My first double petal Shell

[ThePyro174]

Hello everyone. I don't often create a topic and I hope he's in the right segment, but this time it's necessary because I really don't know what to do.

I'm going to build my first 6" double petal shell. I heard that you use KP as a burst charge. However, I have no experience with it because I have always built my 6 "shells (no double petals) with MCRH + slow Flash. I would also not know how much strip I have to paste this shell with, but I am afraid that the break with MCRH would be too weak and the whole work would be obsolete.

I have often read that MCRH would be too weak and you should rather use KP, but do you also use a booster? How much do I have to paste and with what method? And do I coat KP rice hulls with the same method as with MCRH?

I apologise for my bad English and hope you can understand me and answer my stupid questions. I wish you a nice evening.

[Arthur]

It's better to ask questions here that to have to ask the doctor where a body part has gone!

MCRH works OK but meal coated Rice  Krispies works well too! youtube.com/watch?v=z9XNUnbxo50

I did once see a Youtube video of how a double petal shell is made youtube.com/watch?v=XHgV_etnlcU is just one of hundreds

[ThePyro174]

Thank you for your reply.

 

I have seen the video of ned many times, but I am of the opinion that the result does not correspond to a double petal shell.

You should see a clear inner ball and a clear outer ball.

I have already read a lot in the APC forum, especially from fredhappy. He builds his double petal shells by pressing the hemisphere into the burst charge so that a hemisphere shape is created and then takes it out and places the stars in the burst charge.
 

However, he builds his shells with KP and I am afraid that MCRH are too weak.

[Zumber]

If you refer a book "fireworks art, science and technique" by Dr Takeo Shimizu you may end up with all your questions answer. Also there is nice tutorial on 'Westech fireworks manual'.

[Mumbles]

There are multiple ways of doing this. Some are substantially more complex than others. I second Zumber's suggestion to take a look at Dr. Shimizu's book. It very thoroughly covers some of the Japanese approaches to this style of shell. There unfortunately aren't a lot of hard and fast rules within this hobby that say this one specific set of burst, pasting, assembly method, etc. is the best. It is going to involve some trial and error. Even under the best of circumstances, your first attempt at a new effect is likely going to end up leaving you underwhelmed. It will take a little trial and error with your particular materials to see what works best for you.

The idea behind KP vs. BP is that additional petals take up room normally occupied by burst in a typical single petal shell. The thought is to make up for the reduced amount of burst by using a stronger break charge. I personally break my 6" single petals with a potassium perchlorate based burst charge without any issues. BP + booster or even just BP also work fine largely depending on what you're looking for. I don't think you'll necessarily go wrong by using either KP or BP with a booster. My preference has always been to evenly distribute the burst on the BP as opposed to just dumping it in the middle. I would also avoid adding any sort of booster to KP burst. It is much more sensitive to pressure than BP, and I feel it can be very easy to overbreak shells or get inconsistent results.

KP burst is made essentially the same as BP on rice hulls. I typically start with the same amount of pasting as I do with BP. On a 6" shell, I use 13 layers of pasting personally as a starting point. It can go up or down a few depending on what's inside or what kind of paper I'm using. I've moved primarily to hand applied gummed tape pasting, and try to stick with it to keep it consistent.

If possible, I would personally start with what you're comfortable and familiar with. Same burst, same pasting, etc. It will give you a better baseline to build from in my opinion. You know your BP, pasting, and performance. I think it will give you a more informed opinion as to what to change in the future. If you start changing things like adding petals, changing burst, or changing pasting simultaneously it can make it much harder to diagnose what is missing in order to achieve the performance you're looking for.

I'm not particularly familiar with your shells, but I've included some tips that might make this go better from the start.

• If you don't currently, use a tissue paper liner between your burst and stars. If something goes wrong during assembly, it makes it a lot easier to deconstruct and start over.
• Make sure your burst and stars are well consolidated. It will ensure things don't shift around internally during pasting, handling, or shooting.
• An internal casing for the inner petal is not mandatory, but it can help to keep the inner petal a little more spherical if you have issues with inner petal symmetry. If you do choose to use one, consider making it as thin as possible and consider perforating it or punching holes in it for fire transfer purposes.
• Smaller stars tend to make patterns more clear. Too few of stars can tend to hide the symmetry of a petal, whether it's good or bad.
• In relation to the last point, the stars will burn somewhat inside the shell, so very small stars can also be underwhelming or not display long enough.
• Consider a passfire from your fuse to the center of the shell to ensure fire propagates from the center out. This is more important with multi-petal shells.
• I personally favor more pasting instead of more booster if your shells aren't breaking hard enough. I feel like better confinement helps with symmetry.
• I'm also personally in favor of pasting methods/patterns that avoid heavy build up in any one location, and rotating the direction the paper is applied to further reduce build up and keep things even.

 

[Arthur]

In reality you can build from the outside laying the outer petal against the outer hemi then tissue, then some burst then form the well for the inner petal in each half line with tissue then stars then burst to the middle, OR build from the middle - make a (2"?) shell and pierce it several times, prop that in the middle of the sphere and line the outer with stars and fill the gaps with burst.

Remember that there are well regarded traditions from many places China, Japan, Italy, Malta to name a few, If yours works it's your style. Any style can be right if it works for you and your crowd.

Remember that one half will need to be inverted so be very sure that you can easily handle one loaded hemi in each hand. When I made my 16 I decided I couldn't handle both hemis while mating them so the bottom hemi was as normal and stood on a Macdonalds salad dish. The top hemi had it's crown cut out with a saw at the arctic circle position. The ring was placed on the loaded hemi and filled through the hole with inserts and stars right to the top, then the arctic circle disc was pushed and glued into shape. the inner petal was a 6" pair of hemis perforated like a squash ball and filled as a 6" shell, minimally pasted to let the fire in from the outer layer of burst.

[ThePyro174]

Thank you very much for all the answers and tips. I'll try MCRH and some slow flash.

[ThePyro174]

Thats the result. I‘am very happy

 

I use MCRH with a bit slow Flash in the middle and a bit slow flash for the „outer“ burst charge for both hemis. 

Edited Tuesday at 09:25 PM by ThePyro174

[Mumbles]

That looked pretty good. Substantially better than my first few attempts at multiple petals.

[ThePyro174]

Thanks. Do you have any more tips I could have done better? I use 2,5g slow Flash (60/30/10 kno3/al/s) for the inner Burst and 2,5g slow Flash for the outer burst charge. I paste it with 14 by 1 metre of the 50 millimeter gummed tape like a pasting machine. It was a 6“ Shell with a 3“ inner petal.

Edited Tuesday at 10:04 PM by ThePyro174

[pyrokid]

Really a fine shell! Good work! If could offer some ideas for improvement, the inner petal burned slightly fast, possibly larger stars look better. The inner petal was also somewhat small relative to the outer petal. Maybe try 4" diameter instead of 3"?

[Zumber]

5 hours ago, ThePyro174 said:

Thanks. Do you have any more tips I could have done better? I use 2,5g slow Flash (60/30/10 kno3/al/s) for the inner Burst and 2,5g slow Flash for the outer burst charge. I paste it with 14 by 1 metre of the 50 millimeter gummed tape like a pasting machine. It was a 6“ Shell with a 3“ inner petal.

That was very beautiful shell..!!

Inner petal sounded smaller in diameter but that's fine for the first attempt. Double petal looks good if you select star size properly for both outer and inner petal correctly also grain size of burst charge, proper assembly of shell etc. IMHO multiple petal shell looks good in bigger shells say 8 inch or more.

Congratulations again.

[ThePyro174]

Thanks for all the nice comments.
 

I will soon build another 6" double petal and try to improve myself. Unfortunately, I don't know what else I can change to make the break of the inner petal bigger. I don't know if I should take more boosters or make the stars bigger.

 

I used independence red in the shell which burns quickly. Maybe a colour that burns more slowly would be good.

Should I try a 4“ inner petal instead a 3“?

Should I try with KP on rice hulls or continue with mcrh? I have no experience with KP and no idea how to put it on hulls. I don't know if you have to do it in a mill.

 

Any tip is welcome

Edited Wednesday at 07:21 AM by ThePyro174

[Zumber]

Dr Shimizu's book "Fireworks the art, science and technique" covers everything.

I really don't understand what you mean "I don't know if you have to do it in a mill".

You must not put kp in a mill or try to ball mill it with fuel.

[ThePyro174]

so only have to mix following chems for kp?:

70 potassiumperchlorat

18 Charcoal

12 sulfur 

5 dextrin or 6 red gum

 

and put in on rice hulls 7:1?

 

thanks for your comment. I will read the book. Thanks again

[Zumber]

Though it is not sensitive ,treat it carefully. Screen individual chemicals to break lumps before mixing other ingredients and just screen mixture all chemicals gently and avoid harshly rubbing and spillage. Keep away particals that rest over screen and not try to pass it through screen.

Ratio of hulls to powder varies with shell size and not fixed but it would be better to follow previously tested ratios published in book.

[ThePyro174]

Ah, okay. I think I'll keep trying with MCRH and Slow Flash, but I don't have any other idea for a bigger break like a 4" inner petal.

[LiamPyro]

Great shell! One option, mentioned by Shimizu, is to use a finer mesh (more energetic) burst for the inner petal. For instance, if you use BP on rice hulls for the outer petal, you might try granulated BP in the inner petal. You could also just add more booster to the center of the shell. I made a 3” double petal recently… it turned out pretty well, but not perfect. Cut stars, so symmetry was imperfect. I used independence red in the inner petal too (it’s a good choice, nice and bright). 1.5” newspaper hemis for the inner petal, BP:hulls 5:1 throughout, and 3g slow flash in the middle. The petal size ratio was good, as the outer petal was blonde streamer (fast burning, smaller radius). With double petals, relative star burn time (and brightness) of inner and outer petals is a big factor. 

 

Edited Thursday at 12:55 AM by LiamPyro

[ThePyro174]

Thanks. I will try a 4“ inner petal with more booster and finer mesh for the inner burst charge. 

[LiamPyro]

No problem, let us know how it turns out. I realize I was a bit loose with my use of the word “mesh” in relation to burst charge strength above… Shimizu refers to the grain size of the burst getting progressively smaller in each successive petal towards the center of the shell. Smaller grains = higher surface area = faster/sharper spike in pressure. Coated rice hulls don’t really have a mesh size like granular black powder does, but they do provide a smaller amount of burst composition per unit volume, and have less surface area, than fine-grained BP. Since space in a double petal is limited, using granular BP in one or both petals could make sense for these reasons. Keep in mind that this will make the shell heavier, and if the granular BP is too large, it will theoretically be wasteful, as the grains won’t have time to burn completely before the shell opens.