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  • Exploding vacuums?

    I've been cutting a great deal of aluminum recently, and given my "open" machines (IE, not enclosed like a CNC machining center) I usually simply sweep and vacuum up my chips.

    I have two shop-vacs. One's an old Shop Vac that I bought when I opened this shop (and still works fine) and the other is a big industrial Black & Decker unit that was probably made in the sixties, and can, as they say, suck the chrome off a trailer hitch.

    While the big (probably 40 gallon?) B&D is the main shop vac, I have at times used the little (6 gal?) Shop Vac specifically for aluminum, so I can keep the chips cleanish for recycling. (Current aluminum prices are near-nil, but I still prefer to give 'em to the recycler rather than the dump- besides, the recycler is like six miles closer. )

    However, the little vac is too handy- it's easier to tote around in my cramped shop, or take out to the truck to vacuum out the sand and rocks, etc. So what I did was went and picked up a "bucket vac" head from Homey-Dee. Makes a nice light, compact vac and one I can dedicate to just the aluminum chips. (Or if I need it for a different use, I can just swap buckets.)

    Now, the question: As above, I've been cutting a lot of aluminum recently, and for some reason it occurred to me. I use a lot of WD-40 as cutting fluid, and of course WD-40 is flammable. Now, I've been vacuuming this stuff up for years and never had an issue, but I have begun to wonder, am I potentially creating a small bomb here? Even if it just goes "whoof" rather than "BOOM!" it could potentially start a fire.

    Has anyone ever heard of such a thing happening? Am I worrying unnecessarily? Am I not worrying enough?

    Doc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    I have often wondered the same thing.

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    • #3
      There are videos online of vacuums that have jet exhaust. There are a few things that make a flameout more likely. One is the design that routes the exhaust through the filter and then through the motor to cool it. When I sold vaccuum cleaners door to door we were encouraged to use various tricks to show how superior our vaccuums were. The Kirby sucked the air through an impeller and then to the filter/bag so you could drop a couple 1/2 dollar coin and suck up one with the Lux, and the customer would naturally try with theirs. Instant stall. Hoover sucked it through the bag and then past the motor to cool it, so you could show how well the Lux could suck a que ball off the floor and hold it indefinitetly. The Hoover could also do that, but would overheat and shut down.

      The danger in your case, of course, is that it's possible that you are pulling fumes past the brushes of the motor. Fuel + ignition source is a bad thing.

      Dan
      At the end of the project, there is a profound difference between spare parts and extra parts.

      Location: SF East Bay.

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      • #4
        The shop vacs that I've been familiar with (not that way!), have not had the sucking air pass over the motor. The motor had its own little fan. Unless the wd-40 laden air is passing over the sparking brushes, there shouldn't be a risk.

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        • #5
          Vacuum motors used take the air right through the motor but I would say all modern vacuums are bypass cooled with a separate cooling fan for the motor so the ignition source isn't really there. EXCEPT, I used to have a 55 gallon vac and was cutting HDPE and when I went to change the filter the 6" lightning bolt from static buildup hurt like hell! That sure could have caused and explosion if even dust was present.

          My go to coolant for aluminum now is isopropyl alcohol applied as droplets with a fog buster style device. Of course that is flammable so I have to use care in ventilation. Isopropyl in lab tests reduces cutting effort on aluminum almost 50% and chip welding has gone way down for me. Parts are nice and clean not oily and after months of use I'm not seeing rusting of the table or my vices and fixtures which surprises me. Chips are dry too so they vacuum up really easy and do not stick to everything. VENTILATE!

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          • #6
            I've made a vacuum Implode before, but not explode.

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            • #7
              My go to coolant for aluminum now is isopropyl alcohol applied as droplets with a fog buster style device.
              I have been using WD40 but like the sound of this. What concentration? Drug store quality, or something higher and less available?
              "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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              • #8
                I know static can be a serious concern, especially when vacuuming fine dusts like sawdust but it seems unlikely that flammable coolant residue would cause a problem. For the vapors to explode, you would have to have a concentration between the LEL and UEL. Given the large volume of air most shop vacs move, it seems unlikely you'd have enough WD-40 vapor to cause an explosion or fire. I suppose worst case would be on vacuum start up - figure the bucket had just the right amount of time so that you were in the "sweet spot" for combustion. The flammable mixture of WD40 vapor and O2 gets pulled through the filter and is ignited by a spark in the motor. I still think, given the large volume of clean air coming in, it would instantly blow out. You'd probably have a quick "whoof" out the exhaust but unlikely to be hot enough or energetic enough to do any damage, even to nearby surfaces. This is all just my gut reaction... all the usual disclaimers apply.

                I suppose someone could calculate this out if they were really motivated. The SDS should have an LEL or LFL and a vapor pressure listed. I am part of the Emergency Response Team and Safety Committee (no seriously!) at work and we have to do this fairly often for various chemistry experiments using vacuum chambers and flammable gasses like hydrogen or liquids of various types. But I'm not at work so I'll leave it to someone else But I standby my hunch that this isn't a huge a risk.

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                • #9
                  Originally posted by mickeyf View Post
                  I have been using WD40 but like the sound of this. What concentration? Drug store quality, or something higher and less available?
                  What's less available than drugstore isopropyl? These days I can't find it anywhere and we use it all the time for cleaning flux off boards that have been reworked.

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                  • #10
                    When I was 12 my buddy and I tried to make a jet engine with a vacuum cleaner (blowing) and injecting gasoline into the stream. It looked very impressive... Until his mom cut the experiment short. (We did this outside in his driveway - we weren't complete fools.)
                    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                    • #11
                      The drugstore stuff around here is 50% - I was wondering if you need a higher (presumably less available and more costly ) concentration.
                      "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                      • #12
                        A chemist I know had a lab assistant who attempted to vacuum up a solvent spill. I do not recall exactly what solvent, but as I recall it was not an extremely volatile one.

                        The exhaust was actually flaming when he (the chemist) pulled the plug. The assistant had his back to the unit and was unaware of the problem (and unaware of some other things, apparently). That was a unit which was a metal 5 gal pail with a vac unit mounted in the lid. Yes, it was a commercial unit, not some lash-up.
                        1601

                        Keep eye on ball.
                        Hashim Khan

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                        • #13
                          A guy I knew blew up his mom's vacuum cleaner trying to vacuum out the gravel his kids put in the gas tank of his mom's car.
                          Location: Saskatoon, Saskatchewan, Canada

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                          • #14
                            Originally posted by J Tiers View Post
                            A chemist I know had a lab assistant who attempted to vacuum up a solvent spill. I do not recall exactly what solvent, but as I recall it was not an extremely volatile one.

                            The exhaust was actually flaming when he (the chemist) pulled the plug. The assistant had his back to the unit and was unaware of the problem (and unaware of some other things, apparently). That was a unit which was a metal 5 gal pail with a vac unit mounted in the lid. Yes, it was a commercial unit, not some lash-up.
                            It probably doesn't have to be very volatile if you're sucking up an actual puddle. I imagine the air velocity of the vacuum aerosolizes it so the effective vapor pressure is pretty high. I wouldn't recommend sucking up a puddle of WD40, for instance, but sucking up chips that are coated in WD40 seems like a pretty benign activity. But that's just my opinion.

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                            • #15
                              Yes, I think it was effectively "carbureted". The vacuum was of the type where at least part of the thru-air flow went through the motor.
                              1601

                              Keep eye on ball.
                              Hashim Khan

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