AWGB Woodturning Forum
General Category => Tool tips & reviews => Topic started by: The Bowler Hatted Turner on July 29, 2018, 09:24:52 PM
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I am considering putting in piped extraction in the workshop. I am thinking of using the brown soil pipe that you can get from builders merchants.I realise I will have to install blast gates etc.but my question is this. To prevent static electricity building up could I just earth the pipe?Pr do I need to do a bit more than that? I am just fed up moving my flexy pipe all around the workshop all the time and just thought to plumb it in once and for all and just open whichever gate I need for extraction.
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Why would you earth plastic pipe.
Regards George
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John,
I'll have a look through my old records, but somewhere I read or possibly still have an article that said the Static build up in dust extraction was not needed.
Not saying it was right, but the facts and figures behind the article seemed to make sense and agree with my electrical knowledge (I'm an Electronics Eng though).
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Why would you earth plastic pipe.
Regards George
George not sure if you have to but I always thought(perhaps mistakenly) that there is an explosion danger from sparks caused by static electricity. I hope to be proved wrong as not having to worry about earthing it would certainly make life easier.
Thanks Bryan, I wait for your reply.
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John,
I can't find the article I remember, hoever I've attached an article of Earthing Extraction piping, if it's any help, and something I always thought was a brilliant idea.
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Bryan thank you very much for that, exactly what I needed.
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Earthing a non conductive plastic pipe is about as effective as nailing jelly to the ceiling!
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Earthing a non conductive plastic pipe is about as effective as nailing jelly to the ceiling!
Whether this is true or not I can't comment but have to applaud the phrase. LOL ;D ;D ;D
Pete
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I missed this reply from Paul.You are obviously using the wrong nails Paul, you need the ones with larger heads as the ovals certainly will not hold jelly on the ceiling. But I usuallly use velcro as that works so much better and it is easier to remove the jelly once you have finished with it.
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Being a non-technically-minded sort of guy, I'm failing to grasp the issues here. I recall, as a child, rubbing a balloon against my hair to induce static. My hair stood on end and the balloon would stick to the wall, so clearly, static can build up on plastic surfaces (the balloon, that is, not my hair) and therefore can be present in/on the extraction pipes. Are we saying that this presence of static does not pose a hazard, whereas static on electrically conductive materials does pose a hazard?
Help me out, please, somebody!
Les
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Les,
Basically this issue stemmed from Dust explosions in grain storage silos. Dust + static electricity spark = big bang.
For us, it's the movement of dust through the piping that causes static, a problem in woodwork sawmills etc where lots of dust is continuously being extracted. But there is a question over whether there is a case to answer at our level of extraction and dust making.
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Hi Bryan....I understand how the static is generated, what I don't understand is whether or not a spark can be generated within plastic pipes, and therefore, is earthing useful. There seems to be some level of disagreement in this thread.
Les
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Yes, he said, shaking his head!
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Les, firstly you cannot generate static electricity in electrically conducive materials, since they conduct the electric charge to the closest point of discharge. Secondly, in order to create a bang you'd need some way of converting the static electricity into a spark. That's in theory possible, e.g. by bringing a grounded piece of metal close to the pipe. However, it would have to happen on the inside of the pipe, since that is where the dust is. So this is actually now getting quite tricky.
I have read an article from a retired fireman on this subject, and he said that in his entire professional career of around 35 years he had never ever seen or heard of a dust explosion in an amateur wood working workshop. And most pro workshops use 6" metal pipes anyway (which are essentially grounded by connecting them to machines that are grounded).
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You can generate a static charge in a conductor as long as it is insulated from any discharge path. Have you ever got out of a car and got a shock when your foot touched the ground? That's a perfect example of a conductor (the car body) holding a static charge because it is insulated from earth by the wheels.
I'm not sure where this fits in to plastic pipes but never mind ;)
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So after all that (now that I am done with the jelly) have we come to an agreement? Should I earth plastic extraction pipes or not?
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...Have you ever got out of a car and got a shock when your foot touched the ground?...
Yes, at Death Valley, ye gods was that tarmac hot!
On a less flippant note, this is becoming another of those interesting, informative threads on the forum. It is somewhat curious that the links which Bryan posted seem to suggest that earthing is essential, yet what you, Paul, and others are saying makes perfect sense and suggests that earthing plastics is a waste of time. I think that I shall go with the latter.
Les
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Les,
My first post on this thread was to say somewhere I had read an article that says earthing dust extraction was not necessary, but could not find it again.
The documents I posted had useful information if you (BHT) wanted to go ahead anyway. If you don't need it and fit it, its no big deal. More belt & braces.
I do not know the answer.
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Hello The Bowler Hatted Turner
I did exactly what you proposed in your first post about ten years ago except that I used the grey piping. Worked a treat and easy to use. However, in the first five years I had two dust explosions in the piping which was suspended from the ceiling and ran the full length of the workshop. Fortunately, the explosions were only powerful enough to blow the blanking plugs out of the ends, and frighten the life out of me.
I then ran a bare copper wire down the inside of the pipe and earthed it to the body of the wall-mounted extractor - that was five years ago and I haven't had an explosion since.
Fine dust and shavings being sucked along a plastic pipe are ideal conditions for static build-up, it works similar to a Van-de-Graff generator and in very dry conditions the resulting discharges can cause an explosion - both of mine happened mid-summer.
So, I would highly recommend just adding a wire down the inside of the pipework when you build it. It doesn't have to be copper, steel fencing wire would be fine, just make sure it runs down all the pipework and is then earthed to the metal body of your extractor, or to a mains earth.
I guess the guys who have never had an explosion using plastic pipe got away with it because home workshops are notoriously damp places.
Fortunately/unfortunately, mine isn't! :-)
Cheers - John
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John thankyou so much for this. I stand justified for posting my original question. I too have seen dust explosions in industry but was usure about the plastic piping. Once I get round to it I will run a wire all the way through. At the end of the day if I don't need to , nothing will be lost apart from a bit of copper wire, I never throw " it will come in useful oneday" stuff away so I have all the old copper wire from when I rewired the house, that will do the trick. And if I do need to it will be done.
Thanks everyone that took part in this post, I think it was very enlightening.
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Just a final comment on industrial dust explosions ...
Many decades ago, my father worked at an animal food company ‘Up North’. It would import hard, dried, products from around the World and grind them into coarse granules and then mix them into cattle food and other animal feed.
The big grinders generated lots of dust which ended up in the empty ‘attic’ space of the multi-story mill. There were big shutters at each end of the attic to allow the dust to be carefully cleaned out periodically. Unfortunately, after working fine for many years, the cleaning lapsed for quite a while.
When someone finally realised it needed cleaning out, a relative newcomer went up and opened the shutters wide at each end - the resulting fierce wind that blew through the attic lifted enough dust into the air to reach critical density and it exploded, killing the hapless employee and demolishing much of the roof structure. It could have been much worse.
John
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The moral of this story - if you suffer from wind don't do the dusting! ;)