shockie Posted January 18, 2021 Posted January 18, 2021 When pressing BP Rockets I was wondering how long to press an increment of BP powder. I have been searching to see if there is any known info out there about this and can't seem to find anything specific. Vern Estes's Mabel could spit out a pressed BP Rocket motor in 5.5 seconds approximately. So obviously in that time span you : 1. don't have very many BP powder increments and 2. you don't press for appreciable periods of time per powder increment 1 and 2 above would obviously be variable depending on the size of the rocket motor being pressed. For example you can probably make more A size (2 oz) rockets in the same time that you make F size (1lb) rockets because you are using more increments and more time overall. so, what does the collective hive mind have to say about pressing BP in terms of increment size and dwell time.... I mean what will be the overall difference between pressing a known increment at 10,000 psi for 0.5 sec versus pressing the same increment size for 1 second? are their any mathematical calculations that can be done . If everything stays the same other than press dwell time, what will be the major difference between the 2 increments?
NeighborJ Posted January 18, 2021 Posted January 18, 2021 Dwell time on BP motors only serves to allow the tube wall to compress outward and fuel to fill the displaced wall. If the fuel is prepared like estes and fireworks manufacturers do (with water) and using proper pressure (without dwell) then there is already proper tube wall compression. Any further dwell will tax the inner tube layers causing the possibility of tearing. Fuel with a moisture content of 2% compresses instantly requiring no dwell. Fuel using a phlegmatizer requires a balancing act of dwell time and pressure to achieve maximum fuel density before tearing of inner layers occurs. This is why there is such a push recently to revert back to the 1000 year old practices which have served pyros so well for hundreds of years. Long story short: no dwell is necessary with 2% water. This is the method Estes uses and it is the best method.
justvisiting Posted January 18, 2021 Posted January 18, 2021 Completely agree with NeighborJ. I use 2 1/2%, just to be different Shockie, I think the Estes machine made a lot of motors at once, so 5 seconds is not necessarily the time it takes to press one of their motors. I've taken a few apart to measure the density and to just examine them in general. The D motor had fewer increments than the C, and the smallest one (A, I think?) had the most increments. Increment sizes varied as expected. Estes motors are said to use NEPT tubes, but the tubes are of a higher quality and density than the ones we pee-ons get One thing that's been pointed out before is that NEPT tubes can take high pressing forces when supported, but not in a sustained way. I've actually had a couple of 3lb motors split from top to bottom in my hand as soon as I took them out of the support, and just about shat myself. They were over-pressed with dwell.
shockie Posted January 18, 2021 Author Posted January 18, 2021 (edited) Thanks guys for your response. I knew I can always count on people to steer me right here with the info I need to know. I find it interesting that the A have more increments than the D.... have any idea why that might be? Edited January 18, 2021 by shockie
NeighborJ Posted January 18, 2021 Posted January 18, 2021 Larger tubes can take larger increments and still achieve the same grain density.
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