Water condensaton on focus lens. It happned!!

[Tech_Marco]

Remember that I told you guys to watch the temperature on winter? Cold is good but not too cold for a CO2 laser because of "thermo shock" may happne.
Well, today I want to share with you folks that I found another things about low temperature issue - it is condensation.

Last Saturday one of customer came from San Jose to test Pro 640 machine and I was the one to run demo for him. The speed and cutting power was impressed. He was amazed! BTW, he has a bad machine (I mean the machine is down now and I need to repair for him) bought from Jinan, Shangdong, China. You know I keep telling you folks not to buy machine made in Jinan. Most of those are junkies.

Anyway, the first couple tests weren't not so good. Lines went wider and burned darker. I guessed my power setting was set too high because the cutting speed and power % given by him was only good for his machine. And, his laser tube was dyning so power was much less than my new 40W tubes. I tuned my speed higher from 200mm/s to 4000mm/s to do cutting. And the power was set to 30%. It was still showing a lot over burned and charring was happening on the surface. Finally, I have to tuned it down to 8% which is consider the marginal triggering power for the laser tube! He was amazed that how fast the machine could run. But, he wasn't impressed with the result, though. I was wondering and scratching my head also. Then, I removed the laser head tip and looked at the focus lens. Wow There were water drops over the focus lens!! No wonder the beam didn't come up right regardless how hard I tried it. I cleaned it with Acetone with a cotton ball and gave it another try. The power was even higher after that. But the lines was still thicker and wider. We both know that it could be the focus point issue. Remember that I was using a 38.1mm focus lens so the focus point must be set right. After a few tests with my finger to press down the plywood I could find a good focus point. The result, , as you all can expect that was Super! Lines was very fine and less charring.

So, if your location is cold like 55'F or around, you may want to take the laser tip out and check the lens. Condensation may occur on the lens!

That's the tips I found for the day.


Marco

[laserdude]

It's not just temperature, but temperature and humidity. The technical term is dew point. Anytime an object is cooled below the dew point, condensation will form.

[Techgraphix]

At the dewpoint, all other metal- and glass-surfaces will have condensation too.. Did you notice any condensation on other surfaces? Did you had condensation on both ends of the lens or only at the downside? (airassist-compressor)
I thought that compressed air is more humid, that's why compressors are often equipped with de-humidifiers... So if nothing else was condensed but the downside of the lens, a de-humidifier could solve the problem.. Keeping your workshop at a more comfortable temperature too...

Kees

[Tech_Marco]

It was happening on the UP side of the lens but not the downside where air came from the air pump. I think the condensation happened when laser was firing to heat up air inside the barrel, then being cool off so moist condensed. The moist should be coming from the intake hole on top of the laser head.

Marco

[tansh]

It was happening on the UP side of the lens but not the downside where air came from the air pump. I think the condensation happened when laser was firing to heat up air inside the barrel, then being cool off so moist condensed. The moist should be coming from the intake hole on top of the laser head.

Marco

This phenomenon happens when the upper barrel (upside of the focus lens) air temperature is heated up when laser beam is firing. The air basically is stagnant inside. Hotter air carry more moist, and with the cold surrounding, condensation is waiting to happen when beam firing stop. To resolve this, purging air in the upper barrel is needed as well.

[DonL]

If you have air assist, it can cause this as well, more likely than being caused by the laser beam. When air is compressed, it gets hot, the air compressor has cooling fins to remove the latent heat, plus heat is removed as the compressed air travels down the air line. When it reaches the nozzel in the laser head, the compressed air is released, this causes a cooling effect that can lower the aluminium laser head temperature well below ambiant and even below the dew point causing condensation to form inside the laser head and inside the lense, the bottom of the lense and cone are usually dry because air is traveling past removing condensation, same with the outside of the laser head, it is moving in the surrounding air effectively drying it off.

An example of this effect is letting the air out of a large truck tire, after 2 or 3 min, the valve steam will frost up heavily even in 30 degree celcius weather, or those cans of compressed air for cleaning computers, as the gas expands, it cools and the can gets very cold.

N2 and O2 will cool upon expansion at room temperature.

If you turn off air assist, you will not see this happen unless it is very humid where the laser is and if it is that humid I recomend a dehumidifier as it will be bad for the electronics.

To test this, Use a lser temp gun and measure the temp of your laser head, or just feel it, then turn on the air assist and go have a coffee, come back in a few min and check the temp again and you should find it is colder, the more pressure in your air assist, the colder it will get, if you had 100 PSI, it would probably be covered in ice by the time you had a coffee.

And as Marco points out, in the winter, everything is cooler so it doesn't take much to drop below the dewpoint.