TonyW wrote: ↑Wed May 01, 2019 8:20 pm
Hmmm.... a 16mm/foot loco with a steel boiler could be interesting. I wonder, does steel corrode faster or slower than brass...?
Depends on the grade of brass. Mild steel corrodes faster in water than most brasses. If arsenical brass is used to make the boiler, which I believe was the case with the old German toy locos, the boiler isn't particularly prone to dezincification. The low zinc red brasses aren't a problem either.
The main issue with using steel in very small boilers is that the money saved on materials will likely be swallowed up by having to employ a welder with the necessary qualifications. Unless you know the right person and he does it at mate's rates.....
When you move up to the large miniature locos mild steel is the name of the game, although Aust. now allows the use of Duplex steel as well, which is related to stainless steels. It has low corrosion rates and high strength, so thinner plates can be used, but it has to be welded by specialised welders with the right paperwork.
Mild steel boilers need to be manufactured with thicker plates to allow for wastage over time from corrosion. Corrosion rates can be reduced with a good water treatment regime, but not completely eliminated. A large scale model boiler I'm familiar with is now 35 years old and when tested ultrasonically 5 years ago, had lost 3mm of thickness in some areas, even with water treatment.
Mild steel is technically feasible for boilers in the garden scales, but it will be a brave manufacturer that makes the first move. A reasonable lifetime and liability issues are the biggest obstacles, as there's no way that a manufacturer can ensure owners will bother maintaining the water treatment. Duplex steel may be a better bet for sub-miniature boilers if copper becomes unsustainable for hobby boilers.
Anyway......
It costs me about A$50 for the materials for a copper boiler and a couple of days work, compared to something like A$500 for a commercial boiler. As with any commercial product, the material costs are a fraction of the labour costs. Even if the cost of copper were to double, the cost of a commercial boiler would only increase 10%. The real risk to the future of copper model boilers is that the plumbing industry will stop using copper altogether and suitable size copper tube will no longer be manufactured.
Copper is more common in the earth's crust than lithium, so the battery materials will run out first, assuming the hydrogen economy proponents don't win the argument.
Regards,
Graeme