Cast iron porosity.

[airmodel]

I know that air vents are used in sand molds to prevent porosity so in this video plenty of air vents were used in the sand molds. The sand molds were made in a backyard setting and sent to a professional iron foundry to be poured. Watch from 47:39 to 49:34, this is a hour long video. The castings are the worst I have ever seen! Clearly the air vents never prevented the swiss cheese castings from happening so it looks like a metal-mold reaction where excess gas bubbled through the casting.
<a href="https://www.youtube.com/watch?v=L3gzFhcXMWo" target="_blank">http://www.youtube.com/watch?v=L3gzFhcXMWo</a>

[CI]

I use identical sand and resin binder that she uses.

I see several things that could cause problems.

Those type molds should be flamed with a soft propane flame to burn off an uncured resin that is on the surface.
I did not see any mold flaming in the video.

I spray on an alchol-based ceramic mold coat, light that to let it burn off, and then flame that too with propane.
I did not see any mold flaming after they applied the graphite.
Not flaming the graphite can cause terrible gassing/bubbles in the casting (don't ask me how I know that, but I have photos that look like the surface of the moon, from the early days).

She mentions the foundry doing a terrible casting job, but to be fair, she is the one who laid out the spure, runners and gates, and from experience, using a sprue/runner/gate system like that can cause those problems.
I use a sprue that has a smooth transition into the runner(s), with spin traps at the ends of the runners, and thin rectangular gates at the top of the runner.

When the sprue is initially filling, there is a point where both air and iron are flowing down the spure.
Once the spure is full, and if the pour is not interrupted, you have only iron flowing down the spure.
If you don't use spin traps at the ends of the runners, then that initial mix of air and iron can flow anywhere, and really cause a lot of damage.

With the spin traps open to the top of the cope, the initial flow will go into the spin trap along with the initial aspirated air, and any loose sand.
When the level of metal rises to the top of the runner, then and only then should the clean iron start flowing into the mold cavity.
If you use dead-end non-vented runners, the initial air/iron mix will strike the end of the runner, and bounce back into the runner system, churning more air into the iron.

The thin rectangular gates on top the runner also help skim an slag that may be floating on top of the iron, as iron flows into the mold cavity.
She does not use thin rectangular gates.

I use a small small vent hole at the highpoints of each mold cavity, with the vent extending out the top of the mold.
I forgot these vents on one mold, and had two very large bubbles in the casting at the top of the mold.
Resin bound sand is not very permeable, and the high points of the mold need small vent holes.

I think with spin traps at the end of the runners, these defects could be avoided.
I don't have defects like this, using the exact same sand and resin systems.

I don't think this was a venting problem, I think it was a runner with no spin trap problem.
You can also cause a lot of defects if you even slightly interrupt the pour, since that will aspirate air, which can cause defects like this.

That molding sand and resin are great to use, and make very accurate molds that are durable when handled.
I use a slide hammer just like the one they use, and that is why resin-bound molds are so accurate, because the pattern pulls straight out of the sand, and there is no gap between the pattern and the sand.

That is my slant on what went wrong with these otherwise very nice molds.

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[vtsteam]

Thanks airmodel! 

[airmodel]

I spray on an alchol-based ceramic mold coat, light that to let it burn off, and then flame that too with propane.

For many years I used S.S. sand on thin sectioned castings, an alcohol based mold paint called "MOLDCOTE" by foseco, it was a zircon flour with a binder. Never had any problems with it and all I did as the instuctions said was use a match to burn the alcohol off and the mold is ready to use. Some time later I had to cast in iron a headstock for a small lathe in greensand. It needed two cores where the casting is very thick (30-35mm). Cast iron does burn on in thick sections so I used some of that mold paint so the cores could be removed a lot easier. Machining those bores revealed plenty of blowholes close to where the paint was. If more was machined the blowholes disappeared. To me it was puzzling as to why it worked for thin castings but on thick castings it did not. Thick walled castings take a lot time to solidify than thin castings and has plenty of time for the metal mold reaction to happen.

As to why cast iron gypsy castings failed I will give my two cents worth.

Most of those molds she made were thick castings and needed a coarser sand so the gases can escape through the sand instead of bubbling through the casting. It could also be that the pouring temperature was too hot making the thick sectioned castings take a lot longer to solidify and make the problem worse. In hindsight this is what should have been done using a coarser sand for the cores in my headstock casting.

[CI]

They use that same sand and resin at the local Metal Museum, and when they have a big event, they literally pour a LOT of iron.
The sand is OK85; not sure if that means mesh 85 or what, but it is pretty fine and apparently kiln dried sand, all round grain, and all the same grain diameter.
Very dry sand is required for the resin to work correctly (per Ask Chemical, the company that makes the resin Linocure).

I have been to a number of iron pours at the Metal Museum, and seen perhaps 100's of their resin-bound molds, which are OK85/Ask Chemical molds, including Laura's molds.
I have never seen a problem with having the sand too fine, reflected in the castings they make, at least it not obvious to me that it is an issue.

You can get a pinhole in a bag of OK85, and the entire bag will have emptied itself onto the floor by the next morning.

It sure would have been nice to see a video of the pour for those castings.
That would perhaps shed some light on things, with something obvious like an interrupted pour, or a pour that had slag floating on top, etc.

Laura casts some fantastic stuff in iron; she has talent.
She has a very large cupola tatooed on her upper leg in front, which is quite impressive, but my wife does not like me to notice things like that.
The art iron group people are very passionate about what they do, perhaps because many of them sell it as artwork.
And the art-iron folks are the nicest people I have ever met, and will stop what they are doing to answer questions or help you with what you are doing.
Those big multi-cupola iron pours are wild.  If you have not attended one of those, you should try to find one.

Our member "airmodel", aka "Luckygen" has done a lot of cupola iron pours.
He is the king of hobby iron in my opinion.

Edit:
The most impressive cupola tat shown below.
LOL, don't tell Laura I posted this; it can be our little secret.

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[CI]

This is one of the castings made from the molds in the video above.
The surface irregularity is quite odd.
I will try to go dig out the photos of where I used graphite and alcohol, and did not get it all burned out.

This almost looks like what airmodel mentions, the pour was too hot, but OK85 is not prone to burn-in, at least not with cupola iron.
They do use an iron-rated pyrometer at the Metal Museum, to avoid poring too hot.

The thing about metal burning into the sand, is that it produces an additive to the castings.
These defects are negative, and into the face of the casting.
It is a bit odd that it does not occur on the perimeter.
Could have been the graphite alcohol gassing though.

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[CI]

This is a bearing cap I cast using identical resin and sand.
I did not have time to do much work on the pattern.
He wanted to keep the original letters, so I patched up the broken casting, but left some blue tape on it.
You can see the blue tape mirrored into the sand very accurately.

This mold had a coat of "Velacote" (tm) ceramic mold coat, which was burned off prior to pouring.
Not any odd defects like the one's Laura experienced.

I don't see any vent holes in this mold.
Normally I vent the highpoint of the mold.
Edit: Actually I do see vent holes in the cope; last photo, mold on the right side.

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[CI]

The bearing cap casting.
I did not know about spin traps when I cast this piece, but luckily it still turned out ok.

You can see the iron was quite fluid, since it rose up and out the vent holes (2nd photo).

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[CI]

This was the 2nd pour I ever made, and I made a lot of mistakes.
I was trying to use oil-based sand, and sprayed a mixture of alcohol and graphite onto the drag mold, and did not get it all burned off.
I would not suggest spraying alcohol onto oil-based sand anyway, but I had no casting experience, and so learning as I went.

The alcohol flashed and created huge bubbles.
I see some sand inclusions too.
This is a great example of how NOT to cast metal.
Almost everything that could go wrong did go wrong on the casting.
One has to start somewhere, and mistakes will be made if you are going to learn the process.

Also are photos of an ingot that was poured right after this casting was poured.
Note: Tall risers like those in the photos are not necessary; don't copy that.
No bubbling on the top of the casting because the alcohol and graphite were not used on that side.

Comparing this casting with Laura's shown above, it seems possible that her alcohol and graphite gassed.
I think the problems that showed up outside of her casting were from entrain air in the iron.
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[CI]

A camelback and straight edge I cast.
No problems with sand, etc.
Same resin-bound sand.

There was some odd surface wrinkling, I am not sure why, but that was superficial, and the edges/surfaces machined well without any inclusions or hard spots.

The patterns were made by a buddy of mine, who needed them cast in gray iron.
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[airmodel]

It sure would have been nice to see a video of the pour for those castings.
That would perhaps shed some light on things

I found two videos that shows what happens when a metal mold reaction happens.In the first video 6:08 to 6:48 the pouring cup backs up higher than when it was first poured and bubbles constantly until the copper solidifies. 10:26 to 10:50 Drag surface shows lots of wrinkles caused by the bubbles.
<a href="https://www.youtube.com/watch?v=aMejcz3hUFg" target="_blank">http://www.youtube.com/watch?v=aMejcz3hUFg</a>
The second video shows no bubbles when poured. If you thought the bubbles were bad in cast iron watch this video from 3:02 to 3:14 no bubbles at the pouring cup 4:16 to 4:26 plenty of bubbles in the casting!
<a href="https://www.youtube.com/watch?v=LAEyVTAtyJA" target="_blank">http://www.youtube.com/watch?v=LAEyVTAtyJA</a>

[airmodel]

There was some odd surface wrinkling, I am not sure why

If there is wrinkles on the surface on your castings it means that a small amount of metal mold reaction has happened and there may or maynot be bubbles in your casting.

[airmodel]

In the original video have a look at 49:33 to 49:38, the square pouring cup is full of bubbles but as the cast iron flows to the ends of the casting the surface is smooth with no bubbles. This means that that the cast iron has cooled enough by the time it gets to the ends of the casting. Classic case of too high a pouring temperature. There is also a possibility that she put too much of the three part resin which caused the bubbles to rise through the casting.

[Jasonb]

I don't know what foundries policies are when casting into other peoples mould? I would have thought most have a disclaimer as they have no idea of what is going on inside in relation to sprues, gates, runners etc. Also as they do not have the patterns they have no option to cast again if there is a problem.

I did see them flaming off the mould wash so don't think that can be blamed although brushing rather than spraying could leave heavy areas in some places.

Pat mentions excess resin causing more gas and I would imagine it also fills any spaces between the gains more, combined with glueing the two halves together does not leave much room for gas to escape. Bigger bulk of iron is also going to burn deeper into the sand causing more gas than a fine thin part so would flaming off the resin have gone very deep or just affected the surface.

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

At the end of the day it may well have been a combination of several factors. Maybe she will mould them again in exactly the same way and get them  cast as per her usual source which would be the only real way to see if it was foundry or not.

[CI]

I don't think she used too much resin.
She has mixed hundreds of molds, and knows exactly what she it doing, so I don't suspect that.

Bob Puhakka has explained much of these problems in his videos about aluminum casting; much of the same items apply to iron castings.

In the photo below, the iron will strike the bottom of the pour basin and curl up and fold back onto itself before the spure and basin are full.
This churns lots of air into the metal, and is a very predictable problem.

Bob Puhakka mentions that the you must have a smooth transition at the bottom of the sprue into the runner system.
Bob uses various methods to eliminate the air that gets churned into the metal before the spure is full.
Spin traps at the ends of the runners(s) is one way to separate the initial air entrained in the pour.

It is easy to avoid these defects, but most people use old-school sprue/runner gate system, with no spin traps, and gates that are not at the top of the runner(s).
This is why so many castings have defects; the fundamentals that are required for good castings are ignored.
You can see the splashing that happens inside the basin and runners in some of the mold fill simulations that can be found on ytube.
I don't need a mold fill simulation; I understand what is happening and can envision it easily without a simulation program.

The molten metal flow must be laminar.
You cannot just dump the metal in and have it get churned like butter, and expect to have a good casting.
Stevie Wonder could see what will happen.
Garbage in; garbage out.

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[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>

[CI]

airmodel has a very good pouring technique, which can be difficult to do.
If one initially pours too fast, then you may not be centered on the sprue, or the pour stream will be too wide, and metal will go everywhere.
If one initially pours too slow, then you get air aspirated down the spure, and air flowing into the mold cavity.

The trick is to start pouring exactly in the correct spot, and then exponentially increase the flow rate quickly, to fill the sprue and keep it full.
If you miscalculate on the ramp-up speed, again you generally spill metal everywhere.

If you hesitate and the flow stops for even a fraction of a second, you have an interrupted pour, which can cause a lot of problems in a casting.

It is very much an art to pouring technique, and one can be a bit nervous due to the radiated heat, and the images of a spill vaporizing part(s) of your body.
Thoughts linger in the back of one's mind about whether there is some residual moisture in the mold which will cause it to explode, which is always a big surprise.

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[airmodel]

Thanks CI for fixing the video thumb nails. When I tried to post them the forum rejected the email address saying they were invalid. I thought it maybe the videos are old but you were successful posting them.

[CI]

 
Thanks for making so many great videos.  Inspirational stuff !
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[fidlstyks]

I would say that was from the mold. If I had poured it, I would have shown the molder the other castings or any pigs made of the same iron.
  I have seen when greasey unburned scrap do that, but who melts greasey iron down?