Aquarius Posted March 22, 2008 Posted March 22, 2008 I recently had a walk around in the wild (outside my house..) and found some used rockets from last NYE. Many of them had plastic casings with a pressed clay nozzle plug and no endplug. Nothing new so far. I noticed also that that some of them had wrapped the plastic motor casing in paper, probably to increase the diameter and dress up the rocket as well... Now, I would not use a plastic casing for my fireworks, but I am into model rocketry as well. I have seen a few pros and cons regarding the use of plastic motor casings. Knowing there is a wide range of different types and forumlas of plastic material, has anyone made qualified guesses or working drivers using plastic casings? The casings I found had a rather thick wall, 1-2 mm thicker than the "usual" pvc tubes for electrical installations. And they where semitransparent. What kind of plastic tubing are we talking about here?
TheSidewinder Posted March 23, 2008 Posted March 23, 2008 I know what kind of spent casings you're talking about. Several different brands of Class C rockets I've bought, across the border in Wisconsin, use them. I'm not sure what they're made of, but if you get one that's JUST been fired it's not only hot as hell and will instantly burn your fingers, it's soft enough to deform. (Asketh know how I know this. I seem to have issues with burning my fingers. Mom always said I couldn't leave stuff alone.) It sort of reminded me of a high-temp glue stick that hasn't been heated QUITE hot enough. Maybe one of the resident chemists can say for sure. Polyethylene maybe? I suspect that the relatively low cost of paper driver tubes being what they are, there's no impetus to switch to those plastic cases. I can't imagine them being cheaper than paper, and I suspect they're actually a LOT pricier.
Arthur Posted March 23, 2008 Posted March 23, 2008 There s an issue in the UK with a huge (2 - 5 million!) batch of rockets where the plastic nozzle cracks between manufacture and firing and the rockets fly sideways. As these are substantial rockets they can be pretty scary when a few travel sideways at ten feet then the effect head fires touching the ground. The batch is recalled and being safely destroyed in a pit! The problem seems to be that there is a visible split in the nozzle which can only be seen after the fuse shield is removed. Rumour has it that they are nylon.
Miech Posted March 23, 2008 Posted March 23, 2008 I don't think it is nylon what is used. I've a couple unused plastic casings laying around here, and they are made of something that burns completely different from nylon (don't ask me how I know). I would think about some kind of halogenated hydrocarbon, since it is really flame and heat resistant. Some kind of mixture would be possible as well.
Aquarius Posted March 23, 2008 Author Posted March 23, 2008 My guess is that the casings are made of PE (PolyEtylene) or HDPVC (HighDensityPolyVinylChloride). The can be made somewhat fireresistant, but the real issue is softening or structural strength of the plastic casing. I had some 20 mm OD pressure tubes made from PVC lying around and made a very safe driver with it.These tubes are made for lowpressure applications, up to 16 bars.No problems, but as stated before, I will not use these for fireworks drivers if I decide to do more testing. I don't like the eco-part of using plastic casings or plastic hemis for that matter...
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