Suitable boiler materials and size?

[Lakc]

Hello there! Forgive my ignorance, but I am new to the boiler world. I would like to build a small model boiler (approx 3"dia), and while copper is a dream to work with, I am afraid of turning $150 in materials into scrap. I can tig, mig, gas weld, braze, soft solder, and surface mount solder, but every attempt at solver soldering has been a disaster. Actually, I suspect that I have been victim of a cruel hoax. As the solver solder that has been given to me to try, I now believe has a melting point somewhere around inconel/nickel mix. That may be an exaggeration, maybe not, but the experience has soured me on all things considered silver brazing.

Cost and availability make me lean towards mild steel for a boiler. Its been awhile since I have done tig welding and I could use the practice. Corrosion worries me, however, and I wonder if it is acceptable (or ever tried) to copperplate the interior?

I am reasonably certain I could braze with regular brazing rod, but I have yet to see that mentioned.

I am also uncertain as the the actual size of boiler and how it relates to the actual work it can accomplish, i.e. how big a boiler to do 1 horsepower, etc.

I am trying to approach this type of project cautiously. The one "steam fact" that I seem to remember was someone mentioning "the rules of steam are written in blood". That quote stuck very well with me, although the blood part is not as bothersome as potential burns and disfigurement.

 

[Jasonb]

Braze or Bronze welding is not ideal for boilers as the material will suffer dezincification in the presance of steam, same reason you should not us ebrass for bushes etc.

If you go with steel you will not have such good heat conduction which is important on small boilers and you will have to use much thicker wall tube to allow for wasting (corrosion) so if you keep the OD to 3" the ID will be smaller and hence your boilers capacity.

I would be tempted to get some Silver solder (silverbraze) of a known type and suitable flux and have a practice with that, its really very easy once you get the hang of it.

Jason

 

[xo18thfa]

45% silver solder melts at about 1160F and flows right away. It's not that high temp. And it's not that hard to use. If you are comfortable with brazing, you can probably silver solder. They key in silver soldering is applying just enough heat to get the job done. The flux breaks down at about 1450F and becomes worthless, so you cant get too hot. If you are using oxy-acet, use a wide rosebud tip to spread out the heat. Heat slowly and over a wide area.

Don't solder a boiler with phos-copper or any copper based brazing alloy. The zinc leaches out over time and leaves the joint brittle and prone to failure. Don't use brass in boiler construction either. Same situation. Use copper for the barrel and plates and bronze for bushings.

Get some 45% silver solder and matching flux. Practice, practice, practice.

Caution about silver solder: Many brands contain cadmium. Cadmium is an inhaled poison that accumulates in your system. Solder only in ventilated area only.

Check out Stew's thread on the 3.5" gauge boiler he's building. He's got all the bases covered

 

[Lakc]

Thanks guys!
I have read through most/all of the boiler build threads here, and silver soldering doesnt look any harder then regular brazing. I am more and more convinced that what was given to me as silver solder is actually some inconel tig rod, so I am fairly certain I could solder without problems.

The only thing stopping me is the ungodly price of copper and silver solder right now. Scrap bin diving for fun or profit sounds like the way to go, except if there is ever a reason to have the certs for the material, a pressure vessel would be it. Steel, would solve a multitude of problems if it were not for its poor heat conductivity.

 

[steamboatmodel]

Hi Jeff,
Re" except if there is ever a reason to have the certs for the material, a pressure vessel would be it"
Check out Dan's thread on Boiler Codes
http://www.homemodelenginemachinist.com/index.php?topic=8846.0
Regards,
Gerald.

 

[Blogwitch]

As a matter of interest Maxitrack in the UK are now producing copper Tig welded boilers. Whether this will ever filter down to the smaller boilers that are used for small engines can only be guessed at.

They do give the relevent codes and regs pertaining to their production.

http://www.maxitrak.co.uk/boilers.asp

BTW, they are rather expensive and a second mortgage might be required.


Bogs

 

[Lakc]

As a matter of interest Maxitrack in the UK are now producing copper Tig welded boilers. Whether this will ever filter down to the smaller boilers that are used for small engines can only be guessed at.

They do give the relevent codes and regs pertaining to their production.

http://www.maxitrak.co.uk/boilers.asp

Thanks Bogs! Found this very interesting article over there:
http://www.maxitrak.co.uk/grabarticle.asp?article=welded%20boilers.pdf&title=Welded%20boilers Very good reading.

BTW, they are rather expensive and a second mortgage might be required.

I guess you have not heard about our mortgage meltdown. None of our houses over here are worth the first mortgage anymore. ;D

Check out Dan's thread on Boiler Codes
http://www.homemodelenginemachinist.com/index.php?topic=8846.0

I had seen that Gerald, but my interest in knowing the history and alloy of the metal, if not having the certifications outright, were more of a personal satisfaction thing then any legal requirement. With my luck, I could find the only copper plated bismuth tubing in existence in some scrapyard and try to make a boiler out of it thinking its pure copper.

 

[Blogwitch]

I thought you might find that interesting because of your comment about having Tig available.

Looking at Maxitrack's gallery, they show small vertical boilers that have been Tig welded.

I suppose you could use strips of the parent metal as filler rod, but I have no idea about the gas that would need to be used, as my knowledge of welding is rather dated now.

Maybe you should do a few trials and see if it is a viable proposition for you.


Bogs

 

[Dan Rowe]

John,
My arc welding practice is a bit dated also, I knew about Maxtraks boiler and here is a link to another firm welding copper boilers: http://www.steam-technology.co.uk/process.htm

Miller has a Tig welder calculator that has copper as a material choice simply enter the material, thickness and weld type to get their recommendations. http://www.millerwelds.com/resources/calculators/tig_amperage_calculator.php

Dan

 

[johnthomp]

if your going looking in scrap metal yards for a copper preassure vessel i found that inside older types of combi household boilers there is a rather nifty copper heat exchange cylinder that normally has quite a thick sidewall and all the copper pipe you could want inside as a massive coil normally if you state to the lads in the yard what you want it for they usualy show leiniance as letting you have it cheap usually i can get them for £15 they also have a test preassure stamp on them at 7bar so they must be suitable for a small boiler also look out for the copper pipe baskets usualy theres offcuts of industrial 3" copper water pipe knocking abbout just get 12" more than you need wich you can use to cut and leather flat for your plates itll be the same grade and thickness and makes for easier soldering etc
i hope this information helps you on your quest its just something i lerned by chance trial and error and has payed off a few times thing is if you get regular in one or two yards the lads will put things aside for you or fone you when a certain item comes in after all they do sell metal aswell as buy it
reguards john

 

[xo18thfa]

The real trick in silver soldering is learning to read the flux. The flux goes a series of observable change in the process. Flux out of the jar is a white paste. When you apply the heat the water boils off and leave a white cake. The cake starts to turn brownish-black on top. More heat begins to melt all the flux. It turns transparent and "gooey" like molasses. Then it bubbles. Each time a bubble breaks you see very clean shiny copper underneath. Just at this time, the solder is almost ready to ready to go. A little more heat and the solder melts and takes off. Sometimes it needs a little poke with a scratch rod, but once it goes, she's off to the races.

After soldering you have to clean off the excess flux. The excess flux comes off chemically in a "pickle bath". Pickle is normally battery acid mixed with 10 parts water. Some guys use citric acid for pickle, but I have no experience with it. Pickle the part until the flux is gone, 10 minutes or so, then rinse under running water. While rinsing, rub it down with a brass wire brush. It will come bright shiny like a brand new penny.

The hardest thing is soldering pieces of different size. The smaller parts warms up too fast, melts the solder, sucks it all away and the big part is still stone cold. You have to apply heat proportionally. That takes practice.

 

[Jasonb]

John,
My arc welding practice is a bit dated also, I knew about Maxtraks boiler and here is a link to another firm welding copper boilers: http://www.steam-technology.co.uk/process.htm

Thats the firm that do the Welding for Maxitrak. The welded ones are supposed to be cheaper than soldered boilers due to the cheaper welding rod and not having to flange the plates so you could get away with a 90% mortgage.

Jason