Co2 Laser EXPLOSION!

[jeffreythe00]

Hey guys!

Just now I discovered that Co2 lasers and panes of glass dont mix... I really want to pass this along so that nobody else has the same mistake.

Below are photos of the aftermath so If you dont like to read skip ahead.

So anyway, I just got home from work and decided to break out my new co2 tube which I have not used for a month or more because I was in the process of moving when I bought it. After hooking it up and getting it warmed up I had a pane of glass from an old shelf that went into the trash. I decided to try and punch a hole through the glass. Well it wasn't working so I turned off the laser and examined the piece of glass.

The glass was slightly melted but nowhere near having a hole through it. Then something STRANGE happened. The glass made a very loud DING noise as if it was broken! Well to my surprise the small hole I put into the glass was now spider cracked! The strange thing was, It was only cracked where the hole was!

I decided to pick up the glass after it cooled a little and looked at the hole under some brighter light and noticed the spider crack wasn't even all the way through... Then.... A loud DING and the glass or practically EXPLODED in my face and the shards went EVERYWHERE! Glass on my dresser, in my dresser on my other dresser which I was nowhere near! Surprisingly I managed to get glass on the floor :thinking: (Just kidding!)

I am OK and I am glad I had my glasses on because I would have been hit in the eye otherwise! There is a nice big mark on the glasses where I got hit... and I am glad my hands are not cut because this exploded in my hands! I also think this glass was tempered because it didn't shatter like normal glass. Instead it made thousands of little pieces that are not too sharp.

Anyway, I sort of expected the glass to at least crack or break... just not explode like it did. It was almost as if someone blew it up in my hands! I really urge anyone who has a co2 laser or high powered laser that can damage/destroy glass to be very careful. You may not be as lucky as me!

Now excuse me while I clean this awful mess up!

 

[Flaminpyro]

get a new tube and keep going

 

[jeffreythe00]

get a new tube and keep going

Tube is perfectly okay. Im not so sure about the pane

 

[Meatball]

Sounds like a fun day! This is why having a small "chip" in your car windshield can be a big problem later on if its not taken care of.

Same Idea anyways...

A pane of glass under a CO2 beam absorbs a lot of energy. Glass doesn't like to heat up without expanding. And of course if you let it heat too much, it will not be the same "cured" crystal it was before. A small crystalline imperfection can "stretch" out and stress even smaller imperfections through a pane. I think tonight there was a resulting chain reaction because of this...

I'm you're alright, get your room cleaned up and get back to lasing!

 

[Flaminpyro]

Actually car window glass has a layer of plastic between the panes of glass so when it breaks it doesn't go flying all around like this pane did.
I suspect this was tempered glass like is used on the top of an office desk or for a shelf, it has two layers and that is why the cracks did not go all the way through, they only went as far as the first layer. since the layers are glued together stress was imparted on the second layer from the first through the glue joint, with time the stress built up till the second layer couldn't take it any longer and pop.

Many years ago I had the same thing happen to me, I had this pneumatic engraver and this old piece of glass was laying around it was a desk top piece. well me being me I thought it would be cool to drill a hole in the glass with the engraver, I thought it was a single pane of glass, well all started fine the glass was powdering under the carbide tip of the engraver I got to the half way point and noticed it felt different so I stopped and was looking at it and the little pile of glass dust around the hole, I decided to blow away the dust and when I did the whole sheet 4'x5' exploded in front of my face as I was blowing on it, what a surprise I didn't know my breath was so strong. The glass pretty much just layed there and didn't fly around but was now in 10,000 pieces, it was really cool to see as it started breaking at the corner I was working at and progressed across the sheet in an even wave to the far corner and it did this in about 250 mili seconds, scared the bejesus outa me at first then it was

 

[jeffreythe00]

Actually car window glass has a layer of plastic between the panes of glass so when it breaks it doesn't go flying all around like this pane did.
I suspect this was tempered glass like is used on the top of an office desk or for a shelf, it has two layers and that is why the cracks did not go all the way through, they only went as far as the first layer. since the layers are glued together stress was imparted on the second layer from the first through the glue joint, with time the stress built up till the second layer couldn't take it any longer and pop.

Right there I believe you are correct. I checked the glass and it seems it may have been two panes glued or melted together.

 

[ShortyInCanada]

2 panes with a layer sandwiched between and tempered glass.
Tempered glass is made by reheating regular glass and cooling it in such a way so that the outside surface layer of the glass is `tensioned'. It is under immense pressure and all it takes is to cause even the smallest imperfection in the smooth layer for the whole thing to fail. Did you know that the speed at which a crack in glass propregates is faster than the speed of sound and that is why it is so loud ?
Glass is also a super-cooled fluid.
I was just sliced open a couple of days ago by some of that fluid stuff too.

 

[Cyparagon]

if you let [glass] heat too much, it will not be the same "cured" crystal it was before. A small crystalline imperfection can "stretch" out and stress even smaller imperfections through a pane

Not to pick nits, but glass is an amorphous solid - it has no crystalline structure, which is precisely why it is so brittle. But yes, thermal stress is the obvious cause of failure here.

I was surprised to find that Wikipedia actually has an article on spontaneous glass breakage.

 

[icecruncher]

car windows

front is a laminate so you don't go through it on impact and it will hold together.
two sheets of pane glass with a plastic between

Side window are always tempered so that if they break they don't produce shards. Instead they crumble into nice little pebbles that go everywhere

All building glass within a few inches of the ground or so and door panes must be tempered depending on local codes. There are some ways you can use plate glass in buildings but it is very limited.

You also have Lexan which is often called bullet proof glass - that is actually a polymer.

 

[Things]

You need to be VERY careful when heating up glass, as exploding is a definite possibility. I had this same thing happen (But not with a CO2 laser). I was sitting something on a pane of glass and heating it up, and the glass just exploded.

It's all due to the thermal stress you're putting on the glass. When you heat it up, the area you're heating expands (and rapidly). This expansion can't go anywhere, because it's trapped within the rest of the cool glass. The thermal shock develops a small crack in the glass, then the pressure from the heated spot is enough to cause the glass to explode.

 

[Pieznice29]

I've done this quite a few times on accident, followed by on purpose...
I find that if I heat up a tiny spot on thin glass like that of a lightbulb for a few seconds with my 40W CO2 laser, the whole thing spontaniously shatters after a minute or 2 or cooling down.
If you watch closely (with goggles of course) you can see little tiny cracks forming and slowly spreading out over time... Until a large one forms and the whole thing falls apart. I'll have to see if I can get a picture/video one day of the effect.

 

[Xer0]

"Tempering creates balanced internal stresses which cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards. The granular chunks are less likely to cause injury."

 

[LSRFAQ]

Most things called "glass" adsorb 100% at 10 microns wavelength. If you look at room temperature glass with a thermal camera its jet black. I've used Co2 lasers to scribe annealed glass for cutting disks, but I learned to keep the focal spot small and the depth of cut tiny. Commercial CO2 are used to cut glass, but under controlled conditions.

Steve

 

[Flaminpyro]

I have cut my name in glass several times with our 15W Co2 laser I'm sure many others have also so this is a well known fact or at least it should be by now.

 

[Cyparagon]

Most things called "glass" adsorb 100% at 10 microns wavelength. If you look at room temperature glass with a thermal camera its jet black.

The glass must reflect some. Here's me in a regular mirror:

 

[LSRFAQ]

The glass must reflect some. Here's me in a regular mirror:



Is that a 3-5 micron or 8-10 micron camera?,

I think your cooled camera is just insanely more sensitive then the Raytheon TE-cooled Bolometer based camera we had. Although I could detect a squirrel at 300 yards, we only had 7 bit grayscale. But it was 640x380 and worked great.

Unless your defocused, or the grey scale settings were off, we should see some of the veins in your face, most of your facial details, and your nose should be somewhat black at 10u. Are we picture shy or is this low res?

Try a piece of copper circuit board, unetched. Makes a great mirror for thermal imagers, but I would not use it with a CO2 laser, not quite flat enough, and the copper oxide will cause it to burn.

Steve