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blower: ensure presence and functionality #1

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Hurricos opened this issue Sep 13, 2024 · 29 comments
Open

blower: ensure presence and functionality #1

Hurricos opened this issue Sep 13, 2024 · 29 comments

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@Hurricos
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Hurricos commented Sep 13, 2024 •
edited by heaventwig
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The seller does not have a blower for us.

The blower is shown here: https://laboratoryb.github.io/camfive/docs/Laser_Machine_INSTALLATION_MANUAL.pdf#page=8

image

Jake may have access to a blower.
@heaventwig
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For temporary exhaust routing, add a T junction to exhaust fan duct (PVC) overhead in garage, adjacent to exit from garage, and run flex tubing from laser, via rafters, to the T junction. Should have louver-style air handling valves to prevent backflow into either pipe, as the tube draws from (and could return to) house air.

@heaventwig heaventwig changed the title [WIP] Blower ensure presence of working blower Sep 14, 2024
@heaventwig
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Tim says he's trying vent fans from Vevor, says they are much quieter than the "big bois" and rated for twice the CFM (a rating which Tim questions, but the quieterness is nice).

@heaventwig heaventwig changed the title ensure presence of working blower blower: ensure presence and functionality Sep 14, 2024
@heaventwig heaventwig added the noncrit not critical label Sep 14, 2024
@DaBlender
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My in line blower. 4” inch connection, not a lot of duct but it’s not expensive. I have not had any issues with it.
6F70EF4A-EA2F-4D0B-B0A1-F1F3A16F22D0

I forget the tool name to measure flow but would be handy especially to any safety check

@heaventwig
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As I prep tubing for exhaust, I'm curious about reasons for and against including a dust collection system somewhere along the way before the output air (with all of its fumes and combustion byproducts) gets pushed into the world at large...

@DaBlender
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DaBlender commented Sep 21, 2024 via email

@Hurricos
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A common method for air filtration is to use a pre-filter, an activated carbon filter, and a HEPA filter. This ensures that any unsafe particulates are caught in the filter, and the air will be much safer to breathe. You can either apply the filter to your laser cutter's exhaust or duct the air into a fume coffin.

(cited)

I never paid attention to the exhaust filtering setup at Chatt*Lab (@ttsgeb?), but the consensus(1234) seems to be that if you cut certain materials, lasers make nasty fumes, AKA "LGACs" (Laser Generated Air Contaminants). LGACs are primarily a concern when cutting certain metals or plastics5; if those types of materials are on the menu, and you're going to be cutting them in quantity, definitely get a filter.

Footnotes

  1. https://www.instructables.com/Fume-Coffin-Laser-Cutter-Exhaust-Vent-Filter/ ↩

  2. https://www.osti.gov/servlets/purl/1959231 ↩

  3. https://community.glowforge.com/t/fume-coffin/8848/2 ↩

  4. https://www.tlm-laser.com/info-centre/news-and-events/lasers-fumes-and-health ↩

  5. https://ehs.oregonstate.edu/sites/ehs.oregonstate.edu/files/pdf/si/lasercuttersi.pdf ↩

@heaventwig
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heaventwig commented Sep 23, 2024 •
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Okay, so I definitely want to construct an exhaust vent filtration system. Next questions / todos are around defining specs for that device and system.

  • define/identify CFM flow specification for exhaust ventilation from 150W CO2 laser cutter

@DaBlender
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DaBlender commented Sep 23, 2024 via email

@heaventwig
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Beware front filter being anything that melts.

In this I read "leave ample room for exhaust to cool before it hits anything temperature-sensitive."

@heaventwig
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also noting here, for future reference, that 820m3/h is just under 490 CFM (cubic feet per minute).

@DaBlender
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DaBlender commented Sep 23, 2024 via email

@heaventwig
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Adding to concept plan: metal wire mesh grid pre-prefilter.

@heaventwig
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heaventwig commented Sep 23, 2024 •
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ventilation plan:

  1. metal wire mesh pre-prefilter on camfive air outlets
  2. 6" flex tubing to fume coffin (eventually install Pre-Filter Addendum) — need to redesign for higher CFM throughput; this design is specced for 100CFM and we need more like 500.
    • alternatively, use premade air scrubber such as this VEVOR unit, which has 15.5" intake and 8.5" outlet, for which we'd need to supply some size adjustments; note $350 price on this unit in 2024 is pretty close to the total BOM for the above Instructable for the fume coffin, which was priced when posted over seven years ago. (Note also that although this unit advertises 800CFM that's likely assuming no other interference with pressure or air supply.)
  3. 6" flex tubing from blower output on fume coffin up to right-angle turn PVC pipe in rafters; simultaneously or in-line with right-angle joint, step down to 4" PVC
  4. run 4" PVC to in-line 4" VEVOR blower (plug in adjacent to garage door opener)
  5. run 4" PVC to 90º turn with valve flaps (to prevent backdraft from other devices on same exhaust pipe)
  6. T-join (or angle-in join) PVC connection with existing exhaust vent, with added valve flaps (to prevent backdraft into conditioned interior home air from laser exhaust)

@DaBlender
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DaBlender commented Sep 23, 2024 via email

@heaventwig
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heaventwig commented Sep 23, 2024 •
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with the VEVOR filter, we might:

  1. rig a metal ducting box for the 15.5" intake (call that BOX A),
  2. provide BOX A with two 6-inch inlets and a metal wire mesh pre-filter,
  3. run 6-inch flexible metal ducts from the camfive air outlets to BOX A
  4. rig BOX B on the 8.5" air outlet from the VEVOR device, with 4" outlet
  5. run 4" flexible ducting from BOX B to rafters
  6. join flexible duct to 90º PVC at rafters, all at 4" diameter
  7. continue ceiling rig as described in blower: ensure presence and functionality #1 (comment) from point 4 onward.

@ttsgeb
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ttsgeb commented Sep 24, 2024

It's worth noting that the inline blower I'm using is an 8'' one, and it does struggle to keep up with heavy usage.

Chattlab doesn't have any filtration at all, they just pump it all into the atmosphere and this is definitely fine and not a major concern that everyone refuses to address.

@DaBlender
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DaBlender commented Sep 24, 2024 via email

@ttsgeb
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ttsgeb commented Sep 25, 2024

To be clear, the "definitely fine" bit was completely sarcasm.

CFM ratings on fans are relatively meaningless without indications of pressures involved. The inline fan can move a lot of CFM in a world where there are no restrictions on flow, but the use in the laser systems results in substantial flow restrictions so the fan can't reach its advertised numbers. Adding filtration complicates that further.

A potential solution would be to include several suction fans on a fume coffin that is designed to equally disperse flow across all of them. Effectively, you'd want to measure CFM of the shipped system and then build your filtration such that measured CFM through it and all related piping exceeds the original system. This enables you to successfully evacuate the laser to design spec while still leaving overhead for degradation of filter media.

Another data point is that the system the laser I most recently installed shipped with is advertised as to fully exchange the enclosed volume every 5-10 seconds. This is almost adequate, so seeking to exchange every 2-5 seconds would probably be adequate. Assuming the vented enclosure has a volume of 60 sqft, you would want to aim to be filtering >1200cfm of air through your exhaust. Filtering less than 400cfm would likely be the limit where it becomes actively inadequate. When considering the restrictions added by the ductwork, two of the Vevor units linked above would likely be around the minimum for adequate exhaust filtration. (I am not a flow engineer, this is not legal advice)

@heaventwig
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This vevor scrubber, also linked in my above comment, around which I designed the sequence described in this above comment, is rated by VEVOR at 800 CFM with its manufacturer-supplied filters in place.

The camfive laser is specced for just under 489 CFM. 800 CFM should suffice.

With added pressure differentials from the presence of the laser enclosure (restricting inflow) and downstream exhaust venting ducts (restricting outflow), it might not sustain 800 CFM. It's conceivable it could drop below 500 CFM. That's why my design in the above-referenced comments includes an inline VEVOR duct fan in the PVC sequence in the rafters beside the garage door opener (placed just so because rafters, power supply, and PVC ducting all line up in that spot). See point 4 in the first comment.

If that's all insufficient, the simplest fix I see is to use two of the scrubbers, swap the pre-filter union (upsizing a pair of 6" exhaust ducts to the 15.5" intake) for a post-filter union (downsizing a pair of 8.5" exhaust ports to a single 4" duct; keeping the metal screens in the rig where we still need to upsize the flexible 6" aluminum ducts to the 15.5" air intake on the scrubbers), and get 1600 CFM of filtered exhaust vent fans feeding into the exhaust ducts. Seems excessive, but we do like clean air. I suspect the inline duct fan in the rafters would remain essential, in this configuration, for helping all the pressure coming out of those scrubbers find its way down the vents and out to the exhaust port on the side of the house.

@ttsgeb
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ttsgeb commented Sep 26, 2024

I understand this. The reason I said two of the scrubbers is because in looking deeper into it, I found comments from Vevor that the scrubbers are actually rated as "400-800" cfm, so the 800 number is absolute ideal conditions with no added restrictions and the 400 number is likely poor conditions with no added restrictions. Considering there will be added restrictions and I already have experience with items from this company rated in excess of 800cfm not effectively removing the exhaust from the machine, I highly doubt that a single scrubber as linked, even with an added inline fan, will be suitable.

@heaventwig heaventwig removed the noncrit not critical label Sep 29, 2024
@heaventwig
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Vevor fans ordered — one for inline ducting in rafters, one for filtration of exhaust from machine. Expected delivery by 3 October 2024.

@heaventwig
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@ttsgeb how are your Vevor exhaust fans doing with the heat of the air coming out of the cutters? And what's the ducting that you use — metal or pvc?

@heaventwig
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(Also @ttsgeb — have you measured that exhaust temp anywhere?)

@heaventwig
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Relatedly, this piece of the in-built exhaust ventilation system does not appear to be metallic.
image

We could maybe also check inside it for a metal lining and, especially if it's not metal, evidence of melting (eg due to heated exhaust).

@Hurricos
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Hurricos commented Oct 1, 2024 •
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TL;DR at 400cfm with a 130W laser continuous, and generating say 500W from burning material, you should generate a ${\Delta}T = 3.3 \degree \textrm{C}$.

If we ignore that the density of air varies with temperature: at STP, 1m^3 of air is about 1kg. The specific heat of air at the same temperature is about 1kJ/kg*degK. Let's say we move 400cfm =~ $11.3m^3/min$ =~ $0.189m^3/s$. So at 630W continuous laser power + combustion:

630 / 0.19 m^3/s / 1000 J / kg * degK * 1 kg/m^3 = $3.3\degree\textrm{C}$.

Other errata:

  • I'm sure we're moving more than 100cfm of air (lower average deltaT)
  • I'm sure we're combusting material and adding laser thermals (more thermal energy)
  • I'm sure the density of air decreases with temperature (less thermal medium per unit time)

Factors seen and discarded:

  • The specific heat of air varies (in particular, increases) with temperature, but not within the bounds we care about (0-100*C); cite.

(Edit: obviously there'll still be particulate condensed and cooled from the flame, but unless you expect to be unable to control the fire at the laser-point, you don't have to deal with temperature, only particulate.)

@heaventwig
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New ducting plan:

  • no junction with existing ductwork
  • run exhaust duct to soffit vent instead
  • install soffit vent in NE corner of garage

Might want to return 4" Vevor in-line duct fan and replace with 6" model, need to [ ] check tolerances on available soffit vents vs clearance at intended installation site.

@ttsgeb
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ttsgeb commented Oct 2, 2024

I have never actually noticed any issues with exhaust temperatures. It is almost exclusively smoke and resin vapors that cool substantially even by the time they are evacuated from the machine. The main issue with heat is going to happen when there's enough associated mass to cause a problem. Where you might see this is if embers from cutting cardboard make it through the exhaust system, or exceptionally well heated small bits of wood. The real thing to watch is to ensure that your hose doesn't fill with debris or become so heavily coated in residue that the non-hose materials inside the hose offer fuel that can be ignited by an ember.

@heaventwig
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Ducting materials mostly acquired. Not pictured: a roll of pro-grade foil tape.
image
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image

Still need

  • reducer/expander connection from the 8" T out to the 12" collar, possibly in two steps
  • another 90° bend at 8", 12", or maybe 10", to go somewhere between the 8" T and the 12" collar
  • crimpers
  • some kind of gasket sealant or chimney insulation for the joint between the 12" collar and the Vevor intake

Getting the crimpers because the number of (still returnable, unused) connectors in this run makes the price of a pair of crimpers desirable by comparison.

@DaBlender
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9130A2D4-8DA5-46BC-97DD-EBCBBB57F2B6

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@heaventwig @Hurricos @DaBlender @ttsgeb