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Strength Of A Brazed Joint Under Pressure?

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Unread postAuthor: ramses » Thu Apr 05, 2012 8:09 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.


Honestly, I would say solder it. If the joint is .25" long (conservative), that gives you .4638 sq in of shear area. The shear strength of 50/50 lead tin solder is 5220 PSi, so the strength of the joint would be 2421 lbs.

The cross section area in this case is .678 in, so your fail pressure is 3570 PSI. This gives you a safety factor of 4.4. (Check my calculations anyway)

If this is for a barrel, it will never see the full working pressure along its axis; there is nowhere for the pressure to act to pull the joint apart except from projectile friction.
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Unread postAuthor: FighterAce » Thu Apr 05, 2012 8:25 pm

Holy smokes... those numbers are good. Even more so since the joint is .5" long. I thought soft solder wouldn't work for such pressures but I'm glad I was wrong. Its actually for a two stage HP pump. Thanks ramses!
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Unread postAuthor: Technician1002 » Thu Apr 05, 2012 11:03 pm

The problem with lead tin solder is mechanical fatigue. If the joint is subject to repeated stresses mechanically the solder is known for cracking type failures.

In electronics, this is referred to as a cold solder joint. Mechanical stress on components such as volume controls and headphone jacks are a common failure. Another common failure point is power transistors and resistors where they see thermal cycles from heating and cooling. Below is what one of these intermittent thermal failures looks like. A soldered copper barrel may come unsolderd from mechanical fatigue.
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Unread postAuthor: Crna Legija » Thu Apr 05, 2012 11:19 pm

Technician1002 wrote:The problem with lead tin solder is mechanical fatigue. If the joint is subject to repeated stresses mechanically the solder is known for cracking type failures.


that happened to my ps3 it just stopped reading CD's all a sudden and i search on the web lots of people turn it on and wraped it in a blanked to let it get hot and re solder the bad peace, I didn't think it would work but sure enough it did left it for a hour in a blanket in my back yard then let it cool off and it works again just fine.
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Unread postAuthor: Gun Freak » Fri Apr 06, 2012 9:25 am

Haha that's awesome Crna :D

Tech, would the same concept apply to soldered copper chambers?
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Unread postAuthor: jhalek90 » Fri Apr 06, 2012 10:52 am

Little bit of info on brazing, if done correctly, brazing can be stronger than the metal you are brazing.


I did brazing of stainless steel, brass, titanium, and aluminum for about 3 years as a job, every once and a while are parts would be tested in all sorts of fun ways, the SS brazing were able to withstand over 20,000lbs of sheer force, which eventually snapped the SS like a rubber band that you pulled to hard.

Some of our joints were pressure tested as well, i've never had one fail, even at 10,000psi hydraulic pressure.

Brazing, is alot stronger then solder, but requires a little bit of research as to proper filler material (solder?) and flux, as well as temperature.

Most of the stuff i brazed was SS and titanium. Most of the joins were about 1/4'' to 1/2'' and where done at a rather particular temp range.
To hot and you fatigue the metal, to cold and you don't get as strong of a joint as you could.

if you are going to "solder" copper, you should be fine, as long as you make sure your joints are fully soldered, but don't get them to warm.

For copper i use a propane torch, just head the copper, near the join, and let the solder wick into the joint, with the right flux, this is relatively easy.

If anyone is interested, i worked here: http://www.thompsonsurgical.com/
WARNING! the home page has photos of surgery, and is not the the weak stomached.
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Unread postAuthor: cammyd32 » Fri Apr 06, 2012 11:42 am

Some of our joints were pressure tested as well, i've never had one fail, even at 10,000psi hydraulic pressure.

Sheesh! well I think that these joints I'm going to make are going to be perfectly adequate bearing in mind I'm working at 250 psi!
after long hours into the night sourcing parts I've decided on aluminium as a base material seeing as it will come out cheaper, and for some reason only in aluminium can I actually find the pipe bores that I need!
So I'm wondering.. aluminium for pressure? any links to aluminium cannons on the site would be warmly received, and thanks all for the advice!
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Unread postAuthor: Goats spudz » Fri Apr 06, 2012 11:47 am

if your using steel just weld it, i mig welded a hydraulic fitting to my fridge compressor and it has taken 1000 psi easily. also they make 4500 psi air bottles from aluminium.
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Unread postAuthor: Crna Legija » Fri Apr 06, 2012 6:55 pm

Goats spudz wrote:if your using steel just weld it, i mig welded a hydraulic fitting to my fridge compressor and it has taken 1000 psi easily. also they make 4500 psi air bottles from aluminium.

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Unread postAuthor: cammyd32 » Sun Apr 08, 2012 6:32 am

Crna Legija wrote:
Goats spudz wrote:if your using steel just weld it, i mig welded a hydraulic fitting to my fridge compressor and it has taken 1000 psi easily. also they make 4500 psi air bottles from aluminium.

Image


haha, love it! :D
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Unread postAuthor: al-xg » Sun Apr 08, 2012 8:15 am

There are many grades of aluminium out there, the weakest grades having a tensile strength nearly 10 times lower than the higher end stuff.
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Unread postAuthor: Goats spudz » Sun Apr 08, 2012 12:47 pm

Crna Legija wrote:
Goats spudz wrote:if your using steel just weld it, i mig welded a hydraulic fitting to my fridge compressor and it has taken 1000 psi easily. also they make 4500 psi air bottles from aluminium.

Image
http://www.luxfer.net/products/paintball-cylinders/498-l7x-aluminium-cylinder-specifications?tags=undefined silly person go crawl back under your rock.
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Unread postAuthor: cammyd32 » Sun Apr 08, 2012 12:58 pm

There are many grades of aluminium out there, the weakest grades having a tensile strength nearly 10 times lower than the higher end stuff.

If you want specifics I'm talking about standard t6 grade aluminium, about a 1.7 mm wall and 32mm in external diameter.
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Unread postAuthor: Goats spudz » Sun Apr 08, 2012 1:02 pm

if you tig weld it then it will work :D
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Unread postAuthor: ramses » Sun Apr 08, 2012 1:30 pm

Keep in mind that TIG welding aluminum reduces the surrounding area to the T0 condition, and that you can't really heat treat it yourself.
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