NEVER use sponges or sandpaper, especially on SMD irons.
The reason cannot be seen without a microscope or good magnifying glass, but wiping the tip on the sponge often brings away carbonized particles of sponge on the tip surface.
Sand paper is abrasive grit bonded to a paper backing with glue, The grit particles are far harder than the tip, so the sandpaper will abrade the tip surface away and leave particles of it on the tip. The tip can end up with metal and glue residues that are very difficult to see without magnifcation.
In both cases, the contaminant particles will find their way into the solder joints. On large heavy joints, its not so much of a problem, but in SMT it can be a disaster.
Basically speaking, if the tip is “dirty” then the tip is too hot, or , the materials being soldered are contaminated. A universal problem in soldering is too much temperature.
It is critical to realize that most belief and training in soldering comes from the 1930s - 40s, back in vacuum tube days. Back then cleanliness was not important, solder jointe were huge and there was no option but to have a very hot iron or gun as the joints were physically very large. The SMT world is radically different. This is especially critical if you work in a SMT manufacturing or repair operation. In those cases, education and training thru SMTA is important. In SMT soldering, little errors in soldering and manufacturing can cause severe quality problems that are difficult to diagnose.
Remember, soldering is CHEMISTRY first, not mechanical. The process must be pure and clean, and we cant get that with the glue from the sandpaper contaminating the solder.
USe the copper wool and change it regularly. Dont reuse an old band aid!
“Operating at high temperatures, which speeds oxidation. Maintain the temperature of
800°F (427°C), or less, whenever possible.”
This is GROSS error. Eutectic solders melt around 380-400 degrees F. An iron tip need only be that, or slightly higher, temperature to do good solder work. 800F will incinerate a soldering iron tip.
This error is due to a lack of understanding ot thermodynamics. There is heat, there is temperature. They are different things. Heat is thermal energy in a mass. Temperature is the difference in heat between two masses, that results in heat transfer from the hotter to the colder.
If the temperature must be raised much above 400F (its useless to have the joint and tip any higher temperature if the solder melts at 380F) then the tip does not have enough heat (not enough thermal mass) which basically means a larger tip is required to transfer more heat (not temperature).
Such extreme high temperatures immediately oxidize the iron tip and disintegrate the flux, causing bad solder joints and tip destruction.