Copper soldering woes - at the end of my tether

raddy59

I am a sculptor,now working in copper. I am trying to solder pieces of copper wire together using roisin core 2/.0%. My problem - I just cant get the wires to join. I've tried (what I think is) everything.
I had been using the soldering iron for a few years with little to no problems and I thought it could be the tip or maybe 
the iron wasn't getting hot enough.
it was only a cheap one so I invested in another that was a little more upmarket but the problem didn't go away.
I managed to solder a few pieces but then I started having the same problem once more, I've tried multiple tips and they either stop
working after a short while or won't work at all.

 Any advise at this stage would be VERY helpful. I think I'm missing something really basic

JohnB47

I'm struggling to see what can be wrong here. How can a soldering iron tip  'stop working'? It melts the solder, right? Or maybe not.

What happens if you clean the wire with steel wool or sandpaper and then try to run solder onto it? Should work perfectly. Have you tried using flux paste on clean wire too? 

The usual technique is to melt a small amount of solder on the iron tip, then hold that against the copper, wait a few seconds for the heat to transfer through the solder to the copper, then apply the solder to the copper. If the heat isn't transferring to the copper, add a bit more to the tip, or maybe the iron isn't big enough for the job? 

A small iron, made for soldering slim wire and PCB mounted components wouldn't be good enough to solder large guage copper wire or fairly big chunks of copper sheet or plate. Copper transmits heat very effectively, so the heat from a small iron could be just leaking along the copper and never heating the contact point high enough.

Finally, what's the temperature like in the area you're soldering?

Moss5

https://www.youtube.com/watch?v=TPbootw3s1c
Try dunking wires in a pot of flux.

Grey_Critic

Coat each end with solder before joining. Ensure that there are no forces keeping them apart ideally you need to clamp them before soldering - maybe need to trim back after soldering.

matelodave

Make sure that whatever you are soldering is clean and shiny and try using some flux and get a decent sized soldering iron.

I've been soldering stuff for years and for most purposes I use a Weller 48 watt temperature controlled iron but for bigger stuff then you need something a bit heftier 100w or more with a decent sized tip to enable it to transfer heat without cooling down.

You need to get enough heat to the joint so the iron has to have enough capacity to heat the object to be soldered up to the solder flow temperature which could be as hight as 350 degrees or more. A big tip with lots of thermal mass is required.

Something like this might do the job - https://tempsfordstainedglass.co.uk/product/antex-100-watt-stained-glass-soldering-iron/

raddy59

I've asked a mate of mine and he says the correct term is the solder isn't wetting 
hope that gives you more of an idea of what I'm getting 

JohnB47

raddy59 said:

I've asked a mate of mine and he says the correct term is the solder isn't wetting 
hope that gives you more of an idea of what I'm getting 

Well, it seems that localised temperature is the problem. That is, lack of it. Perhaps you could post pictures of the iron you're using and the the thing's you're soldering.

Looks like it's simply down to using an iron that isn't 'beefy' enough and the heat is simply leaking away and the solder isn't melting enough at the contact point.

theoretica

How large are the wires you are soldering?  Jewellers (and plumbers) use a torch to solder, and that might be what you need.  With copper solder, probably, not the electrical stuff.

Alderbank

What does the heated solder look like? Is it nice and shiny like a mirror?
If it's dull or grainy it's not hot enough.

Edited to add: I second the use of a blowtorch

fwor

A few more suggestions:

Once you have cleaned the wire to a new, bright finish, don't touch it between then and soldering - if you do, the natural oils from your skin will interfere with the tinning of the wire.

Solder with a flux core is Ok for circuit board work, but for larger-scale stuff you will get better results with something like fluxite paste.

Although a small blowtorch should work well, you need to use one in moderation. Even the smallest of blowtorches can heat a wire enough to cause oxidisation of the surface, and can also burn the flux to a crisp - neither will make the soldering any easier and both are likely to be visually unacceptable (to a scupltor).

Heedtheadvice

Most of the advice above should help solve the problem but really without seeing what you are doing and the sizes of everything it is mainly guesses that we can have at what your solder failure cause is.

To do proper joints you need several things. Really a collection of above comments.

Clean equipment and parts. Without that the solder will not 'wet' the surfaces. Clean parts with fine emery ppaper or for larger items a wire brush? There should be no verdigree or oxide in the soldering area. Pretinned copper wires are easiest in that respect but still require flux to ensure cleanliness. If not using pretinned wires you should tin them yourself i.e. after cleaning and fluxing solder them with just a little solder to only just cover the area to be joined.

Similarly the iron should be clean and tinned too but not with emery as this affects the tip's surface for some tips.. Once the iron is hot wipe the bit on damp soldering sponge to clean it it and then tin it too. This should be done frequently before and after each jointing operation and before storage.

The iron temperature needs to be appropriate to the solder type in use. Check with the spec of the solder. It is best to use a temperature controlled iron. It needs to be not too hot, not too cold and ( like porridge and the three bears) just right.

Iron size is important to eneable thermal transfer as is the clean tip tinned area. It needs to be big enough to conduct the heat to the wires and solder applied to the tip just as you are about to solder increase that contact surface area and therefore heat transfer. In a cold environment such as out of doors or in windy weaather extra heat is required to reach tempertature during soldering!

The items to be soldered should not move especially during cooling to prevent what is termed a dry joint. That is when the items are not tinned properly or move during solidifying giving a characteristic crystalised look. The final joint should be smooth and shiny. Mechanical means to prevent movement should be employed. Twisting the wires if you can or small clamps though those need to reduce conducting heat away from the joint area too. Clamping a distance away can help here. Dry joints are not good electrically but are also mechanically weak.

If the wires are not of the same size it is useful to apply most but not all of the heat from the iron to the more massive one.

Nothing wrong with using flux cored solder providing it is of a suitable size and the correct type of flux for copper. Avoid old solder as it can deteriorate with age (years!). As a rule of thumb the solder diameter should be similar to the wires or a bit less. Sculpting might suggest very big 'wire' so you may need to move to stick solder and a very big iron or small torch. If that is the case applying separate flux just before or at the time of soldering is then essential.

In the case of solder less is more i.e. better,  long as the joint area is fully coated. Any excess where you do not want it can be wiped off with a damp rag but if that moves the joint or cools to rapidly then reheat with a small amount of new solder/flux.

Hope that helps.

EDIT: As you are into sculpture Silver solder (high content of silver) can be useful. You can look up on the net of course. However (I have not watched it all and youtube videos can be cr*p) this video seems reasonable https://youtu.be/0jdAF4rOQ8w