Fume Extraction

Anything to do with air assist, vacuum tables, fume extraction and related...

Fume Extraction

Postby buildsomething » Fri Jan 15, 2010 6:23 pm

Although this vacuum system may seem a bit excessive, I will be exhausting to the outside. The distance that I need to exhaust to is about 20', so I need as much volume and vacuum to maintain the airflow. The blower will be mounted inside my garage and ducted through a vent through the garage roof. The laser will be in the basement adjacent to the garage.
This will definately keep the noise down as well as any dangerous fumes generated.

The vacuum system that I am using was purchased new here in Toronto from a Woodworking / Metal working retail outlet called Busy Bee Tools at a cost of $159 Can. This system was used as a portable dust collector. It has 600 CFM rating at 8" of water which should do the job providing that I don't have too much in the way of losses. It uses a 1 hp motor at 120VAC. The vacuum systme comes with a dust bag and 10' of 4" spiral ducting. I won't be using the dust bag of course.

The total internal volume of my laser base and enclosure is about 16 cu-ft which means that I should be able to exchange the volume of the enclosure every 1.5 sec approx. By closing off the area that are not being used during the cutting operation, I should be able to get some high velocities around the cutting area....well lets hope so anyway. :D

I have seen this type of blower on other lasers and it really does keep the smell and smoke down quite a bit.

Hope this helps anyone that might be interested in building a DIY laser.

Richard
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Exhaust Vacuum.jpg
Blower - 600 CFM @ 8" of water
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Re: Fume Extraction

Postby bdring » Fri Jan 15, 2010 6:42 pm

The 600CFM and 8" Static Pressure are separate specifications. It will run at 600CFM without back pressure and 8" of static pressure will stall all flow. I have a similar blower for my woodworking. The flow drops off very quickly with pressure. I find that my shop vac usually does better whenever any backpressure is involved. My shop vac has a lot less flow but can pull almost 30" of pressure. For dust collection on my router, it is no contest. The shop vac kicks its but.

The nice thing about those blowers is that they are relatively quiet. You probably don't need too much flow anyway. Be careful to allow enough free air in. 8" can do some damage to large surface areas. I saw a sanding table blow in once when the whole surface was covered.
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Re: Fume Extraction

Postby buildsomething » Fri Jan 15, 2010 7:59 pm

You are absolutely correct there with respect to bowing if sealed up tight. There has to be a good inlet for proper ventilation to take effect. My intention is to have the fresh air inlet at the front of the machine where most of the work is being done. This will then create a good air flow across the material and then exhausted just past it. Most of my colleques are covering the exposed supporting areas with light aluminum and leaving about a 1/2" - 1" gap along the outside edge of the material being cut. This provides a higher velocity across the material face, thus drawing the fumes and smoke particulate away. This does not seem to disturb the material being cut at all. Once I start cutting, I know that there will be some fine tuning to the exhaust system as well.

As for low blower noise....absolutely. I can't believe how quiet these blowers really are.....good impellar design I suppose. :D

Well I'm off the to basement for a bit more work on this machine.

Richard
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Re: Fume Extraction

Postby bdring » Fri Jan 15, 2010 8:32 pm

My machine has good flow, but I do have some smoke staining issues when cutting wood. A little general staining is to be expected, but my flow runs from the front, around the work piece and out the back, so the stains generally go in one direction. I don't like the asymetrical look it gives. The air assist helps a little, but it is still an issue.

I sometimes mask the wood. That helps, but does not always work so well with light engravings. Your perimeter flow method might do better. Even the pros like Ponoko show smoke.

smoke.JPG
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Re: Fume Extraction

Postby buildsomething » Fri Jan 15, 2010 9:10 pm

I was wondering if the air assist might be a bit weak.

What I was thinking about is to have a modified air assist nozzle that would create a swirling effect instead of a direct downward blast....ie having the air assist come in at a 45-60 degree angle using a few small ports. The swirling effect might disperse the fumes more effectively than a coaxial blast of air....but who knows. I guess I'll find out what happens when I get my machine up and running. Oh by the way, its getting pretty close.....maybe one more week if I spend some concentrated time on it. :D

Richard
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Re: Fume Extraction

Postby bdring » Fri Jan 15, 2010 9:46 pm

My air assist is pretty strong. I usually have the valve turned down to about half. I see some people actually try to pull on the air assist to solve the problem. Not a coaxial air assist. The little copper hose on the side style.
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Re: Fume Extraction

Postby buildsomething » Fri Jan 15, 2010 10:04 pm

You said that your air assist is coming in from the side.

That go me thinking again...is the air assist blowing in the same direction as the exhaust direction or is it opposed the exhaust flow direction. I wonder if changing the direction of the air assist might affect the outcome?...worth a try if haven't already. I guess the trick is to get the fumes up and away as quickly as possible from the material. I wonder if hot gases stain more than a cooler gas? Have you tried spraying the material with a fine mist of water prior to cutting? I have seen that done before. Maybe mixing the fumes with superheated steam might do the trick.

Is there room in you machine to exhaust straight up or is that out of the question? Inquisitive minds want to know.... :geek:

Richard
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Re: Fume Extraction

Postby bdring » Sat Jan 16, 2010 12:31 am

My assist is coaxial with the beam. It should blow out pretty evenly around the beam.


nozzle1_thumb.JPG
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Re: Fume Extraction

Postby lasersafe1 » Fri Feb 05, 2010 2:33 am

bdring wrote:My machine has good flow, but I do have some smoke staining issues when cutting wood. A little general staining is to be expected, but my flow runs from the front, around the work piece and out the back, so the stains generally go in one direction. I don't like the asymetrical look it gives. The air assist helps a little, but it is still an issue.

I sometimes mask the wood. That helps, but does not always work so well with light engravings. Your perimeter flow method might do better. Even the pros like Ponoko show smoke.

smoke.JPG



Somebody pointed me at the Epilog Technical Library. Here is a nice tech note on how to remove smoke residue. Wow! That is one fine looking engraving they have there. http://www.epiloglaser.com/tl_wood_residue.htm

You will also see that they have an area for sharing engraving files. Nice.
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Re: Fume Extraction

Postby lasersafe1 » Sat Mar 13, 2010 3:27 am

I had questioned in my own build log why the user manual for my laser would insist that the fume extraction blower be mounted outside with only a suction line coming into the building. I finally realized the answer. If the blower is outside and there is a leak in the system, you are only sucking air into the leak. If you have your blower inside and there is a leak after the blower, you may vent toxic fumes within the living space. Most hobbiests would gamble on this, but the manufacturer couldn't take a chance of suggesting anything other than the safest method.
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