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  1. #1
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    Default Welding fume extraction

    After doing a bit more welding/cutting in the workshop recently, I've realised I definitely need some sort of fume extraction. The plasma cutter in particular generates a huge amount of smoke.

    So....
    I've got these couple of extractor fans from work that came from an old fume hood that got removed.
    Both have the same .55kW motor, but one has a larger impellor (and expanding connection on the outlet) and the other has a smaller impellor and a converging outlet.
    Taking a quick look online, the commercial welding fume extractors seem to start at about 1hp (.75kW) and go upwards, so possibly these might be a little on the underpowered side, but at least it would be better than nothing.

    Any thoughts on which of those 2 fans is likely to work better running a 150mm inlet hose?












    Steve

  2. #2
    BobL is online now Member: Blue and white apron brigade
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    Without putting an air flow meter on them its difficult to say which would be better as power rating is not the only factor determining flow.

    In practice either of those would work fine - its not like you are going to be extracting from a bank of welding stations with long lengths of ducting and junctions between them. Sometimes filters are used which further reduces the air flow.

    Measurements of the diameter and depth of the impellers, and a photograph of the name plate of the first motor might help decide.

    I see the second one has a 3P 240V ∆ motor so it will need a 240V VFD to run that - you will let out the smoke if you try to run it on 415V power.
    Having it on a VFD is useful as you can run it flat out while welding and then back the speed off a bit (quieter) for 20 or so minutes to clear any residual fumes out of the shed.

    I have two ventilators in my shed
    My welding bay fume hood uses a 1/2HP (375W) SP motor and it draws plenty of air and fumes (up to 1600 CFM).
    The other one is at the top of the roofline and uses a 1/3HP 3P motor on a small 240V VFD - @50Hz it draws 1200 CFM.
    I use this one s a general ventilator.

  3. #3
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    Default Welding fume extraction

    Thanks Bob - sounds like these ones have enough power, so hopefully the fans are good enough.

    Both motors are exactly the same - 240v ∆ .55kW
    Outlets on the fans are both the same - 250mm square opening
    Housings and impeller diameters on both fans are the same (approx 300mm).

    #1 ==> inlet diameter 200, impeller width 80
    #2 ==> inlet diameter 220, impeller width 130

    Nothing meaningful to me on the fan nameplates and I can't find anything online about them.






    I've got a small 240V VFD here somewhere so will drag that out and run one up and see how it sucks

    Steve

  4. #4
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    If the fanwheel is selected properly the installed motor should be just about spot on...ie you wont be able to increase speed too much as you will run out of horsepower and or wheel performance. So dont over speed it...maybe max 60hz....fan wheel may not like it either if you spin it too fast.
    What you have there is probably a fan from or for a fume cabinet....think working with pungent chemicals....or could also be from portable extraction system?
    You can help by using flexible ducting on intake side and positioning the intake close to your work. A capture hood will also help.

  5. #5
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    Thanks Eskimo.
    My welding bench sits against the wall in the middle of 2 pallet racking uprights, with the racking beams and solid shelf above it, so its in a bit of a natural capture hood of sorts. I'll get some 150mm flexible metal ducting so will be easy to move around and try out different locations to see which captures the best.
    Spot on as to the origin of the fans too - they were both from the same chemical fume cabinet. Unfortunately I didn't get a chance to investigate the installation more as the cabinet was already on its way to the skip when I found out about it, and the only reason the fans weren't gone too was they were destined for the scrappy.

    Steve

  6. #6
    BobL is online now Member: Blue and white apron brigade
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    Assuming they are both the same RPM the one with the bigger impeller should move a bit more air.

    A big problem with over spinning the motor is it will then draw too much current and eventually burn the motor out.

  7. #7
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    Keep in mind too much air movement will create problems with shielding gases
    You only need enough suction to draw already airborne fumes away from your respiratory area.

  8. #8
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    Default Welding fume extraction

    You mean my welds could actually end up worse??

    Thanks, and good point.
    I watched a few videos online, and it looks like the commercial ones work nicely with the inlet a bit to the side and a couple of feet above the work - so I'll aim for something similar.
    Easy enough to do a bit of rough testing with a mozzie coil or similar smoldering thing. If I can get that happening at less than full suck then I can just wind it up to 11 when I break out the plasma cutter.

    Anything is going to be an improvement on what I have now. Here's a photo of the inside of the shed last night after using the plasma - check out the smoke haze in the light to left!




    Steve

  9. #9
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    In an ideal setup you will have enough articulation points on the duct to be able to position the duct so it is directly in front of you and creating a draw of air from behind you, ie you are always updraft of the fumes.
    Not sure of how much space you have around the shed but if you live in a resi area and have painful neighbours like mine that complain the roller door opening and closing is too loud and the lawnmower fumes stink then you may want to consider pushing the outbound air through a charcoal or carbon filter

    For the record the roller door is still under warranty so itís not an old clunker, and we use battery lawn maintenance equipment...

  10. #10
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by racingtadpole View Post
    Keep in mind too much air movement will create problems with shielding gases
    You only need enough suction to draw already airborne fumes away from your respiratory area.
    That's why a booth is really worth setting up
    This allows the hot fumes and gasses to rise to the top of the booth and that's where I have my extraction.

    Fumehood8.jpg

  11. #11
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    Nice set up.
    They work well until you need/want to weld something bigger than the booth can accomodate.
    Personally I gave up the idea of using an extractor several years ago and wear a mask under my visor.

  12. #12
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by racingtadpole View Post
    Nice set up.
    They work well until you need/want to weld something bigger than the booth can accomodate.
    Personally I gave up the idea of using an extractor several years ago and wear a mask under my visor.
    Yep I agree, but the problem of giving up on an extraction is then you have to wear the damned mask for some time after you stop welding AND that IT eventually produces a grey dust layer over everything in the shed. That layer then sucks up water from the air and turns into goo.

    This is why I have second general ventilator at the top of the ceiling - plus if it gets really "fumey" I can run my wood dust extractor with all the gates open.

    My Dust extractor is 1200 CFM, Fume hood is 1600 CFM, secondary ventilator is 1200 CFM, for a total of 4000 CFM.
    Shed is 3700 CF so that means I can theoretically get more than one complete shed ventilation every minute. In practice it's more like two minutes.
    I still get some grey dust goo but that is from grinding/polishing dust and failing to extract while doing this.

    If you have a big shed, an Evap AC running the fan only is a really good solution. The one at our mens shed produces clearly visible extraction effects in about 30s and clears the air from foggy to clear in about 3 minutes. Sometimes when they don't use it and they then realize, OK its getting a tad foggy in here, and then turn it on it sends a great grey brown dust plume down the street. The key is to turn it on beforehand so the dust concentration inside the shed is never too high and it gets diluted with the large throughput of air these things make

  13. #13
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    Default Welding fume extraction

    Racingtadpole - I'm fortunate in that we're on a larger block and have no direct neighbours so it won't be an issue. Nearest one to the shed is over 100m away across the road, and plenty of vegetation in between to dampen any noise. Compared to the local hoons doing circle work in the gravel intersection I make as much noise as a cemetary.

    Thats a nice setup Bob! Mine is much less refined, but here's a photo. The overhead shelf definitely traps the fumes in a bit.




    Found the HY 220v VFD, so I'll drag one of the fans out later and give it a run.

    Edit: weird how you notice things in photos. I must get the partition done between the bench and the TIG with the sheet covering it - not an ideal fire safety setup at present!!

    Steve

  14. #14
    BobL is online now Member: Blue and white apron brigade
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    Thanks O&B.

    I also use my fume hood as a small spray booth and also do my chemistry experiments there.

    I just realised that was an old photo when I installed the first fan
    Heres a side by side showing old (RHS) and new fan (LHS) and a bit of over spray.
    The wooden T shaped thing in the middle of the table is a Lazy Susan turntable thing I put small things on to spray paint .

    Combo.jpg

  15. #15
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    Hooked up the larger of the 2 fans to a VFD tonight and gave it a run.
    It definitely moves some air at 50Hz. I also found it has a self cleaning function, as it also throws the small gum nuts, leaves and flaking powder coat of the impeller well clear of the outlet!
    At 50Hz it has enough suck on the 200mm inlet that when I placed my open hand about a foot in front it instantly sucked it against the edge of duct before I could react. Lesson learned, and scared the crap out of me.
    30Hz is still moving a fair bit of air - enough to flap the sleeve of my jumper when I put my arm above the outlet.

    Long story short, its got plenty enough suck for welding fume extraction - and will probably do a reasonable job on grinding dust too.

    Steve

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