1/20th Scale Burrell

[glue-itcom]

Some parts make you smile and fixing the Burrell nameplate to the valve chest is one of those.

I used an easy flo ready mixed silver solder paste and as you can see it worked really well.

 

[glue-itcom]

Good to see different techniques - and that they work! Hope the silver soldering to the boiler goes well. A tip? Try using a pencil to mark off the area beyond the joint where you don't want the silver solder to take. Just "shade" the area, but make sure no pencil where you do want the solder. Also using a paste of flux and water pre-applied ensures it fills the gap to clean the surfaces and encourage the capilliary action when silver solder is applied. (But I reckon you know all that anyway.).
K2

Finally I've done some testing to see how well a graphite pencil works as a masking tape for silver solder.

This works quite well.

 

[glue-itcom]

The position of the steam valve and machining it into the saddle has caused me some pain. However, I finally decided that it wouldn't fit into the saddle.



Although painful, this has allowed me to move forward and now silver solder the saddle to the boiler shell.

An image of saddle silver soldered to the boiler.

My test coupons and checking out different silver solder masking techniques paid off.

The engine reassembled and I think it's looking good.

The silver solder coming out from the edge is minimal and yet it is complete all the way round. This will be covered by an insulation sheet and a brass sheet wrap anyway.

 

[Steamchick]

Hi nigel,
having done a few boilers, I strongly recomend that the insulation is built from the following:

1. Wrap the hot boiler outer with aluminium foil, shiny side out: This reduces the radiated heat by half-ish, or more.
2. Cover the aluminium in your preferred insulation fabric: I have successfully used corrugated cardboard, paper (especially if it is embossed o it forms trapped cells filled with air) , wool (knitted fabric), proprietary "flame resistant" insulation sheet, but don't try bubble wrap or anything that will melt or char at the boiler temperature.
3. Cover insulation with a sheet of paper (I use "used" printer paper).
4. Cover the paper with aluminium foil: shiny-side inwards.
5. Then fit your metal cleading as per normal.

The 2 layers of aluminium foil cause 95% of the radiated heat to be trapped - and, as this can exceed the conducted heat through the insulation, it can reduce your "wasted-heat" to less than half of what it would be without the invention of reflecting surfaces by Sir James Dewar . That's a lot of heat made into useful steam!
On my boilers, the main insulation means the outside temperature is below 40degrees C. whereas the boiler surface is above 140degrees C.
And do the same around the firebox if you can?
On tubing carrying steam - e.g. water gauge, (except for the pressure gauge siphon tube) you can also insulate with cotton string wound carefully around the pipework and over the fittings, then painted with domestic matt white emulsion piant - which makes it look like the original asbestos lagging - but is much safer. But your traction engine won't have much exposed steam pipework.
Cheers!
K2

 

[Steamchick]

Here's what Wiki says: "In 1860, the French scientist Jean Claude Eugene Peclet[2] experimented with the insulating effect of high and low emissive metals facing air spaces.[3] Peclet experimented with a wide variety of metals ranging from tin to cast iron, and came to the conclusion that neither the color nor the visual reflectance were significant determining factors in the materials’ performance. Peclet calculated the reduction in BTUs for high and low emissive surfaces facing into various air spaces, discovering the benefits of a radiant barrier in reducing the transfer of heat. "

On Sir James Dewar: "About 1892, the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask (otherwise known as a Thermos or vacuum flask) – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out, it was found possible to preserve the liquids for comparatively long periods, making an examination of their optical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask – he lost a court case against Thermos concerning the patent for his invention. While Dewar was recognised as the inventor, because he did not patent his invention, there was no way to prevent Thermos from using his design.[6] ".

You live and learn...

You can also use "space blanket" material instead of aluminium foil (Baking foil).
K2

 

[Steamchick]

Finally I've done some testing to see how well a graphite pencil works as a masking tape for silver solder.

This works quite well.

Good! Glad to see this knowledge is being passed around.
A centuries old trick... a blacksmith taught me 50 years ago...
K2

 

[glue-itcom]

Hi nigel,
having done a few boilers, I strongly recomend that the insulation is built from the following:

1. Wrap the hot boiler outer with aluminium foil, shiny side out: This reduces the radiated heat by half-ish, or more.
2. Cover the aluminium in your preferred insulation fabric: I have successfully used corrugated cardboard, paper (especially if it is embossed o it forms trapped cells filled with air) , wool (knitted fabric), proprietary "flame resistant" insulation sheet, but don't try bubble wrap or anything that will melt or char at the boiler temperature.
3. Cover insulation with a sheet of paper (I use "used" printer paper).
4. Cover the paper with aluminium foil: shiny-side inwards.
5. Then fit your metal cleading as per normal.

The 2 layers of aluminium foil cause 95% of the radiated heat to be trapped - and, as this can exceed the conducted heat through the insulation, it can reduce your "wasted-heat" to less than half of what it would be without the invention of reflecting surfaces by Sir James Dewar . That's a lot of heat made into useful steam!
On my boilers, the main insulation means the outside temperature is below 40degrees C. whereas the boiler surface is above 140degrees C.
And do the same around the firebox if you can?
On tubing carrying steam - e.g. water gauge, (except for the pressure gauge siphon tube) you can also insulate with cotton string wound carefully around the pipework and over the fittings, then painted with domestic matt white emulsion piant - which makes it look like the original asbestos lagging - but is much safer. But your traction engine won't have much exposed steam pipework.
Cheers!
K2

Hi K2, the only issue is I need to wrap the boiler in a total thickness of less than 1.5mm including the outer brass sheet. I might have to experiment with some thermocoupled blocks to get some comparative insulation numbers. I will set something up and then see if people have different options to test. That sounds like fun actually.

For the firebox my plan is to line this with ceramic, I was going to see if I can machine one of the white ceramic blocks for soldering. I will have a go at this soon to see how it goes. I still need to design how the pipes come out the back of the firebox for the pressure gauge, water gauge, steam valve etc.

Thanks, Nigel

 

[Steamchick]

As the cooking foil is only a thou or so thick it does a lot of insulation for almost no real thickness. The thinnest foil used to be on the inside of cigarette packets - glued onto tissue paper and could be separated - carefully. But you can't get that anymore as they vacuum deposit aluminium onto plastic nowadays - e.g. for crisp packets, etc. - And who has cigarettes anyway?
K2

 

[Steamchick]

On the subject of insulation thicknesses, you can buy proprietary stuff in various calibrated thicknesses, but an old pair of wool suit trousers will give you fabric that needs a few layers to make a mm of thickness. Pure cotton and linen also come in very thin fabrics. Regular print paper can be a tenth of a millimeter. Even nose or toilet tissue is very thin - and has lots of air space and minimal fibres to conduct the heat!
All you really want is air-space for insulation, with enough "fibre" to trap the air from moving (Convection currents - even sub-millimetre - can be very effective at transmitting heat). All these allow you to precisely build-up the required thickness so you have good insulation inside the cleading.
But don't leave out the aluminium foil!
Enjoy!
K2

 

[Steamchick]

Hi again Nigel,
Aha! - having seen the Mamod alongside your engine, I can see why you want to line the firebox with insulation. (I guess you are in the UK?) I have had success with insulating and sealing fireboxes by using Exhaust Assembly paste - from the local car accessory shop - instead of firebrick cement. It sticks better to steel (unpainted, grease-free), and after firing becomes rock hard - and can be quite strong if thick enough, and applied in thin layers and allowed to dry/cure before firing.... Otherwise it cracks (drying shrinkage). But fire-brick cement is harder to achieve a robust lining (and it doesn't stick so well to the steel!). Spread it thinly (maybe 1mm thick?) using a pallet knife or some-such... then let that dry overnight before applying a second layer. After a couple of days for final drying, warm gently - with the meths flame in the boiler should be OK..? and as it gets hot enough it will cure, as there is a refractory element in it, so chemical changes occur and make it rock-hard. You can strengthen it (as with exhaust-pipe repairs) by having layers of aluminium foil between the layers of cement. "butter" the foil with a layer of cement, then apply this as a poultice/bandage to the steel ... allowing a week in a warm, dry place to dry out (The foil traps the inhibitor moisture).
The only problem is that shrinkage during hot curing causes tension stresses in the cured cement, so on the inside of a curved sheet it can pull-away from the steel. But if you follow the "Roman" cementing construction method, you'll do it in strips, with gaps, grouting the gaps after curing the strips... I'm sure you can work it out and save the problem of machining the very fragile ceramic board...
K2

 

[Steamchick]

On another point. I like the experimental way you tackled the meths burner in vertical boiler problem... measurement of heat power, etc.
I did some crude calculations on the heat flow of meths in a Mamod boiler versus using a ceramic gas radiant burner.
A couple of points that may help you?

1. The meths burner was more effective on the horizontal Mamod boiler, because the hot flames/exhaust gas wrapped around the boiler shell. The ceramic only "shone2 radiant heat on the underside, and less than half the radiated heat hit that part of the boiler anyway. But side reflectors increased the heat transmission to the boiler shell to make the ceramic "equally" effective - and more convenient - than the meths burner: BUT you have a flue tube in your boiler!
2. On a vertical boiler, I compared the ceramic radiant burner versus a gas "camping-stove" burner - with same jet, gas and power. The Radiant ceramic "lost" some radiant heat by shining all the way through the flue tubes, but the overall power transmission from combustion to steam was about the same: One was more efficient at heating the bottom face of the boiler, but then had less heat to transfer to the walls of the multiple flue tubes, the other had hotter gas entering the flue tubes, but the exhaust temp was almost the same - ergo the heat transfer was equivalent with the 2 different burners.
3. On an horizontal boiler, with gas burner beneath the long boiler shell, I found I could use 1 jet larger on a ceramic burner, as the majority of the heat was radiated onto the boiler shell, leaving cooler exhaust gas (lower volume and higher mass) to pass through the flue tubes than with the limitations of the flues on the flame gas burner.
4. Noting that Meths needs a LOT of air... and you will be restricted by your flue size and the draught "up the lum", you may find a ceramic burner can give you more "power" from the fuel because you can maximise the air with the gas to get a proper fast combustion of the gas (Light blue cones surrounded by darker blue cones) - providing you don't over-fuel the air intake capabilities of the ceramic burner. The different mix of CO2 and H2O in the gas exhaust, compared to the meths exhaust, may give you better performance? But I reckon you will need a very well insulated firebox in either case to get the hot gas into the flue tube to heat the water to steam. It probably needs a thermodynamics chemist to explain the "better" fuel, but I'm sure with your experimenting approach you'll find the better solution for you.

Cheers!
K2

 

[Steamchick]

Hi Nigel, More musings...
Just in case you have not checked the design of the vertical boiler - and the Burrell boiler - for the flue tube in compression....(The boiler pressure compresses flue tubes): I have a spreadsheet that I use to do some quick calculations, based on ASME (USA) Copper boiler design and testing regulations.
My "quick" check:-

1. for a 10mm OD, 8.6mm bore copper tube in compression in a boiler, with cross tubes, the ASME max pressure would be between 30psi (OK) and 35psi (NG) NWP...
2. for a 22mm OD, 20.2mm bore copper tube in compression in a boiler, with cross tubes, the ASME max pressure would be between 20psi (OK) and 25psi (NG) NWP...

The main reasons for this:

• Copper in compression is only 20~25% of the strength of copper in tension,
• Cross-tubes are "wall penetrations" - so ASME uses a standard "stress concentration factor" of 3.3 - which de-rates the NWP horribly,
• ASME ( as British standards, etc.) use the Factor of Safety as >8 for the design of copper pressure vessels.
• ASME de-rates copper (as naturally happens!) above "room temperature", so the "permissable stress" reduces dramatically with "steam" temperatures. (Halved at 100psi compared to room temp).

So (for example) a copper tube "OK" for internal pressure room temp water at 6 bar (FOS = 8) is de-rated:

• to NWP ~3.5 bar at 50psi NWP steam:
• Then to NWP ~11.4psi if used as a flue tube,
• Then to NWP = 3.5psi if there are "penetrations" - such as cross-tubes.

Horrible?

So please send me your tube sizes and boiler details if you want me to advise on SAFE sizes of material?
Regards,
K2

 

[glue-itcom]

Hi Nigel, More musings...
Just in case you have not checked the design of the vertical boiler - and the Burrell boiler - for the flue tube in compression....(The boiler pressure compresses flue tubes): I have a spreadsheet that I use to do some quick calculations, based on ASME (USA) Copper boiler design and testing regulations.
My "quick" check:-

1. for a 10mm OD, 8.6mm bore copper tube in compression in a boiler, with cross tubes, the ASME max pressure would be between 30psi (OK) and 35psi (NG) NWP...
2. for a 22mm OD, 20.2mm bore copper tube in compression in a boiler, with cross tubes, the ASME max pressure would be between 20psi (OK) and 25psi (NG) NWP...

The main reasons for this:

• Copper in compression is only 20~25% of the strength of copper in tension,
• Cross-tubes are "wall penetrations" - so ASME uses a standard "stress concentration factor" of 3.3 - which de-rates the NWP horribly,
• ASME ( as British standards, etc.) use the Factor of Safety as >8 for the design of copper pressure vessels.
• ASME de-rates copper (as naturally happens!) above "room temperature", so the "permissable stress" reduces dramatically with "steam" temperatures. (Halved at 100psi compared to room temp).

So (for example) a copper tube "OK" for internal pressure room temp water at 6 bar (FOS = 8) is de-rated:

• to NWP ~3.5 bar at 50psi NWP steam:
• Then to NWP ~11.4psi if used as a flue tube,
• Then to NWP = 3.5psi if there are "penetrations" - such as cross-tubes.

Horrible?

So please send me your tube sizes and boiler details if you want me to advise on SAFE sizes of material?
Regards,
K2

Hi K2,

Thanks for the comments on meths versus gas etc. I think I need to find a gas burner for this engine to make my life a bit easier. Some calculations and someone else looking at the boiler size would be much appreciated.

The horizontal Burrell boiler sizes:

• Shell: 44.45mm OD, 1.6mm wall
• Flue tubes: 7 off 4.79mm OD 0.7mm wall
• End plates: 1.1mm thick

I can easily change the end plates and flue.

The vertical boiler was just me experimenting and I must admit that it has been consigned to the do not use this again pile. The simple model was interesting though and as you say, meths needs a lot of air.

Best regards, Nigel

 

[Steamchick]

Hi Nigel,
I'll see what I can prepare today... I'll send a file direct to you if that is OK?
My "bibles":

• Safety of Copper Boilers - Kozo Hiraoka - from Live steam and Outdoor railroading: Issue Nov 2006. (Back copies can be bought from the magazine).
• Model Boilers and boilermaking: by K.N.Harris. - A lot of what he does is correct mathematically, but limits need to be checked versus the ASME stuff by Kozo-san, as Mr Harris was "speaking from and earlier era", without some of the real technical considerations by ASME.

The fundamentals I have found also consider some University technical papers, and "odd bits of advice" from professional engineers who have worked with ASME and other codes, so know what to apply.
The bottom line is that the factors of safety of *, combined with "maximum permissible stress" de-rated by copper at elevated temperature, compression factors, Stress concentration factors, etc. mean that we should be using much thicker copper than Mr Harris postulates.
I don't know the latest UK Regs. - and they seem to be very elusive - so that's why I refer to ASME. ("Half the planet" does anyway).
K2

 

[Steamchick]

I can also do some calculations for the ceramic versus meths... Crude but not "unreal", and (as I make ceramic burners for E&@y) can also make one or guide you to make your own to suit the model.
What size is the internal section of the firebox that will take a burner?
Regards,
K2

 

[glue-itcom]

I can also do some calculations for the ceramic versus meths... Crude but not "unreal", and (as I make ceramic burners for E&@y) can also make one or guide you to make your own to suit the model.
What size is the internal section of the firebox that will take a burner?
Regards,
K2

Brilliant and thanks. The internal section is 47mm wide and 38mm long, thanks, Nigel

 

[glue-itcom]

I machined the double eccentric as one part, thus allowing me to fix it with one grub screw

Thought the setup might be of interest as well

 

[glue-itcom]

After a lot of help from Steamchick I've managed to make and silver solder the boiler end plate stiffeners in place.

I think I'm a gluten for punishment pursuing the silver soldering in a kiln. The Easy Flo 24 did not flow as well as some of the lower temperature silver solders.

 

[Steamchick]

Hi Nigel. I have not tried oven brazing or silver soldering. But in industry, it was common practice for soldering steel tube assemblies, as these could be assembled to jigs, with the self-fluxed paste spelter, then passed through a conveyor oven tunnel for heating to well controlled temperatures, and cooling... A very reliable, controllable, production process. Hope you have more success next time!
Did you pickle clean parts or abrasive clean them before applying paste? Possibly that is a cause of your issues? Or perhaps you didn't hold at top temperature for long enough?
Ken

 

[glue-itcom]

Hi Nigel. I have not tried oven brazing or silver soldering. But in industry, it was common practice for soldering steel tube assemblies, as these could be assembled to jigs, with the self-fluxed paste spelter, then passed through a conveyor oven tunnel for heating to well controlled temperatures, and cooling... A very reliable, controllable, production process. Hope you have more success next time!
Did you pickle clean parts or abrasive clean them before applying paste? Possibly that is a cause of your issues? Or perhaps you didn't hold at top temperature for long enough?
Ken

Hi Ken,
When it works it goes very well. I did an abrasive clean and then a pickle, but the pickle is getting old. I need to refresh.
I think there might be a few things worth looking at: flux, size of silver solder and oven temperature.

The test piece worked very well and I just abrasively cleaned it.

The oven takes time to recover the temperature on the real parts as it is small. I could go hotter initially. Also, during the recovery the flux might get degraded.

I could hammer the silver solder into thinner and smaller parts. This would allow the heat transfer to be better.

The resultant joint is well covered with silver solder, just some parts that haven't fully flowed. So, I'm ok with it.

I keep going back to using the kiln for silver soldering as the results can be fabulous. However, must admit that silver solder paste and a blowtorch gives brilliant results.
Cheers, Nigel