Sand-compaction

I'd like to see some comparative empirical data on the packing density achieved. It's so easy to measure I'm surprised it's absent and makes me a bit skeptical of the claims. My first observation and question would be, though the sand obviously must move horizontally through the holes in the inner wall, what mechanism would keep it moving that direction instead of just sucumbing to gravity immediately after it clears the holes in the inner wall?

In a prior life, I gained a lot of experience packing filter beds with granular media. Density and stability of the packed column were paramount to prevent it from fluidizing......same goal for packing a LF mold. Direction, frequency, and amplitude of vibration were what mattered, in conjunction with using the "shower method" of fill. The media dispersion from the shower made it very fluid when it landed on the building surface and much more quickly flow like liquid into the cracks, crevises and lowest regions of the column and pack very densely. All the commercial LF foundries use the shower fill with directional/frequency/amp vibe control.

The shape of the media matters to. Round(ed) is easiest to pack. Hexagonal close packing is about as dense as it gets for uniform size particles. Nonuniform can be higher density like pouring a bag of shot into a bucket of marbles. The shape of sand grains is less than ideal to initially fluidize and pack but once packed, it is harder to move. Having relatively consistent grain size is helpful too.

All you need is an accurate scale to measure results. For me, I canjust use the same sand chargeand measure the depth at which it fills the flask. Even with just shoveling in silica sand, then vibrating it settles 10%. Another 5% is pretty easy to find by ladling /showering it in a quart at a time as it is being vibrated. I suspect to break next barrier for me would require using different shaped media that is more rounded than than silica sand, but unless you're buying a trainload, it's so inexpensive, (~$1/lb instead of $20/ton or even 8c/lb at the big box stores)......and sand works well enough (for me). Big thing is to keep it dry. I get many reuses but it eventually fowls and doesn't flow as well. I just replace it because the sand is cheaper than the energy to heat/cook out the moisture and contaminates.

Iron LF foundries use a more rounded mullite or zircon media for refractory and then process waste heat in a fluidizing furnace to regenerate the media for re-use. I'm not so blessed.

Best,
Kelly