Brazing: Is Flux Necessary?

HI, I've been in plumbing for almost 3 years but because I keep jumping from site to site, I haven't had to do any brazing yet. The company I work for now, when they braze, they use no flux, and don't even clean the pipes before putting them together, and tell me they've never had a problem.

The company I worked for before, they cleaned, and used flux (though I found it a bit strange because they weren't using brazing flux).

Is flux really necessary when brazing? At a high enough temperature, from what I've read, the filler metal and the copper actually start to weld together. I know they make special brazing flux, but do any of them even last long enough to be present by the time the copper is hot enough for the rod to melt?

I can't get a straight reliable answer.

Thanks

No flux for brazing.

It depends on the rod. Silfos is self fluxing on copper, but when brazing brass, or most other metals, you do need a proper flux.