Is it necssary at some point to warm up a glass CO2 laser tube?

[Doug Fisher]

The recent extreme arctic blasts in the US have meant the unheated area of my basement where my laser resides has reached new low temperatures. Is there a temperature point at which we need to worry about thermal shocking a glass CO2 tube? I have set my chiller to maintain around 18 degrees C year round, but there have been times over the last couple weeks where my water temp has been right around 12 degrees when I went to start up the laser.

Like most smaller chillers, my CW5000 chiller does not incorporate a heater in it. Hopefully it isn't an issue at these temps, but IF thermal shock at the temperature range discussed above is actually an issue worth worrying about, I was thinking maybe relatively gentle heating of the tube could be accomplished by writing a design/program file that fires the laser at the minimum percentage required to fully light the tube for a certain amount of time. For example, 11% power at 1 mm per second speed for maybe 5 minutes? Or maybe stair-stepping it at 11% for two minutes, then 13%, then 15% for two minutes or whatever?

Insights would be appreciated. Thanks.

[Bert Kemp]

Thats a good ? and I really don't know.My thinking on this tho tells me it probably would not be a problem. I would let the water pump thru a while before firing the laser. But like I said I don't really know.

[Kev Williams]

... I was thinking maybe relatively gentle heating of the tube could be accomplished by writing a design/program file that fires the laser at the minimum percentage required to fully light the tube for a certain amount of time. For example, 11% power at 1 mm per second speed for maybe 5 minutes? Or maybe stair-stepping it at 11% for two minutes, then 13%, then 15% for two minutes or whatever?.

Or, you could rig up a cheap bandaid like I did ...
chiller.jpg
I had this coiled up copper tubing in sitting around, so I took it, and a storage container, cut the incoming water line from the tube and connected the ends to the copper tubing. But I have the exact opposite problem you have, water's too warm... I'm using a 3000 chiller on my 80w Triumph. For 10 months of the year it's fine because I can keep the garage shop about 68°. But those other 2 months I struggle to keep the garage below 82°. When my water gets to near 25°c, I just put a few gallons of water and a little ice in the container and it'll keep the temp below 22 for a couple of hours.

--in your case, you would just use warm water... takes only a few minutes for chiller water to raise (or lower) several degrees.

[Nick Hale]

I always get my cooler to atleast 50F before i use it. I'm too scared to shatter my tube. What I planned on doing if I could not get my room temperature high enough. Was to put a space heater next to my cooler and let it heat the water in the tank up slowly.

[John Lifer]

My chiller reads a temp of 12 to 15 degrees most mornings this time of the year. I start the chiller and it cycles at least 5 minutes before I laser anything. So far, in probably 6 months of this, no issue. Summer Temps are about 18 at start of the day.

[Doug Fisher]

Thanks for the replies!

[Dave Sheldrake]

It's a strange problem with thermal shock and DC lasers (water cooled versions)

The problem comes from temperature change / time in most cases.

Start up at 12 degrees won't be a problem unless the tube/coolant is at a far higher temperature than that when the fluid starts to cycle. If say the tube glass is at 75 C and you dump water through it at 10 C it's probably going to shatter, the same the other way, if the tube is at 10 and you fire 70 degree water through it, it's probably going to shatter.

The problem is the ends of tubes are subject to some pretty savage heating when the tube fires so tube type will also be a factor. To be honest the bigger danger will come from the temp change affecting the epoxy they use to bond the jackets on to some tube types (cheaper tubes)

Short version? starting up with the water at 12 so long as the rest of the tube isn't already hot won't be a problem (I've started a few of mine with the water at 6 - 8 and had no problems) (my chillers are all set to a base line of 15 degrees)

ps: Johns idea will work well, run the chiller for 5 minutes before you start the machine, on mine the chillers are never turned off and run 24/7 even if the machines aren't running as the pumps put a little bit of heat into the water

[Doug Fisher]

Thanks, Dave. The chiller, water, tubing and laser tube are all in the same room, so at startup they are all within a degree of each other. The specs at EFR's website say the 80W F2 Series tube's "Operating Condition" is "Standard water temperature: 10-40C" and "Ambient temperature: 2-40C." Hopefully as long as can keep it at 10C or above (chiller kicks on at the target temp of 18 degrees C, +/- 1 degree) the epoxy will hold up!