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Old 04-25-2016, 04:44 AM
elavir elavir is offline
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Default Silver over copper?

Hi all,

I've got a short question. Is it possible to braze silver over a spot that was brazed with copper? The material that was brazed on is cast iron.

Cheers Richard.
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Old 04-25-2016, 07:26 AM
leoitch leoitch is offline
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hmmm...if you just look at the melting temperatures, sure. copper is at 1984F and silver is 1763F..so you should have a comfortable range to work.

but,
I think you have to be careful about the flux burning off before the silver melts!
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Old 04-25-2016, 08:51 AM
billfunk29 billfunk29 is offline
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Default Silver braze on Copper

I silver braze copper wire all the time. Code for high pressure copper air lines requires brazing, not solder. Lots of alloys to choose from. Get the right stuff.
http://www.fusion-inc.com/brazing/silver-brazing/
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Old 04-25-2016, 10:04 AM
crystallographic crystallographic is offline
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Quote:
Originally Posted by elavir View Post
Hi all,

I've got a short question. Is it possible to braze silver over a spot that was brazed with copper? The material that was brazed on is cast iron.

Cheers Richard.
Hi Richard,
Brazing alloy for cast iron is a specific type of material - because of the graphite in the iron. You are seeing the copper portion of the braze, unless some adventurous person was using copper wire to repair the iron ....? If you can get the silver to flow onto the copper it will hold - but will it hold the iron together? Silver brazes of over 50% have the highest strengths, more than copper has, and bond very well to the copper, but I don't know the nature of the strength your repair requires.
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Old 04-25-2016, 11:45 AM
elavir elavir is offline
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Hi Lee and Bill, thanks for the info. So mixing copper and silver will not be a problem.
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Old 04-25-2016, 12:08 PM
elavir elavir is offline
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Originally Posted by crystallographic View Post
Hi Richard,
Brazing alloy for cast iron is a specific type of material - because of the graphite in the iron. You are seeing the copper portion of the braze, unless some adventurous person was using copper wire to repair the iron ....? If you can get the silver to flow onto the copper it will hold - but will it hold the iron together? Silver brazes of over 50% have the highest strengths, more than copper has, and bond very well to the copper, but I don't know the nature of the strength your repair requires.
Hi Kent, thanks for your answer. I don't know the content of the rod but it has an intensity of 480N/mm2. The repair is for a cast iron cilinderhead with a crack. It will be a temporarily fix because there will be little time for a repair and the owner of the bike wants to make a trip of 200km and after that he wants to make a definite repair. Can it hold 200 kms? The owner claims that the bike has run for a long time until it broke down and he discovered the copper repair.
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Old 04-25-2016, 09:47 PM
crystallographic crystallographic is offline
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Originally Posted by elavir View Post
Hi Kent, thanks for your answer. I don't know the content of the rod but it has an intensity of 480N/mm2. The repair is for a cast iron cilinderhead with a crack. It will be a temporarily fix because there will be little time for a repair and the owner of the bike wants to make a trip of 200km and after that he wants to make a definite repair. Can it hold 200 kms? The owner claims that the bike has run for a long time until it broke down and he discovered the copper repair.
What is the CHT of the head while running?
(cyl head temp)
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Old 04-26-2016, 09:27 AM
elavir elavir is offline
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Kent, I don't know. It's a vintage bike(GnomeRhone) from, I think, the thirties. The engine is a 4-stroke of the type, I don't know the correct word, that has the valves on the side of the cylinder so the hot exhaust gasses don't flow through the head and the valves don't give of the heat to the seats and of course the bike runs with low revs so I think the temperature of the head isn't that high as one who has the valves in the head.
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Old 04-26-2016, 10:10 AM
crystallographic crystallographic is offline
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Originally Posted by elavir View Post
Kent, I don't know. It's a vintage bike(GnomeRhone) from, I think, the thirties. The engine is a 4-stroke of the type, I don't know the correct word, that has the valves on the side of the cylinder so the hot exhaust gasses don't flow through the head and the valves don't give of the heat to the seats and of course the bike runs with low revs so I think the temperature of the head isn't that high as one who has the valves in the head.
okay - If your torch is hot enough and you have some copper flux, then why not just mend the copper with copper wire?
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Old 04-26-2016, 02:51 PM
elavir elavir is offline
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okay - If your torch is hot enough and you have some copper flux, then why not just mend the copper with copper wire?
I will give it a try
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