Stuff your 3D printer has made today...

[Agroshield]

Any suggestions? Bigger duct I guess

Make of this what you will:

For HVAC ducting, there is some guidance, DW144 (copy here http://metalproduct.vn/uploads/source/tieu chuan/dw-144.pdf)

Fig. 98 on page 61 of the pdf (59 printed page) suggests that the included angle for reducing should be between 15 and 60 degrees (your current included angle is 90 degrees - which is OK for expanding). On rectangular ducting, they suggest (Para 10.6 page 41) 22.5 degree half angle which is in the same range.

The proportions of these might be a good starting point:

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[DAPPH]

Perhaps a simple swinging louvre blades arrangement on the outlet side duct with small magnetic sticky strips to gently hold them closed till fan pressure opens them should stop any back suction ?????

 

[carbon]

Axial fans create high flow at low pressure, potentially the outlet is restricting the flow and the fan can’t overcome the pressure required to move the volume of air and some is forced back through the blades and back out the front

 

[Onoff]

Perhaps a simple swinging louvre blades arrangement on the outlet side duct with small magnetic sticky strips to gently hold them closed till fan pressure opens them should stop any back suction ?????

That's a given. The problem is as @carbon says, post before this.

Fag packet sketch. Wondering about mounting the fan on the wall then having a length of flexi duct you position next to the workpiece being soldered etc.

 

[carbon]

Can you use the existing duct on the inlet side of the fan to try it? Even if you tape it in place if the mounting doesnt fit

 

[Onoff]

Can you use the existing duct on the inlet side of the fan to try it? Even if you tape it in place if the mounting doesnt fit

It sucks in through a filter at the front:

And expels out the back, full dia:

The first attempt tapered duct screws on in place of the guard with the original screws:

Edit: sorry, see what you mean now! Could likely get some rivnuts in the corners:

 

[Onoff]

@carbon , with the printed duct slapped on the front it restricts airflow a bit but there's nothing coming back at you from the intake side.

 

[DAPPH]

Ya want a four inch black plastic duct about 18 inches long to play with ?
Moist warm air outlet from the air chest to the flexi hose take off , off an old 1400 watt table top clothes dryer .

 

[Onoff]

Ya want a four inch black plastic duct about 18 inches long to play with ?
Moist warm air outlet from the air chest to the flexi hose take off , off an old 1400 watt table top clothes dryer .

Going to stick with the ultra flexible foil duct I think. I've actually to do two "installs". For my brother and niece who both copper / silver smith in their sheds which involves quite a bit of albeit lead free soldering.

My brother's is fairly simple, the portable extractor sat on the bench, flexible hose across the bench to a wall vent in the side of the shed all at one level.

My niece's is more of a pita. Limited for bench depth, she wants the extractor on a bit of flexible duct, to then go through the bench, run along underneath and exit under where the sockets are through a vent there.

She doesn't want the vent over her vegetable patch which is in front of the windows "because of toxic fumes etc"

 

[knighty]

if it's an option, use a bit of 110mm soil pipe for under the bench?

it's shocking how much better rigid duct is better than flexible duct for air resistance

 

[Onoff]

if it's an option, use a bit of 110mm soil pipe for under the bench?

it's shocking how much better rigid duct is better than flexible duct for air resistance

Yep, soil pipe is the plan!

 

[carbon]

If space is tight under the bench this my be of use.
Not sure if it would effect air flow.

 

[DAPPH]

Yep, soil pipe is the plan!

One is cheaper but I cannot re call which UV stabilized grey above ground or orange below ground available as 1.5 mtr lengths I found the local builder merchant cheapest
Concertina aluminium in 4 inch is IIRC even cheaper from Wickes but I used orange as I had a big order for it

 

[Onoff]

One is cheaper but I cannot re call which UV stabilized grey above ground or orange below ground available as 1.5 mtr lengths I found the local builder merchant cheapest
Concertina aluminium in 4 inch is IIRC even cheaper from Wickes but I used orange as I had a big order for it

I've loads of offcuts and bits of removed, "used" soil stack.