Using a microwave oven to harden a sodium silicate core.

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
So I take it that you gentlemen have no qualms about watching videos of the guys doing aluminum castings of fire ant nests? That is, other than the fact they're pouring molten metal into a hole in the ground?
It makes no sense to me why a person would do that but, I prefer to eradicate fire ants as environmentally friendly as I can with boiling water, diatomaceous earth, Nematodes, and beneficial fungi.
My wife keeps ducks ,chickens and also has a koi pond .
I am not keen on intefering with the natural order of things, but that being said, there are things that must be controlled, such as invasive species.
Either you control invasive species, or they take over and cancel all the local wildlife.

And ferral hogs are totally out of control in Texas and surrounding states.

The ant nest castings are interesting in that it seems they are all different, even though they are all ants.
Different shapes, sizes, arrangements.
Seems a bit like the tunnels inside of the Eygptian pyramids; sort of meandering all over.
I think you really need to to a lot of digging and use a pressure washer to retrieve those ant castings.
And those castings seem to sell for a fortune.
Too much work for me, but I do admire them.
Not much different than Pompeii, or near Mt.St. Helen when it went off; stuff like that happens sometimes to many creatures.
Note to ants: If you see some bugeyed nerdy looking person coming towards you with a crucible full of hot metal, don't hang around to find out if that creature is friendly; run like heck.
I guess that is where they got that army expression "Bug-out".

I went to a rental house to paint the interior for my boss, and the walls were covered in sheets of cockroaches.
The roaches moved in waves as you walked through the room.
Creepiest thing I have ever seen, and there are not many things that creep me out.
Took 4 treatments to finally clear them all out.

Bugs I hate Bugs especially roaches ! 😱
My opinion is "When in doubt, vent everything".
Sounds like venting is a lucky charm, you use and it will prevent having scrap castings. The biggest reason why venting is used by youtubers is a mold will not fill up if no vents are used to release the air inside a mold. So I made a video to see what would happen when two molds were poured side by side one with a vent and one without a vent. The first mold with a large vent did not fill up completely and the other two did fill up which was a surprise to me. It could be that I poured a little slower on that mold.

But you are not comparing sand types to venting.

Resin bound sand, in my experience, will trap air easily, and you will have large bubbles if you don't vent the high points of the cope.

So you are assuming that everyone uses greensand, when there are other types out there that may need venting, such as Petrobond, sodium silicate, etc.

If you compare apples to apples, I think you will see why I always vent the molds and cores.
I thought we were talking about venting cores, can't see cores in the video and what you call vents I would call risers.

This lot is about to be poured at the Foundry, couple of those are for me, quite a few more from my patterns. A few have risers, most dont and that is airset


  • thats mine.JPG
    thats mine.JPG
    159 KB · Views: 0
If you look at this video at 4.30 the guy talks about letting gasses out and you can then see them poking a series of holes in with a wire, that is what I term venting.

At 11.50 you can see the grooves cut to vent the cores to the outer edge.

As they pour you can see a small amount of iron flowing out of a larger "vent" which is also mentioned just as the sand is being knocked off at 21.40 also watch for the thin rods of iron where it has flowed up the poked in vent holes.

Riser mentioned early on and you can see it at 20.30.

So depending on the job, sand, etc the appropriate method should be used and what may work on a small pour should not be regarded as something that will work on others

I have never used vents on resin bound sand or SS sand and no large bubbles appeared.
You are still not comparing apples to apples.
The sand grain size figures into it too.
I think you are generalizing; since you did not get bubbles then nobody gets bubbles, which I say from experience is not true.

Coming back to the air vents video the volume of metal going into those "e" shapes is relatively small so the amount of air that is displaced is also small. The permeability of the sand can no doubt cope with that amount of air.

Now to me the "e" looks to be about 20mm x 3mm section but consider if it were say 25 x 25 section then there would be 10 times the volume of air being displaced by the metal yet the amount of and that has to dissipate through remains the same. This may require a means of letting the air out if the existing sand mix can't cope and even more so if the permeability of the sand has been reduced by the addition of binding agents or a finer sand is used as that reduces the permeability.

Another factor is the venting of gasses be they steam or other substances given off by binders, mould wash etc. The small volume of the aluminium being poured in the video will not create anywhere near as much heat as the thicker 25 x 25 section casting would so there is less need to vent the gasses caused as the sand is heated by transfer from the cooling metal. Change the metal to iron which is a lot hotter and you will get even more heating of the sand so more gasses, steam etc that needs to go somewhere.

So no one way suits all, take the job in hand into consideration and use the method that suits
In theory any glue or adhesive could be used but in the real world a lot can not be used for many reasons. To give you an example Liquid nitrogen could be used to freeze sand with a tiny amount of water to make a core. Pros are quick to make and no need to dig out hard cores because the ice has defrosted so the sand just pours out. The cons are liquid nitrogen is hard to get and precise timing is needed to put the core into the mold before it defrosts. I am sure many others could add to the reasons why they would not use liquid nitrogen.
The sand has to be bone dry. Liquid nitrogen requires special vessels to store it and it has a short shelf life. I can not think why the sand stays together after the LN is totally evaporated and is strong enough for pouring hot metal into.
Change the metal to iron which is a lot hotter and you will get even more heating of the sand so more gasses, steam etc that needs to go somewhere.
I pour mostly iron, never vent and rarely get problems with gases and steam pressurizing the mold. If gasses and steam were the problem I would have a lot of molds that did not fill up but that is not the case.
I think you are generalizing; since you did not get bubbles then nobody gets bubbles, which I say from experience is not true.
You must be doing something wrong if you have to vent bound sand.
I can not think why the sand stays together after the LN is totally evaporated and is strong enough for pouring hot metal into.
It does require some water to freeze the sand together. Just how long before the ice defrosts would require a few experiments.
I think the US and Austrailia have a lot more land per plot so have the space. Also not really allowed bonfires so firing up an oil burner may not go down well with the immediate neighbours

I know Pat also melts outside which is less likely to be a problem than UK weather.

I'd also need to be able to do reasonable size iron castings upto at least 5kg so allowing for gates and runners that would be a 6kg melt so that is a fair bit of equipment to store once you include flasks, sand, fuel, raw materials, moulding area, etc when you only have a 2.4 x 4.8 workshop.

lastly for what I can get the iron castings and non ferrous done for it is simply not worth the bother and probably cheaper to have them done.
A viewer posted a comment on my video that wikipedia has three methods to harden sodium silicate for cores and molds. One of the three methods uses a ester based chemical to harden sodium silicate. I did try to get some years ago but had to buy large quantities so CO2 was the go to method until I discovered using a microwave oven.
Sodium silicate - Wikipedia