The Shop > Metal Stuff
Casting a Model Westinghouse-Type Twin Steam Engine in Iron
vtsteam:
Yesterday I cast a block for a model Westinghouse style twin in iron. I'd tried this a few weeks ago with some questionable iron using an old pattern and without cores, just as an experiment to see if the iron would cast well. This second time around, I made a new corebox, and a baked sand core (mentioned in another thread). This time also I used brake rotor metal, which I'd tried successfully earlier in casting a lathe chuck back plate.
My furnace has been acting up a little for the last two casting sessions -- not sure of the reason why other than repairs to the lining lately, but I'm beginning to suspect the jet in my burner might be partially obstructed. Symptoms are, the furnace is harder to light, and slower to melt. I was earlier getting phenomenal melt times of 20 minutes for a pour of this size. Now it's more like 40 minutes -- still reasonable, but I'd like to know the reason for the difference.
The other possibility is that disk rotor metal takes longer to melt. Or a maybe a combination of all of the above.
Anyway, I made up the mold and placed the core in it without any hitches. The facing sand was a little dry (I should have checked in advance). So there was a little breakaway/flash at the seams, but no biggie.
The melt took much longer than expected, as mentioned, and I took some pains to slag the melt twice and thoroughly. Perhaps too long with the crucible out of the furnace, or too cool in the melt, because when I poured the sprue filled and stopped accepting metal before the riser was full to the top. I don't think I've ever had that happen before.
But I was still hopeful because the riser had filled to well above the casting's height.
Here's the breakout about 4 hours after the pour. Notice how well the cylinder cores in the block have worked, and burned to black sand:
vtsteam:
I was pretty hopeful, the detail looked good and the core had worked perfectly:
vtsteam:
But nope, the metal just wasn't hot enough to fill the thinnest area furthest from the sprue. The riser had been closer to the sprue and in a thicker part of the casting, so it filled. I'm pretty sure this would have been a perfect part if the metal had been hotter. Oh well, next time.....
I'll relocate the sprue and give it two gates to either end of the thinner part, plus, of course, pour hotter.
tom osselton:
That is pretty close to working.
awemawson:
Do you have any way of checking the temperature of the melt Steve?
I used to use a ‘disappearing filament optical pyrometer’ , basically just an incandescent filament run through a rheostat Tweak the rheostat until the filament disappeared against the melt and read off the temp from the rheostat dial. Sadly when I dug it out a few weeks ago I found that it had succumbed to dampness and ended up chucking it out.
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