May 1st, 2017 | Posted in Air Cleaners
As a general rule of thumb, when using an 8″ diameter arm for local exhaust ventilation hood (LEV) the user should have a minimum of 900 CFM per LEV hood with a recommended airflow of 1150 CFM per LEV hood. For a 6″ diameter arm the user should have a minimum of 525 CFM per LEV hood with a recommended airflow of 650 CFM per LEV hood. The hood for an 8″ diameter LEV arm should be placed approximately 12 – 18 inches from the welding source and should be placed no further than 24 inches from the source. The hood for a 6″ diameter LEV arm should be placed approximately 8-12 inches from the welding source and should be placed no further than 18 inches from the source.
For ambient cleaning, electrostatic precipitators are a good choice if the wash frequency of the electronic filters is within reason. We generally recommend 8 air changes per hour (ACH) for most ambient industrial applications. To determine wash frequency of the AQE industrial cell, the consumption of the client’s welding material is accounted for. Air Quality Engineering, Inc.’s F62B electrostatic unit is a perfect fit for many welding applications where ambient capture is desired. The F62B has a maximum loading capacity of approximately 1 lb. of smoke. The table below shows the approximate amount of welding that corresponds to 1 lb. of welding smoke.
|Solid core MIG welding: 150 lbs. of solid core wire|
|Flux core welding: 50 lbs. of flux core wire|
|TIG welding: 250 lbs. of rod|
|Stick welding: 65 lbs. of stick|
Example: One customer has 3 welding stations in a 50′ x 50′ facility with 14′ ceilings. The average consumption between the three welders per week is 85 lbs. of MIG welding (solid core), 60 lbs. of rod and 10 lbs. of stick. How do we examine the feasibility of this?
First, let’s look at the airflow requirement for the space in question: 50′ x 50′ x 14′ x 8 ACH / 60 min. = 4,670 CFM required for airflow. One F62B unit is capable of up to 2500 CFM so we’ll be OK to use two F62B units for this space from an airflow perspective.
Next, we need to look at the wash frequency based on how quickly we expect these cells to load from the amount of welding material that the welders there are consuming. To determine the wash frequency we see that: two F62Bs can hold 2 lbs. of smoke (i.e., double the weight capacities shown in the table above). We can use the information from our example setup and the following formula:
[85 lbs. (MIG wire) / 300 lbs. (F62B capacity for MIG wire)] + [60 lbs. (TIG rod) / 500 lbs. (F62B capacity for TIG rod)] + [10 lbs. (stick) / 130 lbs. (F62B capacity for stick)] = 0.48
This means that the welding shop in our example would consume 48% of the F62B’s loading capacity per week (i.e., they’ll need to wash the F62B cells once every other week in this scenario).
Keep in mind that these are rough calculations and the actual capacity can vary based on factors such as how oily the parts are that are being welded, the amount of grinding done after the welding, the type of power supplies used on the individual welders, other applications occurring simultaneously in the space, etc.
When considering media units for capture the following capacities can be expected:
|Type of Filter||Solid Core MIG||Flux Core||TIG||Stick|
|Bag (MERV 14)||300 lbs. capacity||100 lb. capacity||500 lbs. capacity||130 lbs. capacity|
|ESF (MERV 14)||900 lbs. capacity||600 lb. capacity||3000 lbs. capacity||780 lbs. capacity|
|AQE 2000 Cartridge (MERV 15)||Rated to 1200 hours use||Rated to 1200 hours use||Rated to 1200 hours use||Rated to 1200 hours use|
|AQE 4000 Cartridge (MERV 15)||Rated to 2000 hours use||Rated to 2000 hours use||Rated to 2000 hours use||Rated to 2000 hours use|
The same calculations performed in the above example may be used with these media filters. A special note regarding AQE’s reverse pulse systems would be that the filters themselves are rated based on hours of operation by the filter manufacturer. Many factors will account for the actual loading times for these cartridge filters including the type of welding, number of welders, coating on the materials being welded, types of power supplies, other applications in the vicinity of the units, frequency of pulsing, etc. These time ratings are a best guess average from the manufacturer of the filters.
Please speak with your AQE industrial representative for the best recommendations regarding sizing your welding air filtration unit.