Commercial Zink shells and rockets

[ExplosiveCoek]

Does anyone know how these zink shells are made:

 

https://www.google.nl/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=0ahUKEwiI5IeVoMbQAhXCfxoKHV9xAe0QjRwIBw&url=http%3A%2F%2Fwww.feuerwerk-forum.de%2Falbum%2Fshowphoto.php%3Fphoto%3D17565&psig=AFQjCNEzBRoM9MttWzzGw5A2-LnJAaNXXQ&ust=1480243842221612

 

They never seem to have any kind of pasting, not even when used as shells shot out of a mortar, but still their performance is unique and one of the best available on the commercial market.

 

Just curious.

[Mortartube]

This is just a guess, but they may have a smaller, hard broken pasted shell inside of that taped shell casing. The shell casing that you see may just be cosmetic.

[Mumbles]

I've seen sort of a mix between just the band at what looks like at least minimal pasting. http://pyrofire.eu/shop.php?kat_id=27 The minimal pasting is almost certainly applied with one of those cheap chinese pasters that apply in a spiral sort of pattern around the shell and leave holes at both ends.

 

Either way I suspect they use a ton of flash, which is supported by many of the videos I've seen. It's basically the only way to make up for the lack of confinement. This is how stringless cylinder shells are made as well as most of the better commercial and hobby plastic shells.

[ExplosiveCoek]

Yeah, I was thinking exactly the same. Still quite impressive that they never have any flowerpots though, as it's only one layer of masking tape which is keeping everything together.

 

Maybe the apply some glue of some sorts in between the seam. I even saw some 6'' shell's made in this manner, and couldn't really figure out how they did it.

I never got my hands on one either, they're a bit too expensive for disassemble purposes .

Edited December 2, 2016 by ExplosiveCoek

[Col]

possibly 4 part hemi`s glued together with the outer tape just for extra fireproofing.

[Mumbles]

That's a possibility. The 4 part hemis really only need 1 layer of pasting, primarily just for fireproofing.

[pyrokid]

Details on this 4 part hemi construction?

[Col]

Its just 2 sets of nested hemi`s orientated at 90 degrees so the seams dont align...apart from the 2 equatorial crossing points The outer casings are fully glued to the inner shell so it acts like pasting.

Edited December 4, 2016 by Col

[Mumbles]

My opinion is still that they're likely using a bunch of flash, however nesting hemis are not impossible.

 

Nesting hemis are a set of 4 actual hemisheres. They're not readily available anymore, and when they were they were rather pricey. The only domestic supplier I'm aware of is Precocious Pyrotechnics, but I didn't really see them listed anymore. You'd probably need to make your own or find a new supplier or importer from China/Japan. There might be plastic shells with the same idea available from Nitro Paris potentially. They'd be easy to make with a WASP, but then again if you have a WASP, you really don't need nesting hemis. Otherwise two sets of forms or molds would be helpful.

 

You assemble one set like normal and tape together. The shell is then covered in glue and the second set is placed over the top rotated 90 degrees. Typically you carve out a little groove in the lip of the hemis to accommodate the time fuse. The whole assembly is then normally pasted in with 1 layer of paper to hold everything together, fireproof, and make it look nice. Bigger shells require a few more layers of pasting on the outside to dial them in from what I've heard.

 

It's convenient and field expedient but less convenient if you have to make them yourself instead of buying or having some way to mass produce them.

[zan89]

Hi!

 

I have break appart one 4" zink white blinker.

it has 2 rounds with tape around equators. they dont use standard chinese hemis. they have hemis with double edge, so they put glue on the inside edge and close it, like plastic kinder egg. Inside is plastic capsule stucked on the ignitor, capsule is filled with 3g flash(probably slow). then there is 50g bp of fine granulation mixed with stars and all the rest full of 5mm stars with thin layer of prime... and from what is star, that is the bigest guess. but i can tell it is full of metal, probably mg/al.

Edited December 10, 2016 by zan89

[ExplosiveCoek]

That makes sense, and explains their simple design but high quality break. Thanks for your input zan89!

[zan89]

here is picture of the Zink hemis

http://shrani.si/f/Z/11I/C8S5hMG/kugelbombe.jpg

[ExplosiveCoek]

Interesting, where did you get it? Do you have more ?

[a_bab]

Hmmm, look what I found here: http://pyrobin.com/files/zink_fireworks_pics_and_demo_shooting.zip

 

There are some nice pics that would answer most if not all the questions.

[zan89]

Interesting, where did you get it? Do you have more ?

No, i find that photo on Zink page

[Col]

I was expecting something a bit more interesting than a cardboard hoop and some pva glue to provide the confinement

[zan89]

Good things are always simple

[ExplosiveCoek]

That zip file is really awesome! No breakcharge included in the shell's, just flash and glued shell hemi's.. Hm, interesting.

[Mumbles]

I didn't see any flash in the break from any of the images in the Zip file actually. You can break shells from just the prime on the stars, which may be happening here. I've never tried it so I don't really know how well it works. Based on the pictures in this thread from the various sources, it would seem they have at least a couple different shell building setups. I'm not familiar enough with their products to say whether or not there is anything obvious missing here. There is the zip file with no visible flash at least. There are the ones above with the white paper or plastic burst bag or flash bag, and they make cylinders presumably with one of the previous two methods.

[pyrokid]

A few years back there were some fantastic rockets imported into the United States. Unfortunately they were overloaded, but they exploded with a thunderous report and a large, round, dense break. Upon disassembly, I discovered that the shell consisted of a plastic bag filled with round stars and flash (apparently containing dark pyro aluminum) surrounded by a ~2 mm nonrigid paperboard cylinder with glued strawboard disks on each end.

 

I concluded that star priming is the most important factor in device performance. The better the priming, the faster the burst charge that can be used. Faster burst charge allows for shortcuts to be taken in the confinement/pasting.

 

Thank you to the poster of the Zink production zip file! Very informative!

Edited December 14, 2016 by pyrokid

[ExplosiveCoek]

Mumbles, take a look at picture '4_Unterteil_Schub'. You can see, what I believe, some powdery residue where the rocket engine is attached to the hemi's. I think they just dumped some 7/3 flash in there.

If you look at the vid that is also included in the file you'll see the characteristic white flash at the break of the shell's.

[Pyroboy]

Hey Guys,

 

since I live in europe I have access to some products from Zink. For my own interest I once opened a rocket and a 60mm zylinder. And yes they use regular flash. By judging the burn rate it must be something near 7/3. But as far as I know, they use two different methods for the break charge.

 

Like you see on the pictures from the rockets, they just pour some flash between the stars. I checked on a Zink 905. There are several videos of this rockets on youtube: https://www.youtube.com/watch?v=19TSwaPHlUc

The engine is made from aluminum with 18mm OD with a 4mm nozzle and 1cm core. They use about 16g powder for the motor, wich is regular bp and some delay comp for a nice tail. The header contains approx. 44g stars and 2,5g flash powder (I had to sieve it carefully out of the stars, so could have been 3g).

 

For the 60mm zylidrical shells they use flahbags in the centre with 2 g Flash. Its glued to the top of the spolette, wich has 15mm OD.

 

 

I also found a documentation (german language) where you get a glimpse of the production at 26:20: https://www.youtube.com/watch?v=gUTaAzOM97Y

 

 

If you are interested I can take some pictures, the next time I get hand on some of their products.

Edited February 15, 2017 by Pyroboy

[ExplosiveCoek]

Thanks for the additional information! Yes, the pictures would be much appreciated.

 

So apparently their delay is sparky enough to ignite everything inside, even without the use of MCRH or BP in there.