Casting tech corner

Hey all, I would like to start documenting and cross pollinating casting practices past and present. I know Matt has a lot to offer here. While i was looking over the donkey 32 threads, it looks like Peter has a lot of experience in this space as well. I'm sure many others have contributions too.

With thinking about shippable needs and light weight and repeatable and crackless. How close has anyone gotten to the right formulas.

I also understand if people don't want to share their proprietary findings, but I'll take what I can get.

In this thread we are touching on it a bit.
https://permies.com/t/41202/rocket-stoves/Emergency-quick-small-batchbox-sq

Rick Edwards wrote:With thinking about shippable needs and light weight and repeatable and crackless. How close has anyone gotten to the right formulas.

Castable refractories is what I've used with good results, built whole stoves of more than a ton out of that. A shippable core should be lightweight but resilient at the same time, so homebrew refractories are out. The weight can be kept down to do it by the book, using a proper vibrating table and thin walls. The thinnest walls I've ever cast has been about 1" and that is about the minimum. I'd think 1.25" would be safer and better to vibrate. The little 4" J-tube which I am using at the moment is in fact cast with 1"walls, only the tunnel and bottom ends of the feed and the riser. The top end of the feed and the riser are from steel and vermiculite board respectively.

Molding is a problem when repeatability is the goal, wood is out, steel possible in certain circumstances. But for castables the mold has to be absolutely leak free otherwise the quality of the casting is jeopardized. One could be into rubber molds which are beautiful to work with but those are costly and need to be replaced from time to time. The trick is to minimize the cast pieces, for the parts which doesn't need to be heat proof, use other materials. The superwool tubes like Matt is using are ideal for risers, light and heat resistant but can't take abrasion.

But what to think of shipping a DIY recipe and a one-off cardboard mold? Or an outer skeleton of steel where the customer can add his or her own fire bricks? Letting the people who want the stove do the work and provide the means to build the darn thing I would say.

Rick

Byron, yes the inner form will be burned, also using Matt's ghetto casting tech, it seems to need to be burned out to hold its shape until fire cures and hardens it.

Matt, if we wanted to do this nicer and maybe shippable, would you use the spar this or that, and with what other ingredients for thinner walls and crack reduction?

Matt

Yeah, castable refractory of some flavor, and stainless needles. You guys should have both. I think that cracking is a given, but it would probably hold together as long as it wasn't moved around much. Those ceramic fiber risers are a better choice for those design goals, in my opinion.