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Soldering bronze

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Eckart Hartmann06/12/2017 15:50:50
2 forum posts

I want to fabricate a cylinder + piston valve assembly in bronze by machining the different components with steam passages and then silver soldering them together. I have tried it out with brass and after figuring out how to silver solder properly it worked ok. The available bronze though (e.g. SA660) has >6% lead which some websites say can be soldered while others say you can not. I assume though most boilers have such bronze for fittings and it works fine. Can anyone report on good or bad experiences with silver soldering such bronze?

Alternatively is there better option that does not rust?

JasonB07/12/2017 07:29:22
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11686 forum posts
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I have not had problems silver soldering SA660 using just propane. If you use a hotter flame such as Oxy-acetylene that can make the lead contend boil out and weaken the joint.

This cylinder is mostly bronze and the solder took well, hollow 660 for the main cylindrical part

CuP Alloys 107/12/2017 09:24:22
123 forum posts

Hi Eckart.

Any problems associated with silver soldering are due tothe fact that the lead in the bronze ia not alloyed but is present as free lead. It is present as discrete lead inclusions.

When heated, those on the surface melts. When the silver solder melts later, the molten silver solder dissolves it and and alters the composition of the silver solder.

The silver solder becomes less fluid and penetrating.

Overcome the problem by increasing the joint gap and so increasing the volume of silver solder. This dilutes the effect of dissolving the lead. Result ? Better, stronger joints.

Of course, if the operating conditions allow it, you can always use a tin lead or tin copper soft solder.

For more information**LINK**

regards

Keith

Eckart Hartmann09/12/2017 00:28:36
2 forum posts

Thanks for the replies. They both encourage me but I have found a reasonably priced source of PB1 bronze with 0.25% lead and/or I am considering using a 300'C tin lead solder. The parts are mainly held together by end pieces acting as a frame so the solder is just to keep the passages steam tight. I believe a 300'C solder should be good enough. If I go that way I will make a few test pieces to see how well the solder travels in the gaps.

Ian S C09/12/2017 11:29:40
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6491 forum posts
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Eckart, as long as you tin the mating surfaces you should have no problem getting a good joint, just arrange for the parts to be held in position until it cools, the thinnest joint is the strongest.

Ian S C

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