As thte others have said, you're not getting hot enough and you need to use
flux.
Borax is thte flux to use and you can use any borax supply for this. I've
used 20 Mule Team brand borax as a cheap source and it works well.
For more heat with your equipment, use MAPP gass rather than propane. An
O/A torch works better but if you don't have one, the MSPP gas will work.
Brazing is a version of soldering and all of the soldering rules apply.

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Why do penguins walk so far to get to their nesting grounds?