Soldering iron tip turns black after first use, and won't melt solder

Question

I am a beginner in the field of soldering. Two weeks ago a bought a brand new soldering iron for around $15. The iron had a shiny tip, but after I plugged it in it turned black pretty quickly. After doing some research, I found out that this type of soldering iron is made of a copper core with a thin iron coating. The iron coating is needed because, to my understanding, copper corrodes quickly when in contact with hot solder. However, at high temperatures, iron reactas with oxygen and forms a super thin oxide layer on the tip of the soldering iron, which makes soldering really difficult.

Essentially, the solder melts only at the top of the tip, and starts rolling into a ball. It will barely melt at the absolute tip. I have tried using a wet sponge to clean it off, as suggested by the internet, but that doesn't do anything (the sponge is apparently supposed to be used to clean solder rests from the tip and not oxidation anyway). Another internet tip was to gently scrape that layer off with a knife until the iron covering is revealed, turn the soldering iron on, and once it heats up immediately cover it with solder to prevent oxidation. Well, I tried that too, but as soon as the iron heats up, it turns black and repels the solder.

I have heard about using flux (soldering paste) but my solder already has a flux core.

In the two pictures you can see the iron before/after being turned on, (after I had scraped it with a knife). You can clearly see how it loses its shine.

How do I remove this oxide layer without a knife (which risks damaging the iron coating) and prevent it from reoccurring?

(To reiterate, I am a beginner, and I don't want to spend $100 on a fancy, temperature controlled iron. I just want to solder some components to a thru-hole board without buying a new tip every time in need one.).

Thank you very much for your time!

Answer 1

First, go read up on soldering iron care. You clearly didn't keep your tip tinned.

Your soldering iron almost certainly came with some sort of small sponge. This is meant to be moistened. After each use, you wipe the tip against this moistened sponge. That clears off flux residue, and some of the oxidized solder.

When just wiping doesn't restore the tip to shiny condition, you have to add a little solder to re-coat the tip, then wipe. This is called "tinning" the iron. Keeping the tip tinned makes the thin layer of solder oxidize, not the iron coating of the tip itself.

Even if you are careful, black spots of oxide can still accumulate that don't come of with wiping. There are tip cleaners for this purpose. If you have good soldering intuition and know what you're doing, you can very gently scrape the black oxide patches off the tip with a small screw driver, then tin to restore to good condition. The reason this needs to be done gently is to avoid hurting the iron coating. Once that's gone, the tip is trash.

I've seen brass spiral mesh used for the purpose of gently scraping tips, but don't have any personal experience with that.

Despite all the above, if your soldering iron isn't temperature controller, you will have problems. The tip will be way too hot most of the time, and whatever is coating the tip will rapidly oxidize. Fixed-power irons are much more difficult to maintain and to use properly. Their only purpose is to appeal to hobbyists that buy on price. They are not real soldering irons.

If you plan on soldering more than once or twice, get a real soldering iron. Last time I looked, the Weller WES51 was the lowest price reasonable iron out there. You can get much fancier, and pay much more, but the WES51 is still good enough for even basic professional work.

Answer 2

Try to never scrape the tip with anything, especially not a knife, and definitely not when it is hot. Wiping on a damp or moist (not wet), sponge or cloth cleans oxide off the tip best. It is essential that the sponge or cloth is clean. I use a piece of jeans pants leg cutoff, moistened with a water sprayer just before use. Remember to moisten it, or else the cloth will burn and dirty the tip with oxides instead of cleaning it. Wash the cloth or sponge with soap and water, once in a while. Remember to tin the tip in between soldering if the tip will remain hot (essential). Remember to tin the tip before cooling it down (but this is not essential).

At the very least get some sort of voltage regulator for the iron. This will allow you to "dim" the temperature when it is sitting idle.

There may be a few reasons why a new tip might not tin. It may already be covered in oxides or rust, it was heated up too much and oxides formed before tinning, it was tinned with lead free solder and required a higher temperature for initial tinning, the nickel plating extended to the tip... One has to start trying to tin while the tip is first heating up, alternately clean on damp cloth or sponge and trying to melt some flux and solder.

It is easier to tin with the addition of stronger flux, like those used for jewelery or copper/brass utensils. However, they are also very corrosive. Keep the damp cloth handy and wash the cloth after tinning. Do not use that flux for general soldering. Hardware store rosin dissolved in alcohol, works best for soldering.