Advanced air filter design/expanded material capabilities


#1

I have been designing an advanced air treatment system for my lab and it dawned on me that some elements of my design might be applicable to extending what materials one could use in a Glowforge. In the lab setting, I am primarily worried about organic vapors, but acid gases and halogens like chlorine and bromine are also in my design. I am planning a system based on the use of hydroxyl radicals to decompose the organic materials efficiently to carbon dioxide and water. Does anyone know what the volumetric air flowrate the air filter is designed for? Which materials would you most like to be able to use that are problems now? I am in a unique position because I have access to equipment to test the emissions. I would most likely want to react away any acid gases and halogens in a front end prefilter before consuming the organic vapors later in the filter. Longer term, such expanded materials capabilities might give Glowforge another feature that few other lasers could match.


#2

That’s so far over my head. I can just about make out the contrails.


#3

I want to cut ABS but I read that produces hydrogen cyanide. I don’t know if the Glowforge filter handles that or not, and the way they are with information, I doubt they will tell us. I also want to cut PTFE. I read that works but then I think I saw it produced hydrogen fluoride, which I assume is very corrosive.

PVC would be useful to cut but produces hydrogen chloride. Rather than air assist blowing I think it would need a corrosion proof vacuum pipe to extract acidic gasses before they can corrode parts of the machine as well as a filter that neutralises them.


#4

This! :+1:

  1. Nope
  2. I’m going to kill myself with vinyl
  3. Counting on you to tell us the results of the tests before I do.

No pressure. :wink: ROFL!


#5

For things that create HCL, I think you’d need the interior volume of the gf flooded with whatever substance would create a safe reaction (and/or, as @palmercr said, some kind of really serious extraction mechanism). I wonder how plausible the extraction is (because you’d think someone else would have tried it given the huge potential market for zapping pvc). For things that just create toxins or particularly dangerous particulates (I’m thinking teflon in particular) the filter must have a cfm spec somewhere. Tried a quick search but don’t see it, thought I remembered something like 400 cfm, but that could be completely wrong.


#6

I think a major concern for cutting the bad stuff is what the gasses do to the inside of the machine as far as corrosion on PCBs rails and lenses. (and your body:-))

although if there was something that could neutralize these and could be added directly to the air assist that might work!

Anybody got an extra tank of hydroxyl radicals laying around! (I have no idea what that is, hehe)


#7

The hydroxyl radicals will likely take care of the HCN with no problem. In case the competition is reading, I won’t get into the tech in depth. Besides, this discussion might make too many heads spin. I will say this. There are materials that when exposed to light, release hydroxyls readily and other new materials sufficiently unreactive to these radicals that these radicals are stored on their surface until some bad gases come along to react with them. There are some new advanced coatings that might protect all of the internal parts with a molecule thick coat without being visible.


#8

for me the big no-no is PVC, either directly or as a component, like vinyl. Figure out a way to cut that and you can probably change the market. :smile:


#9

As far as the hydroxyl radicals making it out of the filter, extremely unlikely. I can put a sacrificial material at the end of the filter that would instantly react, consuming any hydroxyl stragglers.


#10

I might be able to come up with a protective foam layer that would trap acid gases and could be removed upon demand.


#11

Both air and vacuum might do the trick. Air moves from higher to lower pressure and contaminants move with the air. A vacuum somewhere close to the head and connected to the filter and flowing air coming from around all critical components could do much to move all bad gases to where the filter could remove them. Intake air could be filtered and channeled around critical elements as well.


#12

This is one of those questions that is best answered by @dan.


#13

Interesting. With access to atmospheric analysis equipment you are is a great position to explore!


#14

Unfortunately I don’t have that number handy. The engineering team does, but I try not to bother them.


#15

I’ve been think of that question.

Right now I can say is that there is a gust of air coming out of that hose extended 4’.

Not really concerned at the moment because the solution I have of venting out a window works great.

Have thought of doing this:

Or the next time i find an HVAC tech handy I’ll ask him to about a flow meter on.


#16

Great questions, and it sounds like an exceptionally useful process you’re working on.

In terms of materials and potential outgassing, I’m very interested in working with chromium tanned leather, which releases sulphur, chromium, and occasionally titanium.


#17

Schematically, it is quite simple, as far as processes go. The difficulty is in adjusting the reactivity of pre-filter and filter materials to insure sufficient reaction rate. To do that I must estimate or measure the maximum amounts of a given impurity I want to remove that can be generated by the GF during a given time with a given material. Someone here probably can help in determining when a material is likely to release the most gases, during a fast, high powered cut, or a slower, high power raster engrave. I suspect the latter, but I don’t know. Then, from the volume of material removed by the laser during a known time interval, I can estimate the amount of contaminant, say HCl, that is produced. I design the filter for 3-5 times that amount for safety and to allow for filter degeneration over time. It’s killing me that I can’t reveal more detail.


#18

Designing for a GF is actually much easier in some respects, and more difficult in others. In a lab situation, I am designing for 1200 cubic feet per minute flow with the potential for several hundred grams per minute of volatile contaminants, all vented ultimately outside. Assuming a 400 cfm flow for the GF, and a maximum of 10-20 grams per minute volatiles produced, it should be much easier to do, except for the fact that many units would exhaust into the room. For example, I could easily use aluminum beads in a lab setting as a scrubber for hydrochloric acid, but it would never work for the GF because the reaction generates hydrogen as a byproduct. I would have to use a less active metal like iron or another means to remove it, to avoid the hydrogen problem. In the lab I can more readily remove any heat of reaction, but with a GF I have to be more careful.


#19

3D engrave would (likely) be the worst case, so you could get to an order of magnitude by looking at the video…

Could you generate any useful power either with the hydrogen or the heat of reaction?


#20

I’m totally spitballing here, but I’m pretty confident that the flowrate is something closer to the 110-160 cfm range since the Glowforge has a single 4" fan in place. If it was capable of pushing 400 cfm, the noise on it would be incredibly loud, and the diameter of the pipe doesn’t really support it – you’d need at least a 6" pipe for that. The highest I’ve seen 4" pipes pushing is in the lower 200 cfm range.