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sweating soldered joints

methamon

Well Known and Active Website User
Non-VOC Member
Post war main oil feed pipe to pump; specifically the (soldered?) joint between the (plated steel?) pipe & brass banjo at the pump connection. Yesterday I tried to separate one of these, propane torch & flux all to no avail. Not hot enough thinks I so oxy acetylene played on it with flux. With the pipe held I twisted and pulled at the banjo.........and the banjo broke off at the spigot leaving the spiggot inside the pipe.
Entirely unsuccessfull an an original part ruined. Can anyone explain why the joint would not simply sweat and fall apart with a bit of heat & fux? Also, can they be succcessfully separated; if so how?:mad::confused:
 

john998

Well Known and Active Website User
VOC Member
Oil pipe

Hello, perhaps it was silver soldered or even brazed. If so may be not have been enough heat. Another thought, some old brass castings become brittle. John.
 

clevtrev

Well Known and Active Website User
VOC Member
Hello, perhaps it was silver soldered or even brazed. If so may be not have been enough heat. Another thought, some old brass castings become brittle. John.
Using flux to dismantle is a no no. What happens, is the solder reflows.
The joint would have been silver solder, but what grade, who knows? Brazing would not have been used , because the melting point of brass and brazing spelter is the same.
 

methamon

Well Known and Active Website User
Non-VOC Member
Using flux to dismantle is a no no. What happens, is the solder reflows.
The joint would have been silver solder, but what grade, who knows? Brazing would not have been used , because the melting point of brass and brazing spelter is the same.

Hi trevor, you obviously know what you're on about so can you elaborate on the reason for not using flux; Also, can these joints be succcessfully separated; if so how?
 

clevtrev

Well Known and Active Website User
VOC Member
Hi trevor, you obviously know what you're on about so can you elaborate on the reason for not using flux; Also, can these joints be succcessfully separated; if so how?
Flux is to enable a bond, you wish to unbond.
I`ve attached a pic, to show what can be done.
Had to look first to see if it came through.
Had to find a joint this afternoon to unbond, simply heat with a soft flame, without getting the flame on the tube. I use MAPP gas, took about four minutes.
The silver solder is much to high a grade for this application, if there is any intention to take apart again. I just made it before the brass was about to melt.
 

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clevtrev

Well Known and Active Website User
VOC Member
I thought flux which contains all sorts of nasty chemicals was only needed for cleaning prior to soldering?
Flux is needed throughout the process. If for example you might be bronze welding, the best way for the expert is to have the flux in the flame. Stick welding is difficult without a coated rod. Flux serves several purposes, not just cleaning.
 

dagriise@online.no

Well Known and Active Website User
VOC Member
My knowledge about this is from parting (and building) bicycle frames, and the general saying about sweating out brazes is that you generaly will have problems in doing so, as some of the original elements of the brasing alloy usually get "burnt away" in the first braze process, resulting in much higher temps needed to unsweat a joint. (usually you damage the part..) As mentioned a simple pipe banjo joint should only need a low temp soft soldering. I usually prefer to carefully drill/machine out joints. (have even done it on cast BSA swing arm fork ends.) On round objects you support the parts rigdly and chase the inner hole for lining up the cut.

Regards Dag.
 

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