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Possible problem with copper-phosphorous solder

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Possible problem with copper-phosphorous solder

Postby myles » Tue Feb 03, 2009 6:37 am

I recently contacted one of the solder manufacturers that make both silver solder and copper phosphorous solder, for some technical advice.

I asked the question, were there any advantages between using silver solder and copper-phosphorous, when building a working model steam engine. There are the same factors involved when building a boiler for our use!!

Their response may be of interest to some of us. What they said was:

DO NOT ENTERTAIN COPPER PHOSPHOROUS ALLOYS

Coefficients of expansion are the least of your problems

1. They require more heat. Oxy-gas is required.
2. They do not flow as well to give adequate joint penetration.
3. They are generally more difficult to use.
4. And when in contact with sulphur fumes from coal they become porous.

Other than that no problem!! We recommend the use of 440 and 842 silver solder alloys.

Now I don’t know how much sulphur is in bottled gas, but there is some. Has anyone had a problem with degraded solder joints in the past? It certainly changes my plans for a solid fuelled steam heated still. I hope this is of interest to some of you.
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Re: Possible problem with copper-phosphorous solder

Postby Adverse Effects » Tue Feb 03, 2009 7:12 am

well i use 2% and 5% silver solder so it shouldn't effect me i don't think :|
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Re: Possible problem with copper-phosphorous solder

Postby HookLine » Tue Feb 03, 2009 7:37 am

What do you mean by copper-phosphorous solder?

I have been using a braze (Pro silver 2) that is 2% silver, a dash of phosphorous, and mostly copper, same stuff air-con mechanics and plumbers use. I was told that the phosphorous acts as a flux on copper and is does not form part of the final join, it just leaves some phosphorous compound on the outside of the join that can be cleaned off in various ways. Pretty sure the air con guys in particular would not be using something that could give weak joints.
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Re: Possible problem with copper-phosphorous solder

Postby trthskr4 » Tue Feb 03, 2009 8:18 am

Copper Phosphorous solder is a silver brazing rod substitute I believe that is sold as just as good as silver rods. I have some of both I believe and like the Copper phosphorous just as well as silver and their about $15/lb. vs. $70/lb. for 15% silver. They do require more heat and are harder to clean up after. I like them myself but don't use them where they will come into direct contact with much steam at all.
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Re: Possible problem with copper-phosphorous solder

Postby myles » Tue Feb 03, 2009 8:37 am

Yes I was looking at the copper phosphorous braizing rods used in air conditioning applications. They market 12 different alloys with between 5% and 8% phosphorous, mostly copper and upto 18% silver. They are recomended for producing stable joints at temperatures down to -40 degrees. Air conditioning pipework does not tend to get hot.

For high temperature joints they recomend the use of the silver solders.

It is why I was seeking clarification. They seem to think copper phosporous is the wrong choice in boiler work.
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All copper pot still "Rosie" in development.

Re: Possible problem with copper-phosphorous solder

Postby trthskr4 » Tue Feb 03, 2009 8:52 am

Some A/C joints do get pretty hot, but no where near the temps that can be obtained in a boiler or steam engine. I don't know but I usually don't use them in applications in direct contact with steam, mostly on my condenser joints where it stays pretty cool.
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Re: Possible problem with copper-phosphorous solder

Postby myles » Sun Feb 08, 2009 7:59 am

Update. Was in a DIY shop and saw some Benzomatic copper phosphorous brazing rods so gave it a try on some off cuts.

What a revelation. Dead easy to use with the MAP gas, no flux just heat and apply. Surprised to see it was silver – was expecting it to be copper coloured. Flowed perfectly. Much cheaper than Silver solder. Have no idea what the composition is but I shall definitely use these on condensers etc.

Will stick to the silver solder on boilers and columns just to be on the safe side but I can see now why you folks recommend them. Thanks.
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