Silver soldering

Hello. I have been trying to solder the ends on a small 35mm copper boiler but i just cant get it to work, the best i can get is a little blob on it. I am using a cheap made in china lpg gas torch i think that must be the problem. any help would be appreciated.

Hello Henry,

How long is the boiler? Pretty much any propane torch with a ~12mm burner should should be able to get 35mm tube hot enough, but don't underestimate how much heat you need to put into it. If you can surround it with insulating board (I use skamolex) it will help a great deal.

A photo of your setup would help.

Also make sure you have plenty of flux, and don't melt the solder with the flame, let the work melt it.

Neil

Hi Neil.

The boiler is 4 inch long. i have used flux. I stood the boiler on its end on some asbestos type board then leant another bit at the back. i have held the flame close and tried to hold it further back and there dont seem to be no chance of the work melting the rod.

....What Neil said!

However, I would add that it has to be 'good' LPG and properly burned in a good lamp for any silver soldering....Take a look at the gas cartridge and see if the propane is blended with another gas. Another problem I have had with cheap gas/blowlamps is incomplete combustion such that the joint sooted up before it got good and hot.

To get a good soldered joint you need to get the work 'red' hot, or at least glowing...need a clean joint untouched by fingers and need a good flux such as borax disolved in a little water.

12mm torch - sounds a bit small. If it doesn't flow, you are short of heat. Copper takes loads of heat far more than steel joints. Also, if the torch is too close, you are using the cold part of the flame. The inner cone of the flame is cold gas and the outer cone is the burning and hot part.
BobH

Try and make a 90-degree corner with the board (I hope it isn't real asbestos...) and lie the boiler along it. if you have an ordinary blowtorch set that up to blow on the far end and use the proper torch on the end you want to solder.

Neil

Hello Henry,

The LPG torch is not ideal. You need to have a bit of 'oomph' in reserve which LPG doesnt give.

However, it may be a simple lack of correct insulating firebricks round the job to prevent heat loss and contain the heat in the right place that you are working on.

Asbestos board is insufficient, and you need to go down to your local builders merchants and buy a few thermalite/celcon blocks and cut them up with an old wood saw.

What flux and silver solder grade?

Best avatar pic I've seen on here, and my 2 daughters want your contact details!!

Cheers,

Julian

Edited By julian atkins on 12/03/2017 20:27:46

Edited By julian atkins on 12/03/2017 20:28:54

I am using a lamp connected to a calor gas 19kg gas cylinder but like i say its a cheap one. I am using johnson matthey easy flo rods and flux.i think i need to insulate it better and maybe get a better torch. i thought copper would be easier than brass ect but there is another lesson learned.

Cheers Julian I didnt know i still had that effect on ladies.

What sort of regulator are you using? You want one that will allow at least 2bar pressure. The flat non adjustable ones don't flow enough gas as they are rated in mbar

Henry,

I have one of these sets:www.clarketools.net/clarke-gas-torch-with-3-nozzles

With the aid of skamolex board and a bit of background heat from an ordinary blowtorch I have silver soldered a centre-tube vertical boiler nearly 4" diameter and 8" high.

I do plan on getting one of these somet time as I do feel the vertical boiler was a bit big for my current set : www.clarketools.net/clarke-gas-torch-with-3-nozzles---pc108---3404115-11295-p.asp

(the links may look the same, but aren't).

Neil

Thanks Neil.

The first link is similar to the one i have but. the regulator is an high flow one i already made that mistake. i will try insulating it properly if not i will get a lamp with the big nozzles on it like in the second link.

Henry

More heat. The little blob of solder suggests that the solder has melted but the copper surface was too cold. Remember that copper is a very good conductor of heat so you will need more heat than with brass or steel.

Your boiler is quite small so try "building" a little thermalite box around it to contain the heat. I find this really helps. Also remember that the hottest part of the flame is its tip. If in doubt hold the torch further back from the job (the gas has to be given space to burn).

Silver soldering is very satisfying but one needs a little bit of practice to get the hang of it.

JA

Thanks Everyone i will just keep going until i get it right.

The copper has one major advantage over brass when silver soldering, with LPG you are unlikely to melt the parent metal.

I find that a lot of small jobs, I can, using LPG braze stuff using brass,either wire or strip.

The cage around the fan on my stove top Stirling Engine is made of steel fencing wire brazed together with brass strip.

Ian S C

Edited By Ian S C on 13/03/2017 10:26:35

http://www.cupalloys.co.uk/best-practice/Hello Henry,

If you are having difficulty you are probably not sticking to the overall principle of silver soldering - the use of capillary flow to efect the joint.

There is cleanliness of the joint and correct heating.

Cleanliness at brazing temperature is the important bit. That is achieved by using the right flux Use a flux that matches your heating time and melting range of your alloy. If your silver solder simply melts and goes into a ball you have a flux problem. Simple. There is enough heat to melt the alloy so that is not a problem.

Initially use a conventional low temp flux. Mix to a paste and apply liberally to the joint. Then apply the heat. BE PATIENT. Wait until the flux melts and turns into a clear liquid. The flux isnow working. The flux also tells you that you have achieved brazing temperature. NOW APPLY THE ROD TO THE JOINT.

If you are not melting the flux. You simply need more heat. Fit a bigger burner and burn more gas.

Alternatively, if it is taking a while to get the joint hot enough, the flux may be becoming exhausted. A liberal covering can help or alternatively use a longer life flux eg HT5. It too melts nto a clear liquid as you achieve brazing temperature but protects the joint longer.

Please do not use borax as a flux with cadmium bearing silver solder. It only starts to work at higher temperature resulting in the overheating the alloy with the increased evolution of toxic cadmium metal fume.

In essence either change your burner or change your flux.

For more information go to www.cupalloys.co.uk/best-practice/

Regards

Keith

Edited By CuP Alloys 1 on 13/03/2017 12:07:24

Edited By CuP Alloys 1 on 13/03/2017 12:13:15

Let me guess... No. 8?

Neil

Yep, wot else.

Ian S C

For more information on all topics related to silver soldering/brazing visit

**LINK**

Regards

Keith

Thanks Neil

Edited By CuP Alloys 1 on 15/03/2017 10:37:30

Hi Henry

Using Copper to Copper joints personal preference would be "Silfos" the trade name it is a harder silver solder that does not require flux.

Not being a fan of LPG for silver soldering I use Oxy-Acetylene or Acetylene if it is available.

Keep the flame on the job at all times and adjust the temprature by moving the flame further away or closer.

Waggling side to side will allow the molten metal to oxidize and weaken the joint.

Eric

Silfos "appears" to be phosphorus bearing.

I believe the conventional wisdom is that such solders can be a poor choice for steam boilers. I think the idea is that sulphurous gasses embrittle the joints. Obviously this is less than ideal in a boiler, especially if it is coal fired.