MadMat Posted June 23, 2016 Posted June 23, 2016 (edited) I guess this is a newbie question. I never had any problems with using spiral wound mailing tubes for 2" guns, but am having blow-out problems with using the same type of tube for a 3" gun. First off, I know that spiral wound is not the greatest, but this tube is "resin impregnated" with a wall thickness of 5/32". Also, I coat the I.D. of my tubes with water glass. The last shell I fired (video posted on "priming stars" discussion yesterday.) was the first (and last!) time that gun was fired. The funny thing is, it failed on the top half of the tube, not the bottom as one would expect. I have a couple options; 1. I have fiberglass cloth and resin that I could cover my tubes with. 2. I could paste and wrap the tubes with kraft. 3. I could give up entirely on these tubes and go with fiberglass or HDPE.Any suggestions? Even though the tube let go, the shell still reached an acceptable height. It was a first in a couple categories; my new priming techniques (a success!), and the first attempt at forming a shape; in this case a ring (partial success) Edited June 23, 2016 by MadMat
Alan Posted June 23, 2016 Posted June 23, 2016 The increase in lateral forces on a tube going from <2" to 3" are large, are calculable but I am lazy and this simply mean that fiberglass and HDPE are far superior to thin cardboard. 5/32 is thin. If you impregnate with resin and cover with fiberglass you have achieved an expensive fiberglass tube, but if you invest in some HDPE tubes they will last a very long time and your safety factor goes up. Flower pots are more energetic in 3" versus 2", and ever more so with increased diameter. Been down this road myself, and am very glad for my plastic tubes.
Mumbles Posted June 23, 2016 Posted June 23, 2016 I agree with Dan and Alan. In the long run, I think you're better off with legitimate guns. The other two options probably would work, but might not be long term solutions. Cardboard does have a shelf-life due to the hygroscopic BP residues, and often damp environments the guns get exposed to over a lifetime. If you're deadset on making these work, you may want to take a look at Myke Stanbridge's cardboard treatment method. I have no idea how the resin treatment will influence the effectiveness of this method though. http://www.pyropage.com/Misc/cardboard.html
memo Posted June 23, 2016 Posted June 23, 2016 (edited) platte river fireworks has a good selection, good prices and ships pretty fast. I ordered some 3,4,5,and 6 inch tubes with extra long plugs and a little more lenth and they got them right out. I have ordered from them 3 times in the last year.all there guns are screwed in plugs no staples. memo Edited June 23, 2016 by memo 1
Arthur Posted June 24, 2016 Posted June 24, 2016 There are some 3" card tubes used in industry for shrink wrapping. Mine have about 15mm wall, they are strong enough! I plug the end with polyester resin. Otherwise get some HDPE or GRP professionally made mortars.
MadMat Posted June 26, 2016 Author Posted June 26, 2016 Oh hell, just looked at Platte River's website. For the price, I can't go wrong!
PhoenixRising Posted June 26, 2016 Posted June 26, 2016 (edited) . Edited June 27, 2016 by PhoenixRising
braddsn Posted June 27, 2016 Posted June 27, 2016 HDPE!! I would never use anything else! It is truly some amazing stuff! It will flat out take a BEATING!
MrB Posted June 27, 2016 Posted June 27, 2016 HDPE!! I would never use anything else! It is truly some amazing stuff! It will flat out take a BEATING! Goes soft if you reload a few. Fiberglas is better in that way. And it's lighter. But HDPE has the safety advantage when it comes to shrapnel, or, the lack of it. I'm indecisive. I also cant seam to get hold of either, at this point, which blows.
schroedinger Posted June 29, 2016 Posted June 29, 2016 Goes soft if you reload a few. Fiberglas is better in that way. And it's lighter. But HDPE has the safety advantage when it comes to shrapnel, or, the lack of it. I'm indecisive. I also cant seam to get hold of either, at this point, which blows.No worries about fibreglass tubes. If a salute blows inside them, they do rupture like and flatten out. But don't send shrapnels. From a 3" salute i found my tubes about 1 m away in one flat piece. In the eu i won't think to much about HDPE since fibreglass mortars are cheap and easy to get. HDPE tubes in the correct sizes are harder to get, due to the metric system.
Mumbles Posted June 29, 2016 Posted June 29, 2016 The metric system has nothing to do with it. Just because they're not the same, doesn't mean there isn't an equivalent. There's nothing magic here in the US, people just have done the leg work. All water and gas pipe is measured by the OD. You just need to search around and figure out what standard dimension ratio (SDR) or dimension ratio (DR) gives you approximately the correct ID, while maintaining an appropriate wall thickness. This is the reason there are two different sized "standard" consumer shell sizes. One is based on DR9, and the other is based on DR11. Each gun material fails in it's own way with something like a salute. HDPE sort of turns into a banana or breaks into a few pieces. Cardboard will shred generally, though pieces/chunks can be launched occasionally. Fiberglass is sort of a weird one as there are at least two different products out there. One can shatter and fray, and the other is more flexible and tends to flatten or just tear into a few pieces. The pieces don't fly all that far though in either case. A forum member had a fellow shooter require surgery to remove fiberglass fragments from his leg after a shell went off in the gun while hand lighting. Steel will usually flatten out, but can shatter and make shrapnel. It's really reserved for the heaviest of shells, and should always be deeply buried. If firing salutes, I'd suggest burying the mortar regardless of the material.
Alan Posted July 13, 2016 Posted July 13, 2016 (edited) When fiberglass tubes are used there are still variables that make a ton of difference. The nature of the resin used to impregnate fibers, the volume of resin, the quality of mixing, the volume of fibers, the lengths, and the history of the cure itself make for a mildly variable product. The thickness of sides will hopefully be uniform, but not necessarily. Inconsistencies will lead to variable burst behaviors on the tube, leading to sheets, bundles of fiber, small fragments and other unpredictable debris. Layup errors can create unnecessary weakness points or areas. Fiberglass is ubiquitous and cheap to use. Because of its commonness we start to assume all fiberglass products are consistent. No. Fiberglass seems to me to be the least consistent material for mortars, but good ones obviously work quite well. They fray, though, and lips can shred, making caution in setup wise for those of us who dislike fibers in our fingers. Of course, dropping a 6 inch HDPE mortar tubes on your toe hurts more. Especially a rack full.... Edited July 13, 2016 by Alan
mikeee Posted July 16, 2016 Posted July 16, 2016 Found this at one of the facilities I do work for, 48" OD HDPE 40..452" ID both pieces are about 45 feet long.These are made by the JM Eagle Company, they make large diameter piping but the wall thickness is thinner on sizes larger then 48".
dagabu Posted July 16, 2016 Posted July 16, 2016 I hope you grabbed a couple pieces and put them in the back seat of your car!
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