buildlog.net

Hi,

Wasn`t sure where to post, so here`s a new topic, perhaps folks could post places to find the tubes, sources etc.
I have found one company that sells them of course there are many more, but they seem to be on the affordable side for 60 - 70 watt CO2 tubes. It`s a Chinese company (Shanghai), so there`s the postage...depending where you live of course.
http://www.aliexpress.com/store/700768/ ... -tube.html
(no I don`t work for them or anything like that, not getting paid to promote anyone..."just incase", someone wants to start on that track, just a source and link to possibly assist)

Any other sources I`m sure would be welcome to constructors of this project.


All the best
Nik

Seems the default is set to DHL, switch to EMS and get about 1/3rd the price for shipping. And the minimum tube quantity is two, but I think I can find someone else to get one locally. I have been told that the more you order the better chance of them coming though intact.

My Experience...

DHL: Arrived Broken
FedEx: Arrived Broken
EMS: Not Broken. Arrived Faster than the others too.

They offer different tube diameters. What size would be the best at 70 - 80W ?

Beam dia or body dia? Body dia can hold more gas volume and may last longer on sealed tubes (just a guess). Larger beam is good for focus spot size, but you may need bigger optics.

The larger the tubes diameter the better. It will have more life due to a larger gas charge as pressure will remain more constant as gas is sputtered or helium leaks through the soft seals at the end. I doubt the bore diameter changes between OD sizes though.

Not quite sure just where the helium would leak to as the gas charge within the glass tubes is below atmospheric pressure.

Tweakie.

Helium will migrate through the seals, it does not care about pressure differential. At low pressures gasses act totally different at low pressures. Once it wanders out of the seal its never coming back. This can be seen is old soft seal helium neon lasers, almost none made in their heyday work today due to helium loss. Its also a reason that it is not recommended to sit on a bunch of these chinese glass tubes as they do have a shelf life.

I use helium for finding leaks in vacuum systems with my quadrupole mass spectrometer. It is incredibly sensitive, it will detect leaks down to 10^-13 atm/cc/sec pretty easily. It might be interesting to put a tube in a container and see how much it does leak.

Vacuum systems is another hobby of mine. I have one system with a 70 l/s turbo pump with 200 AMU rga and pressure reducer system. My other system I am building is for thin film deposition, 18" bell jar, 2.5kw 450khz RF Power supply, 6" Diffusion pump, crystal monitor, ferrofluid feedthoughs, the works. Will be able to do evaporative coatings, sputtering, PECVD, CVD.

Helium will migrate through the seals, it does not care about pressure differential.

Wow !! you may have just discovered a 'room temperature quantum effect' here - a low pressure gas migrating through a solid to a high pressure area.

Tweakie.

Things are not as solid as they seem. At the atomic level things are very open. Water molecules permeate and saturate through viton rubber seals, you can have gas pas through what you may think is solid metal due to the direction of grain in the material from forming. Teflon makes a terrible seal due to its porosity. Helium and Hydrogen are notoriously difficult tot keep in check. They will seep through just about anything. To them the epoxy that seals the mirrors on looks like swiss cheese. And thats why helium is used to leak check.

Pressure is just particles colliding with surfaces. Its not like there is a wall of molecules covering the surfaces saying you can not come out! Even at atmospheric pressure the mean free path is about 67nm which leaves all sorts of room for helium to pass by. If the atmosphere contained as much helium in the tube there would be no drop in helium because helium would migrate in at the same rate as it migrates out. But since helium does not naturally exist in the atmosphere (Another reason it used to check for leaks) any helium that does migrate though the seals is lost forever.

There has been some success in getting old laser tubes to work again by putting them in a bag full of helium and let them set for a long time.