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Strength Of A Brazed Joint Under Pressure?

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Strength Of A Brazed Joint Under Pressure?

Unread postAuthor: cammyd32 » Wed Apr 04, 2012 4:11 pm

Hello folks! so, I have found myself in a situation where I shall need be doing a lot of brazing for parts of my next contraption. (One that I can actually afford!)

So my question is, how well do brazed joints hold up under pressure? It won't be in anything extremely reliant on the braze material, but It'l be used like a 'strong glue' for pretty much most of the pressure joints in my gun.
Also for those with knowledge of this stuff: http://www.spudfiles.com/forums/durafix-alumaloy-t23846.html I would love to know anything about it's performance in spudding situations, as I really think that I'm probably going to be going for this stuff, seeing as I'm using a mix of aluminium and steel.

Thanks all, and any help is really appreciated.
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Unread postAuthor: Fnord » Wed Apr 04, 2012 5:07 pm

Brazing or 'hard' solder are required in the refrigeration industry because of their superior bond. I can't really say for sure if it'll work for what you're doing, but as long as you use the proper flux and allow for plenty of surface area contact it should be sufficient. Technician uses it on his cannons, so you might want to talk to him.


Alumaloy won't stick to steel. You *might* be able to get it to stick by first 'tinning' the steel with solder or braze.
I have not used it in a spudding application yet, but from a few other small projects I can tell you the bond is quite strong. I would only worry about using it where rapid dynamic loads and heavy vibration are factors (i.e. an engine).
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Unread postAuthor: Technician1002 » Wed Apr 04, 2012 5:10 pm

I don't know about brazing aluminum, but brass and steel works well. My QDV cannons with steel tanks are brazed.

2 inch valve and fill port are brazed.
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Unread postAuthor: cammyd32 » Wed Apr 04, 2012 5:30 pm

Ahh that's great, thanks for that, those are the kinds of situations I would be using it in. And seeing as it wouldn't be exposed where any kind of vibration factors are concerned I believe that it should work perfectly. Just one last question though, I'm intending to use brazing to help me construct some 'end stops' for pipe. Basically by getting a steel rod that has the same od, to the pipes id, and cutting a 1-2 cm portion off it and brazing it in at the end, would this work with brazing?
Once again, thanks for the help all, and any further help would be really well appreciated.
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Unread postAuthor: jsefcik » Wed Apr 04, 2012 6:15 pm

braze joints hold up very well, even when you braze simple copper pipe, it can withstand pressures alot higher then regular solderd joints
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Unread postAuthor: Gippeto » Wed Apr 04, 2012 9:12 pm

Brazing brass and steel is fine. Brazing copper plumbing pipe isn't so good.

The temperatures required for brazing will anneal drawn copper and reduce it's safe working pressure. This isn't an issue when you're talking "refrigeration" because the tubing in a fridge is already annealed.

Best solder for drawn copper is 95/5 Tin/Antimony. Joints up to 1" are rated for 1090psi.

Might be worth having a look at pg 28 of the copper tube handbook. Note the working pressure of brazed copper joints at the bottom of the page. :)

http://www.google.ca/url?sa=t&rct=j&q=& ... wB3yLmPGBQ
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Unread postAuthor: Technician1002 » Wed Apr 04, 2012 11:21 pm

Another reason silver brazing solder is used in refrigeration is cleanliness. No flux is required so the joint can't shed flux to plug up filters, contaminate oil, and plug capillary tubes or expansion valves. Strength is not the only consideration when choosing connections for freon. A sealed system does not get regular oil changes so it must be sealed clean.

Solder for copper requires flux. This is OK where it can be removed. Bad when it remains sealed inside a system.
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Unread postAuthor: cammyd32 » Thu Apr 05, 2012 4:45 am

Thanks for the link and info all, but I am tending to steer away from using copper pipe, seeing as down here in the east of England it's so darn expensive! - especially If I want to use a variety of different sizes of pipe. Steel I figured would be a better option as it's strength and cost is considerably better than copper. would the same pressure limits for a joint apply to steel as they do to copper when brazing? and is there anything I should look out for when brazing steel? by the way, I've brazed+soldered copper pipe before but not steel, so brazing steel will be new to me! I'm just checking that there aren't situations where I wouldn't be able to braze steel where I could normally braze copper. thankee all :wink:
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Unread postAuthor: Technician1002 » Thu Apr 05, 2012 11:45 am

:shock: How much pressure are you considering? If you need stuff for very high strength, I would suggest is is not a DYI event, but require a certified welder.

If you are considering high strength for high pressure, always have it hydrostatic tested. This is suggested for anything over 2 inch or over 150 PSI. Accidents at high pressure and large container is often something that only happens to someone once as there is often no second chance.

2 inch PVC shattering at 100 PSI is possible injury. A 10 inch propane tank rupture at 300 PSI is possible death. Plan accordingly.
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Unread postAuthor: cammyd32 » Thu Apr 05, 2012 11:51 am

It will be tested, quite a lot actually seeing as I've almost killed myself in the past with things with dangerous explosive potential and know the risks and dangers of compressed gas! I'm intending to run 250 psi through it. (I wouldn't deem that very high pressure) Would it help if I posted some quick m-paint pictures of the kinds of Areas I'l be using brazing for?
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Unread postAuthor: jsefcik » Thu Apr 05, 2012 2:14 pm

Gippeto wrote:Brazing brass and steel is fine. Brazing copper plumbing pipe isn't so good.

The temperatures required for brazing will anneal drawn copper and reduce it's safe working pressure. This isn't an issue when you're talking "refrigeration" because the tubing in a fridge is already annealed.

Best solder for drawn copper is 95/5 Tin/Antimony. Joints up to 1" are rated for 1090psi.

Might be worth having a look at pg 28 of the copper tube handbook. Note the working pressure of brazed copper joints at the bottom of the page. :)

http://www.google.ca/url?sa=t&rct=j&q=& ... wB3yLmPGBQ


brazing is alot better then solder, stronger is better read up on it, b4 you just disagree, are you going to school for it? no, i am, i belive i have a better knowledge, and it doesnt plug up holes , it fills them in, its used alot
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Unread postAuthor: Technician1002 » Thu Apr 05, 2012 3:53 pm

Silver brazing is used for copper. Brass brazing is a metal that contains a fair amount of copper so the copper pipe tends to mix in the brass when brazing making the pipe thin and changing the composition of the brass.

There is only a small margin of temperature range from proper flow of brass to melted copper.. Use silver brazing rods for copper instead of brass.
http://en.wikipedia.org/wiki/Brass Copper and Tin alloy.

It is possible to use brass to braze copper, but it is difficult to do properly.
Yes, I did go to school on it and have brazed it. It is strong, but does not flow well into copper joints. The joints tend to fill with flux and leave the joint weak or full of leaks. It is very difficult to braze a copper joint.

Silver brazing solder joint looks like this and is very strong. It wets the copper and flows out onto it for a leak free joint. Note the small pipe, it wicked the silver to the tip. It is very easy to do this right as it runs like water and sucks right into the joints for a solid seal.
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It is normal for a copper pipe to break near a joint instead of the silver soldered joint. The joint is stronger than the pipe.
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Unread postAuthor: Gippeto » Thu Apr 05, 2012 4:28 pm

Pay attention Jesse...the joint might be stronger...but annealing the copper lowers the max working pressure.
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Unread postAuthor: FighterAce » Thu Apr 05, 2012 5:53 pm

So what would be the preferred method for joining a 15mm OD, 1.6mm wall drawn Cu pipe with a thread to pipe fitting? Operating pressure around 800psi.
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Unread postAuthor: mobile chernobyl » Thu Apr 05, 2012 6:29 pm

FighterAce wrote:So what would be the preferred method for joining a 15mm OD, 1.6mm wall drawn Cu pipe with a thread to pipe fitting? Operating pressure around 800psi.


Tig weld it :wink:
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