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[Video] Gas forge exhaust gas extraction system


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Hello everybody,

I couldn't find any info online about making a proper gas forge exhaust gas extraction system, so I decided to build one and make a little video about it. 

There are very nice smoke extract fans for sale online (ruck.eu), but I decided to buy a cheaper regular steel box fan and retrofit it with a little trick a learned from "Smederij de Waard - Wanroij" in order to keep the motor and bearings cool. The system had to be as quite as possible, the gas forge itself is very quiet, so I don't want the sound level to be overruled by the fan. Two big sound dampers are used, also to suppress the noise as much as possible for the surrounding neighbors.

Specs: Ducting: 250mm Box fan capacity: 2600 m³/h (maybe 2000 m³/h after the retrofit)

So far it is working really well, the motor stays cool. Next thing would be proper electrical wiring and a on/off switch..

 

 

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Unfortunately I can't watch your video at work, but will try to check it out later.  The typical "rule of thumb" for hood capture velocities is around 100 ft/min, so assuming you have a hood on the order of 2' x 4' your current 1,530 CFM should be more than adequate (if it is actually operating at that flowrate).  The 10" nominal duct size at that airflow will result in a duct friction loss of around 1.2" WG/100' of duct (1.2 inches of water gauge head loss every 100' of duct).  This doesn't seem like much until you realize that a duct elbow is an equivalent 15' of duct and the abrupt transition from the hood to duct is equivalent to around 35'.  It can start to impact on your fan selection (fan curve vs system curve), but not knowing the specifics of your fan I can't theorize on what you actually have going. 

My guess is that you are riding the fan curve down and actually the fan capacity is 1,530 CFM at essentially no static pressure loss, and likely a lot less at the current flowrate.  Since you may only need around 800 CFM of exhaust, it is likely not an issue.  In fact at 1,530 CFM I would have selected a 16" duct for both static loss and air noise.  Depending on the specific fan selection, it may only develop 1 or 2 inches of static before stalling, so likely you are balancing out at significantly less exhaust flow than you think.  As I indicated, this may be fine, as long as the cooling effect is working for you.

I'm not a big supporter of having the fan motor being in the airstream for a hot fume exhaust system.  I look forward to seeing your solution for this.  A belt drive system with the motor out of the stack is typically preferable, but you may be capturing enough shop air to keep it running acceptably.  Just make sure you have an adequate makeup air opening to the outdoors to supplant the fan.

I really like your 4-bar forge door, fan powered burner with PID controller and powered rolling mill.  The dies on the bottom shelf look to be for a press as well, so I expect you have a very efficient shop.  It is certainly a lot cleaner and better organized than mine...

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Latticino

Thanks for your technical response. First I will add some fan specs:

• Flow: 2650m3/h
• Weight: 21kg
• Power: 1080
• 4 pole
• 1400 rpm
• Ø 250mm
• Voltage: 230v/50hz
• Dimensions: 450x450x450mm

https://www.spirototaal.nl/stalen-ventilatorbox-2650m3-th.html

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In fact at 1,530 CFM I would have selected a 16" duct for both static loss and air noise.

Does larger ducting make less noise? 

First I made my design with 13" ducting, but that would have resulted in an even larger fan box (for correct intake size) so I choose 10". The system is very quite now, with earplugs in I can't hear it, this is kind of scary because I won't know if it is working, but I do take a look at my CO2 meter often and I have a CO alarm nearby.  

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I'm not a big supporter of having the fan motor being in the airstream for a hot fume exhaust system.  I look forward to seeing your solution for this.  A belt drive system with the motor out of the stack is typically preferable, but you may be capturing enough shop air to keep it running acceptably.  Just make sure you have an adequate makeup air opening to the outdoors to supplant the fan.

Yeah, have a look at the video ;)

Quote

I really like your 4-bar forge door, fan powered burner with PID controller and powered rolling mill.  The dies on the bottom shelf look to be for a press as well, so I expect you have a very efficient shop.  It is certainly a lot cleaner and better organized than mine...

Thanks. Fun fact about the forge, it has ribbon burners, but they are not cast in refractory, just drilled holes in insulating fire brick :ph34r: Working great for over a year now! Much easier to make.

The forge has a PID which works as a thermocouple readout, it is not controlled by it. I'm tuning the gas/air mix while working with it. For instance, when I want less scale or when I take a kerosine weld on a piece of damascus I crank the propane up a lot. When the bricks are hot it idles real nice at 1250 degrees Celsius at the lowest setting. Here is more about it: https://www.youtube.com/watch?v=eNDa3fWvALY

 

Schermafdruk van 2022-07-02 08-42-31.png

stalen_ventilatorbox_spirototaal.jpg

spirototaal_grafiek_2650th.png

15 hours ago, ThomasPowers said:

Do you have an air curtain for the forge's door to shove the exhaust up towards the intake?

no I don't, the exhaust of the forge is in the back so the bulk goes backwards, the door is closed 95% of the time

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