Metal Casting at Home Part 11. Sodium Silicate & CO2 Core Making.

[AsiAzzy]

vinegar + bicarbonate is ok but a slow reaction.

vinegar (or any other acid for that mater) + baking powder ( NH3HCO3 - acid carbonate of ammonium) is a lot faster reaction and gives a lot of CO2 in fast time

[hayati4522]

Thanks...

[gettingahandle]

....... and wallah!

[MyIvank]

Have you ever used this method to make complete molds, like as investment casting ?Love your work and videos, first class, keep up the great work.

[myfordboy]

@MyIvank It would be difficult to get the pattern out of the mould as a solid sand would not have any "give".

I don't see any advantage if this method could be used, the surface finish of the greensand mould is better than the sand core.

[91asraf]

what the defect of CO2 casting process??pleeezzzzzzzzz

[MyIvank]

Fantastic video, you are real inspiration..

[myfordboy]

@matt12466 I dont know the chemistry but the CO2 does harden the sand. It goes even harder if left for a day or put in the sun.

To support the core there will be core prints in the mould which leave holes in the finished casting. The sand can be removed through these holes. You can't realy have only a tiny hole because there would be nothing to support the core in the mould. Video 13 shows the sand being removed.

[Darius12235]

@myfordboy Its probably because of the pressure that the CO2 creates

[iguanian]

@Darius12235

I suspect it it more likely that he is getting a surface reaction of the sodium silicate with the carbon dioxide which forms a variety of silicon dioxide, which is basically sand, but at a near molecular level.

[douro20]

@myfordboy

Na2SiO3 + CO2 --> Na2CO3 + SiO2 + ∆T

Sodium silicate reacts with carbon dioxide to form sodium carbonate, silicon dioxide (quartz) and heat.

[douro20]

I've seen this done on an industrial scale, where they put the casting into a drum and inject CO2 into it. It hardens in just seconds.

[TheSMasa]

Will these cores dissolve with water too?

[myfordboy]

I haven't had need to try this because they can be dug out easily.

[Kulis747]

Your videos inspired me when I was deployed to Afghanistan, and upon returning home I built a furnace and poured my first ingots yesterday. I have two questions regarding what you've taught us and my experience.

1. What is the best ratio of salt and sodium carbonate to use by weight or volume?

2. My aluminum boiled when I poured it into my new steel 3.5 x 12in "C" channel ingot molds I had just made, and idea why?

I would hate for this to happen in the future if I was trying to cast a part.

[myfordboy]

I usualy melt 2 to 5 kg of metal and use a teaspoon of salt and sodium carbonate whatever the quantity.

Perhaps you have the metal too hot and this is causing the boiling when it hits the steel mould.

You should pour as soon as the metal is completly melted. It shouldn't be glowing red.

[Kulis747]

Thanks for the help. I believe it may have been too hot as you suggested. When I looked down in the crucible it was glowing red. Of course it was night, but still it was really hot. I'll try a cooler pour next time.

[xarlock667]

@Kulis747 If there was rust on the steel, you may have inadvertently made a thermite reaction, Iron Oxide+aluminum=thermite.

[indet1957]

I just started in hobby casting hope to be as good as your stuff looks. I am making the Machine shop from scap series of books by David Gingery. I have made several patterns made but my successes look very poor against your work. Thank you for sharing your talent.

[kodak726]

thank you it really helped me understand clearly

[FatherOfTheParty]

All your videos are first rate.  Thank you very much for spending the time to pass along your knowledge. How long does it take for the CO2 to react with the sodium silicate? I would imagine it's fairly quickly. Thanks again!

[myfordboy]

The reaction is pretty well immediate . I left it in the bag for 5 miniutes though. It contiues to harden more over a few days due to th CO2 in the air.

[regpye]

Yes it is a great way to make the cores, been using that method for a while. Also tried making a few small simple moulds using the same method - works OK too.

Dave, you are a wonderful teacher, your videos are so clear and the instructions couldn't be better. The lack of sound instructions doesn't hurt either, everything is explained in action - well done.

[barnza]

another brilliant video, thanks for posting. How do you split your tubing for making the cores so neatly? Is it just pvc pipe?

[myfordboy]

Tube is PVC electrical conduit split with a slitting saw on my milling machine.

[junkman6261]

how does the co2 harden the core?

[myfordboy]

It reacts with the sodium carbonate that was mixed with the sand.

[barumman]

Magic

[myfordboy]

It is only used for making the core and is disposable. Moulding sand will be used for in the

drag and cope.

[EmperorAst]

Excellent!

I very much like the uses of plastic bags throughout the video series!

[myfordboy]

Makes mixing easy!

[EmperorAst]

Exactly! and can be used to make a chamber for the CO2. Multiple uses, that's why I liked how you used it!

:)