Silver solder - soft solder

Hi all, I am making a saddle tank at the moment, brass skin, copper ends.

I have soft soldered a couple of bushes in but on reflection thought they may have been better silver soldered to avoid them dropping off when I soft solder the rest. My question is, how possible is it to clean it up enough to be able to silver solder or is there no chance.

Bill D

I am totally prepared to be shot down in suggesting this but here goes anyway. I am assuming that the "saddle tank" is just a water holder and not a pressure vessel. What about unsoldering the bushes and cleaning up any residues as best as possible until you are back to original metal. Then use high melting point solder......Comsol, or similar ....to resolder the bushes. Then use a lower melting point solder to fix the ends. I think that this is called step soldering.

Mick

Hi Mick, thanks for that. Yes it is just the water tank. Must admit I had not thought of higher melting point soft solder.

Checking what I am using I see it is a Powerflow 99C grade and looking on website has a mp of 228 C, higher than I expected. So I need to find a lower mp or higher one I guess.

Bill D.

Bill, I would not attempt to clean up the soft solder and then silver solder, the smallest speck of soft solder will produce a hale. To re-melt soft solder you need more heat than used to make the joint in the first place. Brass sheet has a nasty habit of buckling when heated beyond the heat for soft soldering. Trust me I know, and it was expensive. The cause was trying to make all the joints in a tank in one go. Plan ahead, make one joint, allow to cool then clean the next joint etc etc etc.

If you can mechanically hold the whole thing together with rivets, screws etc, then you can apply solder paste and put the whole thing in the domestic oven. It then heats up and cools down uniformly and buckling/twisting is much reduced. Just make sure SWMBO isn't around!

Thanks guys, confirmed what I thought really, a no go.

It is rivetted / bolted together as well so will have to persevere.

Bill D.

I did a saddle tank for a Sweet Pea loco, brass, with copper ends. I tinned all the joints, clamped it all together, and tried to solder it using ordinary plumbing solder (lead based). It was the hardest job of the whole locomotive build (the boiler was bought in). As I soldered one seam, another would open up. I managed it eventually, but Duncans idea sounds the best way. I would also use plenty of rivets to try and keep the seams together. It would be a lot easier to just rivet//bolt it all together, then use some sort of tank sealant, say Petseal. If it can cope with petrol, water in a saddle tank should be no problem. Good luck whatever way you do it.

John.

Don't unsolder the bushes, make some sort of heat sink for them, and with carefull soldering with a lower temp solder(electrical rosin cored). Pre tin the joints, and I would use a large soldering iron, if I had to use an electric iron I would use the 175W iron to get the heat into the joint quickly.

Ian S C

An old trick that might help someone was to lay a wet rag on the part to cool it.