yvariro Posted June 9, 2013 Posted June 9, 2013 Hi all, I was planning to make some 3/4" rocket motor today,every thing was on course,until I started to ramm the nozle of the motor,the convolutes tubes that I bought cracked when I was ramming the nozzle,not a big crack,but it can make the motor CATO,I've tryed two time,and I decided to stop because I was out of my nerve I was thinking that it was due to the humidity of my tube,so I dryed them with a fan heater for 30min,then,i let them cool and I tryed without succes to ram some motor Somebody could know why my tube crack when I ramm the nozzle ? I use 7Gr of bentonite,maybe i ramm the motor too strong ? I will make a sleeve if the problem is my fault,but they don't sell 22-25mm metals tubes in the hardware store,PVC sleeve can work ? Regards,Yvariro
LTUPyro Posted June 9, 2013 Posted June 9, 2013 Looks like tubes are too weak. Also make sure you use fine betonite, because then you ram betonite in granular form, it basically expands.I never tried PVC tube as sleeve, but I dont think it would work well because it cracks pretty easy too.
AdmiralDonSnider Posted June 9, 2013 Posted June 9, 2013 I´ve heard about people who use a slotted plastic tube with lots of hose clamps as a sleeve.
yvariro Posted June 10, 2013 Author Posted June 10, 2013 I use approx 325meshs bentonite,so it's a very fine powder,I've heard that the convolute tube are the best for ramming rocket motor,I was certainly wrong I bought some parallel tube,I'll see the result,but I must make a sort of à sleeve with hose clamp,thanks you for the idea !As you said I think the problem come from my tube wich are too weak,I know some people who don't need sleeve when ramming their motor,so guys don't do like me,the more expensive tube are not always the best quality ! xD
dan999ification Posted June 11, 2013 Posted June 11, 2013 (edited) I've rammed 3/4" rockets with no sleeve and a 2# hammer but these tubes have 5mm walls.Thinner tubes will need support to get consistent results.Convolute and parallel are the same thing, in any case you can get spiral tubes to work with a bit of trial and error but you will need a sleeve. PVC tube supports have been pressed over 4500 psi so are strong enough for ramming, this was covered here recently by psyco and nater. Try ramming with slightly softer blows you may just be ramming too hard Dan. Edited June 11, 2013 by dan999ification
leedrill Posted June 11, 2013 Posted June 11, 2013 i press with pvc and t bolt hose clamps up to 10 000 psi {1 square inch} to a 1" id tube with no problems { i had problems with the worm drive hose clamps at 8000 psi though} but after testing things always use the best support possible
yvariro Posted June 12, 2013 Author Posted June 12, 2013 Oh so I'm definitey going to buy pvc ! definetely cheaper and more flexible than metal sleeve! I'll wait to have a sleeve before making news motors,I don't want to take the risk,I'm afraid that if i ramm softer the powder will not be rammed enough Thanks you for your answer,I'll be posting a test between a motor rammed softly without sleeve,and one rammed hard with a sleeve,I'll shot the rocket tomorrow if the weather is good Thanks you for your advices guys !
a_bab Posted June 12, 2013 Posted June 12, 2013 (edited) When you use the mallet, all it takes is 10 blows, not very vigorous. Also use a rubber mallet. Do some experiments as to how many blows it takes to have the tube crack on you. Normally no sleeve is needed unless you press, but if your tubes are really weak then the mother of all sleeves/supports won't do much since the tube expands and compresses, weakening the structure as the fibers break - that's why dense paper tubes are the best, while chipboard/cardboard ones are crap. A picture of your tube, and the source will also help us avoiding those bad tubes in the future. Edited June 12, 2013 by a_bab
Mumbles Posted June 12, 2013 Posted June 12, 2013 I'm going to have to disagree with you on the use of a rubber mallet. Typically, this causes more trouble in my experience. Rubber covered is fine, but a solid rubber mallet will not get you the appropriate compression. The rebound of the rubber tends to takes away some of the force you want to incorporate into the fuel grain. I prefer a good heavy rawhide mallet or good heavy dead blow hammer if I can get them.
yvariro Posted June 18, 2013 Author Posted June 18, 2013 Hello,sorry I had no access to the computer this week because I was not in my home these days I know that a rubber mallet is not the best choice,but I never had an issue with this,if one day I'll ram some bigger rocket,i will certainly buy a good and heavy hammer I've made a sleeve and now i can ramm very hard without problems I don't want to make bad pub against the supplier where i bought the tube,and it might be my fault because I stocked them in my garage this winter,and then put them in a dry room so it might had affect the fiber of the tube,if one day I'll buy some other tube of this supplier,I will check the quality I will upload soon a picture in this post,I can't now
dan999ification Posted June 19, 2013 Posted June 19, 2013 I agree with mum, I was sold "weak" tubes and told to use a soft hammer, I suppose to not break the tubes.Generally you want the support and hit hard.I've rammed with rubber mallet and spiral tubes supported and not, but I've never had a motor Cato using a 2# hammer ( its better) Dan.
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