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WHERE TO PLACE THE SYSTEM ı

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FINDING THE BEST SOLUTION:
To determine the filtration best suited to your facility, begin by considering the current level of activity, as well as what's likely in the future.  Ambient air intake filtration, where plant dusts and welding emissions are filtered together, may suffice if there's just one welding operation and welding is incidental.  Where welding is multi-station or ongoing, source capture, through the use of an air intake hood system in close proximity to the workstation, will be needed to be effective.  By "effective", we mean capable of capturing, efficiently and consistently, both fumes and heavier particulates.  The second part of being "effective" is that the device can do its work for extended periods, and without creating a maintenance issue.

If source capture is required, the first step is to quantify the airflow required to draw fumes and fine particles away from the welder.  As a practical matter, to collect all particulates would require such a huge airflow that it would be detrimentally affect the welding process.  So, the largest particulate will not be extracted.  The collection of fine particles and the fumes that OSHA regulates is the mission.

CONFIGURING EQUIPMENT:
The second step is to configure the equipment.  The distance from the source(s) to the collector is key.  Will one collector serve multiple hoods?  If so, duct losses will increase, and the airflow required for efficient collection will rise.

The capture velocities required to collect the material and the sizing of the ducts transporting the material regulate to the development of static pressure, the airflow required with the proper horse power to achiever proper draw.  This the most critical calculation, and the single most important reason why filtration is generally not a simple weekend D-I-Y.

It was recommended earlier that shops consider future requirements right from the start.  The reason is that any addition of equipment, or increase in the distance between system components, necessitates revision of the design.  Systems designed with a fan operation at a given RPM will produce a given cfm against a given static pressure.  Change any element of this equation and you change everything else.  The airflow required to achieve a given result rise or falls based on the length and diameter of the ductwork and the size of the hoods.

Where to Place the System
Step three is to decide where it all fits.  Assume the room is 30" long, and the collector and one welding station are installed at opposite ends.  Given this distance, the system losses, which include the hood, duct, elbow, collector and fan stack, are calculated at 8.0 in. water gage, a measure of air flow resistance.  At that point, the collector and the fan can be properly sized.

For a typical welding application involving carbon steel material, the normal air-to-media ratio is approximately 2.0 to 2.5:1.  That is 2 to 2-½ cfm of air for every one ft. of filter media.  If we use 3,000 cfm and divide that by the air to media ratio (2.5), that produces a requirement for 1,000 ft. of filter media.  That value is then divided by the square feet of media in the filter (assume 226), and the result will indicate a requirement for 5.3 cartridges.

ıPhil Weber, Welding Processes Pose Tough Challenge for Fume Filtration, (Welding Design and Fabrication) 9/03

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