PyroCube Posted August 23, 2014 Posted August 23, 2014 Hi all Can someone tell me to which pressure a blackpowder endburner should be pressed for the best performance? Thank you and best regards
dagabu Posted August 23, 2014 Posted August 23, 2014 Forgive the less than specific answer but the truth is that there is no hard and fast rule, ESTES has a certain pressure and dwell time so do us all. I just pounded about 100 1/2" ID endburners with a plastic mallet and no tube support, others at my table pounded around 150-5/8" and 3/4" core burning rockets. We used waxed tubes so the compaction was less an issue than it once was. I like about 9000 LPI on all fuels with a one second dwell time when pressing.
PyroCube Posted August 23, 2014 Author Posted August 23, 2014 Thank you Estes presses the rocket motors to 15000 psi as far as I know. Would this be a goodstarting point? And what means LPI ? Thank you and best regards
schroedinger Posted August 23, 2014 Posted August 23, 2014 I think he meant libits per scare inch (lpi) its the same as pound per square inch (psi)
dagabu Posted August 23, 2014 Posted August 23, 2014 No, actually it's Loading Pressure per Inch. Ask Steve LaDuke exactly what that means but it is not quite the same as raw PSI. We have a guy over at Fireworking that worked for ESTES, he will not give an exact pre4ssure or dwell but you are close enough. We dont press to that pressure normally due to the clay a lot of use use, the equipment used and the tolerances. If you can do the 15k then by all means, try it.
PyroCube Posted August 23, 2014 Author Posted August 23, 2014 So the more pressure the better right?Can you explain the problems with the clay and equipment a bit further, dagabu?Thank you
dagabu Posted August 23, 2014 Posted August 23, 2014 Yes, love to. Estes uses a machine with very rigid rams and tooling to make the motors, there is no movement and the pressure all goes down to the increment being pressed. The tube supports are also very rigid, they also don't' move. The tubes are kept in a climate controlled warehouse, they don't vary by more than a few percentages in humidity. The BP is made by an outside company, it is made to their exact standards. More pressure is not better, you WILL crush the tube after a certain point. BP only presses down to a certain point (ask others about the pressure) and if you have a mushy tubes, the risk is greater to damage the tubes. In any case, consistency is the key, make the the same every time to get the same results.
pyrokid Posted August 24, 2014 Posted August 24, 2014 Dag is the mushy tube issue mitigated by the use of a tube support?
ddewees Posted August 24, 2014 Posted August 24, 2014 No, because the tube still gets "mushed" inside the support.
pyrokid Posted August 24, 2014 Posted August 24, 2014 No, because the tube still gets "mushed" inside the support. Can you describe this a little bit please?
ddewees Posted August 24, 2014 Posted August 24, 2014 The pulpy tubes he's describing are quite thick compared to nept tubes. So, lateral pressure will compress/collapse/deform/squish the wall of the tube against the support... which can supposedly weaken the overall strength of the tube. Kind of like stepping on corrugated cardboard... you can feel it crush under your foot. I have no idea if this is true or not though, since I don't use those tubes... but I'm fairly certain that's what he was referring to. 1
Carbon796 Posted August 24, 2014 Posted August 24, 2014 (edited) A mushy or pulpy tube is weaker and softer or more compressible than say a NEPT tube. When your ramming or pressing the nozzle or end plug in the tube. Even though the tube support keeps the outside of the tube from expanding much. The inside of the tube walls will still compress, as the nozzle or plug bites in. The same thing happens when you load the fuel. Each time a increment of fuel is compressed, it bites into the tube wall. At higher pressures the fuel grain can actually pull the tube wall down with it, while being compressed. This may/can tear the paper fibers, and make the tube considerably weaker. The more pulpy the tube, or higher the pressure, the more likely/easier it happens. In some instances you will be able to see the compression marks on the outside of the tube. Sometimes the tube can be noticeably shorter after pressing. Edited August 24, 2014 by Carbon796
dagabu Posted August 25, 2014 Posted August 25, 2014 You two are both correct in the individual issues that are found with compression of weak/pulpy tubes but I was actually speaking of only the inner compression that breaks the fibers as the inside diameter expands. A good stout support goes a long way to minimize this but does not completely stop the effect. Waxing tubes also minimizes and tube shrinkage and compression marks all but disappear. I use cheap and pulpy tubes all the time, the motors I make are low impulse BP motors that only need to lift small weights or end burners that fly for about 10 seconds. I save the NEPT tubes for whistle and strobe rockets.
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