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5 Responses to Dull Grainy Solder – Why?
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Hi Ben
You have what is called a dry solder join which means the soldered item has moved while the solder is cooling or the iron was not hot enough when soldering there are a number of things that cause this the iron is too small for the job, not quite enough solder on the join, just reheat again and don’t let it move or add more solder the finished join should be smooth and bright
Dull grainy looking solder joints are usually caused by one (or both) of two things.
The pieces you are joining are not clean, and you are not providing enough heat at the joint.
The pieces to be joined (wire to rail for instance) should be clean, not oxidised.
Put some solder flux (Resin is best for wiring) on the two components to be joined. You do not need much, a toothpick can be used to apply a small amount.
The soldering iron tip should be clean. A wire-brush wiper, or the bronze-looking “coarse wire wool” or a moist sponge or moist wad of paper towel will do. Then immediately tin the end of the bit with resin-cored solder. It should coat the surface of the bit, “wetting” it with solder, bright & shiny. Lightly wipe the bit on the damp sponge or paper towel wad, so the tip is still bright& just touch the resin-cored solder to it. That should leave just a small amount of solder on the tip of the iron. Then apply that bright-shiny tip to the joint. If you have put the resin flux on the joint, the solder should flow right away. If you do not have that small liquid solder “blob” on the tip, you may not have good heat transfer, hence your cold, dull grainy joints.
If you are still not sure, “tin the two places to be joined with solder before you put them together to be joined. A clean soldering iron tip & that tiny amount of solder should do the trick.
Bigger jobs can require a bigger iron, but most model railway jobs do not need so much power.
Practice, it’s not difficult if you remember the small blob on the end of the tip of the iron and flux first.
Cheers,
Bernard
This dullness may be due to movement, cooling rate or oxidisation.
Bernard’s soldering advice is sound. Dry joints may be caused by dirty or corroded wires or terminals, or by too low soldering iron temperature. Electrical solder is flux-cored, but a little extra flux applied in advance can be helpful, particularly with old wires or components.
I must respectfully correct Kevin: the term “dry joint” describes a lack of full contact between the (apparently) soldered parts, which is (often only) detectable under magnification, or by the the wire being loose when wiggled. The symptom is bad or intermittent electrical contact. (Image attached.)
However, if the wires are securely electrically joined by the solder, the surface appearance is totally irrrelevant, so don’t worry about it.
It is an art to soldering. You have to heat the work so that the solder will flow into the joint. You have to use the correct solder. Solder is usually made of two metals lead and tin. Some contain 50% lead and 50% tin. This is good for soldering pipes together as you can use a lot of heat and it needs a flux ( paste for the joint ). For electrical joints you should use 60% tin and 40% lead. This will work way better. There is some solder that has some silver in it for better electrical joints .Remember to heat the metal so that the solder will flow into the joint. Them remove the heat and let is cool without moving the joint. It should only take a moment for the joint to cool. This is very important. If you are working near plastic parts it may pay to cover the plastic parts with a wet paper towel. Have a soldering iron that has the wattage and tip size for the job. This should get you on the right track.
Dull soldering joints are the result of using a too low temperature iron.or choosing the wrong wattage for the work in progress.
It can be that the iron is deffective or you did not wait long enough to make the solder flow on all surfaces.
Soldering wires to HO rails are demanding a 75Watt to 100 Watt iron. This will prevent that the heat will travel through the rail while soldering the wire. This happens when you use an iron of low wattage.
Small Irons have not the capacity to maintain temperature when soldering tip touches large objects.