fireworks Posted September 30, 2009 Posted September 30, 2009 A few months ago, I ordered 3 pounds of unmilled sodium benzoate for whistles from skylighter during their half off sale. Knowing that it was hygroscopic, I took about 30 grams from the container straight into the mill. After milling for more than a day, it is not anywhere close to finely powdered. Some of it is fine but other parts of it are around 40 mesh and it doesn't break down into a fine powder. What is going on? Is it possible that it could have absorbed moisture before it was packaged at Skylighter's Factory?
Mumbles Posted September 30, 2009 Posted September 30, 2009 Very likely actually. Commercially it just comes in paper sacks. You might want to try drying it efore milling. Making sure your jar and media are bone dry is also essential.
Arthur Posted September 30, 2009 Posted September 30, 2009 Take a sample and weigh it then dry it til the weight is constant. Estimate the moisture content. Some things that clump in the mill will stay as free flowing powder if you add something. Less that 1% cab -o-sil will change the flow properties of ingredients and not aflict the properties too much, may be worth further opinion and experimental evidence.
Ventsi Posted May 10, 2010 Posted May 10, 2010 I have a pound of this stuff and out the bag its small 2-3mm dense and hard pellets. Very hard to crush. I threw half a pond into my 3lb jar with some brass media and after almost a full 16 hours of milling some of the stuff is over-airfloat and some of it barely passes 40mesh. The NaBenz formed clumps similar to writing chalk...I dried the Benz in the oven for a few hours along with the jar and milled it for a few hours again. Still , nada. I decided to only put in 100 grams in the mill and add in the catalyst thinking it might work as a free-flow agent. Still I need to go out to the paint store and buy some Cab-O-Sil, do you guys think this will work? http://www.tapplastics.com/shop/product.php?pid=44&
dagabu Posted May 10, 2010 Posted May 10, 2010 I just throw it into my blender and grind it until I see it flow freely. I screen it through a 100 mesh screen and throw what hasn't ground down back into the blender. It takes about 2 solid hours to grind a bag of NaBenz to powder. D
Ventsi Posted May 10, 2010 Posted May 10, 2010 (edited) Hmmm, I was thinking of doing that before throwing it in the mill to save a little time. I like my stuff really fine, at least 200-325 mesh. I know that finer is better for whistle, so I wanna suck out all the power I can. Edited May 10, 2010 by Ventsi
dagabu Posted May 10, 2010 Posted May 10, 2010 I dont use any finer screens then the 100 mesh. I have never found need of them. My whistle is strong and it is all blender ground. Here is a video of a 1/2" UT hybrid rocket using 75% K Benzo and 25% BP (willow) that I sent up tonight, it had 300 grams dead weight on top to test out the lift. VIDEO
Mumbles Posted May 10, 2010 Posted May 10, 2010 You might want to try to grind it with a blender or coffee grinder first to kind of pre-crush it. Those 3lb mills aren't very efficient, so I'm not all that surprised it isn't crushing the material all that well. I've also heard that cylinders are additionally more inefficient at crushing if you were to actually do a screen analysis.
dagabu Posted May 10, 2010 Posted May 10, 2010 Vincent, Are you "wet mixing"? You may be able to pull more power out of the fuel with wet mixing after milling the NaBenz with the catalyst. I am sold on the mineral oil method but will do the wet method next to power up my mix a bit. D
Ventsi Posted May 10, 2010 Posted May 10, 2010 Yes I plan on it. I'm going with the white gas/Vaseline wet mix. I just wanted the catalyst to be as intimately mixed so it can do its job on a microscopic level better. I plan on making it "soupy" and then stirring the living heck out of it while the solvent evaporates. I plan on making some 1/4" mini-whistles and I'd love if I can get a decent mini shell/LaDuke header on top of them,
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