Purging during evap brazing?

[slavic1705]

Can someone please explain the pros and cons of purging while you braze you evap. :confused:

Thank you! :banana:

[the_new_guy]

no cons

purging prevents oxidation in the evap

[johann]

no cons

purging prevents oxidation in the evap

There is one con, not everyone has purging equipment

[SustaiN]

Soem who have tried it find that the evap is more clean when purging with propane instead of nitrogen but purging with propane can be dangerous. I did it myself but if you don't feel comfortable with it I wouldn't recommend it.

[slavic1705]

Thanks for the replys! I am currently looking for someone local that can rent me a can of nitrogen seeing how I don't want to blow my self up.

[Bergo]

I use Argon to purge while brazing, anyone know if this has any added benefit over purging with nitrogen or propane? I know the argon is a bit more expensive (here in Canada anyway) but i"m not really paying for it

[the_new_guy]

they use argon with tig welder i think

[Stewie007]

Soem who have tried it find that the evap is more clean when purging with propane instead of nitrogen but purging with propane can be dangerous. I did it myself but if you don't feel comfortable with it I wouldn't recommend it.

That's hogwash... propane purging is not more effective... plus it can add unwanted residue that you can't see because it doesn't turn black. Dry nitrogen does not.

So it is not dangerous like propane, and it is actually cleaner...

[Bergo]

new guy: correct, Fathers owns a mobile welding company. free argon. :D they use robotic tungston inert gas welders to run titanium piping among other things, the robotic welders are pretty cool, and they use x86 based mobile computers to run them.

[Coyote]

stewie, do you actually do some research before flaming on using propane as a shield gas??

propane, is a hidrocarbon, in presence of oxigen (from the oxidized copper) + heat, the propane steals the oxygen from the copper. so it is better than just using nitrogen or other inert gas.

its chemistry dude, you cant fight that.

[slavic1705]

Is there some reason why everyone uses the cap tube as an inlet for your purging gas. It seems like if you used the suction line as your inlet the cap would be a good restrictor in order to allow just enough movement of the gas, but what do I know that's why I'm asking.

[ayrtonsenna]

you are less likely to get a flash back when purging through the cap tube, when using propane.

[slavic1705]

you are less likely to get a flash back when purging through the cap tube, when using propane.

So if I use nitrogen I can use either the captube or the suction line. It just seems like the suction line would be easier to hook up.

[ayrtonsenna]

i dont see why not.

[Stewie007]

stewie, do you actually do some research before flaming on using propane as a shield gas??

propane, is a hidrocarbon, in presence of oxigen (from the oxidized copper) + heat, the propane steals the oxygen from the copper. so it is better than just using nitrogen or other inert gas.

its chemistry dude, you cant fight that.

Lets go over the idea of purging, since some of us obviously think that a properly purged system will form oxidation. The idea of purging with nitrogen is to push all oxygen out of a system. You hook up your nitro, let it flow, allow time for proper penetration of the system and begin brazing. No oxygen, means no oxidation. The tubes come out clean, as shiny as they were when you put them on; I have tested it many-a-times and it works. Propane would equate the same results, but is far more dangerous. It does not need oxygen to combust; heat is plenty enough. I remember a certain Praxair plant where explosion after explosion of sealed tanks of various different flammable gasses occurred. That explosion occurred BEFORE exposure to oxygen. Only heat.

The only thing that allows for you to be lucky enough not to burn yourself is the fact that you're dealing with low pressure.

But try brazing when your propane tank is almost empty, and the outgoing pressure drops to a point where flashback is possible. The results could be serious. Plus, extreme heat also causes other reactions with that propane that do not involve oxygen. Nitrogen is inert.... so its pretty clear.

I've been professionally trained, and use this in the industry and it has been proven that it works. What are your credentials?

[Coyote]

a piece of copper is oxidized even before starting to braze it, remember, the atmosphere is full of oxygen.

shielding with propane or any other hydrocarbon, not only shields as good as nitrogen, but it also converts previous oxidized copper back into copper. something you cant do with nitrogen or any other inert gas.

you use the cap tube to regulate the propane flow, theres no way you can have a flashback going through the cap tube.

It does not need oxygen to combust

are you real for that??? my god, where you got your credentials from??

you can have an explosion, caused by heat, but that doesnt mean theres no oxygen present.
get a 200bar cylinder, heat it up, pressure raise, cylinder explodes. flammable gas gets in contact with all the oxygen it needs from the atmosphere, and with just a little spark, you have a nice fireball. but no oxygen?? sorry mate, you are talking nonsense.

shielding with propane is simple, you use the cap tube to regulate flow as in a phase change unit. flow is really low, you can actually light the propane right of the cap tube and it wont be dangerous.

your posts are full of fear, bits of information, but no logic at all.

shielding with propane isnt more dangerous than cooking with a stove. but i guess you must have an electric one ...

i dont need any credentials, i think ill do fine with knowing what im talking about. i think its called chemistry.

[wdrzal]

If your using dehrdrated copper,as you should, there is NO oxidation since it comes shipped filled with a inert gas.

The danger comes from guys not being aware of the dangers, how many guys just learning how to braze, burnt or caught somthing on fire while admiring their work,instead of keeping a eye on the flame. what if you burnt the hose the propane was flowing thru, just 1 example of what could happen.

[hatemi]

It is better to purge through the capline because you dont want to rise the preasure inside the evap while brazing. That way the gas has an easy way to excape from there and the filler metal can get to the joints without any bubles and leaks.

Good point there Walt :)

[Coyote]

If your using dehrdrated copper,as you should, there is NO oxidation since it comes shipped filled with a inert gas.

thats correct for the pipes, but the evap is another story. and if you touch it its even worse. so having it completely clean, its a nice start.

The danger comes from guys not being aware of the dangers, how many guys just learning how to braze, burnt or caught somthing on fire while admiring their work,instead of keeping a eye on the flame. what if you burnt the hose the propane was flowing thru, just 1 example of what could happen.

well, like it or not, brazing has its risks. ppl with experience avoid them (most of the time), n00bs get burned.

the hose flowing with propane might be dangerous, but if someone is careless enough to do that, it migth also burn the hose that goes to the torch.

fear doesnt help at all, but you need to know the risks and be carefull.

[bh2k]

*starts a fight in every thread*...

[yngndrw]

If your using dehrdrated copper,as you should, there is NO oxidation since it comes shipped filled with a inert gas.

Alittle off topic, but I dont think it's worth a new thread just to ask this:
If say you was to buy 15 meters of tube, but only used 5 meters, how should the remaining 10 meters be stored ? Are you ment to refill it with an inert gas and crimp the ends before storage or what ? Because otherwise you would end up with oxidation inside the pipe when you come back to use it.

[wdrzal]

Yep, if your going to be useing it within 12 months you can just put the caps on or crimp it shut.. I usually blow the air out with nitrogen then put the caps on it keeps well like that. ............your actully just getting a little tarnish from the o2. its when the tube is heated and 02 is present that big flakes of oxadized material form.

[yngndrw]

Oh okay then, cheers. :)

[Stewie007]

Coyote.... never did I say anything more than explosion. But in the purging case, the possibility is generally flashback. You can argue all you want, but if that happens, you wouldn't be around to argue with me about it any more. In fact, I'd see to it that you were placed in the Darwin Awards for thankfully removing your genes from the gene pool.

Jesus wannabe.... I will say what I want when confronted with a method of absolute idiocy such as this. Purging with flammable gas. You might as well use plastique as a patch for a leaky tire. BOOM! Oops... The guy on that web forum told me it was safe....

Sorry, but the idea behind purging with propane is stupid. It also does not hold up to know-it-all theory that it works better than nitrogen purging, or any inert gas. It does not. Quote redox, quote whatever kind of science you want. Without oxygen, there is no oxidation. I don't care WHAT you're purging with.

And yes, propane can explode, key word explode, without oxygen. You read too much into it when you think I care about what happens after the initial pop. You wouldn't be around after that anyways. But go ahead if you want. Compromise your safety because you're cheap. You won't argue so passionately that its perfectly safe when an accident happens to you. I only mean to discourage potential on lookers and lurkers trying to learn from using this method as it is dangerous.

[Cpt Twitchy]

*starts a fight in every thread*...
QFT

[afireinside]

Here comes the safty police...

[Stewie007]

Whatever.... Just a buncha bull headed geeks... not like I can stop you anyways.

[aussie_guy00000]

I think from now on as soon as I see someone mention purging with propane, i'm gonna head for the hills.

[Cpt Twitchy]

Stewie its not that you don't have good points but you come across in such a way that you turn many away and they don't wanna listen to you. Your ideas could be much more helpful if u didn't attack everything.

[Carlz0r]

Purge. I went cheap and didn't purge mine. Guess what? Now I have to get some new parts for my evap. Copper oxidized so badly inside that the evap blew open during a pressure test.

[godmod]

evap bottom plate must have been too thin. cant be just because of oxidation imho

[aussie_guy00000]

Purge. I went cheap and didn't purge mine. Guess what? Now I have to get some new parts for my evap. Copper oxidized so badly inside that the evap blew open during a pressure test.

:eek: What pressure did you test it too??, it's more then likely what godmod said is the case

[Carlz0r]

It was the evap shell that blew open, for lack of a better word, and I don't think it was too thin as chilly1 himself supplied me with it. I pressure tested at 150 psi. It held for about 15 seconds and then tore open.

[jinu117]

It was the evap shell that blew open, for lack of a better word, and I don't think it was too thin as chilly1 himself supplied me with it. I pressure tested at 150 psi. It held for about 15 seconds and then tore open.

Over heated and weakened it probably. Or solder ate through evap... it happens when you over heat. Gotta keep the flame moving constantly around to keep temperature around even while brazing to do so. It was hardest brazing for me to get used to myself too. Ate through total 3 or 4 evap till I got it down right. (never got hang of harris #8... bleh... using silver 45 do help a lot on this account though)
Now it is easy for me but occasionally, I do make mistakes. Few things to make sure...
1) Clean, clean, clean some more.
2) Give wide spacing around when brazing evap as I am constantly circling around it.
3) Don't use TOO much silver solder. And when cleaning afterwards, don't use things like dremel lol. Best way to introduce micro leak that are found later (sometimes after a day or two of leak test)
I usually make few evaps at a time, let them sit in water @ 175 PSI for few days before brazing it shut, etc for later use.

[wdrzal]

It was the evap shell that blew open, for lack of a better word, and I don't think it was too thin as chilly1 himself supplied me with it. I pressure tested at 150 psi. It held for about 15 seconds and then tore open.


can you post a pic, a lot can be learned by determining how and why the faliure happened.

[Carlz0r]

can you post a pic, a lot can be learned by determining how and why the faliure happened.
After reading jinu's post, it might have just been me not moving around, as I had it heating in one spot for quite a while on a leak I had found. If I had a camera I'd take a pic.

[epion2985]

Quote redox, quote whatever kind of science you want. Without oxygen, there is no oxidation. I don't care WHAT you're purging with.


I dont think he ever sugested there would be. He said the copper is already oxidized long before you got to it because we do have oxygen in the atmosphere after all. And the presence of a hydrocarbon such as propane for example converts previous oxidized copper back into copper.

So no propane does not shield any better. But yes propane will convert the already oxidized copper back in to copper.

[Thrilla]

So no propane does not shield any better. But yes propane will convert the already oxidized copper back in to copper.

Quick question not worth a new thread: if I soak my evap and some copper tubes in liquid propane or have propane blowing on them the oxidization will just go away?

[Carlz0r]

Quick question not worth a new thread: if I soak my evap and some copper tubes in liquid propane or have propane blowing on them the oxidization will just go away?
Only if it's burning I think.

[Thrilla]

I think burning only speeds up the chemical reaction :P
I'll ask my chem. teacher see what he says, lol I fear propane.

Will argon (or liquid argon under some pressure) work?

[epion2985]

I think burning only speeds up the chemical reaction :P
I'll ask my chem. teacher see what he says, lol I fear propane.

Will argon (or liquid argon under some pressure) work?

Do not fear propane, fear ignorance. If you think things though you will stay safe.

I do not belive argon is a hydrocarbon, so no.

[godmod]

NOT only if its burning!
it should not burn! it is just burning at a outlet...
inside the evap the reaction starts when its just hot enough.

imagine, if it would be burning inside, there would be sone reaction between oxygen and propane and this could let the copper oxidize too...

[Unknown_road]

Quick question not worth a new thread: if I soak my evap and some copper tubes in liquid propane or have propane blowing on them the oxidization will just go away?

liquid propane????? big propane cloud forming and boom!!

And no it will not cause the oxidation too go away. oxidation goes away because the propane "falls apart" due to the extreme heat. The "parts" take the oxygen atoms to become stable molecules again.

Lots of people here should just get an inert gas for purging or else their will be a major accident soon.

[epion2985]

liquid propane????? big propane cloud forming and boom!!

And no it will not cause the oxidation too go away. oxidation goes away because the propane "falls apart" due to the extreme heat. The "parts" take the oxygen atoms to become stable molecules again.

Lots of people here should just get an inert gas for purging or else their will be a major accident soon.

Alot of people here purge with propane, the risk of flashback though a capillary is much much less then you getting killed in a car crash going to work/school. So if you want to avoid such small risks then you should also avoid the bigger once, logicaly... So stop driving or using public transportation. Dont use stairs because thats also a much bigger cause of death. What else are you going to stop doing to avoid a risk? If you want to avoid such small risks there are alot bigger risks you are neglecting, so it doesnt make any sence to avoid the smaller once if you still dont the bigger once.

In my expirience 99% of accidents happen to people who dont think things though. So if you dont have much mental capacity then sure I agree, dont use propane. But if you have a good head on your shoulders then these is less to worry about then you choking on your dinner roll...