Saw duct collection ideas?

[Southside]

There are always smaller particles in with the bigger ones. Grain elevators can be quite spectacular when they suffer a dust explosion. 

If you have ever seen the back of a combine when it's running in a field you can get a good idea on how much dust is mixed in. 

[Ianab]

I think what often happens with industrial dust explosions is that fine dust gradually builds up in places. On cable trays, tops of beams and conveyors etc. Then some event occurs like an electrical short or machinery failure that both dislodges some dust and provides an ignition source. The fireball then kicks up more dust increasing the size. Because this is all contained in a building, it becomes an explosion that can certainly demolish things. 

Controlling that stray dust is a big issue in factories that have that sort of risk. Milk powder is another risk material as it's both fine and flammable. 

[Don P]

The only one I've had was a damp morning, fine dust inside the electric box on the planer. I assume the damp in the air that morning and probably a trail of damp dust. I hit the on switch and the box shot maybe a 4' fireball. I did some rewiring and better taping and added that to the cleanup list. We would usually clean everything 4th of July and Christmas, beams, conduits, all that fine high dust. 

[Ianab]

You can imagine how that small dust accumulation fireball (from an arcing switch?) could have kicked up and ignited more dust, and pretty soon you have a 40ft fireball. 

[VTwoodworker]

I am not suggesting this to others as safe or a best practice but most of my dust collection in the workshop is via sch 40 PVC.  I ground it with bare copper wire taped to the outside with aluminum HVAC duct sealing tape.  The tape has a lot of surface area and seems to eliminate any detectable static.

[kelLOGg]

All this info about dust explosions reminds me of when I was a child in the early 50s. A friend and I would play at a very large neighborhood construction site where many houses were being built. Dust from sanding hardwood floors was dumped on the ground and my friend and I would set it on fire. You could hardly see the flames until we tossed small pebbles in it and heard a "poof" and a flame shoot up. (not like Ianab's but we thought it was neat). The fire would soon go out and no problems ensued. Can you imagine doing that today?

[Don P]

Down in Durham as a kid something similar. I can't remember all the whodunits but it involved fresh floor sanding dust thrown out back, pine woods, don't know what kindled it (hot nail?), and happily a passing HS bus with an alert and helpful driver. The kids got it out. Can you imagine that happening today.

I'm still not wrapping my head around this. What is carrying the static charge, the machine different potential, the insulating plastic, the air, the dust? what am I trying to ground?

[kelLOGg]

Actually, it was Charlotte. 
I think it is the moving dust that creates the charge and it gets transferred to the plastic pipe. 

[aigheadish]

@Ianab that is incredible. I have a fair amount of dust and a leaf blower I could likely rig something to. That big an explosion may bring out some flashy lights but I think I could work up a smaller one that would still be pretty cool. 

[YellowHammer]

The PVC pipe acts as capacitor because it is an insulator and builds up an internal electrical charge.  When (if) the charge gets too great there is a dialectic breakdown in the PVC and the insulator becomes a conductor, and a spark will jump from any point on the surface to any nearby conductor. Similar to what a conventional capacitor or even a battery, which is in essence, a capacitor will do.  The energy of the spark is dependent on many things, including the material being charged, just like a true capacitor, some can store and discharge some serious energy before they suffer a breakdown.

The charge on the PVC is caused by the movement of particles across its surface, and called the triboelectric effect.  Dust particles moving across pvc will build up a charge in the insulator, and at some point in time, there can be a dielectric breakdown in the PVC material and there is a sometimes high energy arc.

So the best solution is not to have any non conductive piping in a dust collection system. If the piping is only even barely conductive, high resistance but conductive, the charge can't accumulate.  It will slowly bleed off.  It's not caused by any electrical panels or service voltages.  Running a wire down a pipe, either inside or out, will basically allow a controlled point for the electrical discharge, it will not bleed the charge, but will only work once dielectric breakdown is occurring.  The closer the contact of the wire to the PVC will shorten the arc, and reduce the voltage (potential difference) of the arc.  Generally, longer arc through air are higher voltage so that's bad.  

There are many ways besides wire to dissipate voltages in insulators, one of the easiest is a black, carbon loaded or even metallic conductive paint.  Spray the outside of the pipe with conductive paint and ground it and sparks can't jump to an external surface.  Even something so simple as wetting the surface will allow the charge to slowly bleed off.  

In rocket motor cases, such as the Pershing incident, Kevlar was used as composite case material, and that is very good electrical insulator and so is the rubber liner that bonds the propellant to the case.  One thing that we learned and has become industry standard for decades is to use graphite fibers, which are carbon, in our rocket motor cases because graphite is conductive so would bleed off any charge. Similar to a graphite fishing rod...it's highly conductive so put them down in a storm.    

[kelLOGg]

The concept of the PVC pipe being a capacitor make sense and helps me understand the process better. Thanks.

[rjwoelk]

Thanks to every one that commented 
This has been a eye opener,  I am getting my shop ready  for service g up the collection system, and will take this all to make sure things are grounded. 

[sawwood]

I have a small shop 16x20 and I mounted the dust collector out side on the shop wall. The collector is a 2hp unit with a 5" inlet. I use metal pipe run over head and its just a short run of about 20 feet. Then I have a short drop down of flex tubing to the units.  sometimes when running the planer I get a shock from the plastic tube. the tubing is just about 4 foot to the metal pipe and out to the collector. Should I ground the metal pipe to ground to reduce the shock I am getting ?  If so how would I ground the pipe or the collector. The plastic pipe on the planer is the only one I am close to when the planer is used.

[Crusarius]

One thing I have not seen anyone mention is the sawdust storage. 

First off, we now all should know the dust is very dangerous, explosive, and flammable. But don't forget what happens to sawdust with any moisture. 

The moisture creates heat! If left it could create enough heat to cause the sawdust to start burning. This could be burning for a very long time before you know it.

It is always best to have your sawdust hopper outside of the building in case of fire or explosion.

I learned a long time ago that normal materials that are not flammable can actually explode if in powder form. An example of this was some grinder dust from a job I did. It was just mild steel grinder dust. In powder form it actually ignited in a small fireball just like the video above. 

Since my shop is not the cleanest there is a chance it was mixed with sawdust and other materials. But I will warn everyone that anything in dust form is quite a bit more dangerous than solids.

[YellowHammer]

Yes, I think I see what it looks like, but you could run a wire from your metal dust collector pipe, along your flex hose, touching in a few places to give it a place to ground, and then to your planer ground which woulds also be an electrical safety ground.  The thing to remember is that the plastic pipe will still build up an internal charge, but the wire run along its outside and touching it will give electrical contact and should help bleed the majority of the charge off.

[sawwood]

Thanks Yellowhammer for the info. I will install a wire from the planer up along the flex hose to the metal pipe.  Its just a small shock but don't like the Suprise.

[YellowHammer]

To keep the flex pipe flexible you might even wrap the wire around a few times up it length, and get it to contact the plastic in as many places as possible.

[sawwood]

I am going to try and add photos of my dust collecting system. The photo of my planer has a single hose and the two hose are for my tongue and Grove atchment on the woodmaster. I have my blower is out side on the wall with a barrel to collect the dust. I use metal pipe with flex hose to each mechine. I have a 5 inch metal pipe that will replace the 4 inch I have now. Just need a few more things to go with it.  

 

 

 

 

 

[sawwood]

I forgot to take a photo of my dust collector outside. Will take some when it stops raining so i can uncover it. Not sure why the
first photo is up side down. I posted it from my cell phone and need to learn how on it.

[rusticretreater]

When you add it to the thread, in the popup just above the link that says Insert the image into your post, there are some buttons that allow you to rotate the image. crop & rotate, +90 -90

[sawwood]

Thanks I will look for it next time. Still learning.