Yes l use waterglass a lot but never heared of it hardening with CO2! This opens so many posibilitys!
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I think you did use CO2 before. When you put insulation inside your chargas generator for your MBZ e230 you used a torch to harden the waterglass. The torch makes CO2.
Rindert
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I admire you remembering my waterglass/rockwool experiment but l cant seem to remember pre hardening it, except with the gasifier it self. Culd be old age 
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I suspect that liquid is “diesel” or a fuel oil. According to wikipedia it is also used as an additive for a reducing agent which prevents the metal from sticking to the sand. The way it is burning, it looks like some was already in the sand. My guess is if you pour hot metal into a closed cavity with diesel in it, it results in the diesel catching fire and blows the aluminum out of the cavity.
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Lights a bit to easy for diesel. Maybee kerosene?
Culd it allso be burnt to soot the surfacem
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I think Kristijan has the right answer. I have seen a mold maker dust the inside surface with powdered graphite. It made a very smooth surface on the casting. And Petrobond sand contains oil and makes beautiful smooth surfaces.
Rindert
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The first attempt at a core was not entirely successful, but showed some promise. I think i needed to be more gentle with the removal. I waxed the core box with paste wax, and it didnt seem to stick too bad. Would dry powder be better for release?
Why dont I start out learning on a simple project like a normal person?
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Andy,
It’s common to put a thick piece of wire, like from a coat hanger, in a long slender core like that. Think about the rebar they put in concrete. You are almost there man!
Rindert
Rindert, thanks for the input. I can always count on a response from you in this subject.
I actually put a wire in the middle and pulled it out to make a vent hole. Maybe i should put some glue on and slide it back in once the core is hardened.
I also considered the possibility that i didnt compact the sand consistantly.
The fins are pretty thin, its a tall order to keep them strong enough.
I just thought with your concrete analogy, maybe I could add a little fiber to hold it together better.
By the way, looking back on previous posts, i noticed on your molding flask you use crossway dowels to hold the screws. Thats a good trick I dont see uses often.
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Maybe you could put two in and pull one out to make the vent. The vent is necessary too. I want to see this nozzle working. I think you have a good idea
It’s cheap and strong. That’s why I do it. But its doesn’t look nice, in a fine woodworking sense, so you don’t see it around often. Furniture makers used to do it when one side would be hidden. They didn’t drill all the way through. Then manufacturers started making dowel nuts, and you know the rest of the story…
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Here is a foundry/forge using a waste oil burner. It looks like it needs some adjustments to make it more viable. Like when it is tilted in forge mode, it looks too low, but it is about right for casting, so it needs a height adjustment. I think it could be modified slightly to use propane and/or wood/char gas as well. It also looks like it needs wheels. but that is all nitpicking, it seems pretty solid.
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I never knew there was such as thing as a jewelers charcoal block until today. Apparently, they are used for soldering jewelry like silver/gold/platinum, and they use them for melting small bits back together like a kiln.
They make a compressed charcoal block but I have no idea what they use for a binder.
“Specially compressed charcoal delivers a super-hard, reflective surface with a much longer life than soft charcoal blocks. Charcoal blocks reflect heat efficiently while creating a reducing atmosphere around the pieces you’re soldering or fusing, which helps to reduce oxides.”
It makes sense but I never knew.
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I would form a pleated shape somehow with aluminum flashing, and pack it full of sodium-silicated sand (or even just greensand) for the core. The aluminum flashing will keep a little strength during the pour, and weld itself to the molten aluminum.
Also, I used to putz around with baking soda and vinegar, and even dry ice, till I discovered how inexpensive it is to just get co2 from a gas supplier. I suppose for a tiny one-off project you might not want the overhead of tank rental, but I wish you success and hope you do many more cores and casts so that cost is justified after all.
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My 2 cents on the metal casting topic. Aluminum bronze is a popular marine alloy. I got the copper from a local scrap yard in the form of copper wire. Firing the oil burner this hot usually destroys the intake tube of my furnace.
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I’ve really wanted to attempt an aluminum bronze nozzle for a cross draft or a downdraft. Maybe print it with a wax type filament and do Lost Wax casting to have NPT threads.
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Would be very interesting to see how that would work. The melting point could be an issue, but it might be overcome by the thermal conductivity of the alloy if there was enough heat dissipated back through, it to the outside.
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I would probably do as little preheating as possible ie fresh air coming in to cool the nozzles, and moistened charcoal to keep the reaction a bit lower if it’s in a downdraft.
Making them very thick would likely help as well.
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You can do lost PLA casting.
I think there was a method to do it in the microwave as well but don’t use a microwave used for food. And you can actually melt the material in the microwave.
If you have a model say made of clay or whatever. They sell a reusable, pourable material called Alumilite. It is like jello. then you can pour it in to get the reverse, cast a low melt wax into it. then do the lost wax casting.
You can do a homemade version of it, without looking up the recipe, it is glycerin, gelatin, and water.
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I think that would work. Or if you have the ability to melt copper, straight copper would maybe transfer heat a bit better.I had limited success with my aluminum nozzle. See it in the charcoal nozzle thread.
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That’s an idea worth trying! The weather is getting warmer, I think the foundry will have to wake up soon.
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