Egg Crate Stars
Entry posted by Swede
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It's been a long time since I've done a blog entry. I know a lot of people are following the perchlorate adventure - believe it or not, I still have not tested the lead dioxide anode. It is bagged and hanging from a hook on the wall. With the arrival of summer, as any homeowner knows, there is always work to be done that gets in the way.. real work. We had a massive storm this spring that dropped a 50 foot pear tree across a neighbor's fence. Stuff like that gets in the way of life.
Anyway, with the fourth of July coming, I realized I needed to get in gear and get some stuff prepared. I am not very experienced at traditional shell construction, and I don't have a star roller. The only other way to make a number of stars is to either cut them, or pump them. I tried pumping... takes forever, and the consistency of the pumping depends upon the composition. Some comps pump nicely, some don't, and I was a bit tired of it, to be honest. A star plate is something that is in my future as far as a home project, but as of now, I don't have one.
In one of the APC threads, the use of egg crate lighting covers was discussed to create stars. I decided to give it a try. Egg Crate has nothing to do with real eggs. It is simply a plastic fluorescent light cover with regular, 1/2" squares. Unfortunately, most are 3/8" thick, so they create rectangular pieces rather than cubes, but that is OK. Rectangles burn fine.
I started with a test - a section of egg crate about 18" x 18" and 500 grams of Shimizu chrysanthemum #6. Rather than use SGRS, I substituted dextrin for 1/2 of the binder, so it was 50% SGRS and 50% dextrin to bind. The binder was 75% water and 25% isopropyl alcohol to wet. The #6 was ball milled with my new stainless media, which worked great. 2 hours took the sugar-textured potassium nitrate to airfloat, and it was mixed perfectly.
The #6 was turned into a standard star dough, probably a little shy of water. Work starts by laying the egg crate on a nice, flat surface, and the star mix is spooned on. To make consistent, dense stars requires a bit of physical manipulation. I found that the heel of the palm works very well at compacting the dough into individual cells. Without this physical manipulation, some of the cells ended up being a bit lighter (and more crumbly) than others. I found it was important to press vigorously to create good stars; but still, it was easy, MUCH easier than cutting.
This particular spoon has a flat edge. Any flat scraping surface will work. By scraping the dough, it is easy to create a reasonable (but somewhat rough) surface on the exposed portions of the star.
Inevitably, the edges of the egg crate will have incomplete stars. While the dough is still damp and pliable, these are poked out with any handy object, gathered together, and used to fill up other incomplete cells.
At the end, I had what felt and looked like a full honeycomb. There was one thing I failed to do... I should have used my hands to smooth out the rougher stars, which would have made them stronger, I think. I did mist them a bit, and at least with this charcoal comp, the mist wicked right in, which (in terms of binding) is probably a good thing, again, increasing the strength of the stars. As it was, a portion of the cells had smooth faces, and others had rougher faces.
The fun part - The star "honeycomb" was hung in a shaded area to partially dry. The 500 grams of comp. took no more than 15 minutes to pack into the cells... it was rapid and quite easy. I could easily picture a dozen of these 18" x 18" egg crate sections, each packed, scraped, and hung, for some serious production. Since this was a test, all I did was the one section. A rough idea of the mass, and amount of egg crate needed, is 250 square inches or 1600 square cm of egg crate for 500 grams of composition. This will vary with the comp, but should be close, with cells to spare.
The egg crate was left to hang for about 4 hours in 90-degree weather, in the shade, but with a breeze. This dried it sufficiently to allow extraction without crumbling. I had hopes that manipulation the egg crate would cause the stars to drop out, but this was hopeless. The easiest way to get them out was to angle the egg crate on a handy dowel and poke them out individually with a square rammer, in this case, a piece of 1/2" square aluminum.
As each row is poiked out, the dowel scrapes the row to the left, and the next row (or two) is poked out.
It took less than a second per cell... poke, poke, poke, they dropped right out. Very quickly, the entire egg crate section was cleared, with very little waste or breakage.
The bulk of the stars were well-shaped, with good integrity. There were a few that flaked, and a few that were underweight. A bit more care in the packing stage would improve the performance of this system, as would a misting and smoothing of the cell faces after they are packed. The scraping action of the spoon left behind a rough surface, and I found those cells with rough stars didn't extract as nicely.
Summary - I like this method. If you don't have a star roller, I think this is the easiest way to make stars. They have a much greater consistency (in my opinion) compared to cut stars, and the speed of production is excellent. A half-dozen modest sections of egg crate could handle 3 kg of typical star comp. The stars measure 1/2" X 1/2" X 3/8" or so. I think this is worth pursuing further, and I recommend this method for small-scale production of simple stars.
Postscript: comments from the Random Thread....
Mumbles mentioned a wetness significantly beyond traditional for cut stars would be appropriate, and I agree. The comp could almost be wetted to a spackling paste or body putty density, and literally wiped in, as the cells form supporting walls, like individual molds, and the stars are dried significantly before extraction. I wouldn't go nuts, but the comp can definitely be more pliable, wetter, less grainy. You certainly do not want water oozing out, and I'd increase the % of alcohol to avoid dissolving nitrates or perchlorates excessively. A spray mister is very helpful.
This batch is about 90% dry (it's hot here) and I've noticed that the stars that are less dense (those that were not packed as much as others) are not physically as strong as the better stars. These whimpy stars total about 10% of this test run.
So the best methodology must be one that compresses the comp as much as practical. The heel of the palm thing did work, and the superior stars came from the areas that were heaped high with comp and then really massaged down, with the excess comp flowing to the side. A touch more binder and water or alcohol will also be helpful. SGRS is probably better than dextrin. Red gum, I don't know, but I suspect it would work well with egg crate stars. Alcohol should be fine on the plastic.
More thoughts... a sheet of thin brass or even stiff plastic or cardboard could mask portions of the eggcrate while massaging the comp in. Excess comp flows onto the sheet, which is then moved, and the comp gathered on it is dumped into the now opened cells. Or, one could have a thicker metal plate, preferably aluminum, heap the comp thick onto the egg crate, lay the plate on top, and tap it in (maybe even press it) with a rubber mallet. Or skip the plate entirely, just wail away with a rubber mallet onto heaped comp.
I had also meant to dust the egg crate with graphite, which might help a little with the extraction. My egg crate has zero taper; those WITH taper are golden. I also need to try drying it longer. A day or more of drying should see the stars contract more and also be stronger, allowing serious manipulation of the egg crate to get them to fall free.
The best part, the stuff is very cheap. A 2' X 4' section is just a few bucks, and I've seen it in trash cans many times, because they break, and people throw them away.
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