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Pure Teflon taking heat.

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MikeT1982

Thu May 24 2007, 02:38AM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
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I have seen a few Tesla coil spark gap setups using teflon to hold the arcing electrodes, there are some on ebay right now. The white plastic part is 100% pure teflon not plastic. Thats impressive, if it can withstand that kind of heat!, I'm thinking I could use blocks of teflon with appropriate size drilled holes to hold my ruby rod at both ends,and even the ends of the quartz flashtube no? I will only be pulsing the laser once every 3 minutes or so, the thing will be it's air cooled and the tube will be taking 5600 volts from a 244uF bank so I don't know how hot it will get. Does anybody have experience with using teflon in applications like this?

Chris

Thu May 24 2007, 03:27AM

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The white plastic part is 100% pure teflon not plastic.

Teflon is a type of plastic.

I'd be careful using teflon (or any fluoropolymer) to hold a high powered spark gap. While completely non-flammable and more temperature resistant than many plastics, if it heats above decomposition temperature, which for PTFE starts around 350C, it will give off hydrogen fluoride and fluorophosgene gases. Needless to say, you do NOT want to be breathing those, they are very deadly.

...

Thu May 24 2007, 03:32AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
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It is somewhat common to mount the rod in a PTFE block, you should be able to get away with it.

For an estimate on how hot the tube will get, you have ~1kcal of energy in you cap bank, so you can heat a 10g sample of water 100degreesC.

kalenedrael

Thu May 24 2007, 03:34AM

Registered Member #5 Joined: Thu Feb 02 2006, 04:18AM
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Some kind of metal, perhaps aluminium, is a much safer and cheaper option. It is also much easier to work with. Teflon will change shape if you look at it the wrong way, while aluminium will not. You do not need an insulating material to hold the rod and flashlamp; just make sure that the two ends are electrically isolated. Any stiff, hard plastic would do well for a base, and keep the two supports isolated. If you are using a metal reflective cavity, be sure it is isolated from each support as well.

MikeT1982

Thu May 24 2007, 06:49AM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
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Cool, thanks guys! One question, after a single flash would it be safe to say that the tube "to the touch" would be under say 300 degrees farenheit, or do you think the outer envelope will be glowing hot? I know you said it could boil 10grams of water, I'm trying to think-convert this to outer tube temp, trying to get a feeling of what kind of beast i'm working with here....like the light will melt plastic on its own kind of craziness, or the surrounding chamber will just get warm type of heat...

I know the flash energy is about 3.9 kilojoules. Dick Anderson of Anderson Lasers whom I visited told me DONT DONT DONT flash the tube in the open. I'm just the kind of guy who wants to flash the tube without the case on it and without the rod in it to see how hot it feels and how bright a helical pumping lamp really is. He said whatever I do DONT flash the darn thing in the open LOL....maybe I can if I wear a welding helmet? I'm the type who loves to experience things so I can have a real perspective on them, sort of like touching a Tesla coil just to feel a few (million?) volts....

I may just end up being the first idiot who was blinded before their laser lased.

Steve Conner

Thu May 24 2007, 08:25AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, the big photo flash units used in studios can have over 1kJ of stored energy, and they are used to photograph people, and don't seem to burn their faces off or set clothes on fire. So I wouldn't worry too much. I still wouldn't risk looking directly at the lamp itself, though.

What Chris says about Teflon is correct, it will stand a lot of heat, but once you overheat it, it turns nasty on you. I've heard tales of fluoropolymer gaskets in car engines decomposing into hydrofluoric acid and causing nasty burns to someone taking the engine apart.

Dr. Shark

Thu May 24 2007, 02:38PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I once had makeshift ruby laser setup with a few kJ of flash energy, and I remember that it melted / blew off the aluminium foil that I used for the reflector (yes I said makeshift), feel free to extrapolate what would happen to your eyes in place of the foil. OTOH, intensity falls off with the square of the distance, so from just a few feet away and _not_ looking at the lamp, you would be safe.

I am very surprised someone sold you a helical flashtube for a laser, I thought they died out in the 1930s or so. While the light from a liner flash tube can be focused perfectly on the laser rod, you will probably loose a great deal of the light output. I can also imagine that the high inductance of the helix gives risetime problems, and unlike YAG ruby does not lase CW, so you do need a fast pulse.

One last note: A ruby laser absorbs its own light with the portions of the rod that are not pumped to the excited state, so you must mount the laser tube in a quartz envelope or so. Clamping the rod in a metal support as it is common with YAG will not do.

Carbon_Rod

Fri May 25 2007, 09:10AM

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Teflon is neat stuff... just remember to keep it away from birds as its rumored trace amounts (as mentioned above) are fatal to pet parrots etc. IIRC...

Ceramic laminated Styrofoam (5cm) seems to work for most weight restricted projects I have tried...

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