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MIG fume exhaust (have side wall exhaust already) - still smelling fumes

jillerica

Plastic
Joined
May 24, 2017
I'm using a basic MIG welder and have a through the wall 24" square exhaust fan rated at 1,075 CFM about 10' to 15' from my welding table. I still smell fumes for about a minute after welding (I'm usually close to the work area since I weld very small things). Do I need to get an overhead hood (only about 10' ceiling with offices above me - can't go through the ceiling), or maybe just a flexible duct (with or without an inline exhaust fan) with a little hood that I can move directly over the active area connected to existing wall fan? What size exhaust in line fan (if I need this in addition to the wall exhaust fan or that would be overkill)? What size ducting - can I just use dryer vent ducting?
 
Look up "fume extractor", you need to literally get the inlet as close as you can to your weld without messing up the shielding gas. When I'm welding say a cube that is four x four foot, I will pull the extractor directly over each corner as I go around etc. I bought mine at an auction for $1200. 14ft arm, no motor. Then put on a 1.5hp blower. You need a high pressure blower, not a fan. Fans give you no water column when they meet resistance in the line. Best of luck.
 
PS, you want 1.5HP, or 2HP blower, 6" ducting. Make sure your arm has a joint at the wall, and half way out so it can scissor, as well as move up and down. Most fume extractor have a ball/swivel fitting on the final "snout".
 
IMHO zero smell is unrealistic, but not enough fume to make life unplesant is pretty easy, look at on the gun extraction, they work awsome, but you will still need general area extraction, the fan - extraction for that wants to be over head and infront of your working area to catch the most not low down or beside u.

A big part of how effective ventilation is is not down to the fan sucking it out but how well and were the fresh air enters, you ideally want as near to non turbulent flow across your space as you can get, if you want no smell escaping to other areas, you also need enough extraction to keep that area slightly negative pressure wise, just a few 1/16" of water columb is all it takes. Manufacturers fan numbers are under ideals, add some ducting and some grills and you probably get a tiny fraction of that number. Air flow velocity meters are dirt cheap on ebay, measure your air speed and work out your own actual extraction rates!!!
 
not sure what you mean by "water column". any chance you could send me a picture of the set up with the arm ducting and extractor with the "snout"? I need the blower set to go into the ducting to suck away the fumes, correct?
 
my shop is pretty big and open - at least 20'x30' (I share with two others that are rarely there). what do you mean by "just a few 1/16" of water column is all it takes"? I could look into the air flow velocity meter - measure right where I'm welding about 10-15' from the through the wall fan going, you mean?
 
A cheap "test" setup could be some cardboard taped into a rectangular funnel shape, if you make two of them, one could be placed over the fan, one on some sort of support over your weld bench. Have the small end about 8" square, the large end about 1.5 to 2ft. Use a 8" flexible duct like this: Titan Air 8 Inch Duct, 8 feet by 8-inch aluminum flexible ducting, ventiation - - Amazon.com .

Use plenty of "duct tape" (not duck tape, the feathers get everywhere) to mate the two cones, and experiment with placement of the pickup end to see where it does best. You may decide that the pickup cone needs to be smaller, rectangular, round, etc. - cardboard makes it easy to reconfigure. And obviously, pay a lot of attention to not allowing sparks or hot weldments to catch the ducting on fire!

Once you have something you like, remake the parts out of aluminum sheet, and use industrial grade silicone fabric duct hose for the permanent setup.
 
not sure what you mean by "water column". any chance you could send me a picture of the set up with the arm ducting and extractor with the "snout"? I need the blower set to go into the ducting to suck away the fumes, correct?

Water column referees to the pressure. A house furnace blower will typically be about .2 to .3 inches of water. You want the extractor to have a vacuum at the hose "snout" inlet. From there through the hose to the blower to the the outside.

Tom
 
A cheap "test" setup could be some cardboard taped into a rectangular funnel shape, if you make two of them, one could be placed over the fan, one on some sort of support over your weld bench. Have the small end about 8" square, the large end about 1.5 to 2ft. Use a 8" flexible duct like this: Titan Air 8 Inch Duct, 8 feet by 8-inch aluminum flexible ducting, ventiation - - Amazon.com .

Use plenty of "duct tape" (not duck tape, the feathers get everywhere) to mate the two cones, and experiment with placement of the pickup end to see where it does best. You may decide that the pickup cone needs to be smaller, rectangular, round, etc. - cardboard makes it easy to reconfigure. And obviously, pay a lot of attention to not allowing sparks or hot weldments to catch the ducting on fire!

Once you have something you like, remake the parts out of aluminum sheet, and use industrial grade silicone fabric duct hose for the permanent setup.

If by "fan" you mean a propeller type air mover, then this approach will probably not work. Fans or meant to handle large volumes of air without duct work. McMaster-Carr

You will need a blower, the squirrel cage air handler. They don't handle large volumes of air, instead they produce pressure to move air through the duct work. McMaster-Carr

Also, go to the local hardware store and ask for aluminum flashing. It comes in rolls and is thin enough to cut and form with hand tools, scissors, blocks of wood, etc. Best is you can use it under actual conditions and not worry about it catching fire.

Tom
 
Yes, it's not optimal, but it's quick/cheap and will give some spot extraction which can determine if a more elaborate setup will be worthwhile. An 8" ID hose should be large enough to flow sufficient air, even with a household-grade box fan of roughly 18" blade diameter.
 
Mig is one of the worst processes when it comes to fume generation too, you will need a fair bit of extraction. Its one of the reasons i don't have MIG here but use TIG exclusively.

Worth adding you want some kinda filtration if this exhausting out of a building any were near any ones cars or there all going to end up covered in rust marks.

My TIG extractor setup here is about as crude as you get, nothing more than a 6" inline bathroom extractor fan, really needs a bit more suck, but when the inline filter box is kept reasonably clean its easily posible to weld non stop in my small shop with out chiokeing to death. For the amount of smog of mig though your going to need a lot more extraction The above posters are spot on, look at the comercial units and copy them or buy one, you need a real world 1-2 hp of good suction to keep up with MIG.

Welding with and without integrated fume extraction - YouTube

Is the on the gun type approach im mentioning, its the best way to really get the low levels most regulations aim for these days then use good general ventilation on top
 
Is the on the gun type approach im mentioning, its the best way to really get the low levels most regulations aim for these days then use good general ventilation on top

Interesting info in that video. No doubt the self-extracting torch will make your wallet hurt, but still cheap when compared to a new set of lungs. I bet someone could make a snap-over hood for a standard handle to give much of the same benefit using a remote Shop-Vac as a draw.
 
Well im assuming hes trying to weld profesionaly and no one on the planet is running stick indoors everyday apart from a few weird cranky pipe fitters.

I also forgot to mention fire - forge welding too, the forge no doubt makes even more smoke than stick.

But out of the every day common industrial welding processes i still hold MIG will make some of the most air born particulates going. TIG and most resistance welding processes are incredibly low emission in comparison! Both normally only burning off any oils prescient on the materials. Sub arc whilst you would expect it to be on a par with ARC welding, at least in my experiances its less smoky than MIG by a fair bit!
 
you don't think the wall fan will provide enough draw at 1,075 cfm through the hose - once I hook up this duct with rectangular funnels? if you think i still will need an in-line blower to suck up air at the funnel end near my work - could you recommend a specific one?
 
also great advice, thank you! I took a TIG class about a year ago and thought I understood that fume extraction wasn't needed. maybe I interpreted that wrong - class was held in a large and very open garage (door closed due to winter though). I really need to practice TIG - not as comfortable with it plus I weld on tiny pieces so I'm often melting through them when I try with the TIG. Do you keep the bathroom fan end of the hose close to your work - any chance you could post a picture of your set up?
 
If the nearby wall fan isn't enough, I would look into a supplied air helmet.

These are popular in the flux core welding area's (much more smoke than MIG there Adama....:D)

Getting too high a suction, too close to the weld can cause problems with gas
shield coverage.
 
not sure what you mean by "water column".
Water column height is one way to measure vacuum/suction pressure. Inches of mercury is another way to do the same thing. 1/6"WC is pretty low pressure, as you want high volume at low pressure (opposite of your shop vac, basically) for fume collection.

I got an AirFlow PCH-1 for my shop for when I stick weld. It does a fine job, but it has a 1HP fan in it and sounds like it.
 
you don't think the wall fan will provide enough draw at 1,075 cfm through the hose - once I hook up this duct with rectangular funnels? if you think i still will need an in-line blower to suck up air at the funnel end near my work - could you recommend a specific one?

The reason I brought up the topic of fans vs blowers is that when you connect a hose to the fan, the internal friction of air moving in the duct will significantly reduce the flow. With duct you will need a blower.

Tom
 








 
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