Cutting rigid PU foams?

[Tim Courtland]

Sorry if this has been covered already, but I can’t seem to find the other discussion on it.

I was under the impression that polyurethane was a big NO, it produces HCN. But so does PS apparently.

However many online cutting services and my local cutter have no issue with rigid polyurethane (PUR) foam.

http://www.eurolaser.com/materials/polyurethane-pur/
http://www.cutlasercut.com/laser-cutting-materials-laser-engraving-materials/grey-polyurethane-foam
https://www.youtube.com/watch?v=ErernoyeoHM

Would it just come down to the quality and cost of fume extraction/filtration? I use PUR a lot on the CNC, it would be
amazing if I could safely laser cut it as well. Saves stocking different materials.

Tim

[j. eric townsend]

On 4/22/15 08:14, Tim Courtland wrote:
> Would it just come down to the quality and cost of fume extraction/filtration? I use PUR a lot on the CNC, it would be
> amazing if I could safely laser cut it as well. Saves stocking different materials.

and replacement cost of glass and metal parts, similar to the cost of
new end mills, drill bits, etc. For some shops that cost is just
factored into the cost of operations. I was looking at some nicely
lasercut Kevlar a few months ago then looked up the MSDS and thought
maybe I can't afford to cut Kevlar.

The Lasersaur at CMU is starting to get a layer of corrosion on the
exposed steel parts (ex: the axle that drives the Y pulleys) but it
still functions as expected and might never be replaced. We're going
to swap out mirrors soon, those are probably also sacrificial gear in
the final cost analysis.


--
J. Eric Townsend, IDSA
design <http://www.allartburns.org>
hacking <http://www.flatline.net>
consulting <http://www.functionalprototype.com>

[Steve Baker]

Polyurethane contains nitrogen...when you laser polymers with nitrogen in
them, you're going to get hydrogen cyanide gas and various nitrous oxides
produced as a byproduct. Neither are very nice to have in your lungs!

Wikipedia says: "Polyurethane polymer is a combustible solid and can be
ignited if exposed to an open flame. Decomposition from fire can produce
mainly carbon monoxide, and trace nitrogen oxides and hydrogen cyanide.
Because of the flammability of the material, it has to be treated with
flame retardands (at least in case of furniture), almost all of which are
considered harmful"

So while the polyurethane itself may not produce enough cyanide and
nitrogen compounds to cause you harm...the mysterious cocktail of
flame retardants probably do.

Without the flame retardants, you're going to have to worry about a laser
fire because you'd certainly be exposing it to an open flame.

If you can find polyurethane foams that you know for sure are NOT treated
with flame retardants...then *MAYBE*...*IF* you are 100% confident that
your ventilation system is adequate - *AND* you're able to extract out the
cyanide before venting it out into the outside world.

If you're not venting the cyanide along with the exhaust gasses, then you
need to ask whether your local pollution laws are OK with you venting
cyanide into the environment...and at what concentrations. The legal
penalties for getting caught venting cyanide if/when your neighbors find
out might be kinda extreme!

In truth, it's all about concentrations...

Firstly, all venting systems are going to leak some material out into the
room where you're operating the laser cutter...if for no other reason than
people rarely wait for 60 seconds before opening the lid of the machine at
the end of a cut - so they get a face-full of smoke and fumes when they
do.

Secondly, when cutting foams, everything depends on the density. If there
is relatively little solid material present - it's not going to produce as
much cyanide as a very dense foam or a solid.

Thirdly, the inside of a laser cutter gets encrusted in various kinds of
tarry goop that has to be cleaned out periodically. I'm not confident
that there wouldn't be a buildup of toxic compounds in that residue.

There is no doubt that some of these big laser cutting services have very
good ventilations systems and/or very lenient local environmental
protection laws (eg if they outsource to China where you can get away with
almost anything) - and probably they have a reliable source of
polyurethane that doesn't have fire-retardants and they may well cut it in
a machine that's flooded with some inert gas to exclude oxygen and prevent
a fire.

So I certainly wouldn't cut polyurethane foam in my lasersaurs without
taking a heck of a lot of extra precautions - it's on the "Definitely Not"
list for me!

-- Steve



Tim Courtland wrote:
>
> Sorry if this has been covered already, but I can’t seem to find the

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-- Steve