The tip will oxidize and become pitted depending on the quality of the tip.
In other words, when it looks fugly and won't clean up, time for a new tip.
The reason to clean the tip and prime it with solder (called tinning) is to remove the burnt flux and oxidation before soldering a joint.
Also when you end your soldering session, turn off iron, clean the tip, and apply some fresh solder to coat the tip.
Soldering station tips
Moderators: pompeiisneaks, Colossal
Re: Soldering station tips
Tom
Don't let that smoke out!
Don't let that smoke out!