Sceadwian
Banned
The problem isn't so much the heat but what it creates (oxides) that build up on the tip, then the solder rides up on the oxide rather than wetting the tip because it's oxidized or it could be solder impurities as well. You could nip this in the bud with plenty of flux. As long as you use neutral no wash flux or an acid based encapsulated flux with a quick wash afterwards things like this will not happen.
Once the oxides are mixed with the solder from a dirty tip (you can't always see it) that's it, that solder is done, outside of perhaps a harsher acidic flux it will never flow right again.
Once the oxides are mixed with the solder from a dirty tip (you can't always see it) that's it, that solder is done, outside of perhaps a harsher acidic flux it will never flow right again.