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Saw duct collection ideas?

Started by tacks Y, November 15, 2022, 12:39:58 PM

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tacks Y

I have a 2hp motor I mounted to a belt drive blower. 6" inlet from my planer and wide belt going to 4" plastic drain pipe. I run it 40+ feet and put an elbow on it facing down. In the spring I shovel and gather it up. Hoping to build a box to blow into and try to contain. Any ell cheapo ideas? Trying to slow down the chips going in, maybe a down pipe with 1" holes?  Thanks Tom  

bigblockyeti

How big of a box?  That will help dictate what kind of a diffuser would work best.  Typically chips, dust & air are shot in the tangent of a short cylinder on top of a funnel (cyclone) with an open top to allow the air to escape while the chips & dust fall out of suspension then into a receptacle, like your box in this instance.

tacks Y

I am thinking 5 foot square or so, hoping to remove one end and get loader bucket in there.

Southside

What if the pipe took a turn up, blow the shavings into a box with the bottom open so they loose velocity and then fall into the collection bucket or whatever at the bottom? Messy version of a cyclone basically. 
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YellowHammer

Build a home made funnel or centrifuge cyclone and pipe the air in the side of the upper third of the body and the sawdust will spin out of the bottom and the air will go out the top.  I used one for years and it worked great.  There should be a vertical pipe running about halfway down inside, that is also the air outlet in the top.    

There was post just recently about a hand made one that worked very well also.

The air goes out the room the sawdust and chips fall out of the bottom, mostly.  

Here's mine first generation one with a cannibalized Oneida cyclone tub.  



 d
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

kantuckid

Plastic dust pipe='s a potential explosion. Ground it or risk it. 
Kan=Kansas;tuck=Kentucky;kid=what I'm not

kelLOGg

I use a 10 foot long 6" diameter flexible rubber pipe to suck planer chips from the planer to the collection barrel. I put a bare copper wire inside the pipe for grounding any static charge from flowing chips. After a few years, chips built up between the wire and the inside wall of the pipe and restricted flow severely. I couldn't figure out how to make the wire adhere to the inside pipe wall to prevent trapping chips, so I removed the wire. Any solutions?





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Don P

Zip tie a stranded wire to the outside, all that matters is the end connections from machine to machine, or metal to metal. You are removing any difference between the charges in the metal parts. It could be a wire running on the floor between planer and blower for that matter.

Andries

The chips going through the plastic pipe are creating static electricity under low humidity conditions.
KelLOG; if the black pipe in your photo is made with a metal coil in the walls, just expose that wire at both ends and ground it to the planer or dust blower at either end.
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YellowHammer

Andries, you da man, you beat me to it as I was typing out a long winded reply....

I also have short flex lines or drops from machines to metal ductwork and that is generally considered OK.  The two mechanism for fire are in the pipe itself or plenums, and static discharge from the insulator to a grounded item and externally sparking a fire in flammable material, such as built up dust, rags, etc.  

Some flex ductwork is sold as conductive.  I try to buy it specifically for that.  That pretty much solves the issue.  

Some plastic flex is conductive because of the material they use to make it, even if it wasn't intended.  So you may not have a problem anyway.  If you want to check, put an Ohm meter on to to check, if it is at all conductive, you are in good shape.  Even the slightest bit of conduciveness is all that is needed, anything but a pure insulator.  Black plastic is generally made with carbon, and it is conductive.  

I have found that in my case, even where I had installed non conductive flex line (ordered in a pinch, from Amazon, don't we all do it? :D :D) that I reach in there and scratch the inner spiral wire in a few places with a boxcutter, to expose the metal, near the ends so that when I slide the flex line over the metal chute of the machine as well as the metal ductwork the wire is in electrical contact at both ends.  So now my machine is in electrical contact with the metal ductwork, but I just use the metal wire in the flex hose as a conductor to do it.

I haven't done it, but it occurs to me that I could reach up inside the flex hose and do the same up the hose, to expose some of the wire and scrape some of the plastic and insulation off and use the wire in the flex line itself instead of running an inner wire (I don't for such short runs).

A little background for those interested, dust collector explosions and fire are not uncommon and any dust collector that is over 1500 CFM (label plate on the machine) are (can be regulated by the NFPA) and they post excellent guidelines for them.  Here is a reference to a very good document on them:  Quote from "Designing your dust collection system to meet NFPA standards — Part I, Gary Q. Johnson, Workplace Exposure Solutions" ---"About 40 percent of combustible dust explosions reported in the US and Europe over the last 25 years have involved dust collectors. Dust collection systems are now a primary focus of inspections required by OSHA's National Emphasis Program on safely handling combustible dusts."

Anyway, I applaud kelLOGg for being proactive.  I know of two woodworking facilities nearby by that have suffered dust collector explosion property damage, no injuries.  

 
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

kelLOGg

Thanks for the replies.
I checked resistance and found it infinite - electrodes stuck in the rubber close together and ohmmeter set on 10,000 ohm scale and got no response. So my rubber hose is not conductive.
It seems to me that a continuous conductor inside the hose is the best solution. I don't see how scraping the rubber to expose the wires at only the ends of the hose can be very effective at discharging static charge that may be created mid hose. What am I missing?

I don't understand why adding another outside ground wire is helpful because the planer and blower motor already have a common ground.
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Southside

They have an electrical ground to the grid, the static in the tube will not have a ground until it finds one in the form of an arc, which is where the fire / explosion danger exists.

I recall a dust explosion at a pellet plant, blew out a block wall.

A fuel / air bomb, very effective in warfare, is basically a dust explosion, but instead of using sawdust a petro chemical is dispursed into the air and ignited.

So yeah, you are playing with fire when it comes to airborne dust and static electricity.
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JD Processor
Woodmizer LT Super 70 and LT35 sawmill, KD250 kiln, BMS 250 sharpener and setter
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Woodmaster 725 and 4000 planner and moulder
Enough cows to ensure there is no spare time.
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rusticretreater

Because "things" happen. Having another ground even if not necessary doesn't change a thing.  Not having a ground when it is needed changes alot of things.

You use an equipment-grounding conductor (EGC) to ground the noncurrent-carrying metal parts of equipment. Its function is to keep your equipment as close as possible to ground potential and provide a safe path for ground-fault current(electricity taking an unplanned path to ground) to flow.  This is a standard practice in factories with big equipment.

Electricity always follows the easiest path, so by providing a solid path to ground you invite it to do what you want.
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Andries

Quote from: kelLOGg on November 21, 2022, 09:41:24 AM. .  So my rubber hose is not conductive.
. . . It seems to me that a continuous conductor inside the hose is the best solution. 
The continuous conductor inside the pipe causes two problems. First, it will cause the pipe to clog, when normally it would stay clear without the wire. Second, sawdust is very abrasive and some of it is really acidic - when the copper wire parts ways with the collector you won't know it because you can't see it. Thats when the sparks will happen, on mine it was like touching an electrified fence.
My advice is to buy a plastic flex pipe with conductive wire coil inside it. As YH described, strip or scrape the wire free of plastic on the inside on the pipe, then attach to the machinery.
 The bottom line: the pipe is making a bunch of static electricity. Give that energy somewhere to go.
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kelLOGg

I got a better understanding now (I hope). I was trying to understand it from the viewpoint of a chemist (my field) where charged particles (ions) had to contact an electrode (wire in this case) in order to be neutralized. Not the case in dust collection where there are not charged particles but charged surfaces due to friction between the surface and wood dust. Is it like walking across a carpet on a dry day and touching a surface and getting a shock? The surface you touch may be a good conductor like a doorknob and you get a big shock or poor conductor like a wooden door where you get smaller shock. In either event the charge is "drained".

My dust hose has short lengths of the coiled wire exposed at the ends of the hose to which it would be very easy attach a ground wire to the planer and dust collector as Andries suggested. Now that I understand that I am not neutralizing flowing charged particles I can see that this will work.
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

firefighter ontheside

I should re-visit my grounding wires for my collection.  Originally I had it all set up nicely with wire wrapped around my pipes and grounded at each end.  I feel like I have changed some things and not re-connected the wires like I should have.  I have witnessed little sparks at one end or another of ducts in the past.  I'd hate to be that firefighter whose shop burns down because of something like this.
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aigheadish

Thanks for this thread gang. I'm still likely a ways out from really getting a dust collection system going but there is good info here for when I get started.
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Old Greenhorn

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YellowHammer

In many cases, the sparks are of low enough energy to not cause problems, such as discussed with static sparks from people to doorknobs.  That is a low energy but higher voltage discharge, and general only has enough energy for someone to yelp, at most.  

However, the level of charge build up is a function of the type of insulating material and the storage capacity of the material as well as atmospheric conditions, among others.  In essence, the material can become a charged battery with significant stored electrical energy.  The sparking action is called ESD or Electrical Static Discharge, and the buildup of static charge on an insulator do to movement of particles is called Triboelectrification.

As a side note because some people may find it interesting, arguably the most famous and potentially catastrophic (nuclear war) case of tribielectric discharge was several decades ago when a Pershing ICBM, at the time our benchmark of our nuclear MAD deterrence, was being uncreated and assembled in Europe, and the rocket motor, which is quite large, blew up.  Very, very bad, soldiers were killed and injured, and it could have been anything from sabotage, fence line shooting, prelude to war, etc.  It turns out that the most reasonable explanation was a case of ESD due to the Kevlar (highly insulative) motor case rubbing against the packing crate material in the cold of European winter.  The composite motor case built up a massive electrical charge and then discharged, igniting the missile propellant, which is by definition very high energy and boom! It was one of the first big investigations I worked on when I started my career as an engineer at the Army Missile Command.  At the time, ESD was thought to be relatively low energy, but this incident threw millions of dollars and man hours at the issue and it turns out that with any high energy system, this is a real and hazardous issue.  The solution is to have everything grounded with high resistance so it discharge slowly, with no spark, because sparks and explosives = bad.

https://apnews.com/article/6917dd39c45dacc8ebbf8c61859b53f8

https://apps.dtic.mil/sti/pdfs/ADA181932.pdf

It may also be interesting that another fatality I know of happened due to the simple and apparently innocent unrolling of old school friction tape, while handling ordnance ignition wires.  The tape was highly insulative, build up a triboelectric charge simply by unrolling it, and it discharged to an energetic material and someone was killed.

As another note, whenever we worked with explosives, rocket and missile propellant, we had to always wear grounded and conductive material, but it couldn't be too conductive so as to prevent a spark, typically, we were required to use 10K Ohm resistive materials or more for a slow bleed down on first touch.  So for explosive safety, we had to wear conductive safety shoes, which is exactly opposite of what is required for an electrician, which needs non conductive safety shoes.  Triboelectrification is now a huge field of expertise encompassing everything from explosive to computer chips.

https://workingperson.me/what-is-conductive-footwear/
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

kelLOGg

My planer and drum sander share the same dust collector so the ground connection is a wire with an alligator clip.



 

 
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Larry

Something I've thought about and don't have a answer.  How much and what size of fuel does it take for a explosive to occur?  Taking a heavy cut with my planer creates a different size chip than a 37" wide belt sander makes.  I can see dust from that sander creating a big hazard and would want all metal grounded pipe.  Big chips and low volume from typical home shop type equipment maybe not much problem?

Just idle speculation on my part.


Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

YellowHammer

Yes, you are correct, the dust particles need to be fairly fine for the most part.  I'd thought that about 400 micons was the threshold diameter for wood dust, but now I'm reading on the web where it was raised to 500 micron and higher, which is about half a millimeter.

The whole dust collection combustion process is interesting to me, considering my background, and in the majority of cases, at least in my reading, the reaction may initiate but generally not propagate in a high velocity flame front with a differential density of particles, such as in a relatively small dust collection hose with the blower running.  There may be a spark, and a very local combustion process, but it extinguishes quickly because the dust has to be in a stable combustable air/fuel mixture to sustain combustion, and the turbulent air does not provide a homogeneous environment to sustain it.  However, partially ignited particles can go into the dust collector storage area and ignite an explosion there, or even start a conventional fire.  The two dust explosions that I know of occurred in a plenum area, where mixing of dust must have occurred and the proper air fuel mixture was reached for a relatively large amount of fuel.  In both cases, the overpressure blast safeties blew, one causing a little damage with them functioning as designed, the other causing a couple weeks of shutdown because the blast safety doors actually blew off and flew across the facility.  Boom!

I think of equal or more risk in a homeowner system over 1500 CFM, is the issue of external sparking to flammable materials, and the energy released by the spark is a function of the capacitance of the material storing the electrical energy.  A static discharge of a person touching a doorknob will most likely not ignite something, unless it is a very flammable fuel, but a spark from a very good capacitor such as PVC, can.  I myself witnessed big sparks coming from one of my first dust collection systems, a PVC piped one, and the sparks were loud enough to be heard over the machines and could be seen from 20 or so feet away.  I was sparking from the PVC pipe to an anchor bolt in my building, and when I climbed a ladder to investigate, there was a little pile of years old, dry as a zombie, pile of fine sawdust right there.  Happily, it didn't ignite, but I shut the system down and rebuilt the entire thing from scratch with metal.  It wouldn't have exploded, but could have simply ignited a small fire that may have grown into a real problem.  Nothing happened, except my heart skipped a few beats.

Atmospheric conditions play a very large part in the process, ESD is typically is more prevalent in dry cold winter air.  That's when mine started sparking.  It never sparked before that I know of, conditions had to be about perfect, and I had been using the ductwork for a year, at least.

I don't think is a big panic issue, but knowledge is key, and as an existing dust collection system gets upgraded or modified, then it's a good idea to keep ESD guidelines in mind.    

 
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

aigheadish

YellowHammer- is 400-500 microns the high side of what is considered explosive? The bigger chunks and particles wouldn't be as much a hazard, correct? 

Also, not nearly as exciting but a decent story of warning just the same and on the tip of ESD... I used to build printing devices that used an ink that was thinned (and helped to dry) with Methyl Ethyl Ketone (MEK) and part of my training was a story that the previous guy had. We'd use MEK to clean the parts so ended up using lots of it and having a fair amount of controlled waste. One day the guy had a glass beaker of the MEK and (as I understand it) he was pouring it into a metal waste container that was ungrounded. As he poured the static charge built up, in the glass I believe, and a fireball shot up out of both the metal container and the beaker. 
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Ianab

Quote from: aigheadish on November 22, 2022, 01:52:25 PMYellowHammer- is 400-500 microns the high side of what is considered explosive? The bigger chunks and particles wouldn't be as much a hazard, correct? 


Correct. It's a matter of not just the air/fuel ratio, but also the surface area of the fuel. As the dust size gets smaller there is more air and fuel in contact, and that determines if a fire front will propagate. In your MEK solvent example, the fuel is a vapour, single molecules mixing with the air, so surface area is huge, it takes very little to ignite it, and the fire spreads fast.  With coarser sawdust it's much harder to ignite and sustain the flame. 

Here's a deliberate sawdust fireball. You can see that it needs the fine dust (sanding dust) and air mixed (by blowing it from a tube with compressed air), and an ignition source (a road flare). But if you watch the 2nd 1/2 is slow-mo and you can see exactly how the fire spreads though the fuel mix. In open air this is an impressive fireball, but in an enclosed space it would be very damaging. But it needs a very specific set of conditions to happen. 

Sawdust Cannon from Mythbusters' Viral Videos episode. on Vimeo

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Larry

Wow!!! what a cool video.  Wait till next 4th of July. :D

Here honey, hold my beer. :)
Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

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