Supporting > Casting
Steam engine cored passages attempt
CI:
I made some passage cores for the green twin, but not with iron.
I did not have the iron casting process completely worked out at the time, and so I had a lot of core blow, etc.
I know Stuart and I am sure other kit manufacturers use small passage cores.
Some of the passages seem to remain in the correct alignment, and some don't see to remained very good alignment, but can still be usable.
I think small cores can work, especially with aluminum.
I ended up drilling my passages on the green twin, but I was very close to success with cored passaged; I just ran out of time to experiment and had to finish the engine.
Here are photos of the passage coreboxes I made, and some cores.
And a few cylinder casting photos in iron, which show core blow.
I have seen some recent information about putting strings in the core, to vent it.
I recall using fine stainless wire in some of my thin cores, to reinforce them.
I was not aware that sodium silicate cores may contain moisture, and may need to be baked, and so I did not bake my passage cores, and that is probably what caused the core blow.
I think I could successfully cast passages in iron castings these days if the cores were made from resin-bound sand, with fine stainless wire inside, and flamed before casting to drive off moisture.
I don't really think that venting of the passage is critical, but that is a guess, and small passage cores may need strings in them to make tiny vent holes.
The string would have to be burned out I think, else the string would burn during the mold fill, and that would cause gassing.
I also came up with what I think is a good oscillator passage shape, for good steam/exhaust flow, and it is not a linear passage.
I think these photos show my first attempt to make passages that key into the bore core.
I used a stepped core design, perhaps to try and cast the counterbore into the cylinder.
I later discarded the stepped bore core, and went with a straight sided design.
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CI:
A few more pics.
As I recall, these cores were all made using sodium silicate.
I remember having problems with core weakness, and it was due to me over-gassing the cores with CO2.
5 second max gassing on sodium silicate cores will give excellent core strength, and cores with a long shelf life.
Any gassing longer than 5 seconds will produce cores that start to crumble within minutes.
The recommended percentage of sand to sodium silicate ratio (I forget the exact number; seems like either 3% or 5%) does not need to be increased if you maintain a 5 second gassing time.
Increasing the sodium silicate percentage makes the cores rock hard, and very difficult to remove.
Cores made at the recommended ss ratio will break up easily after casting, especially if water is added.
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CI:
Here is another attempt at using cores with the green twin cylinder castings.
You can see how I transition the turn in the passage to maintain the sectional dimensions.
Looking back on this attempt, I see that I used quite a bit of furnace cement to adhere the passage cores to the bore core, and I think it was the furnace cement that gassed, not necessarily the cores.
These days, I always vent bore cores with at least a 1/4" vent hole that extends out the ends of the bore core, and is vented up and out the top of the cope mold.
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CI:
Here is a photo of the passages mounted on the bore core, with the bore core in the cylinder molds.
I think this arrangement would have worked if I had used a very small amount of the modern commercial mold adhesive that I have now, which is "Zip Stik tm" LH20 adhesive.
Also a photo of the passage cores in the outer cylinder support.
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CI:
Here is a video by Ask Chemical, illustrating how very complex cores can be assembled using their core adhesives.
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http://www.youtube.com/watch?v=8X_T6nRrtzE
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