As I understand it Bronze welding is the recommended method for frames made from chrome moly tube (Reynolds 531). I have an ancient CCM chassis which I assume was bronze welded but the joints are smooth rather as if it has been brazed. What I'd like to know is that if I want to make some minor changes to the frame, probably using mild steel, would it be best to weld, braze or bronze weld it? Also does the nickel plating (which is knackered) change anything in terms of welding (ie should I blast it first)?
We are talking in general, and ideal situations there is some cross over from one to the other.
Brazing and Braze Welding (bronze Welding) are almost the same, brazing most usualy uses brass filler rod (alloy of copper and zinc) the the other bronze (copper and tin) the melting point of both is roughly similar. But you can braze with silver, special stainless, and plastic welding is effectivley braze welding with plastic, but I will only refer to steel/brass and bronze here.
Brazing would most usualy be used where joints are socketed such as in push bike frames or old harley/brit bikes where you had pre made joints into which the tubes were inserted.
Braze Welding would most usualy be used where the tubes are butted together.
either is used in applications where some give is required and a normal welded joint would crack, although strictly speaking the weld is stronger than the original material, and cracks normaly appear to one side of the weld site or the other. With either type of brazing the steel to be brazed is not heated as hot therefore does not harden in the same way and the filler is flexible as opposed to a steel filler.
A bronze welded joint appears as the bike frame at the start of the thread, a more usual brazed joint is the picture below. In a proper brazed joint you should only see a thin line of filler, in a welded joint you should see the "stack of coins" pushed over look, even were it has all been filled down if you see a big broad band of filler then it should be welded.
Your problems arise when people braze with brass when they should be welding with bronze, there are lots of people who dont appreciate that there is a difference.
Without seeing your frame I would suggest that it should be bronze welded, and I would clean off any plating prior, the nickel will only be a thin coat, and it would have been applied after the original jointing of the tubes.
Either brazing or braze welding can be used to join disimilar metals such as
Mild Steel - Galvanized Steel
Stainless Steel - Copper
Mild Steel - Stainless Steel
Stainless Steel - Copper-Nickel
Mild Steel - Cast Iron
The technique to use should be dictated by the way in which the tubes are jointed together.
