Exhaust Fan Motors and dust

[cosimpson]

I was wondering if anyone has an issue or have input on my wondering?

Wondering since my fan 12 inch turbo type if the motor which has magnet or magnetic fields would attract fine metal dust blowing over them and building up as air passes across. This is in regards Plasma Table Down Draft system.

Am I over thinking or could this be an issue.

Chris

[acourtjester]

Yes it will happen and no you are not over thinking it
you will not believe how fine that dust is.

[cosimpson]

Acourtjester - Thanks for the reply

SO - that's open's up the next question.

How do you reduce it, and how is the best why to remove every so often?

I know that a squirrel cage fan would be better. but takes up more space and plumbing.

input from all is welcome as this is a Forum

Chris

[rdj357]

I'm using the inline 12" utility fan from Northern Tools. It works great and I got the recommendation from someone on this forum I think. It's relatively inexpensive so even though I havent heard of a high failure rate from those here using it, it wouldn't be hard to replace.

Probably the best would be a fan with the motor designed outside the air flow, like an explosion proof fan but I could replace this one many times for the price of one of those!

[cosimpson]

rdj357 - I use the same fan, for the same reason.

Has anyone ever put a large magnet in the tube before the fan?


I know water tables large filter system are used to do this. Looking for a poor man solution.

Chris

[davek0974]

If its a standard AC motor and the case is sealed - a TEFC (totally enclosed fan cooled) type motor then you should be ok, the magnetic field is very weak on the outside as it is focused internally on the rotor.

The fastest way to kill a motor is to allow the muck inside it, i had very short lives with the cheapish inline duct fans from xpelair etc, i think they're called mixed flow fans?? I killed three in a year with cast iron dust from a lathe.

The external motor fans are definitely the best but much more expensive.

[srp]

Just a note about squirrel cage fan - Don't use them. They are designed for clean air and when used in dirty air the blade quickly fill up and then the capacity goes to nil. Backward inclined blades with the motor outside the dirty air stream would be my recommendation. Your exhaust design is very important. You are not only dealing with dirt in the shop but dirt in your lungs. The real damaging products for you health you can not even see. One of the most important considerations would be to have the operator in the fresh make-up air. You will be removing dirty air out through the exhaust plenum and replacement air needs to come in from somewhere.This is just as important as the exhaust side of the system. Plan how you are going to supply this air and have it pass through the space where the operator is breathing this fresh air.. 30 years down the road and one can't breathe - Do it right so you are not is that situation. Doing it right is not cheap. Be informed of what good design parameters are for your particular system. There is good info on this forum. - John

[cosimpson]

I have a 36 in fan feeding the room and a 12 inch exhaust on table.

Chris

[whiskeymike]

Can't you put your filters prior to the fan? Hepa style for particulates and charcoal for fumes? That's what I plan to do, although I'm also planning to use a cyclonic form to drop the big particulate first and include a small water tray to capture & retain to protect from explosion. I'm also running multiple cheap box fans with cheap filters attached. There are several good threads on welding web and garage journal.

[jimcolt]

Just building two of these small 2 x 2 tables now. One will be at the Sema show (Vegas)the first week of November showing Hypertherm plasma, the second will be at the Fabtech show in Chicago the second week of Nov.

These have my hybrid fume control. First, the heaviest particles from cutting hit a water tray (positioned just low enough to not allow water splash on the plate) which traps 60 to 70% of the particles, then remainder of the smoke is pulled via a side/downdraft through 3 welding fume filters by a custom built 16" fan. I bought 1/3 HP 16 inch TEFC fans and then enclosed them in a rolled tube to increase the efficiency (higher vacuum at the filters), the motors are on the outside for better cooling efficiency.

These systems allow us to cut live at trade shows while producing no smoke.

The mechanical x, y and z motion components came from Precision Plasma LLC. I'll post more pics if anyone is interested...

IMG_3483.JPG

Jim Colt

[davek0974]

Nice,

more pics are always good

[jimcolt]

Here are the fans being modified...

IMG_3499.JPG

IMG_3494.JPG

IMG_3492.JPG

And a another of the machines.

IMG_3491.JPG

[davek0974]

Looks like axial plate fans and you fit them in a custom duct piece with flanges??

Nice

I presume one fan is enough flow??

[jimcolt]

Yes.....I bought axial plate fans with a wire guard on one side and a TEFC 1/3 HP motor, 16" diameter. By reversing the direction of the motor and mounting them in a tube they essentially become a "tube axial" style fan with higher pull power (vacuum). You can buy adequate tubeaxial fans that would have worked perfectly for my machine application, however they are pricey and it put me outside of the budget for these two machines. So I put some "sweat equity" in these two fans and they appear that they will do the job.

From a previous build on a similar 2 x 2 machine with the hybrid fume control I used a smaller fan without the tube......worked well until the filters started to build up. This newer design has more power on the fans and should generate a higher vacuum, I also added a third filter (previous design had two) so I expect filter life to be better, maybe even get us through a 4 day trade show without changing them out.

I'm installing the cnc controls (Hypertherm industrial CNC), the limit switches, emergency kill switch and all wiring to the Kollmorgen AC Brushless servos today, should be cutting by the end of the week with these machines.

Once the machines are done and tested I will post more details on the build and performance. After these come back from the shows I will swap out the drives with stepper drives from both CandCNC as well as Flashcut to see how they perform. The motion control mechanics were designed to work with either servos or steppers for this reason!

Jim Colt Hypertherm

IMG_3495.JPG

[davek0974]

Nice work, sounds like a dream job you have there


Are the filters cleanable or disposable?

Agree, three is a much better idea, much more surface area.

My fan is a tube-axial type, 12"dia 3000m/hr flow with only a 20" total duct length so no loss of flow rate, i have high expectations of this unit, a test shows that with the fan running as it would be when cutting in the shop, it was difficult to open the door Obviously my make-up air will come via the open door which is behind me and the bale is in front so i am pretty much assured clean air to breathe.

My only concern is noise - its very loud and may give me grief with the neighbours, its auto-controlled via g-code so no risk of it running when not needed but what a noise!

[whiskeymike]

Jim, do you run the water low because you don't want the water splashing at the show? Or do you prefer the two method system combining water table and air filtration in general non-tradeshow use?

[jimcolt]

Water touching the plate....even splashing, creates more dross and a rougher edge. Water droplets on the surface of the material affects the accuracy of the ohmic contact plate surface sensing as well.....which affects cut quality and consumable life. I have always been a fan of downdraft for plasma tables with less than 200 amps of plasma cutting power, and water tables for 200 amps and above all in favor of better cut quality.

Using both water and downdraft creates the best of both worlds from my experience. Using filters I would only recommend for low duty cycle cutting such as just prototyping or trade shows. The filters are over $100 each, they can be cleaned but it is messy and time consuming!

I use the water to trap the larger particles.....with the water far enough from the plate so no splash occurs.....this makes the filters last longer.

For production use I would use the hybrid system but without the filters....and duct the fan flow outside. There would be far less particulate going through the duct as the water will catch the majority.

These show tables have a nice ball bearing slide on the water tray that allows me to easily retrieve parts as well as clean out the slag...

Jim

Jim, do you run the water low because you don't want the water splashing at the show? Or do you prefer the two method system combining water table and air filtration in general non-tradeshow use?

[luckydogdennis]

got to see Jim's table at SEMA a couple of weeks ago. was ready to buy a Torchmate system but after talking to him have started to build my own system. Table is now built and I have all the other parts to get it going. I'm still deciding exactly how i want to set up my table as far as fume control.

Thanks Jim

[hsolve]

Good morning to all.
I have been running a 300mm (12") duct to a fan 500liters /sec.(125gal/sec), however this is still not enough. When cutting lower current settings 65amps and less is OK with the non used parts of the table covered. However at higher settings 125amps on thicker plates the fumes generated are massive, it is also the duty cycle, the time at those higher currents to cut larger parts. I will be extending my table to 5' by 10' so am organising at present duct of 600mm dia (2') and a fan that will move 4m^3 a sec. (1000gal /sec). This will vented outside through a roof vent. All I have is a down draft table to do plasma, milling and routing, and am going to this trouble as have no intention for a water table. Without this the workshop fills up with fume and even thought I have fans in the roof it is not enough to clear these fumes. It takes a long time even though the jobs have been completed.

[hsolve]

Good morning to all
Just forgot to mention, filters are a great idea, however they require maintenance, cleaning and subsequently replacement at cost. In Jim's application they are great, especially in the show application due to fume. However in reality too costly to maintain unless there is a specific application similar to Jim's. Most workshops don't want the added cost and complexity of filters, it is just as easy to vent your fumes outside and keep you work place fume free.

[jimcolt]

Couldn't agree more on the filters, assuming they are disposable. Many industrial shops use large industrial filter systems that are self cleaning....in this case filtration is a good idea as you can keep the heated air in your shop as well as control smoke, dust, fumes.

My two machines (pictured in this thread being built) were just at the Sema show in Vegas and at the Fabtech show in Chicago. Each cut for 4 days at the shows on one set of filters.....very little smoke even on the last day of the shows.

Jim Colt

[Brand X]

Had one of these for about ten years.. I have a pusher on the other side.

http://www.ebay.com/itm/MOPEC-MVB-AC-AI ... 2000339492