Thick Pulpy Tubes vs NEPT for strobe rockets. Tubes keep splitting @ 7500 psi

[DecimusMaximus]

Hi everyone, after many attempts to make a strobe rocket I was finally able to successfully launch one 2 days ago and it was absolutely amazing!! It went up into the clouds and disappeared!! This was done on a thick pulpy tube. I do not have NEPT yet. 

In that excitement momentum, today I attempted to make more motors with my process.

However, I am running into major issues of the same exact tubes SPLITTING!! I have attempted 6 today and all tubes have split!!! It is extremely frustrating. 
Are NEPT tubes less prone to splitting?  I just ordered a batch after trying to fuss with thick pulpy tubes for wayyy tooo long.

Why do my motors keep splitting but that one time it didn't? These were even soaked in wood hardener and waxed!

I am using PVC or Brass Shim for tube support and it doesn't matter what I use, the tube still splits! I am pressing at 7,500 PSI on the composition. At first I thought maybe I was not pressing straight enough but after I made sure of that, it started to split on all sides instead of one side....

 

Things I have tried to fix the splitting issue but didnt seem to help:

1. tightening the clamps on the pvc tube support

2. adjusting brass shim stock

3. made sure to press straight down and not mis-aligned with the press

4. waxed tubes

5. smaller increments, slower pressing

6. soaked thick pulpy tubes in wood hardener

 

[DavidF]

This video by Florida Pyro might help some. At least it will make you feel good about buying NEP tubes

Also, the only tubes I have ever had split were tubes that were hardened. They were impregnated with phenolic resin. The same tubes (Phil's) without being hardened worked fine for me. Also worth noting is that Florida Pyro waxes his tubes by a new method. Have you tried not waxing the tubes at all? When you are pressing the first increments, you are pressing at a higher psi than 7500 because of the space the spindle takes up. Lubricating the tube by waxing, in combination with the higher pressure in those first increments, might be just over what those thick pulpy tubes can bear before splitting. Just spitballing here.

I've made plenty of strobe rockets with the brass shim stock, and Laduke has made waaay more using the PVC support method, so I don't think the supports are your issue.

[DecimusMaximus]

5 hours ago, DavidF said:

This video by Florida Pyro might help some. At least it will make you feel good about buying NEP tubes

Also, the only tubes I have ever had split were tubes that were hardened. They were impregnated with phenolic resin. The same tubes (Phil's) without being hardened worked fine for me. Also worth noting is that Florida Pyro waxes his tubes by a new method. Have you tried not waxing the tubes at all? When you are pressing the first increments, you are pressing at a higher psi than 7500 because of the space the spindle takes up. Lubricating the tube by waxing, in combination with the higher pressure in those first increments, might be just over what those thick pulpy tubes can bear before splitting. Just spitballing here.

I've made plenty of strobe rockets with the brass shim stock, and Laduke has made waaay more using the PVC support method, so I don't think the supports are your issue.

I was hoping you would see my post! Glad you did. And yes, I did use non hardened tubes because i ran out of all of my wood hardened soaked tubes from all the splitting.

Even the non-hardened tubes were splitting. 

About the first increment, i can never get to the full 7500 PSI because theres not enough comp to handle it without getting to the no pass line. Sometimes on the first increment, i would put more comp to try to get to the full 7500 but that doesnt help either and still splits.

I can see the tube start to split because the pressure to force gauge shows a leak or sudden loss of pressure as I am putting load on it. 
 

To address the pyroflorida video, he mentioned that was pressing 10,000 psi+. I'm not doing that and my splitting is seen from the outside.

I will try not waxing next.

Edited June 13 by DecimusMaximus

[DecimusMaximus]

Unwaxed tube, non hardened still splitting. Seems like it actually splits a little easier. 
Ive tried both brass shims and pvc support. Maybe somehow they are not holding tight enough? The pvc metal clamps could be loosening or some partially stripped as i press? because i hear creeks and stuff as I press.
 

my brass shims is not as clean and flat/straight anymore so maybe not really hugging the tube tight? 

[DavidF]

I saw by the spiral lines on the motors that the brass has been damaged. I use a plastic washer under the brass to prevent that. Some folks use a double PVC support, a 'sleeve in a sleeve' of sorts. That said, PVC supports used to be what everybody used, even when pressing to 9000psi for whistle rockets (not with pulpy tubes though). I can press a motor to 7500psi on the comp area using a mylar support with a NEPT tube.

One thing I'd wonder is how you know that you are pressing to 7500psi? Could it be that you are mistaken somewhere, and actually pressing much harder? The creaking noises lead me to think this. Can you tell us more about the pressing? I'd also wonder how much phlegmatizer (and what phlegmatizer) is in your whistle mix. Ben Smith specs 4% I believe, which is too much (in my opinion).

All that said, it's known that pulpy tubes are not the ideal choice for rocket motors, and some pulpy tubes are probably much weaker than others.

 

[DecimusMaximus]

1 hour ago, DavidF said:

I saw by the spiral lines on the motors that the brass has been damaged. I use a plastic washer under the brass to prevent that. Some folks use a double PVC support, a 'sleeve in a sleeve' of sorts. That said, PVC supports used to be what everybody used, even when pressing to 9000psi for whistle rockets (not with pulpy tubes though). I can press a motor to 7500psi on the comp area using a mylar support with a NEPT tube.

One thing I'd wonder is how you know that you are pressing to 7500psi? Could it be that you are mistaken somewhere, and actually pressing much harder? The creaking noises lead me to think this. Can you tell us more about the pressing? I'd also wonder how much phlegmatizer (and what phlegmatizer) is in your whistle mix. Ben Smith specs 4% I believe, which is too much (in my opinion).

All that said, it's known that pulpy tubes are not the ideal choice for rocket motors, and some pulpy tubes are probably much weaker than others.

 

I use plastic underneath too like you mentioned in your youtube videos. I think that damage is from trying to get the brass shim off past the bulge and it scratching it on the way up and out.

For the pressure, I made my own pressure to force gauge using these instructions: https://www.skylighter.com/blogs/how-to-make-fireworks/arbor-press-force-gauge

I calculated the measurement and laid it out on an excel sheet:

 

For the whistle mix, I am using skylighters toned down version here: https://www.skylighter.com/blogs/how-to-make-fireworks/whistle-mix

My NEPT tubes are coming in next week. I think i give up trying to make it work with thick pulpy tubes.

[DavidF]

I'll admit that I have no head for math, but the force readings on your chart agree with the force readings on the charts I have. I use PtoF gauges from Woodys and Wolters. Maybe somebody more proficient might see something I don't, or maybe you have it perfectly right- probably the latter

Maybe it's worth mentioning that the whistle that is commonly used as the booster for strobe rockets (except for Ben Smith's) is Steve Laduke's #2 whistle, which is:

76- potassium perchlorate

23- sodium salicylate

  1- red iron oxide

 3- Vaseline

I use 2.5 of paraffin wax dissolved in naphtha instead of the 3 parts Vaseline. Laduke's formula  will allow a shorter column of booster than with Skylighter's formula, because it's stronger. More room for strobe  The slower whistle is better for the delay above the strobe though, because it burns longer- in my opinion.

You'll probably hit one out of the park when you get the NEPT tubes. Video or it didn't happen

[DecimusMaximus]

1 hour ago, DavidF said:

I'll admit that I have no head for math, but the force readings on your chart agree with the force readings on the charts I have. I use PtoF gauges from Woodys and Wolters. Maybe somebody more proficient might see something I don't, or maybe you have it perfectly right- probably the latter

Maybe it's worth mentioning that the whistle that is commonly used as the booster for strobe rockets (except for Ben Smith's) is Steve Laduke's #2 whistle, which is:

76- potassium perchlorate

23- sodium salicylate

  1- red iron oxide

 3- Vaseline

I use 2.5 of paraffin wax dissolved in naphtha instead of the 3 parts Vaseline. Laduke's formula  will allow a shorter column of booster than with Skylighter's formula, because it's stronger. More room for strobe  The slower whistle is better for the delay above the strobe though, because it burns longer- in my opinion.

You'll probably hit one out of the park when you get the NEPT tubes. Video or it didn't happen

I hit one out of the park 3 days ago on Tuesday lol and it was absolutely amazing and it was with Thick Pulpy Tubes using brass shim as the support. It did bulge the tube abit on the lower 1/3 of the tube but no cracks or splits. I still launched it and it worked! That feeling of your first strobe rocket with whistle going sky high into the clouds was unreal so now I'm addicted and want to make more.