Silver soldering mamod loco's?

[brian777999]

 

The Mamod boilers themselves are made of a good grade of quality brass, and are soft soldered together with a high melting point soft solder (Pewter grade), not silver solder.

 

The reason for this is that silver soldering brass sheet risks burning up the zinc content, and rendering the brass brittle, or even porous,if wildly overheated.

 

This is the reason that brass fittings are not used on any boilers in direct contact with heat, or soldering by brazing, or silver solder, bronze is used instead. It is called de-zincing, and is dangerous on larger boilers.

 

If the Mamod boiler is simply leaking from a seam, it should be cleaned out inside with a good kettle de-scaler, and then the outside cleaned with a stainless steel brush, a plumbers flux added to the repair,and soft solder of a high melt point added, the old fashioned Tinmans grade. A 60/40 solder could be used for pin hole repairs. It will usually need a small gas torch to get the required heat, or a very powerful electric iron.(150- 200watt).

Modern pure tin solder is quite all right for repairs, the lead free type of solder with a higher melt point.

 

Once Brass has been soft soldered, it cannot then be silver soldered, the lead contaminates the surface, and silver soldering cannot take to the metal properly.

 

Silver soldering is strictly a gas flame job at 600c or more, dull red red or more, and is done on new metal, and rarely brass, except where no further heat with be applied. Easy flo silver solder is the usual grade used a medium free flowing solder, used with Easy Flo flux.

 

So in all the Mamod is a safe, soft soldered boiler, at a suitably low pressure to meet the regulations for toy and model uses

 

 

 

''Soft solder of a high melting point'' : could you be more specific as the solder temperature required ? I have some 243 degree solder here. Is that adequate for soft soldering tiddler boilers (not Mamod) fired by meths burners ?

[peach james]

OK, so my experience is generally of bigger- but not by all that much !.  

 

If I was making a boiler for a 16mm engine, I would dig up my notes from "The Generating Game" in MRC ~1985 or so, and KN Harris, Model Boilers & Boilermaking.

 

I probably would use copper, and silver solder the lot.  The costs of the materials are in proportion to the labour, tiny.  I did most of the work on a 2 1/2" OD boiler when I was perhaps 11 or so.  It never got finished, but I did the math, and the fabrication of all the bits.  We got as far as the inner box/tubenest being done, but never finished it.  

 

Key idea is clean.  Clean clean clean !.    I prefer propane because it makes it hard to burn the materials- be them brass (fittings), or copper/bronze.  Oxy-anything is a poor idea unless it is steel that you are silver soldering, or have lots of experience.  (you know how you get experience?  from good judgement.  You know how you get good Judgement?  From bad judgement...)

 

I'd suggest this thread possibly belongs down in the 16mm section of the page, although it is definitely a skill !

 

- as regards boilers being calked with soft solder, I have one here that is run at 40 PSI, and dad had a railway engine that was around 60 psi, and were done with Comsol, AS A CALK ONLY.  mechanically, both are held together by other fasteners- the one downstairs by rivets, the railway engine would have been a mixture.  That's the tinman's solder, as it melts at a well hotter temperature than 60-40 does.  It is not unusual for pre 2nd war engines to be constructed that way, and it is an acceptable way of constructing a boiler.  However, they have much less resistance to mal-treatment than a silver soldered boiler.

 

James

[brian777999]

I usually build my boilers out of copper and silver solder and they work well. However, I have picked up a pre soldered brass boiler from Sussex Steam on ebay. I may want to add some fittings such as a safety valve and pressure gauge to this boiler so I want to be able to solder some new pipework onto it without melting what is already there. Any suggestions ?

[bertiedog]

Adding to an existing boiler should be Ok if your careful. A boiler should be very carefully cleaned in acid, ( citric will do or acetic), and all existing joints examined for defects like dry joints etc. It may pay to actually re-melt any suspect joint with lashings of Bakers fluid flux. it will be best to use 60/40 lead/zinc solder for additions. The old joints will probably melt at a higher temp than the fresh solders, so you have a margin.

Use an intense small gas flame to raise the temp locally on the additions.

 

To add several items, make only one connection to the boiler, and let that feed a steam turret where the unions are added to each feed. Saves multiple joints to the boiler.

 

A small steam turret is a square bar of brass drilled through, but leaving the far end, and the steam enters the end via the threaded hole, the units are added to half frilled holes that enter the already drilled centre.

 

Try to go into the boiler at the end, not the barrel. As the new union has no thread the union must have a large flange around it to maximise the soldered area. The flange can be drilled with three/ four holes AFTER the soldering and carefully fitting tapped brass screws into the holes, then re heating and caulking the screw heads with more solder. This is just a bit more security than no screwing at all being involved.

This type of union is not really commercially made, but any engineer could make one, or you may find a commercial unit that is close enough. The popular thread for unions are 1/4x 40 tpi, and 3/16th x40 tpi, or use the BA sizes nearest, 0Ba and 2BA if you make your own unions.

 

Stephen

[brian777999]

 

Try to go into the boiler at the end, not the barrel. As the new union has no thread the union must have a large flange around it to maximise the soldered area. The flange can be drilled with three/ four holes AFTER the soldering and carefully fitting tapped brass screws into the holes, then re heating and caulking the screw heads with more solder. This is just a bit more security than no screwing at all being involved.

This type of union is not really commercially made, but any engineer could make one, or you may find a commercial unit that is close enough. The popular thread for unions are 1/4x 40 tpi, and 3/16th x40 tpi, or use the BA sizes nearest, 0Ba and 2BA if you make your own unions.

 

Stephen

 

The end of the boiler : I had not thought of that but it makes sense. I have taps and dies up to M6 metric coarse and also for 1/4 X 40 and 3/16 X 40. 

 

Is soaking in white vinegar acceptable for cleaning brass and copper ? This is  what I usually use to clean metal before and after silver soldering as it is very cheap. I also give everything a good scrub with a wire brush. I have citric acid powder but the vinegar seems to work just as well.

[bertiedog]

Just use the vinegar or mixture reasonably hand hot, not boiling, it cuts the time down over a stone cold acid. If your cleaning fittings then boil the acids and drop fittings in for a few minutes to clean, Always rinse out afterwards.

For tougher cleaning the Drain Clean acids, for clearing up bunged up drains will work on brass, especially the type with Hydrochloric acid, but do not leave long and rinse immediately.

For the thin shell boilers use only the 40 TPI thread versions, Metric series are far too course.  

[Killian keane]

I usually build my boilers out of copper and silver solder and they work well. However, I have picked up a pre soldered brass boiler from Sussex Steam on ebay. I may want to add some fittings such as a safety valve and pressure gauge to this boiler so I want to be able to solder some new pipework onto it without melting what is already there. Any suggestions ?

Was it not supplied with a safety valve?

P.S about mamods only being capable of working at 15 psi or so, I have known them to be ran on 20-30lb psi, indeed, mine is fitted with an adjustable s/v made by Tom Cooper