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Faster extraction ??
Posted: Sun Apr 12, 2020
by Ignas Kaz
Ran a first test of production cutting PETG film yesterday, 1hr test. (Cutting face shield visors).
At the moment inbuilt fan is not doing much to help with extraction, it takes forever until i can get the lid open.
Current situation is as follows - my machine has inbuilt fan (50W, 150mm), which is pulling air to 1m long 150mm duct, which is reduced/connected to about 15m of 100mm rigid pipe to exhaust outside where another fan (300W impeller) sucks on the exhaust. Without suckage from that fan, the inbuilt one doesnt do much at all.
Problem is, we are in production at the moment (or starting monday anyway), where cut process is about 10sec and then i need to open lid, replace sheet, cut again in as fast a succession as i can. Now i cant as i will drown in PETG smoke/particulates.
I’m planning on wrapping machine in duct tape to close off any gaps in panels, leaving only air inlet under the lid and some for cooling electronics cabinet. Create as much negative pressure as i can.
We also have bigger dust extractor on wheels thats connected to big CNC router machine (3x2m celtek 8kw spindle) which we’ll probably pipe in at the end to suck on the pipe from afar (noisy). The extractor specs state 2500 cubic metres of air extraction (per hour?).
Filtration is not in question now, as we work in absolutely desolate place with workshop gate wide open and pipe end sticking out…
How much airflow would you think i would need to have for quick lid opening action ?
Also, probably critical to leave air inlet at business end of tube to prevent smoke settling on beam output window and first mirror …
Any thoughts on how to proceed for better turnaround time ?
Re: Faster extraction ??
Posted: Sun Apr 12, 2020
by Jeffrey Aley
Ignas Kaz wrote: Sun Apr 12, 2020
Ran a first test of production cutting PETG film yesterday, 1hr test. (Cutting face shield visors).
At the moment inbuilt fan is not doing much to help with extraction, it takes forever until i can get the lid open.
Current situation is as follows - my machine has inbuilt fan (50W, 150mm), which is pulling air to 1m long 150mm duct, which is reduced/connected to about 15m of 100mm rigid pipe to exhaust outside where another fan (300W impeller) sucks on the exhaust. Without suckage from that fan, the inbuilt one doesnt do much at all.
Problem is, we are in production at the moment (or starting monday anyway), where cut process is about 10sec and then i need to open lid, replace sheet, cut again in as fast a succession as i can. Now i cant as i will drown in PETG smoke/particulates.
I’m planning on wrapping machine in duct tape to close off any gaps in panels, leaving only air inlet under the lid and some for cooling electronics cabinet. Create as much negative pressure as i can.
We also have bigger dust extractor on wheels thats connected to big CNC router machine (3x2m celtek 8kw spindle) which we’ll probably pipe in at the end to suck on the pipe from afar (noisy). The extractor specs state 2500 cubic metres of air extraction (per hour?).
Filtration is not in question now, as we work in absolutely desolate place with workshop gate wide open and pipe end sticking out…
How much airflow would you think i would need to have for quick lid opening action ?
Also, probably critical to leave air inlet at business end of tube to prevent smoke settling on beam output window and first mirror …
Any thoughts on how to proceed for better turnaround time ?
For my particular laser, the issue is often not the extraction pressure, but the amount of make-up air available. I get better extraction with the lid open by about 4 inches. Some of that has to do with available make-up air, and a lot of it has to do with creating laminar air flow across the workpiece. So you might try running with the lid open (possibly even wide open) if your safety standards allow it (I'm just a hobbyist, and not a production shop).
Re: Faster extraction ??
Posted: Sun Apr 12, 2020
by Ignas Kaz
I have about 2 inch gap between lid and base. Still smoke just lingers for a bit.
By the end of the 1hr run i was just opening the lid to do cuts faster. Workshop stinks now
Re: Faster extraction ??
Posted: Sun Apr 12, 2020
by Gene Uselman
If you can avoid the 100mm reduction I would- the builtin fans are not good either.
Re: Faster extraction ??
Posted: Sun Apr 12, 2020
by Tim Mellor
As you are in a remote location I would be tempted to get a good organic Spray Painters mask on for the operator and shove the Laser near a Roller door or even outside and take the lid off for the job. The moving job will make it a net time saver as you can just swap the sheets out with zero wait time.
A while ago Gene (snippet below but I can do some actual numbers if needed for you) and I were chatting about Duct size and Losses. With a 15m Run unless it is smooth bore rigid with swept bends you will likely be choking your secondary Fan. Later on consider an upgrade and even bump it to 5" Depending on the actual fan in use some of them Suck but in a bad way when it comes to reduced inlet pressures.
If you hook it up to your Dust Extractor if the Bag/Outlet is inside the shop it will still stink so duct it outside if you go down that path.
'Equivalent' is made up of duct plus an allowance for the number of bends or other fittings in the pipe run. So sharp elbows at 90 add more than 45 which are more than long radius bends etc.
What this means is that to push 350CFM through an equivalent pipe length of 100' of 4" duct you will need 1.5kPa of pressure to overcome friction but for that same 100' you can push 650CFM through 5" and circa 1000CFM for 6". Using these numbers if you have a more likely example of a 33' run you will only need 0.5kPA of pressure to push the air at those flowrates.
Now it gets to rubbery numbers due to the blower you showed only lists PEAK numbers and it is for 50Hz not the 60Hz you run 2 pole motor with a maximum pressure of 1.7kPa so it is safe to assume it will produce somewhere under that at a reasonable flowrate.
Without a performance curve for the blower the numbers are a bit of a guess as all you have are 'peak' claimed Chinese spec ones
The figure of 18 cubic M/min of flow that works out to a bit over 600CFM PEAK?
Re: Faster extraction ??
Posted: Tue Apr 14, 2020
by Ignas Kaz
I have removed in-built fan this morning - difference is staggering. Nothing escapes even with hatch wide open. And, remember, i'm cutting PETG. That stuff smokes A LOT.
Also replaced mishmash of different diameter corrugated/rigid pipes with 160mm sewer pipe all the way from the back of the machine and to blower outside. That, coupled with removal of obstruction in the back of the machine (in-built fan) made all the difference in the world.
Upon removal of the fan i noteiced its only 23W, i thought it was 50W. Not that it makes it more useful at the job though...
Blower is not even sealed, btw, its just sitting against the end of the pipe, sucking air. No flanges, no duct tape, just butted agains the pipe...