AzoMittle Posted August 24, 2016 Share Posted August 24, 2016 So a bit of background on why I came up with this method: I have a gorgeous 2.5" comet pump from Wolter, unfortunately I have not been able to invest in a real press yet. Hand ramming with this size isn't really advised, beyond a 1/2" to 1" thick (depending on composition, binder, etc) and the comets tend to crack and crumble. I've had good success with making them thinner than that but at that size they tend to not be usable for any real application. SAFETY: All the usual rules regarding hand-ramming (or pumping if you go that route), composition/chemical compatibility, general safety, etc etc, still apply. When in doubt, google it and/or ask around. This process is messy and produces volatile fumes, so wear gloves/respirator and work in a well ventilated area. What I recently realized is that I can take these thin pucks and stack them to the desired height. What I then do is take the bottom layer dip the top in NC lacquer (with either BP or monocapa, depending on how hot of a prime you need to light the next layer), let it partially dry, then dip another layer, and repeat until I have a good thick, even, and flat layer of 'glue'. I press two pucks together, making sure there are no gaps or air pockets, and let them set. Repeat with each puck until it is the final desired height. I then wrap the entire thing in gum tape, two or three layers, and pleat over a chipboard disc on the bottom side. Let dry. I prime by dipping the top side first in a NC slurry (of either BP or monocapa) and then dipping into granulated BP. I try to not wrap the top one all the way to the very top but instead leave some of the comet's side exposed. I originally tried just stacking and wrapping them without the intermittent NC glue layer however the burning surface was just too large and it caused them to break apart like a rocket CATO. Something like this: http://i.imgur.com/uWr5DiZ.png Link to comment Share on other sites More sharing options...
dagabu Posted August 24, 2016 Share Posted August 24, 2016 Have you tried phenolic resin and hexamine? There were about a dozen HAND RAMMED 5" comets shot at PGI using this comp instead of the binder. Im happy to send you a chunk to try if you would like. Link to comment Share on other sites More sharing options...
AzoMittle Posted August 24, 2016 Author Share Posted August 24, 2016 I haven't tried that actually, thanks for the suggestion! I haven't messed with phenolic much at all really, tried rolling it a couple times and tried pumping some small 3/4" crossettes with it but just had one issue after another, I think I may have over-wetted it each time. Any suggestions on how much acetone to try? (Other than just "less" obviously ). Or should I use more/less phen/hex, etc? Any suggestions in general are always welcome. I have about 1/2 pound (I think, haven't weighed it) of phenolic left to experiment with, I appreciate the offer though! Link to comment Share on other sites More sharing options...
OldMarine Posted August 24, 2016 Share Posted August 24, 2016 I thought phenolic resins and hexamine were alcohol activated but I could be wrong. Usually am. Link to comment Share on other sites More sharing options...
dagabu Posted August 24, 2016 Share Posted August 24, 2016 (edited) YUPPER! Alcohol based, just use denatured alcohol 50:50 with the resin, allow it to become a liquor, add 4% hex by weight and use as is. Sub the binder 1:1, i.e. 1000g batch, 5% binder, 100g liquor. EZPZ! Screen it twice to mix the resin in and let sit for an hour to temper, pump away! Edited August 24, 2016 by dagabu Link to comment Share on other sites More sharing options...
Mumbles Posted August 24, 2016 Share Posted August 24, 2016 You have to heat the comets up for the hexamine to do anything for what it's worth. 1 Link to comment Share on other sites More sharing options...
dagabu Posted August 24, 2016 Share Posted August 24, 2016 (edited) You have to heat the comets up for the hexamine to do anything for what it's worth. Sorry, yes, 130°F 175°F (thanks Mum) for a couple of hours is what is recommended. Edited August 30, 2016 by dagabu Link to comment Share on other sites More sharing options...
Mumbles Posted August 26, 2016 Share Posted August 26, 2016 I just came across Jim Widmann's article on this for his phenolic. It's linked from his website. He suggests greater than 160F, and anything lower than 150F is not very effective. The curing time depends on the mass of comp, but most things were done in 60-90min, with large 8" comets (10Kg) taking overnight. What resin are you using Dag? https://ctpyro.com/content/phenolic-resin Link to comment Share on other sites More sharing options...
calebkessinger Posted August 26, 2016 Share Posted August 26, 2016 Thanks for the clarification. If we hear it enough maybe some of us will remember when we go to make comets. Link to comment Share on other sites More sharing options...
dagabu Posted August 30, 2016 Share Posted August 30, 2016 (edited) I just came across Jim Widmann's article on this for his phenolic. It's linked from his website. He suggests greater than 160F, and anything lower than 150F is not very effective. The curing time depends on the mass of comp, but most things were done in 60-90min, with large 8" comets (10Kg) taking overnight. What resin are you using Dag? https://ctpyro.com/content/phenolic-resin I was using my very bad memory to answer that question instead of looking at my notes as I should have, my apologies. My notes say that without the hexamine, the phenolic resin will dry well when liquefied in denatured alcohol when heated to 120°F (49°C) but will not work with the raw, powdered resin. Heated to about 175°F (80°C), the resin can be used alone as a powder add to the comp or hexamine added as Jim's quote suggests. "Hexamine cures the resin by further linking and polymerizing the molecules to an infusible state." The docx is also available on pyrobin: http://www.pyrobin.com/files/Pheno-Hex%20Binding%20ISF%202015.docx Edited August 30, 2016 by dagabu Link to comment Share on other sites More sharing options...
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