Soldering/brazing a boiler.

Placing solder around the joints : Yes, I did it this way when I was soldering the cylinder to the spacer. I did not have the full flame burner then and I could not get the metal hot enough to solder it properly. But by heating the metal parts as hot as I could then heating the solder which I had already placed in position I was able to achieve a good join.

I think you can only do it this way when you have a ''horizontal ledge'' on which to place the solder pieces. This method would not work when soldering the top and bottom caps of the boiler but it I may use this method when soldering the chimney, steam outlet and safety valve.

1. It is good to know that the solder has a higher melting point when heating it a second time. That is very useful information. Why is it so ?

2. Placing the metal parts in citric acid for a few hours seems to get everything much cleaner then using sandpaper. Is this an acceptable method to clean the metal prior to soldering ?

Edited By Brian John on 06/12/2014 08:32:32

Edited By Brian John on 06/12/2014 08:32:52

Edited By Brian John on 06/12/2014 08:40:42

There is some sort of chemical action that alters the structure of the filler rod, I'm sure Keith can explain it better if he is looking in.

Sandpaper and emery cloth are not ideal as they can contaminate the surface. Try a Scotchbrite pad, wire wool or a fine steel wire brush.

How long should the item be left in the citric acid pickle ? I would think that once it is clean and shiny then it is okay to remove it. Many people say that they leave it in over night but I do not see the need for this.

Brian, good to see you have got a good torch.

Just out of interest, you could not buy a cylinder like that one in NZ, dark coloured cylinders where banned last year, and only white (and I think yellow) cylinders will be filled. The cylinder I have for my emergency cooking set up is blue, and due for retesting, it will require a new cylinder. Reason, over heating when left in the sun, ie on the BBQ.

Ian S C

I think it's just a matter of convenience Brian.

For me it often depends at what time of day I finish doing the work. If it's late then I do leave things overnight so they are ready for the next day but if it's earlier - then I do tend to fish them out quicker but mainly to see what they are looking like. I don't think I've had any problems by leaving things in for longer but I wouldn't just leave work 'soaking' for very long periods though.

Regards,

IanT

> It is good to know that the solder has a higher melting point when heating it a second time. That is very useful information. Why is it s

I think it's due to the evaporation of tiny amounts of tin, raising the melting point.

Certainly if you allow the flame to melt solder before the parent metal is hot enough, it takes more heat to melt it again than it does to melt fresh solder.

Neil

Most silver solder alloys don't contain tin. I suspect the real reason is that it absorbs copper from the parent metal thus changing the composition. Perhaps our expert from the supplier will explain better?

Russell

Stage 2 : I soldered the top cap (which is at the bottom in the first photo) and the bottom of the chimney (which is at the top in the photo). As mentioned previously, I fluxed the chimney and put some small pieces of solder around it. I then concentrated on soldering the top cap. Once I hit the boiler with the full flame it did not take long for the metal to get hot. By the time I had finished soldering the top end cap, the solder had already melted around the chimney : two jobs in one go. The second photo shows it cleaned up after one hour in the pickle.

In the third photo you can see what I have to solder tomorrow : the top of the chimney, safety valve and steam outlet which will all be done in one go. I think I will place small pieces of solder around the required areas and use the medium burner...not sure yet.

How do you clean the inside of the boiler ? I have to remove the black stuff from the outside by rubbing with a sponge which I cannot do on the inside.

Edited By Brian John on 07/12/2014 03:09:08

1. Update : I realised that I have the pinpoint burner which has a heat output of 0.75 kW compared to the full flame burner which is 7.00 kW. For doing the smaller parts, I think I need the medium burner which puts out 2kW. I doubt that the pinpoint burner would get the job done but any comments would be welcome.

2. What sort of solder do they want you to use when they specify soft solder : plumbers solder, electrical solder or something else ?

Edited By Brian John on 07/12/2014 08:48:50

Soft solder for this sort of thing would be plumbers solder 50/50, it has a slightly higher temp than electricians 60/40 solder. There is another grade used by car radiator builders, it has a temp rating a little higher than that used by plumbers.

With silver solder , one of the alloy metals evaporates, and the rest alloy with the metal being joined, to start the remelt I touch the joint with the rod(when the metal is hot enough), and away it goes, it's a bit different if you'r using oxy acetylene, or oxy gas.

Ian S C

Personally I would use the 7kw burner as you will still need to get the copper hot enough to form the joint not just the little fittings. Keep the flam playing mostly on the copper and the fittings will soon warm up with it. Infact if you ait to do te top chimny joint and teh two bushes in one go the heat from doing te chimney will likely spread far enough to do the bushes too.

Yes just plumbers solder will do, you will most probably find that it is lead free and get a suitable flux from the same supplier as your silver solder flux can't be used.

I did use the full flame burner and the job is now finished but not without a slight problem. Look at the chimney in photo 2 : what has caused this...is it too much heat at this point ? I did not think brass would do this.

Edited By Brian John on 08/12/2014 05:56:38

Edited By Brian John on 08/12/2014 05:57:45

Edited By Brian John on 08/12/2014 05:58:10

Yes too much heat, the brass has almost become liquid and sagged under its own weight. I expect you were concentrating on the joint area and did not see the chimney getting hot further up. Solder joints a very good though.

So this burner can melt brass ! I did not think it could get that hot. Any thoughts on repairing the damage : a sleeve around the chimney perhaps or just leave it alone ?

How do other people clean the inside of the boiler once all the soldering is finished ? I was thinking of dropping some small ball bearings inside and shaking it up.

Brian, yes it will melt brass, often when I'm joining steel I use up some of a supply of scrap brass sheet, or brass wire if I can get it, my metal supplier doesn't stock it any more. I use a similar torch to your's.

Ian S C

You need to reheat, remove chimney and fit new one. If you dont you will never be happy with it. Re soft solder, ensure you buy a reel which has lead in it. You can still get it and its loads better than the lead free stuff.

Something will have to be done ; overnight it has developed a small hole. My option are as follows

1. Remove it and get a new one. I do not really fancy trying to remelt this solder as I would have to melt both ends at once to get it out.

2. Cut it off and have a short chimney. This is probably the easiest option but it will look a bit odd.

3. Resleeve it with copper or brass tubing. The current chimney is 16mm OD (5/8'' = 15.875). I need something that will be a good fit. I will do this if I can find something to fit ie. ID is 16mm.

A bit of copper tube the same size could have a short length expanded at one end for a few mm, the damaged chimney cut off, and the copper one fitted over the stub and silver soldered on.

Ian S C

Yes, I have been thinking along the same lines. I was down at the hardware store today (Bunnings) but they did not have any copper or brass tubing that was a good fit. There was some steel pipe which was a perfect fit but I will leave that for the moment.

Tomorrow I will try the plumbers supplies for offcuts of brass and copper and I also have the number of three scrap metal merchants...somebody must have something.

Why did Midwest supply a a brass chimney anyway ? I would have thought a copper chimney would have been the sensible option.

Edited By Brian John on 09/12/2014 12:26:12

Edited By Brian John on 09/12/2014 12:26:27

As I'm not a model builder, I have no experience of soldering model boilers but from my experience in plumbing and electronics manufacture, I'd be wanting to use the lead / tin rather than lead free (ie almost entirely tin) solder.

Apart from lead free solder having a higher melting point, it has lower surface tension and doesn't benefit from the more gradual solidification you get with lead itself - and leaded solders. It doesn't wet and fill gaps as easily and when it flows it's a lot more mobile. You certainly wouldn't be able to "wipe" it with a moleskin like the traditional plumbers used to for instance.

Although plumbers are required to use lead free solder for pipework that is carrying drinking water (similarly for electronics), presumably you can still find leaded solder if you look. If I didn't have some already I'd be looking to get some before tackling a job like this.

Murray