W., 2005 Particle Size Distribution of Gas Metal and Flux Cored Arc Welding Fumes

FIGURE 1

particular system based on airflow (CFM) requirements and its ability to capture submicron weld fume before it enters the welder’s breathing zone.

The collector draws smoke and fumes from each weld cell, pushes the contaminated air through its 24 nanofiber cartridge filters, and recirculates clean air back into the facility without losing heat. At the same time, the system’s self-cleaning mechanism periodically shoots a blast of compressed air through the center of each filter, causing weld particulate to pulse off the cartridges and into a hopper for disposal.

“Even though it was a little louder [than exhaust fans], I immediately noticed the difference in air quality,” Casey said.

The NPC/NAVIT staff was happy with the cost savings in heating bills, but also very pleased that the fume collector was able to remove hazardous submicron contaminants that more than 75 percent of welding processes generate (see Figure 1). This is possible because of the combination of the system’s optimized pulse-jet self-cleaning mechanism and ProTura™ nanofiber cartridge filters.

“Basically this was for the students’ health, but also for my health. I knew I’d be there long term and my other instructors would be there long term. I just don’t want to have any [health] surprises later in life,” Casey said.

Nanofiber filters are coated with a surface treatment of fibers about 0.1 to 0.5 micron layers deep, which capture submicron particles and prevent them from passing back into the airstream. This means that the most hazardous fume particulate is contained

within the collector and not reintroduced into the welders’ area. This provided efficient fume capture right at the source of generation for each student.

“There is a noticeable lack of dust particulates in our welding facility since the system installation, and the ability to return filtered air back inside the welding lab instead of exhausting it outdoors has led to an increase in energy savings,” NAVIT Superintendent Chester Crandell said.

“The difference is obvious,” Casey added. “The allergy symptoms I might have displayed before are gone now. Healthwise, I knew this was the right thing to do, and it’s been well worth the investment.