Building a Disk Turbine
The new stator is milled the vertical rotary table I designed as part of my milling attachment. The twelve small scrolls that I'm cutting will diffuse the compressor wheel output and direct it toward the rear of the turbine. Probably it's time to clean up the swarf!
|April 28, 2003 Cont'd.
I dug a small recess in the hot coals, and set my smaller crucible, a cast iron plumber's lead pot, right in the fire. I'd loaded it with a discarded piston, and a couple of old sprues from a previous pour. The mould was already made up. It was an easy one -- the pattern I'd used was the same one used to cast the first turbine stator.
I did wonder if the fire would get hot enough to melt the aluminum -- we were burning some green pine, and there was no blower. The cast iron pot was fairly massive. So the odds were against it. But, if it didn't work, my foundry setup was nearby, and at least the fire would pre-heat the metal so I wouldn't need so much charcoal. Since I've been involved in casting, I've found that charcoal costs more than any other raw material.
After about forty minutes I saw a piece of a sprue that had been sticking up, fall off into the pot, a sure sign that a pour was imminent. I picked up my stirring rod and gave the sprue a poke. It toppled over and I saw a quickly growing puddle of silvery aluminum in the bottom of the crucible. At this rate, the metal would be ready to pour in a minute or two. I grabbed my leather welder's gloves and helmet ( a welder's face mask with a clear eye-plate) and my skimmer. The mold was ready.
I skimmed carefully because quite a bit of ash from the fire was floating on the surface. This actually helps to protect the melt from oxidation, and is easily removed. The metal was definitely hot.
(c) Copyright 2003, Stephen Redmond, all rights reserved
I poured the mold quickly, and then emptied the excess into a muffin tin that I always keep nearby. The aluminum actually looked a little hotter than I normally like to pour for a fairly massive casting. There's a greater chance for flaws, gas bubbles, or metal tears when the metal has too much heat. Thin castings on the other hand require hotter metal so that the mold can be completely filled before the metal freezes
Obviously, there was no problem melting aluminum in an ordinary open wood fire, even without a blower. I'd like to experiment a little further possibly using a pit, and firing it with cordwood ... or even stacked sticks to see how much I can minimize the melt time and fire size.
After a half hour wait, the mold was ready to break open. The stator ring came out bright and clean, and ready to work on.
The new stator design. Twelve small scrolls give it a mandala-like appearance