The Bronze Wire Splitting Solder Joins Mystery

A few months ago I started having a strange problem. The solder joins on some of my 2mm bronze wire bangles started to split as I was making them. Three out of five of a set I was making split and I had to start them again.  Bearing in mind I sell a lot of bangles and have made hundreds of them without any solder join problems occuring before I was baffled. I also had a few solder join splitting occurances with 3mm bronze wire and 2mm copper wire.

One of the joins on the 2mm bronze wire came open literally as I got the bangle out of the pickle pot and others would start to split when I put pressure on the join either by rounding the bangle on the mandrel or by hammering it on the mandrel.

I thought about what I was doing differently..... but I wasn't doing anything differently from how I made all my other bangles! I use wire ranging from 1.8mm up to 5mm in copper, bronze and sterling silver. The process is the same - cut the wire, file the ends flat using a mitre jig, bend the wire into a D shape to get the ends together, pickle then solder with hard solder. So why was this suddenly happening?

I decided to do a test with some of the problem 2mm bronze wire.

This is what the bangles look like after soldering. The joins look ok.

After pickling I then round them up on the mandrel.

Then I file and sand the joins until there is just a thin silver line of solder remaining. Again everything looks fine at this stage.

But pressing the join fairly gently against my bench pin resulted in this...

Opening up the joins I can see the solder isn't flowing through it properly and instead seems to be flowing around it.

So it looks like either the joins just aren't tight enough for the solder to flow properly and form a solid join or the surface of the wire is dirty. What I didn't understand was WHY this was suddenly happening?  

Then I starting thinking about what was different. The 2mm bronze wire I was using was a new batch. Previously the supplier sent me dead soft bronze wire which was a gold colour but this latest batch was half hard and darker in colour but really that shouldn't make any difference as I've used the half hard darker coloured bronze wire before without any problem. I did check with the supplier to see if the 2mm was a different type of bronze but they couldn't cast any light on the problem. 

I then wondered if it was because I'd started using some new hard solder..... or maybe my flux was contaminated? I also started to seriously doubt my ability to solder! However the problem was mostly restricted to soldering with 2mm bronze and the other bangles I was making at the same time were fine. 

It certainly made me very paranoid! To the point where I threw away my hard solder and cut up a new batch, threw away my flux and started using a new lot. I even tried using medium solder with the bronze wire to see if it made a difference {not really, the joins still split} and using Easi-Flo paste flux which I hate because of the mess it makes on my soldering boards. Nothing made any difference.

So I reluctantly came to the conclusion I wasn't getting straight edges when I filed the ends of the wire. I even used a spirit level on my mitre jig just in case I'd filed the side of it away and made it uneven. It wasn't.

Then I noticed this...

This photo shows the ends of the wire after I've filed them using the mitre jig and a metal file.

You can see the file pushes the metal to one side creating a lip around the edge and some small burrs sticking up. I wondered if this was causing the problem but again I've done this since I started making bangles so why would it start being a problem now??

What I now do differently.......
So I'm still none the wiser what the problem was exactly apart from maybe it was the 2mm bronze wire as that was the wire I had most of the trouble with. I also wondered if I'd become a bit blase about it because I make so many bangles so maybe I just wasn't taking enough time to get the ends right....but then why weren't all the bangles I made doing the same.....?? Who knows!

I do now make sure there are no burrs on the ends of the wire before I bring the ends together.

I've also changed how I solder and instead of pick soldering I now place the join over the piece of solder and heat from above so I can see the solder being drawn up through the join.

Not a great photo but the solder join was fine on this one!

I've also gone back to using my normal hard solder, liquid flux and I've nearly stopped worriedly checking the join on every single bangle I make everytime I do anything that puts pressure on the join {nearly!}

This set of 3mm bronze bangles was ok and the solder joins held up fine when the bangles were hammered and since I've made myself take a bit more time over filing the ends of the wire there have been no more problems when I use the 2mm copper and 3mm bronze wire.

The 2mm bronze wire problem still hasn't been resolved though and is off the menu for the time being until I have the chance to have another go at it. Maybe the different way of soldering and making sure the ends are perfect will sort it out.

It may take a while 'til I get round to it but I refuse be beaten by it!!