The Shop > Metal Stuff
Casting a Model Westinghouse-Type Twin Steam Engine in Iron
awemawson:
I’d be very interested to find out the composition of the brake disks you’ve used, obviously there’s something in them that’s making them slower to melt so presumably raising the melting point as well as influencing the final casting properties. I wonder if they are actually a semi steel ?
vtsteam:
Agreed Tom it's high. But I'd like a good casting first, then start reducing the ferro, and increasing the brake disk content gradually to see where the middle ground is:
Also remember, we already have tested single iron types with normal additions of FeSi:
1.) 1.34" dia iron bar, 100% radiator iron, (0.35% FeSi) --> 100% gray iron.
2.) Westinghouse twin #3, 100% brake disk iron (0.35% FeSi) --> white iron ingots, and chilled spots in casting
Andrew, I wish I had your metal analyzer -- might explain a lot! And for sure the metal is longer melting (higher temp) than the radiator iron. The brake disk melt took an hour, the radiator metal took a half hour, and the latest pour of a combo took 45 minutes.
Of interest, not 15 minutes ago I broke up another disk rotor, and the inner rim bent for several blows of the sledge before breaking -- much more bending than you would normally see in thin cast iron. Ductile iron, perhaps???
What might also complicate things, guys is, I'm pretty sure these rotors (from different vehicles) probably vary in composition. So it may be hard to come up with a hard and fast rule for rotors.
vtsteam:
Well the operation was a success, (gray iron), but the patient died :bang:, Faulty riser position allowed a major shrink depression.
I should have known better. This particular engine pattern really needs a riser bang in the middle of the casting, right on top of the exhaust port boss. I've seen this particular problem before, and solved it. Not sure why I tried a different riser location -- I guess I just thought a really big one off of the casting would preserve the boss detail.
Here's a photo of the new 4th casting on the left with shrink depression (looks much worse than photo shows) and the third casting on the right, which had the riser on top of that boss and no shrinkage. The riser did kill the detail of the boss, but I could have whittled it back into shape. I'm going to guess that radiator metal also shrinks more than disk rotor metal -- I did get some shrinkage in the iron bar I cast. Oh well..... More to keep in mind.
Sometimes I long to go back to aluminum casting. Iron is tough. But there is the thrill of really hot scary iron and a roaring furnace, and the reward ......some day....... of seeing what you want finally accomplished. Uh...I hope.
vtsteam:
Nope, probably not ductile iron. According to online sources, ductile has a lower melting point than regular gray cast iron. Probably not semi-steel either -- that's an old low grade of iron scrap mixed with steel, according to online defs. Unlikely to be used in rotors
One possibility is a modified gray iron with Titanium. Another possibility is "Automotive Malleable Cast Iron", which has the highest melting point of the common cast irons, lowest carbon, and produces a solid white iron that must be annealed @ ~ 1650F. At least in characteristics, that sounds like the particular brake rotor metal I had. If brake rotors were frequently of that type, it would also explain the Windy Hill foundry always kilning the castings.
Brake disk compositions do vary, so that one rotor may act completely differently than another. In fact it was the second rotor I've tried and I don't think that the first one I melted behaved similarly.
Modifying the rotor metal with radiator metal would raise the carbon, silicon, and phosphorus contents, and lower the melting temp. I could also try adding carbon itself -- similar to the way Ironman made cast iron from steel.
Much to experiment with and think about.... :coffee:
vtsteam:
Andrew, if I sent you a small sample of that disk rotor, would you be interested in giving it a go through your metal tester?
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