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Correct pressure on comps


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#1 Tim1877

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Posted 17 November 2017 - 11:10 PM

From what I have read the desired pressure on black power comps is 6500 psi. My first question is when pressing core burners the area of the rammer is almost cut in half by the spindle hole should I figure this into my pi r squared calculation. The reason I ask is when I press my 1/2 inch rockets to the 6500 psi on the comp I get wrinkles in the tube I'm using 3 ton arbor press and nept tubes my tooling is a 4 oz rocket set from Wolter pyro
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#2 stix

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Posted 17 November 2017 - 11:53 PM

I'm not into bp rockets, but I've read somewhere on this forum that waxing the inner of the tube can help eliminate wrinkles. I'm sure someone will chime in and point you to that thread.

 

Also packing smaller increments should help.

 

[EDIT]

 

Here just one:

https://www.amateurp...ube#entry172630

 

There is a sh*t-load of info under this rocketry section - you just have to search for it.

 

cheers.


Edited by stix, 17 November 2017 - 11:58 PM.

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#3 pyrokid

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Posted 18 November 2017 - 02:25 AM

Experience and testing are valuable with fireworks. In this case, it could be that you could deviate from the suggested 6500 psi value to a lower one and eliminate the tube wrinkling dilemma whilst maintaining adequate fuel compaction! I also suggest hand ramming a few rockets. I've been surprised a number of times by rockets that function perfectly despite numerous shortcuts being taken in their construction.



#4 calebkessinger

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Posted 18 November 2017 - 07:09 AM

No support?
Pvc support?
Loose support?
We generally press rockets with a support anywhere up to 9000 psi on the comp. I never change the pressure for the holed rammers.
They will work fine with less pressure though. :)

Pressing those without a support sure scares me. It's so easy to hand that tiny spindle when you are pressing the last few increments.
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#5 pyropro

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Posted 18 November 2017 - 07:49 AM

If one doesnt use thick tubes and has a good spoort waxing isnt really need.Rockets have neen made ofr over a hundred years without adding another step.i know Df and hes a great guy and when he first started waxing well better I say if your using thick tupes waxing is fine I never did but hey thats me.I do know after having many conversations with master rocketmen well take Estes do you think they wax tubes?. Check out the tube thickness they use.



#6 Tim1877

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Posted 21 November 2017 - 08:10 PM

I was wondering if there are thicker walled tubes out there then the nept tubes I have I know the 3/8 tubes I got from Caleb have a much thicker wall.
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#7 OldMarine

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Posted 21 November 2017 - 08:49 PM

If the paper is good you don't need that thick of a wall. If I recall correctly Caleb's tubes are the pulpy ones and they need the thicker wall to keep from splitting. I routinely press ¾" rockets in Phil's spiral wound tubes with no fear of a CATO. I use a support that fits them tightly,wax my tubes to prevent shrinkage and fly my rockets with confidence. I haven't had a CATO since I started following Dave's advice. I miss that Canuck!


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#8 Tim1877

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Posted 21 November 2017 - 09:49 PM

That's kinda what has me confused I can press the softer tubes from Caleb with no support over the 6500 psi with no wrinkles but the 1/2 inch nept tubes which are harder wrinkle before I get to 6500psi I'm making a tube support so I guess I shouldn't worry about it it but as much as we pay for nept tubes they shouldn't wrinkle
Tim

#9 Col

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Posted 21 November 2017 - 10:09 PM

A soft 3mm wall could squish to 2.5mm without showing any sign on the outside of the tube. A tube support wont prevent soft wall compression, it simply contstrains the outside diameter. Wrinkles are usually due to vertical compression, if the tubes are genuine nept i would check the increment size isnt too large. The best way to compare tubes is to test them to destruction in your press, tests done on different presses cant be compared directly.



#10 calebkessinger

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Posted 22 November 2017 - 07:46 AM

I'd just press them with less pressure and go on. If your rockets work pressure is meaningless.

You can build ya a little pvc support in short order.
I have no idea how you got those pulpy tubes to hold that much pressure. I usually just press the. On my drill press which only will do about 600lbs of actual force.

That's about 3300 psi. I believe.
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#11 Mixer

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Posted 05 December 2017 - 10:59 AM

From what I have read the desired pressure on black power comps is 6500 psi. My first question is when pressing core burners the area of the rammer is almost cut in half by the spindle hole should I figure this into my pi r squared calculation. The reason I ask is when I press my 1/2 inch rockets to the 6500 psi on the comp I get wrinkles in the tube I'm using 3 ton arbor press and nept tubes my tooling is a 4 oz rocket set from Wolter pyro

So many people over press their BP rocket motors. I find It`s really unnecessary to go more than 4,400psi on the comp (with support).  A good tube will not wrinkle at this pressure. I press all my rockets at this - I don`t wax them, and I don`t have cato`s. Yes you have to calculate the right pressure for the solid rammer.


Edited by Mixer, 05 December 2017 - 11:01 AM.


#12 MrB

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Posted 05 December 2017 - 07:59 PM

What pressure is enough? What ever makes it sound like a ceramic if you remove the tube, and knock to pieces together. What pressure i that? Depends a lot on your charcoal, i suppose.

I kinda think it is impossible to "over press" BP.


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#13 stix

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Posted 06 December 2017 - 01:00 AM

Yeah, I too would have thought the denser, the better. This means you can pack more fuel in, which means you need less weight for the motor casing, which means you can add more more goodies on top. Overall it's an advantage.


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#14 Col

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Posted 06 December 2017 - 07:59 AM

As long as you dont compromise the integrity of the tube in the process ;)



#15 MrB

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Posted 06 December 2017 - 02:02 PM

Of course. Tube supports, and sturdy tubes let you use higher pressure.



#16 Mixer

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Posted 07 December 2017 - 08:08 AM

What pressure is enough? What ever makes it sound like a ceramic if you remove the tube, and knock to pieces together. What pressure i that? Depends a lot on your charcoal, i suppose.

I kinda think it is impossible to "over press" BP.

it`s not so much pressure on the BP that could be a problem - it`s the fact that many types of tubes can have their inner layers perforate at high pressures - which often lead to CATO`s

You would need massive pressure to get a motor core to `chink` when tapped. Some commercial motors do, but they achieve that by using additives which in turn requires less pressing pressure.

It`s virtually impossible ( with the modest pressures needed to consolidate BP motors) to get a ceramic type outcome with a dry mix.



#17 MrB

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Posted 07 December 2017 - 08:33 AM

It`s virtually impossible ( with the modest pressures needed to consolidate BP motors) to get a ceramic type outcome with a dry mix.

 

Weird statement, but sure, i'll play.

 

While i don't do much rocketry, (This does however don't mean i do no rocketry, just not "as much" as some of you guys) i do press a lot roman candles, and drivers for those rotating things that throw sparks everywhere. Meaning the fuel is less energetic, so the risk of a CATO is lower, sure.

Rockets, drivers, or roman candles and fountains, i press them all in the same way. I dry-press them with the hand-cranked hydraulic press, and any time i have a dud, i take them apart, trying to figure out why they didn't perform as intended. They always make a nice ceramic sound if knocked with anything, after you remove the tube...

 

Now... If there is a issue with consolidation, due to the powder being dry, then just don't press them dry? Depending on both what charcoal, and the die i use for corning BP i use 1 or 2% water, no added binder, and they are easily dry enough not to hurt the paper tube, should you desire to put the composition in a rocket.

I'd suggest less is more, of course, since adding 10% water would possibly turn the tube to pulp.



#18 Mixer

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Posted 07 December 2017 - 08:54 AM

With my 50 years experience in rocket manufacture - I don`t think that is a `weird` statement at all.

 

It may be just that we have different perceptions as to what a ceramic sound/feel really is.

 

I have come across commercial motors that were so `ceramic like` (which had a high pitched chinking sound to them) that the only way to break them is a hard hit with a hammer. That would be my definition of ceramic.

 

The main purpose of my post was to help Tim 1877 with his question and not to have him mislead into thinking he needs high pressure to achieve an acceptable BP motor, but I guess there`s always someone that wants to challenge you.

 

Game over. :P



#19 Col

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Posted 07 December 2017 - 01:26 PM

Its better to have the option of the higher pressure even if you choose not to use it ;)  In Tims case, i would try to identify the reason he cant use 6500psi before settling for something less. Wrinkling can be caused by overly large increments,

for 4oz motors i typically use 2-2.5ml increments which produce a density of 1.7-1.8g/cc after pressing (willow charcoal). A larger increment tends to lock itself into the tube wall before its fully consolidated which results in the tube being pushed downward by the locked increment. If the force exceeds the beam strength of the tube it will wrinkle (aka crumple). The ideal solution is to reduce the increment size not the pressure. Waxing (lubricating) the tube will likely fix it too but, like reducing the pressure, it doesnt address the actual cause.


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#20 MrB

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Posted 08 December 2017 - 05:07 AM

The main purpose of my post was to help Tim 1877 with his question and not to have him mislead into thinking he needs high pressure to achieve an acceptable BP motor, but I guess there`s always someone that wants to challenge you.

 

For what it's worth... Nobody said you HAD to use infinity high pressure, or challenged that you could get fully workable rockets without it.

But for as far as i know, using the highest pressure you can get away with, gets you the most energy in the same volume, ending up providing more overall thrust. If you could press it dense enough to counter it's thrust, making it unable to lift, or simply compact it enough to the point that it just wont burn anymore, then there would be an argument for that being "to much force" but short of that, i doubt there is any disadvantages.






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