After some research, and a vigorous discussion with some of the fine folks at the Brass Goggles Forum I have made a number of revisions to the steam engine design and materials test plans:
First, the boiler. Because of both the intensity of the testing required, as well as the durability, I’m not going to be using a food tin for the boiler tank, but instead, a copper tube. To keep in the vein of recycling, instead of buying the copper materials from the store, I’m going to hit the local scrapyard and trade out some steel and aluminum I’ve been stockpiling in exchange for some copper and brass. I’ll do some practice brazing first, then braze together a boiler tank from scratch. My only concern is whether or not the new metal will transfer the heat from the coal as well as the tinplate steel did. My guess is that it will, as copper is 23 times better at conducting heat than steel, and the steal boiled just fine. Silver would be the best material for an efficient boiler, but unless some rather generous reader wishes to provide the materials, we will have to settle on copper. And so, the new boiler draft:
Those following this project may recognize this as a much more legible version of my tin-can boiler draft. The principles are pretty much the same. A gap between the front (read: left) of the tray and the chimney in the opposite side of the coal chamber will provide airflow to feed the coals while the bricks, lined with aluminum, will retain and reflect the heat onto the boiler. The bricks will form a base surrounding 3 sides of the boiler (note the light-gray lines), while a steel armature holds the boiler in place, suspended above the coals. The refill cap will be of the typical garden-hose variety, which will are easily found in abundance. Two pressure tubes will exit the boiler, and braced rubber hose will lead from each to a valve.
The first rubber hose will lead off to an emergency pressure release valve, set to pop at about 30 psi, which should be far below the tolerance of a properly brazed copper boiler. However, because I don’t fancy a boiler explosion ruining my day, a shield with gas baffles will surround the boiler and the emergency release valve. Preferably, this will be a Lexan shield so that I can actually see the boiler, but if it comes down to it, a heavy-duty trash can with some slits in the side will do fine. Traversing the shield will be the main hose with a pressure gauge that I can read safely on the other side of the shield from the boiler, as well as a manual pressure release valve if I want to lower the tank pressure before it hits critical levels. The control valve will allow me to let pressure build a bit before it hits the engine, as well as the intensity of pressure hitting the engine.
The engine itself is a very simple piston-valve engine. I don’t trust myself with anything more complex at this stage. Pressure will enter from the primary boiler hose once the control valve is opened. It should push the piston, which will in turn push the crankpin and turn Flywheel #1, which is connected to Flywheel #2 via a cam. Flywheel #2, out of phase from #1 by 90 degrees, should turn also, and after 90 degrees rotation, crankpin#2 will force the rocker assembly to turn, pushing the valve in past the piston-head. At this phase in the cycle, the engine should resemble something like this:
The pressure from the piston chamber is then shunted out the valve chamber. The valve, which is then blocking the path of the steam, is then pushed back across by the pressure from the boiler so that it slides the rocker back 90 degrees, continuing the rotation of the flywheel, and eventually forcing Flywheel #1 to turn, crankpin #1 to revolve back around until the piston is forced back into Phase One, at which point the valve has also been pushed back into Phase One, and the cycle begins again. As for the belt assembly along the cam, eventually, after I’ve proven the steam engine works, I’ll add it. What will it do? It’ll turn the wheel on my Wimshurst Machine. My what?
Why, you might ask, would I want to build one of those? Three reasons: One, it generates electricity. Two, you see that spark there? That electrical arc? That’s cool. Three, because I want to. But that’s a project for another day. Also, as it turns out, brass and copper scrap are considerably harder to get than I thought they would be, and while I hoped to get some brazing practice in this weekend, I’m beginning to doubt I’ll have the time to do so. Still, the more I plan ahead, the less uncontrolled the variables when the time comes. I’ll get some good footage in once I’m able to resume work on the project.