silver solder disaster

Hi guys, big depression over the south west at the moment.

Finally got round to silver soldering in the tubes on my GLR vertical boiler.

Pickled, washed, dried, fluxed tubes and end plate, fixed solder rings around tubes, applied heat with Sievert propane torch. Some solder flowed most of it did not, especially the tubes in the middle of the pack.

Flux easy flow, solder 455 grade cadmium free, 1.5mm dia from Cup alloys.

Any ideas where I have gone wrong?

Earlier attempts, soldering in the end plate and firehole ring looked excellent.

Bill D.

not enough heat or if your sure it was hot enough then the flux has burnt out for sure.

Hi Bill,

Not done too much but I would guess that your flame was too small and too fierce so that you heated the outside but not the middle where the heat has radiated away down the tubes.

I would say you need to have a big flame burning gently so that you heat the whole boiler evenly. All the tips I have read say to watch the flux; you would have seen some boil while other stays a paste.

I am curious to see what others say as I have to follow in your footsteps sooner or later.

Andy

Hi Bill,

If the end plate and firehole went well you are obviously doing something right!

The information is a little "patchy" Two main reasons for the alloy not flowing,

1) the joints dd not get hot enough. This is easily done in a nest of joints.

Do the inner joints first and let the heat dissipate outwards.

Fit a bigger burner

2) the flux became exhausted during heating.

Or give us a call on Monday

regards

keith

Switch to a longer life flux like HT5

....like I said.....

for what its worth i find the ht5 flux has a very different effect on the silsol, it doesnt flow nearly as readily which can be used in ones favour if the gap is a tad oversize. It realy does last a lot longer too. I reserve its use for oxy jobs only as easyflow is exhausted very quickly if you make a wrong move with the torch! The ht5 is also very good at 'cleaning' the substrate.

Thanks for prompt replies so far. Now that its cooled down have had a close look. It is a tadge better than I expected, the tubes seem to be firmly attached so I guess some solder has found its way into the joint albeit remains of solder rings are still visible.

However I am working on the assumption that the joints are not good enough to hold pressure.

I have dropped it into the citric acid mix to clean it up and will have another look tomorrow.

What I was wondering is the feasability of now soldering from the other side, ie inside the fire box.

Bill D.

Where have I gone wrong? You have, it appears tried to solder through the nest of tubes. In your last post you have described the right way and that is from inside the firebox. You then get the heat where you need it and that is where the tube comes through the tube plate, some of the flame will go into the tube and help with the solder flowing. You will need a neck tube burner and another burner to provide the background heat. Doing it the other way the heat is absorbed by the nest of tubes and conducted away from where the heat is needed.

Neck tube burner is where the burner head is carried on an extension tube of about 9" length, the air is admitted by a hole at the farthest part of this tube from the burner. If you try to use an ordinary burner it will blow out as there will be insufficient oxygen in the air that close to the flame.

Hello Bill,

The burners refered to by Dusty are called cyclone burners. The neck tube described fits directly onto your propane torch handle. I suggest you opt for the larger of the two available ie 10kw,

Another option is to use oxy-acetylene inside the firebox but that opens another can of worms. Unless you are careful, the intense localized heat can cause more problems than it solves eg holes in tubes!

If you can, stick to propane.

regards

keith

Had a look this morning and the pickling had removed all the gunge as intended showing that several of the tubes were loose. Non of the rest looked satisfactory.

With regard to my method, this was described in an article that came with the boiier kit and written by Stan Bray in ME. Having another look, it definitely shows the firebox right way up with the flame through the tubes, the firebox surrounded by firebrick. I am wondering if I did not get enough firebrick around the firebox allowing too much heat to escape. So the question now is how do I get out of this, try to resolder as it is or unsolder (if possible) and start again. Is it possible to solder a row at a time so I can get in with with solder wire individually or is the whole nest at once the best method. Keith I will e-mail you separately to sort another burner, my current one incidentally is a 2941. Sorry my paragraphs have gone to pot, I can't scroll down all of a sudden, just not my day is it!. Thanks all for assistance so far. . Bill D

Bill

I would be careful of photo's in books showing how something is done, they tend to be posed and in consequence not always accurate. I know it is stretching it a bit far, but would you try chopping down a tree in the middle of the wood from the outside of the wood? The answer is of course no. Yes you could insert the tubes a row at a time but it is not advisable. The more times you heat the assembly the greater the chance of failure. I would favour pickling it, cleaning with a bit of scotchbrite pad flux it, then resolder, from the inside, if possible within the hour after removing from the pickle. I would not remove the tubes unless absolutley neccessary.

Hi Bill,

You do need to surround the job with refractory, this will retain heat allowing for a quicker temperature rise (so's not to exhaust the flux) and a better spread of heat throughout the job. The best refractory is not normal firebrick or old storage heater bricks. These are intended to absorb heat and relaes it slowly, it will take a longer time to heat the job and can lead to flux exhaustion. The best refractories to use are the softer, white refractory bricks containing a high proportion of perlite (not pearlite). These will absorb little heat and reflect much back into the job, as a reverberatory furnace does thus shortening heating time and saving gas as it is more efficient.

By the way, solder will follow the heat, experienced professionals will heat the whole job, then concentrate on a small area to start the solder flow and move the flame around the joint to be made and the solder follows. In silversmithing for example it is important to use as little solder as possible while obtaining a sound joint. Work will be ruined by the excess solder that I see in model boilers. It have often seen model boilers that look as though the maker was trying to increase the thickness of the end plates with silver solder . I know that the working pressures are not the same but no one want to be scalded caused by a failed joint on a coffee pot or hot water jug handle - yes, silver ones are still made in the great British tradition

Best regards

Terry

Hello Bill,

The remelt temperature of the 455 is higher than that of the original alloy. That will offer some help in not remelting what is there.

Use plenty of flux to protect the joints already made.

The use of a kaolin clay insulation blanket might offer advantages over bricks as it is more flexible and can be placed more easily.

Be careful with scotchbrite, grit wheels or emery cloths when cleaning. They can leave fibres or deposits that the flux will not be able to move and possibly creating pinholes in the joint. If you want to "tickle up" the joint better to use a brass brush.

regards

keith

PS Thanks to fizzy, Dusty and Terryd in their efforts to help a customer.

Thanks again for replies and comments. Having had time to ponder I am fairly confident (dangerous) that I got too much heat on the flux/solder and not enough in the metal.

Have ordered a cyclone burner to have another go inside the firebox this time. Will make sure it is well packed with insulation as well.

Yours apprehensively

Bill D.

Bill, avoid getting heat directly on the solder, if the solder wont melt from the temperature of the metal alone you will be lucky to get any joint at all.