Flux?

[Readingplumber]

Hi - I know flux does 2 things - helps solder flow and cleans the pipe -

Am i right in saying when you heat a pipe up without any flux on you can sort of see a thin layer on the pipe ie when you move the blow torch up and down. Am i right in guessing this is an oxide layer - would this be the oxidiation, the bit that the flux cleans off to allow contact to the copper?

Thanks!

 

[dontknowitall]

I'm a plumber too and I don't know what this is. I know how to solder, why flux is used (like Readingplumber) and make a water tight joint and how to measure the pipes for cutting and stuff like that.

I'm sure it's not important, this oxidisation or whatever it is, but I'd like to know the answer too.

I play the organ at funerals and am paid to do it. But that doesn't mean that I know all the hymns that people want me to play.

 

[Dannypipe]

That's funny, I play the organs for weddings!! It's a funny old world huh! LOL, I joke of course.

Flux stops oxidisation of the joint when you apply heat. It also helps the capilary action (sucking the solder into the joint) What more is there to know than that?

Heat up twp bits of pipe. One fluxed and one not. Let it cool and observe.

 

[dontknowitall]

LOL - The bit we're asking about (and only for interest) is when you run the blow torch up and down the pipe it looks as if steam is about to come off the pipe. Maybe no-one knows and we need to ask on a chemistry forum!

 

[Garryaca@yahoo.]

Your assumption is correct young man..flux is formulated to remove the thin film of oxides that form on a metal when it exposed to atmoshpere..however it doesn’t remove corrosion thats what wire wool is for!..Think of it as car wax in reverse..look at what happens to water droplets when you wax the car they are cohesive and dont adhear to the car, and compare them to trying to solder a dirty unfluxed joint......then look waht happesn to water on an unwaxed car the water adhers to the car

 

[dontknowitall]

AHA!! Magic! Thank you. So Readingplumber was right then!!!

 

[Dannypipe]

All you're seeing is the heat traveling up and down the pipe. It does alter it's molucular structure.

You've heard of toughened steel? Well you can toughen any metal. Heat it till it's red hot, and cool it suddenly. It becomes harder but more brittle. If you heat it and let it cool slowly, it becomes softer but more flexible.

So you are just witnessing heat (around 400deg Celcius) and the copper conducts this heat well. So you can see the heated part move as you move your flame.

Does that answer your question?

 

[dontknowitall]

Thank you for that - unfortunately with all that typing it was the oxides bit that I was querying. Now off to more practising - got a gig tomorrow.

 

[kay-jay]

All you're seeing is the heat traveling up and down the pipe. It does alter it's molucular structure.

You've heard of toughened steel? Well you can toughen any metal. Heat it till it's red hot, and cool it suddenly. It becomes harder but more brittle. If you heat it and let it cool slowly, it becomes softer but more flexible.

So you are just witnessing heat (around 400deg Celcius) and the copper conducts this heat well. So you can see the heated part move as you move your flame.

Does that answer your question?

well said that man!

just beat me to it, its called annealling and the hardness of the metal you are trying to achieve is dependent on what heat colour is achieved directly before cooling for example red hot, white hot, blue etc

as danny says when running a torch up a bit of pipe the change in hue is simply the molecules reacting to the heat in a basic way.

KJ

 

[Bernie2]

Lots of copper tube is covered in an oil layer to prevent discolouration and Verdigris forming, as you heat it up it burns off and gives off fumes and what looks like steam.

Medical grade copper for oxygen is especially cleaned of these protective layers.

Flux as is said, helps clean the pipe but also has another role.

It excludes oxygen from the surface to be soldered, that is why you can't get solder to stick on a pipe without flux, even if you take all day cleaning the area with wire wool.

The old Fluxite never cleaned the pipe, you where required to use wire wool, so what was the point of using it if it wasn't to exclude oxygen?

If you solder steel, solder will not stick unless the area heated is thick with flux. Its why borax based flux is used for higher temperature silver soldering, its melting point is higher, so it doesn't run off the area before the solder sticks.

What you are trying to do is get solder to stick under a pool of flux that is keeping the air out.