Issues trying to silver soldering a 3" copper tube

Hi! I'm constructing a boiler following an youtube video from Myfordboy. I'm in the soldering phase and came across an issue. I soldered the two plugs on the top cap with ease but when I tried to do the same for the water gauge plugs at the tube the silver solder didn't flow. I'm using a MAPP torch with 30% silver stick. The tube is a 3inch by 1.5mm. I mantained the torch open for more than 5 minutes but failed. Do I need a more powerful torch?

Thank you!

Carlos Moura

Sao Paulo, Brazil

Hi Carlos welcome to the forum. 

It sounds that you need a larger blow torch and what are you using to sit the tube on as you will need a hearth to contain the heat whilst getting it hot enough to flow.

David

Edited By David George 1 on 17/08/2020 19:56:11

Edited By David George 1 on 17/08/2020 19:56:32

Hi David!

I bought a mini oxi-acetylene torch ( it will be delivered wednesday ).

I'm using some bricks where I place the parts to be soldered.

Thank you very much for your help.

*** I'm returning to the model making after 30 years and I'm new to the model steam world.

Cheers

Carlos

The oxycetaline torch is OK for local heat but I believe a propane large heater is better for large pieces to silver solder. You will need some long lasting flux and some heat reflecting blocks and matting. Have a look on this web site Cupalloys. For demo and suplies.

https://www.cupalloys.co.uk/home/index.asp

David

Thanks for the hints! The website has lots of good information.

I'll try again using your advice!

Cheers

Carlos

I was surprised at how much hotter a propane / oxugen torch is compared to MAP gas.

Today tried to braze held a small part and the MAPP gas torch melted the brazing rod onto the job after 4 or 5 minutes. Tried the oxy torch on a very low flame and melted in less than half a minute.

Paul.