Merlin Posted December 17, 2015 Posted December 17, 2015 Lift. Can 4fa be safe to lift a 5 inch plastic ball shells or would it be too violent? Also how much 70/30 in the central flash bag or how much nitrate flash. The remainder burst would be MCRH.
braddsn Posted December 17, 2015 Posted December 17, 2015 4FA is fine.. I use 4FA to lift 5's and 6's. As for the 70/30, start with 4g.
dynomike1 Posted December 17, 2015 Posted December 17, 2015 I use 4G. 70/30/10S in 5 and 6's. But unless you get the shell sealed good it's not going to work.
Seymour Posted December 17, 2015 Posted December 17, 2015 I would be happy to use anything from 1g to 10g of 70/30 with dark flake Aluminium in a 5" shell. As the other have said, 4g sounds about perfect for a hard burst shell, without it being crazy (like 10g). However this is for paper shells. I have nearly no experience with plastic.
lloyd Posted December 17, 2015 Posted December 17, 2015 About twice a year, I teach a beginners' class on 4" plastic ball shell construction to theme-park pyrotechnicians and new amateur pyros. You can download a .pdf of the course here: http://www.pyrobin.com/files/shell%20class%20handout.pdf It'll give you some hints about the whole process, and a 5" requires only 1.5x to 2x the amount of flash in the coupette to do the job. (be conservative, at first. If you have good polverone or grained powder, it doesn't take much flash to do the job, and too much will detract). Lloyd
Merlin Posted December 17, 2015 Author Posted December 17, 2015 About twice a year, I teach a beginners' class on 4" plastic ball shell construction to theme-park pyrotechnicians and new amateur pyros. You can download a .pdf of the course here: http://www.pyrobin.com/files/shell%20class%20handout.pdf It'll give you some hints about the whole process, and a 5" requires only 1.5x to 2x the amount of flash in the coupette to do the job. (be conservative, at first. If you have good polverone or grained powder, it doesn't take much flash to do the job, and too much will detract). LloydI use the exact method you speak of with 4 inch plastic ball shells and it worked every time. This year I plan to scale the 4 inch plastic ball shell method up to 5 inch. You specify 5 grams 70/30 in central flash bag for the 4. So what your saying makes perfect sense. The only difference is I planned to use MCRH in the 5 inch. It's more potent than my granulated BP was last year so I thought about keeping the flash the same with 70/30. JOne thing more would it be suitable to use say 10 grams of nitrate 5/3/2 instead of 70/30 in the 5? I will be using 70/30 for the smaller shell and Crossette break but to be honest I like the sound of the nitrate flash. Just wondering -I don't want to waste any 5s on experimentation.
dynomike1 Posted December 17, 2015 Posted December 17, 2015 (edited) What are you going to put in the 5"? You could be putting something in it that might not require a hard break. For instance Go Getters. What are you using to seal the hemis with? I am using 5G 70/30 this year, but i haven't tried any yet. Edited December 17, 2015 by dynomike1
lloyd Posted December 17, 2015 Posted December 17, 2015 The purpose of the flash is NOT to "burst the shell", it's to instantaneously ignite all the black powder filler in it. So long as your coupette load is strong enough to accomplish that (and NOT emit undue 'flash' outside the burst), then it will be fine. I don't use nitrate burst, so I cannot speak to the amount, but I'd say that it's probably less than half the strength of 7/3, so yes; I'd double the load over a 4". Too many folks use too much flash in coupette breaks. It unduly detracts from the effect by emitting a strong white flash when the shell opens. As it turns out, flash, alone, doesn't do a very good job of breaking shells, because it's a "negative explosive". That is, the combustion products (when cooled to their condensation temperature) have a lower total volume than the original powder. So... the flash only 'works' while it's emitting super-hot gaseous products to ignite the BP filler. Once it's done that job, it's over-kill to add more. Lloyd
Merlin Posted December 17, 2015 Author Posted December 17, 2015 What are you going to put in the 5"? You could be putting something in it that might not require a hard break. For instance Go Getters. What are you using to seal the hemis with? I am using 5G 70/30 this year, but i haven't tried any yet.I plan to use metallic fueled color tailed stars some pumped and some cut to 1/2 inch. I use methylene chloride to seal then a heavy coat of weld-on 725 PVC cement over that. Lloyd has the method on passfire.
dynomike1 Posted December 18, 2015 Posted December 18, 2015 How long does it take methylene chloride to dry? I use Xylene mixed with plastic for the second coat and it takes 24hrs. to dry.Tried acetone and it dried to fast.
Mumbles Posted December 18, 2015 Posted December 18, 2015 Methylene chloride will dry even faster than acetone. It also is a little difficult to work with as it attacks most gloves, and is painful to get on your skin. If you want something in between acetone and xylene, you may want to look into methyl ethyl ketone or toluene.
lloyd Posted December 18, 2015 Posted December 18, 2015 Methylene chloride 'bites' enough to strongly hold the shell halves in about 60-90 seconds. It takes - oh - maybe an hour to completely permeate the plastic and be dry enough to shoot. When I do my 4" shell class, we normally glue the shells (with methylene chloride), have each student hold the shell tightly closed for about two minutes, then set them aside, and break for the evening meal. That's about an hour's wait, during which the shells ARE handled by the shooting crew, and when we finish eating, we shoot. They work every time!LLoyd
dynomike1 Posted December 18, 2015 Posted December 18, 2015 (edited) The last time i tried acetone looked like it was dry before i got all the way around the shell. Reason i asked. Does methyl ethyl ketone or toluene bite pretty good? I usually put my shells in a clamp till dry. Edited December 18, 2015 by dynomike1
lloyd Posted December 18, 2015 Posted December 18, 2015 Mike, you have to FLOOD the joint, not just "paint it on". Use a big plumbing dauber or a squirt bottle. It should completely SATURATE and FILL the entire joint while it's still a free-flowing liquid. You also cannot 'dip then assemble'... there just isn't enough time. You need to assemble and clamp the shell dry before flooding the joint. Then pour a great excess of solvent into the joint, all-'round. Keep it clamped until it's dry. Again, with Methylene Chloride, that's just a couple of minutes until it's secure enough to handle, and less than an hour before you can shoot. Lloyd
Merlin Posted December 18, 2015 Author Posted December 18, 2015 I made a dozen with Lloyds method. It is fast and easy as there is no pasting. All the shells performed great. I used an applicator with a needle tip to flood the joint -just close the hemis and apply. I would try twisting and applying pressure by hand. In a minute you can see the plastic start to fuse. I used methylene chloride after it fused I would then apply a thick coat of PVC cement around jointsThe time fuse washer and lift ring are done this way as well. Of course hot glue inside and outside of the fuse.
lloyd Posted December 18, 2015 Posted December 18, 2015 Merlin,To be perfectly clear, the hot glue INSIDE the shell is only to secure the fuse/burst bag assembly so it doesn't move around while filling the fuse ring. Any such 'minor' seal won't prohibit lift gasses from getting in -- it would blow out into the shell. allowing gasses in. It's just a "place holder" so things don't get out of whack when applying the real seal outside. Gaskets (of all kinds) only work properly under compression. Lloyd
dynomike1 Posted December 19, 2015 Posted December 19, 2015 Since i have some Acetone i'll try that tomorrow. Didn't figure you would get enough in there to hold. I have always put them together in the clamp not all the way together, then flood them and finish, let set then put a seal of plastic+ Xylene.
lloyd Posted December 19, 2015 Posted December 19, 2015 (edited) Commercial plastic shell builders (now very few) used to soak the 'male' portion in Methylene Chloride for a good ten seconds or so before quickly assembling the shell. It actually melted the surface into a sort of "instant plastic glue". But whacking a shell together like that takes a real "knack" and a lot of skill and confidence. Capillary attraction will 'suck' the solvent into the joint pretty well. The joint the solvent makes is mechanically strong enough, especially considering how the shell lifts relative to the seam orientation. If using something less-aggressive than M.C., I suggest flooding the joint a couple of times. But when we do it by flooding instead of soaking, of course there will be pinholes, because the plastic doesn't all swell up enough to totally close the gaps in the joint. That's why I teach to add a secondary seal-coat after gluing. The secondary seal ensures none of those pinholes pass fire. Lloyd Edited December 19, 2015 by lloyd
dynomike1 Posted December 19, 2015 Posted December 19, 2015 I looked through the PDF and the only problem i had was drying time which is not that big of a problem, it just limits me to 3 shells a day. My shells actually are holding together and getting good breaks. I'll see if i can find some Methylene Chloride tomorrow, and try that.
Mumbles Posted December 19, 2015 Posted December 19, 2015 It's not all that easy to find over the counter. There used to be a graffiti remover by Klean-Strip that was pretty high in it, but they've changed formulations. The same company makes several other products with a high methylene chloride content though. I'm not sure if you're aware of the household products database, but it's good for this purpose. I'm not sure if that link will work, but otherwise just go to the homepage and search for methylene chloride. It's also known as dichloromethane, so you may need to seek out both names to find what you need. http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=118&query=dichloromethane&searchas=TblChemicals
Merlin Posted December 19, 2015 Author Posted December 19, 2015 I think I got it at skylighter -at a price!
lloyd Posted December 19, 2015 Posted December 19, 2015 Any local plastics shop that sells acrylic glazing will have acrylic solvent-cement available for the material. That's 90%+ methylene chloride, and works perfectly on the styrene from which most plastic shells casings are made. It can be had in bulk, but also in 2oz, 4oz, 8oz, and pint cans with dauber-style applicators. Lloyd
dynomike1 Posted December 19, 2015 Posted December 19, 2015 (edited) Thanks Mumbles after looking at the database i noticed i have some Klean strip Aircraft remover. 70-90%. I thought Dichloromethane looked familiar we use Dichlorobromomethane in safety valves on our anhydrous pumping station. I just noticed that Klean strip Mfg. is just 30mi from here.Didn't know that. Edited December 19, 2015 by dynomike1
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