Cast iron porosity.

[Jasonb]

So are you saying it was down to the gates, spill traps, basins etc?

If so what did she do different to the "100s" of moulds she gated, etc previously?

[CI]

This video by John Campbell (Bob Puhakka's mentor) discusses aluminum pours and bifilms, and also addresses many ways you can entrain air into the metal when pouring.

<a href="https://www.youtube.com/watch?v=9_w3OZ2b02A" target="_blank">http://www.youtube.com/watch?v=9_w3OZ2b02A</a>

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[CI]

So are you saying it was down to the gates, spill traps, basins etc?

If so what did she do different to the "100s" of moulds she gated, etc previously?

She normally does artwork, where she does not have long runners and such.
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[Jasonb]

I would have thought some of those smaller components were "artwork" sort of size. The long fence being an exception but that was probably the best of the castings.

This one looks around a similar size

<a href="https://www.youtube.com/watch?v=peyew3ITZVo" target="_blank">http://www.youtube.com/watch?v=peyew3ITZVo</a>

[CI]

This defect appears to me to be a not completely burned off mold coat.
The defects at the bottom of the sprue on the long casting seems to be entrained air.
If you entrain air at the bottom of the spure, then some of that will most likely travel into the mold cavity.

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

[CI]

You can get away with almost anything in art-iron casting, since they are generally not structural, and also generally you don't cut them open to look for defects like entrained air.
If you watch John Campbells video, there are several methods to get rid of the initial air that gets entrained into the melt (happens before the sprue is full).
The most simple approach is to use spin traps at the end of the runners.

The spin traps also avoid dead-end runners, which will splash back.
If the molten metal hits the end of a dead end runner, it will cause a high pressure jet flow on the nearest upstream gate, and so more defects.

The rules are really simple.

1. Fill the sprue as fast as possible.
2. Use a smooth transition at the bottom of the sprue into the runner.
3. Use spin traps at the end of each runner.
4. Vent the spin traps out the top of the cope, such as with 1" diameter vents.
5. Gates at the top of the runners, so the gates flow last.
6. Control velocity at all times using some method.  I use thin rectangular gates for velocity control so that I don't get high velocity spraying through the gates into the mold cavity.
7. Sweep the initial entrained air/metal into the spin traps.

These methods work well; this is not hypthetical conjecture on my part.
Very few people use these methods; I am not sure why.
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[Jasonb]

I just watched that video of hers that I linked to.

Defects on all the castings and she even says they are not great but I would have thought ART castings much like our model castings are very visual where you want a good surface. Certainly would not want that textured surface you got on the straight edge or her sandy pock marked surface on something like the BHM tank all over the writing. To me a clear example that there are problems with either her patterns or the art casting. Can't blame that on a commercial foundry.

As for prizing the wood pattern out with a chisel and damaging it and the sand thats another matter

[CI]

Resin-bound sand generally will give good surface finish, even if not coated with mold coat.
Not quite as good as oil-based sand, but close.

The art-iron folks make all sorts of shapes and sizes, and I have not really seen any consistency with sprues/runners/gating.
Sometimes you can get away with a lot of sin if you don't section or machine the casting.

Bob Puhakka makes structural castings, and he x-ray's his castings.
There are no bubbles or other defects in Bob's castings, and so I pay close attention to what Bob does and says.
Bob's methods are evolving, but the fundamentals remain the same, ie: control the metal velocity at all times, no abrupt changes in direction or shape of the metal delivery system, skim out the entrained air, maintain laminar flow, gates at top of runners act as final slag skimmers.

High quality iron castings can be made in the backyard if you adhere to Bob's methods.
The resin-bound sand is specifically designed to work well with iron and steel, and those molds do work very well if you don't ignore entrained air and velocity.
I can get consistent repeat results without random errors, and that is really the name of the game as far as the engine and other castings I make.

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Edit:
I would not recommend brushing on a mold coat with resin-bound sand.
The sand is porous, and it can soak in too much mold coat.
I spray on a very light and even amount of mold coat, and burn it off immediately.

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[CI]

I watched this video.

She did not use ceramic mold coat, and so that affected the surface finish quite a bit.
As I mentioned, very typical art-iron sprue/runner/gating, but it does not matter if there is entrained air inside the casting or not, since it is not structural, and not machined.

The snap flasks that she uses are quite interesting.
I prefer to make dedicated flasks for engine pattern, and not try to reuse flasks.
It does not take long to make a flask, and I have long pre-cut pieces at various heights.

I prefer to pour straight down the sprue, but I do use a round ring as a sort of pour basin on top the mold.
It is best to pour as close to the mold as possible, and not waterfall the metal any more than necessary.

I have also noticed that it seems to matter if the piece is cast up or down.
I have gotten better surface finish when casting face down.
I will post an example.

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<a href="https://www.youtube.com/watch?v=peyew3ITZVo" target="_blank">http://www.youtube.com/watch?v=peyew3ITZVo</a>

[CI]

These were some castings I made during COVID, just to have something to cast, since all the art-iron shows were shut down along with almost everything else.
These used a sprayed-on commercial ceramic mold coat (Velacoat tm), and you can compare with Laura's surface finish in the video above.
I used a dry paintbrush to clean the sand off these iron castings, and there is no sand adhesion, and a very smooth and shiny surface right out of the mold.

I used a 3D printed curved face pattern which was filled in the same fashion that I filled the BHM fuel tank logo pattern half.
Open-face pour; I just literally poured it into the open molds.

This was a fun thing to do.

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[CI]

More photos.
There was no buffing on these pieces; I literally turned them over out of the mold, and brushed them off with a dry paintbrush.
Not bad for just playing around.

I was comtemplating casting belt buckles, but these are a bit large unless you are a big-hoss individual.

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[Jasonb]

Just like the ones done by the foundry which also had a better bottom face as bubbles and gases will tend to rise.

Open faced like yours also allows plenty of venting and also takes the gating, etc out of the equation. With less to potentially go wrong one would hope to see better results.

[airmodel]

It would have been interesting to see those parts saw through to see if it was right through or just the upper surface.

That is a great idea! I made a video showing a casting I poured and cut in half to see if there were any bubbles in the casting. Watch from 7:19 to 10:21. This mold had no spin traps, over sized sprue in fact everything was done to create bubbles in the casting. Also no air vent in the core made from epoxy resin.

It seems that the youtube link does not work anymore so here is the title of the video, "Melting crankshafts" by luckygen1001

To be fair the last video showed no bubbles so this video shows a casting I poured but the mold was made by another hobby caster from sand I gave to him because it was the cause of bubbles in in my castings and he knew the reason why I gave it to him.  It seems the bubble problem has gotten worse! Watch from 0:00 to 3:10. Does anyone have any ideas as to why there are so many bubbles?

This one does not work also  This is the title "My worst casting EVER!!!!" by luckygen1001

[CI]

Here is the first video:

<a href="https://www.youtube.com/watch?v=PVIwU7at7mw" target="_blank">http://www.youtube.com/watch?v=PVIwU7at7mw</a>

[CI]

Here is the second one:

<a href="https://www.youtube.com/watch?v=F_Nmt06lHsk" target="_blank">http://www.youtube.com/watch?v=F_Nmt06lHsk</a>