KP Burst 3inch

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sambo
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KP Burst 3inch

Post by sambo »

I'm looking for an opinion on this. I've always burst my 3 inch shells with KP. I like the convenience of mixing it, although not the cost, and I usually have good results in 3inch shells without the need for anything else. However, this time I change 2 things and ended up with a bunch of 3 inch salutes. I'm frustrated with myself for not having tested first before pasting them up. I change the Rice Krispies I normally use for Rice Hulls, simply as I find them easier to pack into a shell and they don't roll all over the place and I switched the +5% dextrin for +2% PVB. The results have blown me away, literally. The number of pasting layers and the method was the same. Was it the PVB or was it the rice hulls ?
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Boophoenix
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Re: KP Burst 3inch

Post by Boophoenix »

Not that I'd know for sure, but I'd supect the rice hulls to have more surface area speeding things up. Add to that the extra fuel value from PVB minus the slight slow down from dextrin. So you increased two fold with the change would be my guess.
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Pyro-Gear
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Re: KP Burst 3inch

Post by Pyro-Gear »

Well Sam might be a good plan to give us the stars used and also the prime you used, sounds to me like the stars blew blind.
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richardh08
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Re: KP Burst 3inch

Post by richardh08 »

I reckon Bradley is correct on all points.

I tend not to go for particularly hard breaks and I've always had satisfactory results with straight milled BP in 3-inch shells, either corned to 4FA or, more recently, coated 5:1 on rice hulls.
Even when I'm wrong, I'm convincing.
sambo
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Re: KP Burst 3inch

Post by sambo »

Actually they're all good points. In fact, I read Ken's message a few times thinking what was he getting at ( as the stars did of course blow blind ) but then I twigged - the stars were all primed with pinball ( Jopetes Purple ) so essentially the entire shell was full of KP. Had they been charcoal stars I probably would have gotten away with it. Anyone using KP burst regularly ?
Mixer
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Re: KP Burst 3inch

Post by Mixer »

Personally I have never found it necessary to use KP. I rely on the number of pasted layers to adjust burst strength.
Pinball prime has never let me down, provided there is a good BP prime outer layer.
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biffo
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Re: KP Burst 3inch

Post by biffo »

Hi Mixer, can you give us an example please like how many layers is the difference between a hard and a soft break,say on a four inch ball shell?what do you paste with and do you use a wasp what are you using to burst the shell.many thanks Biffo
Mixer
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Re: KP Burst 3inch

Post by Mixer »

Hi Biffo,

It all depends on the bi-directional strength of your Kraft strips which can be found using a simple pull scale.
In the case of a 3" shell using a good quality Kraft paper with the required strength (found through calculation) it would need 4 layers for a soft break and 6 layers for a good break. Just 2 extra layers (8) (with booster) will give you what would look close to a 4" break. Any extra layers would most likely lead to stars being blown blind.
If you want to keep it simple 2-3 layers per 1" shell diameter of a good quality Kraft should get you close.
I don`t use a Wasp. Paste is ready mixed Solvite. Burst is BP (willow) on rice hulls 4-1.

Here`s the formula...
Number of layers required is 8.7 x the diameter of the inner hemi in cm x the mean strength value of Kraft in kg per 1cm width.

For example; 8.7 x 7cm = 60.9 / 10 mean paper strength = 6.09 pasted layers.

So, if you had weak paper at half the strength you would need double the layers.
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biffo
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Re: KP Burst 3inch

Post by biffo »

Thanks Mixer, I had no idea there was a formula. Regards B
Redbullzuiper
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Re: KP Burst 3inch

Post by Redbullzuiper »

Good info Mixer!
Mixer
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Re: KP Burst 3inch

Post by Mixer »

Redbullzuiper wrote:Good info Mixer!
YW :)
sambo
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Re: KP Burst 3inch

Post by sambo »

V. good info. Thanks. I'm using 6 layers which is my standard for 3 inch. I guess what I'm really looking at is my most economical in terms of time, safety and cost method of bursting these shells if I want to make say a batch of 100. the KP avoids milling BP which is a significant consideration, but having read your comments I'm leaning back to bursting with BP. In fact, I'm pasting a BP 5:1 on rice hulls 3 inch as we speak. Thanks.
Mixer
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Re: KP Burst 3inch

Post by Mixer »

Actually I don`t mill my BP it`s just hand mixed, and it is as fast as I will ever need it to be.
All ingredients are superfine of course.
sambo
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Re: KP Burst 3inch

Post by sambo »

Mixer wrote:Actually I don`t mill my BP it`s just hand mixed, and it is as fast as I will ever need it to be.
All ingredients are superfine of course.
ok now you really have my attention, I've seen some of Dave's posts regarding this. Do you mind just clarifying for me what "superfine" actually constitutes. For example if you have granular KNO3, how long would you pre-mill that for and similarly with your charcoal. Are you using a particularly hot charcoal ?

thanks,

Sam.
Mixer
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Re: KP Burst 3inch

Post by Mixer »

In my particular mill - Kno3 milled to flour 1.5-2 hours. Straight willow charcoal to air-float 1.5 hours.

I dampen with 18% water +1% Dextrin for granulation.
Alternatively for quickness 1% red gum +alcohol, but the grains will be softer.
Last edited by Mixer on Sat Nov 11, 2017 1:16 pm, edited 1 time in total.
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Boophoenix
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Re: KP Burst 3inch

Post by Boophoenix »

Sambo, a lot of Dave's testing was done with 304 stainless media. He started out with a test batch of 5/16 media. That ventured into various sized SS media tests eventually. Then someone got him on the track of screen mixing. While it wasn't the hottest BP he ever made it did beat Goex powders in performance. I should add he did press and corn his tests for better consistency. Granulating as many do would add to the performance.

Dave often milled for 6 hours for most of his testing because that is where he started his tests. To keep similarity between tests he continued that process. Although one round of testing was done at around 2 hours I do believe.

We use to have many in depth conversations on the subject of charcoal. He did lots of rocket testing with Pete's rocket acme stand to the point of deminished returns on flight. When some of that wasn't being accepted by the community Ed Brown got him into pressing and corning powders for consistency.

Dave has taken a subatical from pyro it seems so hitting him for further information may not be possible. It's a shame I miss the long conversations with him on various topics. Most of his info he was comfortable with the accuracy can be found at Ned's. On a side note he was really enjoying Ken's mill for testing since he wasn't making huge batches like before. Hopefully he'll get the bug again and come back with all kinds of useful information. He is quite the creative and innovative fella.

I should add since charcoal is the huge variable in BP much of Dave's testing leaned towards it. Mill the fire out of it is where the key was it seemed. With the stainless there was no lead contamination. Which he tested once and didn't seem to be any issue. I still wonder on that one.
sambo
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Re: KP Burst 3inch

Post by sambo »

ok you guys, you were all right, of course and you knew it. I've come full circle. I have just tested 4 x 3inch ball shells all burst with MCRH. Spectacular. I've been using a waxed kind of craft to hand paste my shells, although I have a WASP - I haven't wanted to add any new variables so I've continued to do things this way for this size of shell. I switched the glue from wheat paste to pure PVA both for convenience and because with this kind of paper I didn't really notice any advantage to it soaking in or shrinking the pulp on drying. Would you believe this is what made the difference - it dries much harder and the added confinement was virtually causing my KP bursts to become salutes. Now I probably could reduce the no. of layers of pasting and boost these for the same result but I'm happy as I am and very pleased. Thank you for all your help.
Sam.
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Boophoenix
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Re: KP Burst 3inch

Post by Boophoenix »

Congrats on getting it worked out and thanks for sharing.
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richardh08
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Re: KP Burst 3inch

Post by richardh08 »

That's interesting, Sam.

These days I very rarely make shells, but when I do they are generally 3" spherical with nothing but MCRH burst, and I've never had cause to complain about their performance. I haven't ever felt the need to enhance the burst with any kind of booster.

But I do use slightly diluted PVA to paste them in, so maybe that's the reason. I hadn't previously thought about the possible effect of using different types of glue/paste. This is an area that might be worthy of further investigation...
Even when I'm wrong, I'm convincing.
Mixer
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Re: KP Burst 3inch

Post by Mixer »

My`go to` adhesive is Ready Mixed Wallpaper Paste.

I tested many different adhesives when i was rolling rocket tubes, and this paste came out far superior than all the rest in every respect. It has a very low water content, and for gluing Kraft paper It`s all i will ever need to use.
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