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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<a href="https://www.youtube.com/watch?v=8X_T6nRrtzE" target="_blank">http://www.youtube.com/watch?v=8X_T6nRrtzE</a>

[CI]

Here is my attempt to cast the passages in the face of one of the cylinder supports.
This core was not successful, but I think the process would be valid and usable if made and assembled correctly.
These are sodium silicate cores.

As it turns out, the passages on an oscillating steam engine can be machined directly into the face of the cylinder support, which is how the original green twin supports were made.
The passages do not have to be embedded in the castings, although there would be a bit less leakage if they were imbedded.

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[CI]

The cored passaged for the green twin cylinder came very close to working correctly.
I believe that if I had used the Zip Stik (tm) core adhesive, that would have eliminated the gassing problem that ruined these iron castings.

You can see that the passage enters the bore in the counterbore area, which is why I was using a stepped bore core.

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[CI]

Here is the simple straight core that I ended up using, with drilled passages.
The high points of the cope mold with resin-bound sand must be vented, because resin bound sand will trap air in the top of the cope mold, and cause large air bubbles in the casting.
I ruined two good base castings when I forgot to vent the tops of those molds.
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