Soldering/brazing a boiler.

[MuzzerParticipant @muzzer]

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

[Keith HaleParticipant @keithhale68713]

1) Lead bearing soft solders are readily available as solid or flux cored wire.

2) Citric acid pickle turns blue due to the formation of copper citrate during the cleaning. Copper citrate is blue.

3) The remelt temperature of silver solder is due to mainly

a) the silver solder dissolving copper/zinc/iron from the parent materials so changing the composition or

b) to a lesser extent the loss of cadmium during heating

Regards

Keith

[FMESParticipant @fmes]

Posted by Brian John on 09/12/2014 12:25:50:

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

Could possibly be because it was supposed to be soft soldered and not subjected to the temperatures of silver soldering.

I admit I refer a fair bit to boiler construction books from both Martin Evans and KN Harris and as far as I recall the use of brass in direct construction of a slver soldered boiler was not recommended by either.

[Neil WyattModerator @neilwyatt]

There should be no problem with brass for a chimney, as it's not a structural element of the pressure vessel.

Neil

[FMESParticipant @fmes]

Posted by Neil Wyatt on 09/12/2014 18:22:45:

There should be no problem with brass for a chimney, as it's not a structural element of the pressure vessel.

Neil

As a chimney, possibly not, as a flue running through the boiler it supports the end flanges.

If it has got hot enough to melt then there is the possibility of de-zinctification and resultant brittleness of the brass at the copper joint.

[JasonBModerator @jasonb]

Yes its a structuarl part of the boiler just like any tube in a loco or TE boiler.

On the question of brass I don't think its likely to be such a problem on a small boiler like this, after all Momods all have brass boilers throughout. And if it does fail the water will just put the fire out a bit like a fusible plug.

[Neil WyattModerator @neilwyatt]

You mean it goes right through?

I thought it was fitted over the end of the central flue. I wondered why it wasn't just a push fit.

If it was my boiler I'd separate chimney and flue (checks) like I did with my boiler… but then I think Tubal Cain pointed out that brass on a small boiler might become brittle after a century of intermittent use.

Neil

[Brian JohnParticipant @brianjohn93961]

I went to the scrap yard this morning and a found piece of copper tube which fitted nicely over the brass tube. I also found some copper tube the exact same size as the brass chimney so next time I build one of these I will use a full copper chimney right through which is what Midwest should have done in the first place. I decided to remove the damaged part of the brass chimney ; I think this was a mistake as it would have helped keep everything upright by leaving the full chimney intact.

As you can see from the photos below, after the solder had hardened the chimney is not perpendicular…very frustrating as it was perfectly straight when I started soldering. I suspect that the top of the boiler may have changed shape and buckled a bit or the copper sleeve was not as good a fit as it could have been.

After putting it in the pickle for one hour a decided to give it a quick test to see if it actually produces steam as there would be no point putting the insulation and wooden lagging on if there was a leak somewhere. In the photos below it is not actually under pressure as I left the fitting out for the steam outlet but the water does boil and steam comes out of the hole so something should happen when I connect it up.

I really must buy another one of these and do it properly next time ; both the boiler and the engine could have been much better. I am not sure if it worth trying to remove the copper sleeve as that would require a lot of heat and it may ruin all the other solder joints.

NOTE : It does not look too bad in the photos but it is actually quite bad……seriously thinking of grabbing the blow torch and trying to remove it !

Edited By Brian John on 10/12/2014 03:10:04

Edited By Brian John on 10/12/2014 03:10:53

Edited By Brian John on 10/12/2014 03:34:07

[Neil WyattModerator @neilwyatt]

Brian,

The copper should now be in a very soft state, A bit of broom handle down the chimney and very gentle, controlled pressure should see the chimney upright. Just be very careful not to dent or crease the boiler – you will need to find a way of holding it that gently spreads the load.

Neil.

[Brian JohnParticipant @brianjohn93961]

Thank you for that suggestion ; it worked well. I had a piece of wooden dowel which was a perfect fit and the chimney is now straight. So I decided to fire it up and see if it runs the 3BIM engine from PM Research. Nothing much happened for a while : there was a bit of steam and some water but that's is all. Then I noticed the boiler was turning a golden brass colour. I did not like the look of this so I removed the flame to see what the problem was. In all the excitement I had forgotten to fill the boiler with water !

I let things cool down and filled the boiler. This time I think I had too much water ; the steam engine was a water pump with water and oil being pumped from the exhaust but after a few minutes the water level in the boiler dropped and things started to run perfectly. So my first boiler is a success. I still have to add the insulation, wooden lagging and the brass stand.

I do have a few questions :

1. I used silver solder (hard solder) on this boiler even though I did not have to. When is silver solder essential ?

2. Why did the copper go a golden/brass colour ….what is happening there ? Will it stay that colour ? I notice that the chimney is now reverting to its usual colour but the boiler is not. I am just curious.

3. Have you ever done anything as stupid as not filling the boiler with water ? I guess it is like running out of petrol in your car…it is something you only ever do once in your life.

4. I was wearing full face protection and leather gloves during this testing. Do you wear eye protection at all times when working with live steam or am I being over cautious ?

Edited By Brian John on 11/12/2014 02:39:47

[Brian JohnParticipant @brianjohn93961]

I dropped it in the pickle and the copper colour was restored ! I ran the twin cylinder 7BIM engine today and all went well. I did not forget to add water and only filled the boiler about 3/4 full. This engine really needs a slightly bigger boiler but it did turn over and ran quite well.

The little wobbler engine runs but only for about 15 seconds then it runs out of steam. I suspect that the piston is not a good fit. I mucked it up when soldering the piston rod to the piston. I have tried to build another piston (which was a perfect fit) but the problem is trying to drill a hole exactly in the centre to take the piston rod ; I am always slightly off-centre. I know it would be easy with a lathe but there must be some other way to get it right ?

 

Edited By Brian John on 12/12/2014 02:37:11

[JasonBModerator @jasonb]

Brian, the change in colour was just the copper starting to oxidise, as you have found the acid soon takes it off.

One thing that will reduce the amount of water and condensate being spat out of the engine would be to have your rubber tube sloping back DOWN to the boiler, just stand the engine on something to raise it up a bit.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Brian John on 12/12/2014 02:32:42:

I have tried to build another piston (which was a perfect fit) but the problem is trying to drill a hole exactly in the centre to take the piston rod ; I am always slightly off-centre. I know it would be easy with a lathe but there must be some other way to get it right ?

.

Brian,

Yes there is … but it is extremely tedious:

Drill the hole [as best you can], in the centre of a slightly oversize blank, and fit the piston rod.

Now take a piece of wood [or whatever] with long groove in it to accept the rod, like a shallow vee-block … the Piston blank needs to overhang.

Now proceed to file the blank to the correct diameter; whilst rotating the rod a little, under your fingers. … With practice, it is possible to file a good cylinder this way.

But: You will almost certainly mess-up the first few attempts; and will be yearning for a lathe of some description.

MichaelG.

[JasonBModerator @jasonb]

I think I an right in saying that there is no end cover on the cylinder so there really is no need for a concentric round piston rod, it just needs clearance to miss the crankweb. So take a bit of the rod you have that is a good fit in the cylinder, file the two sides to leave a narrow "rod" and then cross drill for the crank pin.

If you wanted you could also file the other two edges

 

Edited By JasonB on 12/12/2014 08:41:08

[pgk pgkParticipant @pgkpgk17461]

JasonB's answer is way simpler than what i dreamed up:

Which was to drill right through an oversized piston block, bond a length of piston rod right through. Find a way of clamping your drill horizontally after drilling through 2 blocks of wood.. source some cheap bearings to fit the rod and the timber holes.. smear the outside of the bearings with slow set epoxy then clamp the whole shebang' sections down – effectively giving you a temporary lathe jig. If you can then find/make 2 blocks as referece for the finished piston height then you have further reference for filing/sanding

The slow set epoxy gives you time to set it all up

Edited By pgk pgk on 12/12/2014 09:20:21

[Brian JohnParticipant @brianjohn93961]

Some good ideas here. I will think about it tonight. 

1. I have another small problem : how to cut a NEAT 3cm diameter semicircle in the brass sheet which acts as the stand for the boiler. I do not want to hack away and leave a mess. I need to cut a semicircle in the brass so I can use the metho burner. The original design was for the brass cylinder to sit over a cup filled with sterno. The brass sheet is 0.12mm thick and is still currently in a flat shape. Any suggestions ?

**LINK**

2.  What do they use to solder real full size boilers as on a steam locomotive ? Is that silver solder…is it the same technique ? It must be quite expensive to solder a boiler of that size !

Edited By Brian John on 12/12/2014 12:48:59

Edited By Brian John on 12/12/2014 12:55:55

[JasonBModerator @jasonb]

1. a few cuts with your junior hacksaw will remove most of the waste and then a half round file will take care of the rest.

2. They generally used rivits for the plate work and the tubes are expanded (stretched from the inside) so they are a tight fit in the holes. Mostly all steel construction.

Edited By JasonB on 12/12/2014 14:46:30

[Gordon WParticipant @gordonw]

Modern boilers are all welded.

[Brian JohnParticipant @brianjohn93961]

I could not get the brass plate to cut neatly and it seemed quite flimsy anyway so I have cut away the bottom 40mm which forms the base. I will make a stand of my own either by cutting up the angle brackets shown in the photos or some brass strip (not sure yet). But I added the fibreglass insulation and the wooden lagging which is held on with the brass bands : you just about need four hands for this !

First I added the layer of fibreglass insulation ; it stuck to itself quite nicely and held itself in place. Then I added the brass plate which I have now cut to fit the boiler ; it no longer forms the stand. This brass plate was held in place with masking tape which had to be left on. I hope it does not cause problems when I next heat up the boiler ? Then the wooden lagging (already painted with 3 coats of estapol) was stuck to a long strip of masking tape and wrapped around the boiler. It was held in place with the masking tape until I secured it with the boiler bands then the masking tape was removed. In theory I can now pick it up while it is still hot but I am yet to try it .

I might give the chimney a coat of pot belly black heat resistant paint as it looks a bit shabby due to the heat.

1. What do most people usually do with the chimney…paint it or not ?

2. Would the original brass chimney have stayed nice and clean ?

3. The wooden lagging was coated on both sides with three coats of estapol many weeks ago. Do most people give the lagging a coat of something or do they leave it as bare timber ?

4. I wore latex gloves when handling the fibreglass insulation . Was this necessary ie. do fibreglass fibres stick into your skin like needles ? What is the usual insulation for boilers ?

 

 

 

Edited By Brian John on 14/12/2014 05:37:16

[JasonBModerator @jasonb]

Unless you have an unhealthy liking of polishing metal then the black paint is the way most people would deal with a chimnet. A copper or brass trim could be fitted to the top and kept bright for decoration.

No the brass would also have tarnished

Yes usually oiled or varnished

Usually not a problem on fingers but some people are more sensative than others

J

 

PS New rivited boilers still being made just like the old ones or a combination of rivits and welding eg welded barrel and firebox but externally rivited. Nice little rivited one here

Edited By JasonB on 14/12/2014 07:44:30

[Brian JohnParticipant @brianjohn93961]

I tried to paint the chimney today after carefully sanding it clean with 1500 wet/dry then wiping down with metho and letting it dry. The boiler itself was masked off. I had about six different brands of high heat paint to choose from all of which stated on the can ''no primer required''. I chose Hammerite High Heat Paint (black) in an aerosol can. Trust me to choose the dud brand ! It did not stick to the metal at all ; the chimney looks like it is covered in black fluff. I have no idea what went wrong here. I have done a lot of airbrushing on metal and I have never seen this type of result before. It even looked fluffy on the masking tape so I suspect a dud product.

Edited By Brian John on 15/12/2014 05:41:24

[Ian S CParticipant @iansc]

I used an aerosol BBQ matt black paint on my stove top hot air engine, it soon turned grey. Here it is when first painted, and before the fan guard was fitted. Ian S C

[Brian JohnParticipant @brianjohn93961]

1. I may have another go at painting the chimney while the weather is fine. Is special high temperature paint really necessary ? What sort of temperatures are produced by a metho/spirit burner anyway ?

2. This model boiler came with fibreglass insulation which was then covered with a thin brass sheet and then the wooden lagging. What else can be used to insulate the boiler as I am not sure where to buy this thin fibreglass insulation ?

3. I am puzzled why my engines spit out water from the exhaust for a few minutes before running on steam. I do not see other steam engines do this. Do I require some special valve to stop this from happening ? I have set the engine a bit higher than the boiler but the problem still occurs.

[JasonBModerator @jasonb]

1. It will get to a couple of hundred degrees so yes best to stick with HT paint.

2. Have a google for Kaowool you may find it availbale more locally as that is one of the makes.

3. The metal parts of the valve and cylinder will be cold, the first steam comming into contact with the cold metal will condensate on teh surfaces and this is where the water comes from. Larger engines will have drain cocks to allow this water to be removed rather than blown out teh exhaust but not practical on a little one like yours. The higher engine just stops the steam that condensates in the pipework also making its way to the engine.

J

[Brian JohnParticipant @brianjohn93961]

Some problems solved : I have remade another piston. Finding the exact centre is easy when you know how. First make a dot in the centre by eye using a fine tip marking pen. Then check it by putting it in a drill : look at it end on while you turn on the drill. If the dot wobbles about then you are not in the centre. ''Rub it out'' by holding the end of the piston on some 600 grit sandpaper while it is still in the drill. Do this again until the dot does not move when you activate the drill…it should stay in the centre like the North Star. Carefully make a punch mark on the dot and check this again with the drill. If you are in the centre then put the piston in the vice and drill the hole for the piston rod.

I did try using a centre drill to drill the holes but I found that these wander off-centre even more than normal drills. I think what is really needed is a spotting drill which is not something I have ever seen in any tool shops. Anyway the new piston is made and it works. It gives a much better seal than my first attempt. This time I fixed the piston rod to the piston and the big end using Loctite 263 which worked really well. A previous attempt using silver solder and a blow torch resulted in the piston rod bending like it was made of rubber …too much heat softened the brass !

I am still not finding any insulation material which is suitable for building boilers. What do they use when building model steam locomotives ?

Edited By Brian John on 25/12/2014 04:10:18

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