And So Castings Made of (Kinetic) Sand . . . Turn Out Pretty Well, Actually

That kinetic sand stuff is pretty cool. It’s soft, it builds motor skills, and outside of sprinkling it on carpet, it’s not messy. If you don’t know, it’s 98% sand and 2% polydimethylsiloxane, which is a major component of Silly Putty, and according to a certain yellow and red clown, it’s safe enough to put in chicken nuggets. [Chris]’s wife bought him some, probably because she wanted to see him play around with something that isn’t potentially deadly for a change. In the course of researching its magical properties, he found out that it doesn’t really have a thermal breakdown point, per se. At high enough temperatures, It vitrifies like a sand castle in a mushroom cloud. Between this property and its malleability, [Chris] thought he’d have a reasonable substitute for founding sand. As you can see in his latest experiment, he was right. As a bonus, he managed to turn the benign into the dangerous.

[Chris] had never cast aluminium before, so he decided to start small by making an offset cam for a rotary broach. He packed some magic sand in a wax paper cup and shoved the cam in to make the negative. Then he cut down some aluminium rod and put it in a graphite crucible. He stuck his DC arc welder’s electrode down into the crucible and cranked it up to 50A. That wasn’t enough, so he went to 110. The crucible was soon glowing orange. He carefully poured the molten aluminium into the mold. Make the jump to see how it panned out.

Spoiler alert: there’s no cussin’ this time!

33 thoughts on “And So Castings Made of (Kinetic) Sand . . . Turn Out Pretty Well, Actually

  1. One of the important properties of casting sand is that its grain size is a compromise between small enough to provide an acceptably smooth surface and large enough to allow gases to flow through it. I’m surprised this plastic-coated sand has similar properties.

    On the other hand, I’m curious about applying this kind of coating to tungsten powder to make sintered bullet cores.

  2. It looks like his aluminum has a lot of trapped gases. When he turns down the cam, he may find the surface marred by lots of little bubbles.

    Grind up some chalk, wrap it in a piece of aluminum foil, and stick it in the molten aluminum and push it to the bottom with a steel rod. This will degas the aluminum and give a better finish when turned down.

    (The heated chalk emits CO2 which bubbles up in the aluminum. These bubbles contain no nitrogen or oxygen, so the dissolved gases in the aluminum tend to equalize the partial pressures – the gases leave the aluminum and dissolve into the bubbles.)

    1. That is good to know. I have worked with castings that were too porous and usually ended up leaking because it wasn’t possible to create a good sealing surface.

      1. The casting co. that was making the housings that I worked with ended up adding something to the mix. I have forgotten what it was, but will add it here when I find out again.

      2. I’ve not tried Morton’s lite salt. Online discussions indicate that people use it for a flux, not as a degasser. It’s “lite” means that about half of the salt is potassium chloride instead of sodium chloride.

        There’s several chemicals you can drop in to degas the metal – it only needs to generate gas at the bottom and percolate up. Some people inject Argon and let it percolate up through the aluminum. Some people use pool shock tablets (generates Chlorine).

        Google “casting degass aluminum” for lots of info on this.

        You can get a box of blackboard chalk for $1 at the dollar store, so that’s what I use.

        Flux is a material that melts and covers the top of the molten aluminum to prevent oxidation. People online seem to prefer Morton’s lite salt. You still have to wipe off the dross that forms at the top because there’s always some oxidation on your source material, but otherwise the flux will keep you from losing much to oxidation.

        Have a look around BackyardMetalCasting.com and you’ll find lots of HowTo information on casting. It’s not hard, there’s only a few tricks you need to come out with good looking casts.

        http://www.backyardmetalcasting.com/index.html

        I’m excited to try kinetic sand. One problem newcomers have with sand casting is getting the right consistency of the green sand. A ready-made green sand that doesn’t dry out and is reusable would make the task much easier.

    2. so in summary, if I understand right
      – while melting the aluminum, throw in lots of borax or no-sodium-salt to form a layer on the top which will prevent oxidization
      – a bit before pouring, foil up and throw in chalk to pull out bubbles
      – skim and pour

      yes?

  3. with an open top mold like this the gas can escape up without a problem, does it also need to escape to the sides?

    1. I can’t comment on this particular material (yet), but in normal sand casting no gas escapes through the sand.

      A typical 2-part casting has one vertical channel for the aluminum to enter, and one or more vertical channels for the aluminum to come out. You pour in enough to fill the mold cavity and channels to their tops, and the channels are cut off after cooling.

      The vertical channels generally have to start from the highest points in the mold cavity, lest trapped gases cause a void in your poured casting. The sand is slightly wet, mixed with a little clay, and contained in a box (the drag and cope) so very little gas goes through the sand.

      There’s a zillion aluminum casting videos on YouTube explaining the process. This one below (and all the others done by the same person – all of them) are particularly interesting and informative. Well worth watching:

      1. Just watched the first two, but I have a feeling I’m going to be pretty busy catching up on myfordboy’s channel. These are excellent

  4. Melting aluminium with arc is not popular in industry. I have been told by metallurgist that it makes some hydrogen and quality of the aluminium itself is weakened during arc-process.

    1. I make large graphite crucible for melting ~2000lbs of aluminum at a time. All my end users inductively heat the graphite to melt the aluminum.

  5. I am not surprised to see kinetic sand used like this. The various kinetic sands looks like made for this… ;-)

    In addition I some years earlier, just for the fun of it, looked into one of the producers of the stuff, Delta of Sweden, a rather small Swedish company. They have for example the sand brands(!) Bubber, Moon sand and Deltasand, but that is not what is interesting. What is is the name of their street “Gutaregatan” “-gatan” means street, but the other part is someone working in a foundry, leading to the assumption that there might have been a foundry in that area earlier, or maybe even still is.

    My conclusion is that at least for this producer this product probably is a spin-off or a way to look for other markets when the original market is smaller or not even there any more. When I think of it it is quite logical. Some sands of their is harder and probably almost good enough for cores, others softer and probably good for the rest of the mold.

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