LiamPyro Posted February 26 Posted February 26 I hate to start yet another thread on bentonite nozzles, but here we are. I've been using the granulated sodium bentonite clay from fireworks cookbook, which looks similar to the cheap cat litter that many swear by. I press it to 4000-6000 psi in granulated form, without pre-powdering it, to provide some "bite" into the tube wall and a nicer-looking (and dust-free) nozzle. I added some paraffin to my first batch by first (partially) drying the clay at 250 deg F and then adding the melted wax in a petroleum distillate (white gas, Coleman) solution. I ended up adding too much liquid and had to add some more un-dried clay from the bag to soak up the extra, resulting in a mixture with about +8% paraffin. The clay, when dry of solvent, was a darker beige color and had a thin, visible coat of wax. It compacted well and produced satisfactory nozzles. I recently made another batch, this time by fully pre-drying the clay (it lost ~10% of it's weight in water in the oven) then adding the same percentage of wax in solvent as before. However, this time it seems that all of the wax was absorbed into the clay granules - the clay looks almost the same as before the treatment. I used less solvent, and all the clay was fully dried (more clay mass, less water mass, lower effective ratio of wax to clay), which may be why. Oddly, the same volume of this mixture compacts less than the previous, resulting in a thicker nozzle for the same increment size. This seems to indicate that some amount of moisture in the clay is actually good for consolidation (like how some folks dampen their BP before pressing). It could also be that the surface wax coating facilitated slippage of the clay grains past one another, allowing for higher densities at a given psi for that mix, whereas as the new mix lacks this coated look for whatever reason. I dried the clay fully with the goal of getting a more accurate mass measurement for batch to batch repeatability, but if the bagged clay has a standard "native" moisture content and the wax "locks" the moisture content at that given level, I guess it doesn't matter much. Any thoughts? Is it best to add wax to the clay without heating/drying it first? How big of an issue is humidity-driven expansion/contraction of finished bentonite nozzles anyways? I want to put more of my attention towards the other variables in rocket/driver construction besides the dang clay!
DavidF Posted March 1 Posted March 1 Well, since nobody else has commented, I'll offer my two cents. Bentonites are extremely variable, being a natural product. I didn't like using 'regular' sodium bentonite, as I found it to be too 'squishy'. I did the wax thing too, and I forget why I didn't like it much. The late Edwin Brown (from Estes) suggested using Dr. Elseys Precious Cat litter (blue label). Estes make end burner motors. It's the best stuff I've used. If used straight out of the bag, it will build up on the spindle, which I don't like. Sprinkling a teaspoon of fine graphite powder per cup of Dr. Elseys and shaking to evenly mix it really helps with that issue. More graphite isn't necessarily better. Some pyros say all kitty litter is the same, so just use the cheapest. This is not true. Some clay litter granules are very hard, and not easily consolidated into a good compact nozzle, especially when hand-ramming. But they do bite the tube. Every brand is different. What I have done before is to mix the Dr. Elseys half and half with the cheap, hard-granule cat litter, to get a nice smooth nozzle that also has good bite on the tube.
LiamPyro Posted March 2 Author Posted March 2 Thanks for the response! I think I'll give Dr. Elsey's a shot. Did Edwin Brown say that any additives were used in the nozzle mix? Estes motors must be relatively shelf stable, so maybe the addition wax is simply unnecessary in most cases?
DavidF Posted March 2 Posted March 2 No additives. The shaking on of the graphite was something somebody came up with later, I forget who. Estes press their motors to a very high pressure compared to what we do. It looks like Dr. Elseys on my D-12-3s, but something different on the smaller motors. IIRC, a lot of nozzle mix recipes involved wax, maybe because people were using cheap kitty litter that didn't compact well, and the wax helped make it work. It was probably 10 years ago when the Dr. Elseys was first mentioned. As soon as I tried it I just stuck with it. Just for larks I pulled a hunk of clay off the bank of Lake Erie, and processed it into modelling clay, which I then granulated, dried, and made nozzle mix with. It worked fine. I probably could have just screened the clay as it came, dried it and used it.
LiamPyro Posted March 9 Author Posted March 9 Update: I just got some Dr. Elsey’s and pressed up a sample nozzle with stinger tooling. It made a nice looking nozzle nearly identical to one pressed with the granulated sodium bentonite clay, although with a slightly different color (more grey, less beige). It looks just like Estes indeed! Both clays press nicely in their pure form, compacting to the same height from a given increment size. I couldn’t help myself and adulterated 500g of the Dr. Elsey’s with graphite and paraffin, this time without heat (just a solvent) in my star roller. This batch turned out more like the first (good) batch I made, with a light “glaze” of wax. Maybe I’ll get around to doing an erosion/thrust comparison at one point…
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