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View Full Version : Corrugated Plastic can be dangerous...watching the first flame



Mayo Pardo
03-20-2015, 12:07 AM
I made a fixture from cardboard, and for the backing of it I used a scrap piece of a corrugated plastic real estate sign. In order to remove the pieces I was engraving, I cut a hole (with the laser) in the corrugated plastic in each location so I could poke my finger in and pop out the pieces. The holes cut fine although not quite through completely, so I ran it a second time and was ready for production.

Fast forward after that job I thought, I wonder what else I can do with this corrugated plastic?
I decided to try cutting one of my other designs that I normally cut in other material.
Still being new at this I didn't keep track of what settings I used when I cut the holes mentioned above and I'm sure I increased the power setting since it didn't cut through 100% on my first try at the holes. I don't remember what the settings were and most likely your machine will be different power anyways (us 40 watt guys seem to be in the minority here).

So I load the new job and start the cut and literally within TWO SECONDS, the corrugated plastic catches on fire! Fortunately I was standing right in front of the machine watching it and I immediately lifted the lid to shut off the laser, leaned over and was able to blow out the flame with one full breath. I was ready to lift out the piece of material and toss it on my concrete floor and step on it if it didn't go out but that wasn't necessary.

So, not unlike the surfer who has to get back into the water after healing up from the shark attack, I decided to try again!

I lowered my power setting and increased my speed. Ran the job and it caught on fire AGAIN!
Same routine - lift lid, blow out flame. Regain composure from freak-out.
(By the way, I was using air assist but perhaps not enough pressure - it could have possibly extinguished the flame as it went)

My lessons learned here -
Keep better job setting records either in Job Control or on paper. When I temporarily changed settings to cut the holes I did neither. And secondly, don't assume that something WON'T catch on fire just because you previously cut it without incident. I am SO glad I was watching the machine when I ran it and the material caught fire. I was able to avoid a real serious situation. When people on this forum say "it happened so fast" you have no idea what that means until it happens to you.

I also keep a spray bottle of water next to the laser in addition to a commercial fire extinguisher mounted on the wall next to the entry door.

I still plan on making more test cuts on the corrugated plastic - but the next times I will document the settings.

Chris J Anderson
03-20-2015, 1:16 AM
does the plastic contain pvc ?

Joe Pelonio
03-20-2015, 7:33 AM
Generally, no, it does not contain PVC, the brands I have used are polypropylene.
I have cut it too, without any flame, but use a lower frequency/ppi and 2-3 passes. The flames come due to the air inside the flutes which you don't have on solid products. I also use 25 lbs. of air assist to help blow it out, and yes, always watch your job run and keep a fire extinguisher handy.

Michael Hunter
03-20-2015, 11:59 AM
Corrugated cardboard can be a fire risk too - especially the triple walled stuff.
After cutting I inspect all the edges very carefully, as I have previously found it smouldering long after removing it from the laser.

Guy Hilliard
03-20-2015, 2:11 PM
Mayo;

For something to flame that quickly sounds like you were trying to cut it at a very high power, low speed, and out of focus.
Also check that your optics are clean.

Clark Pace
03-22-2015, 11:29 AM
Mayo;

For something to flame that quickly sounds like you were trying to cut it at a very high power, low speed, and out of focus.
Also check that your optics are clean.

I have not had any fires yet. And it cuts ok. I generally have to make a second lite pass as parts fuse back together a bit. I have not play much with the settings so this may not be necessary.