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Thread: Co2 Laser Re-Gas discussion

  1. #11
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    You apparently missed part of David's post:

    Quote Originally Posted by CountFunkula View Post
    We need more info. What kind of tube?
    The type of tube you are trying to re-pump is very important! You haven't answered this question yet.

    When describing the steps you took, you said you filled with CO2. Do you mean you used pure CO2, and not a gas mix? Because Steve's post clearly said:

    Quote Originally Posted by mixedgas View Post
    Diffusion Cooled RF lasers start with the ratio of 3:1:1 + 5%. (Helium, Carbon Dioxide, Nitrogen then add Xenon at 5% of best fill pressure.)
    So if you haven't tried this mixture (or at least the 3:1:1 He/CO2/N2 base mix, if you can't source Xenon), then that would be a good starting point.

    But note also that Steve had this to say about the exact mix:

    It is excitation, cooling, catalyst, tube and optics dependent.
    RF tubes get a different mixture that self catalyzes in a different way then DC tubes.
    So, again, the type of tube is very important. And thus far we have no idea what you are working with.

    Also, David asked about diagnostic data and/or instrumentation for the fill system. Mixing the gasses is tricky, and if you don't have good control over the process you can end up way off on the gas ratios. So here, too, we need more information on how you're doing this to be sure you have sufficient control.

    Or, if you don't care about getting it perfect, then you can continue to do what you've been doing. Admittedly if this is an inexpensive glass tube, you're already spending more money on the re-fill than a new tube would cost, so I can see why you might not want to get into the details. But doing things cheaply means you will have to live with the poor performance. The difference between 50% of rated output and 100% will be down to how well you can adjust the gas mix to match the tube's parameters.

    Adam

  2. #12
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    Default it is a sealed glass co2 DC exited tube

    Quote Originally Posted by buffo View Post
    You apparently missed part of David's post:



    The type of tube you are trying to re-pump is very important! You haven't answered this question yet.

    When describing the steps you took, you said you filled with CO2. Do you mean you used pure CO2, and not a gas mix? Because Steve's post clearly said:



    So if you haven't tried this mixture (or at least the 3:1:1 He/CO2/N2 base mix, if you can't source Xenon), then that would be a good starting point.

    But note also that Steve had this to say about the exact mix:





    Also, David asked about diagnostic data and/or instrumentation for the fill system. Mixing the gasses is tricky, and if you don't have good control over the process you can end up way off on the gas ratios. So here, too, we need more information on how you're doing this to be sure you have sufficient control.

    Im usin pre mixed 99.99999% pure gases in 9:23:68 %Ratio

    Or, if you don't care about getting it perfect, then you can continue to do what you've been doing. Admittedly if this is an inexpensive glass tube, you're already spending more money on the re-fill than a new tube would cost, so I can see why you might not want to get into the details. But doing things cheaply means you will have to live with the poor performance. The difference between 50% of rated output and 100% will be down to how well you can adjust the gas mix to match the tube's para

    Any advice welcome

    Adam
    So, again, the type of tube is very important. And thus far we have no idea what you are working with.

    Glass Dc exited cheap chinesse laser tube

    Also, David asked about diagnostic data and/or instrumentation for the fill system. Mixing the gasses is tricky, and if you don't have good control over the process you can end up way off on the gas ratios. So here, too, we need more information on how you're doing this to be sure you have sufficient control.

    Im usin pre mixed 99.99999% pure gases in 9:23:68 %Ratio

    Any help , advice welcome,

    btw I know those lasers are cheap to be re gassed, but i managed to source all parts to start assembling, filling and aligning the tubes myself so i want to start doing this, as there is no local source for these tubes.

    Thanks

  3. #13
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    Quote Originally Posted by sinfocomp View Post
    Glass Dc exited cheap chinesse laser tube
    Got it. Do you know if the tube incorporates a catalyst to re-combine the carbon monoxide and oxygen that are formed by the arc? And if so, is it a heated catalyst?

    If the tube does not have a catalyst (or if the catalyst is fouled), then you are probably getting a performance reduction from the CO2 disassociating. I've read about additives to the gas mix (water vapor, or extra CO and O2) that can speed up the re-combination process, but I have no data on exactly how much to use for a given tube...

    Im usin pre mixed 99.99999% pure gases in 9:23:68 %Ratio
    I'm assuming you mean 9% CO2, 23% N2, and 68% He.

    In that case you're in the ballpark, but you are not at the ideal values for standard DC-excited tubes. (Sam's Laser FAQ lists the ideal mix at 9.5% CO2, 13.5% N2, and 77% He.)

    Note that the mix Steve posted above was for an RF-excited tube that gains additional cooling via diffusion across the long metal electrodes that run down the length of the tube. But that doesn't apply to your style of tube.

    Given that the mix you are using is a bit low on Helium, over-population in the E2 level might be limiting your power by preventing re-excitation of some of the CO2 once it has lased. (Helium helps to quench the E2 state back to the ground state.) Helium also aids in heat transfer, so this could be changing the thermal characteristics of the tube. (Which would be even more important if the tube has a hot catalyst.)

    Then too, while the Nitrogen is important because it remains in the excited state for a long time and is also efficient at transferring energy to CO2 via collisions, your mix has more than twice as much Nitrogen as CO2. That's probably hurting your output as well, since all that excess excited Nitrogen does you no good.

    I know those lasers are cheap to be re gassed, but i managed to source all parts to start assembling, filling and aligning the tubes myself so i want to start doing this, as there is no local source for these tubes.
    If you can source different gas mixtures, you might try one that has less Nitrogen and more Helium. However, I suspect that the cost of obtaining a custom mix of gasses (apart from what you already have) might end up being more expensive than the cost of a new tube. Unless you plan to try mixing them yourself, that is...

    Adam

  4. #14
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    Default will get the new mix

    Quote Originally Posted by buffo View Post
    Got it. Do you know if the tube incorporates a catalyst to re-combine the carbon monoxide and oxygen that are formed by the arc? And if so, is it a heated catalyst?

    If the tube does not have a catalyst (or if the catalyst is fouled), then you are probably getting a performance reduction from the CO2 disassociating. I've read about additives to the gas mix (water vapor, or extra CO and O2) that can speed up the re-combination process, but I have no data on exactly how much to use for a given tube...



    I'm assuming you mean 9% CO2, 23% N2, and 68% He.

    In that case you're in the ballpark, but you are not at the ideal values for standard DC-excited tubes. (Sam's Laser FAQ lists the ideal mix at 9.5% CO2, 13.5% N2, and 77% He.)

    Note that the mix Steve posted above was for an RF-excited tube that gains additional cooling via diffusion across the long metal electrodes that run down the length of the tube. But that doesn't apply to your style of tube.

    Given that the mix you are using is a bit low on Helium, over-population in the E2 level might be limiting your power by preventing re-excitation of some of the CO2 once it has lased. (Helium helps to quench the E2 state back to the ground state.) Helium also aids in heat transfer, so this could be changing the thermal characteristics of the tube. (Which would be even more important if the tube has a hot catalyst.)

    Then too, while the Nitrogen is important because it remains in the excited state for a long time and is also efficient at transferring energy to CO2 via collisions, your mix has more than twice as much Nitrogen as CO2. That's probably hurting your output as well, since all that excess excited Nitrogen does you no good.



    If you can source different gas mixtures, you might try one that has less Nitrogen and more Helium. However, I suspect that the cost of obtaining a custom mix of gasses (apart from what you already have) might end up being more expensive than the cost of a new tube. Unless you plan to try mixing them yourself, that is...

    Adam
    Thanks for your reply and explanation of the gas interaction process in co2 laser

    i have two type of tubes, one that has a catalysing coating inside the tube bore, and one that has no catalyzer at all, the one that has catalyzer is getting 80 out of the 100watts rated at, while the one
    with no catalizer is getting 28 out of the 40 rated watts.

    the catalyzer coat is in the cavity bore itself, i will post some pictures of the tubes.

    i will get the new gas mix and get back to you, the custom gas mix cost is gas dependant, the current mix cost $150USD and since i have invested well over 10k on this proyect another 150 wont hurt as much as a failed proyect.

  5. #15
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    Default

    Something else to consider is the possibility of sputter from the tube electrodes getting on the optics. Not much you can do about that, unfortunately, with sealed optics and all, but if you see evidence of that it would definitely be a cause of reduced power output.

    If the catalyst is fouled there may be a way to clean it. (Pictures should help) I'll defer to Steve or David on how to best clean it, however!

    $150 for a custom gas mix is actually better than I expected. Please post your results with the new mix.

    And if you're interested in the physics behind the tube operation, Sam's Laser FAQ has a huge section on CO2 lasers with lots of good info.

    Adam

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    Default pictures of re gas

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ID:	54593Here you can see the vacumm controller im using, the tube under test, the test current, and the measured power, also i have included a picture of a tube bore that has the catalyst in it (pinkish coating)


    also, as i turned the laser on to take the pic i found that after a few hours of standby it is now putting out more power than freshly filled.

    any toughts ?

    Click image for larger version. 

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  7. #17
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    When refilling I mix my own gases for precisely this reason. You really cannot diagnose the problem with just two gas mixes. You may also need an electrode activating sequence or have cheap electrodes that are good for only one process session that died when their barium/calcium activated inner surface hit air again.
    ~

    I can't tell what you may have done wrong, too many variables. Co2 laser tubes have to reach a gas equilibrium, rarely do they "clean up" on the first run, and they can take hours to stabilize. You may not have enough trace gas, you may not have baked out or hot flushed the tube enough, you may need to run ultra pure oxygen at very high current density to clean and activate certain copper - aluminum alloy based cathodes, noting that O2 poisons most other types.
    ~


    Steve.
    Last edited by mixedgas; 09-24-2018 at 11:30.
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    Default gas mixing setup

    Quote Originally Posted by mixedgas View Post
    When refilling I mix my own gases for precisely this reason. You really cannot diagnose the problem with just two gas mixes. You may also need an electrode activating sequence or have cheap electrodes that are good for only one process session that died when their barium/calcium activated inner surface hit air again.
    ~

    I can't tell what you may have done wrong, too many variables. Co2 laser tubes have to reach a gas equilibrium, rarely do they "clean up" on the first run, and they can take hours to stabilize.
    ~


    Steve.
    what would be the way to setup a gas mixing rig ?
    and how do you measure each gas going into the mix ?
    i would buy separate gases if needed

  9. #19
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    Gas regulators designed for UHP gas service, bellows grade sealed vacuum valves, flow restrictors on each gas line on the low side so the "regulators" do not go to wide open flow into the vacuum and explode., capacitance manometers and TC Gauges. You need cold traps on your pumps and plasma traps to keep plasma out of the manifold. The whole manifold has to be baked to minimum of 250'c without ruining the gauges which need to stay cold. . Did I mention the RGA again? Cajon fittings with silver plated gaskets for all tubing.. Introducing water vapor has to be done by thermally outgassing a sorbent, spraying water into the vacuum will cause the water to instantly freeze.

    ~
    If you have spent 10k$ now, you are only half way there. My station parts came out of a bankrupt tube factory, otherwise I could have never afforded it.The tubes I process run at 18 to 60 amps, so my setup has many differences from what you want. If your gasses do not start at 750$ a bottle, you probably have the wrong gas supplier.

    ~
    How I pulse my gasses without needle valves in took me years to perfect, that detail goes to my grave. In your case that means bellows driven micrometer needle valves and dozens of feet/meters of ultra small bore SS. gas chromatography tubing to limit flow. If your valves don't come with rebuild kits, you probably have the wrong valve.

    ~
    In your case with Chinese tubes you may need to heat the electrodes or over current the tube, which is tricky or may need an induction heater. You may need a heavy inert gas such as neon or argon to clean the tubes. You need a tube oven, too..~So NE, Co, H2O, N2, He, co2, and maybe h20 and o2 on station. A pinch tool for metal seals is another $3200 these days.
    ~
    I had an Angel Investor who needed to learn to pump tubes. My wages for developing the project was my own station. Pro tip: Pure nitrogen or air running on its own in a glow discharge generates large amounts of excess heat and "Nitrides" or corrodes most electrodes.
    ~
    ~
    For those really old tube designs your running:


    Carbone, R. J., IEEE J. Quant El, QE-3, 373, 1967.
    Carbone, R. J. IEEE J. Quant El, QE-4, 102, 1968.
    W. J. Wittemann, “Sealed-ff high-power CO, lasers,” PhillipsTech Rev., vol. 28, pp. 287-296, 1967.
    Steve
    Last edited by mixedgas; 09-24-2018 at 12:33.
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  10. #20
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    Quote Originally Posted by mixedgas View Post
    Gas regulators designed for UHP gas service, bellows grade sealed vacuum valves, flow restrictors on each gas line on the low side so the "regulators" do not go to wide open flow into the vacuum and explode., capacitance manometers and TC Gauges. You need cold traps on your pumps and plasma traps to keep plasma out of the manifold. The whole manifold has to be baked to minimum of 250'c without ruining the gauges which need to stay cold. . Did I mention the RGA again? Cajon fittings with silver plated gaskets for all tubing.. Introducing water vapor has to be done by thermally outgassing a sorbent, spraying water into the vacuum will cause the water to instantly freeze.
    ~
    If you have spent 10k$ now, you are only half way there. My station parts came out of a bankrupt tube factory, otherwise I could have never afforded it.
    The tubes I process run at 18 to 60 amps, so my setup has many differences from what you want. If your gasses do not start at 750$ a bottle, you probably have the wrong gas supplier.
    ~
    How I pulse my gasses without needle valves in took me years to perfect, that detail goes to my grave. In your case that means bellows driven micrometer needle valves and dozens of feet/meters of ultra small bore SS. gas chromatography tubing to limit flow. If your valves don't come with rebuild kits, you probably have the wrong valve.
    ~
    In your case with Chinese tubes you may need to heat the electrodes or over current the tube, which is tricky or may need an induction heater. You may need a heavy inert gas such as neon or argon to clean the tubes. You need a tube oven, too..
    ~
    So NE, Co, H2O, N2, He, co2, and maybe h20 and o2 on station. A pinch tool for metal seals is another $3200 these days.
    ~
    I had an Angel Investor who needed to learn to pump tubes. My wages for developing the project was my own station.

    Pro tip: Pure nitrogen or air running on its own in a glow discharge generates large amounts of excess heat and "Nitrides" or corrodes most electrodes. For those really old tube designs your running:1

    Carbone, R. J., IEEE J. Quant El, QE-3, 373, 1967.


    Carbone, R. J. IEEE J. Quant El, QE-4, 102, 1968.


    Steve
    this is the most valuable part of your comment:
    Pro tip: Pure nitrogen or air running on its own in a glow discharge generates large amounts of excess heat and "Nitrides" or corrodes most electrodes.

    trust me, i have done things that no one belive posible with trash equipment, i will find a least expensive way of doing it, since im already $10k into it and BTW the 10k is doing what most people do with 100K, so no problem,

    Thanks for the tip

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