My stars crackled and crumbled

[pyroguy1960]

it can be bought online as well for something like 15.00 for 5 lbs......nothing expensive about it...

[FREAKYDUTCHMEN]

50AE, beware the binding characteristics influences the burn speed. If GA makes rock hard stars, they'll probably burn longer. I've made stars with sgrs which formula didn't ask for sgrs, well those stars burned extremely ugly, so bad that I can't describe how ugly they burned.

 

Peret, making 1kg dextrin out of cornstarch will probably cost me 3 bucks more or less and many hours around the oven, I rather choose to buy. The stuff is one of the cheapest chemicals needed in pyro.

Edited May 11, 2011 by FREAKYDUTCHMEN

[50AE]

I made some dextrin today, I was tired of waiting the guy, so I went to the local store and bought some starch. I made some dextrin. Gonna bind some of the compositions and share the result in a few days.

 

Freaky, I'm aware of course. I haven't noticed this with SGRS/dextrin substitution though. But it's evident with GA.

[50AE]

Soo, what can you say about this?

 

http://img18.imageshack.us/img18/686/picture106ge.jpg

 

I say I feel like meeting Mr. Forli right now and SMASH the rest of the composition IN HIS FACE, WET of course

 

I guess you will ask me how I processed the stars. Of course, I will tell you how:

-5% dextrin, 100% water, stars prepared for cutting.

-Stars were too crumbly, I decided not to add wheat paste though, suspecting it as the trouble maker.

-Because they were horrible, almost falling appart, full with cavities, I gently put into a bowl in the goal of making them into a round shape

-I successfuly did, then I primed them with a layer of green mix and then meal powder.

[FREAKYDUTCHMEN]

They look like tiger nuts hehe, guess they don't taste like them.

 

How much water did you add to the stars?

First you tried to cut them, but later you decided to roll the wet composition?

Did you make them that big in one time?

[pyroguy1960]

A few questions, suggesstions here.

 

You removed the GA from the formula entirely corrrect?

 

You say the stars were crumbly when you tried to cut them, this may seem like a silly question, but you added enough water to make it into a putty correct? Like the consistancy of playdoh? Like Dutchman I find it odd that you were able to roll them at all if they were wet enough for cutting.....

 

There is nothing really out of the ordinary about that formula, perhaps it time you buy some commercial dextrin?

 

Also you ask me that's not the greatest formula, way to heavy on the Mg/Al for my taste and that much Mg/Al may be causing some of your issues...

 

For a slow burning green I use:

 

barium nitrate 58

sulfur 9

parlon 14

mg/al -200 4

Al 12 mic atom. 9

red gum 3

dextrin 4

 

 

For a faster burning green I use:

 

barium nitrate 58

parlon 14

mg/al -325 12

red gum 6

pot perc 5

dextrin 5

Edited May 15, 2011 by pyroguy1960

[50AE]

Yes, I added water until the composition reached a playdoh consistency, then I cut them. They were very fragile, in a way the composition wasn't holding very well together. If you've made stars with bright Al, you will know what I mean.

I cut them and then I placed the cubes in a round bowl and I hand rolled them. From cubes, they turned to almost round balls.

Then I primed them while they were still wet.

 

I just want a fast burning formula that uses PVC as the chlorine donor and Ba(NO3)2 as oxidizer. It doesn't need to be bright, but it has to be quite deep.

I also suspect the PVC as the problem, it is a very fine powder. I've made forli white composition before, pressed 15mm stars and then primed in meal powder. They didn't crack

His white composition is very similar to the green, it doesn't have the PVC

 

Barium Nitrate 48

Magnalium, granular, -200 mesh 19

Potassium Nitrate 14,5

Sulfur 10

Gum Arabic 5

Red Gum 3,5

 

My other option would be to bind the stars by dissolving the PVC.

Edited May 15, 2011 by 50AE

[pyroguy1960]

Hm, I don't have any experience with PVC so perhaps you're right that it is causing the issue. Why the commitment to that donor? Parlon works well in greens for me....I get very nice color in both those comps....

[Mumbles]

I suspect it is an availability issue. Parlon seems a bit harder to come by in Europe, and Saran seems to be very rare.

 

I really don't know what to tell you. It would appear to be a problem with the PVC. I've made a few PVC stars, but the stuff I have seems to be somewhat coarse. There are a lot of different types of PVC around, different plastic blends, mesh sizes, properties, etc. It may be that your product is somewhat hydrophobic, probably not unlike bright Al. Some alcohol may help, but again it's hard to tell you for sure. The cracked prime layer could be due to adding the prime before the stars were dry, which it sounds like you did.

[FREAKYDUTCHMEN]

There are quite a lot of suppliers who offer parlon here in Europe. PVC is less common, or at least not the best quality IMO. Long time ago I've bought some 100 mesh stuff from a european supplier which was very hard to press comets with, I prefer very fine PVC, as fine as dust.

[50AE]

Mumbles, if what you say is true, then why the first batch of stars crackled as well? They were fully dried before priming.

[FREAKYDUTCHMEN]

These tigernuts stars were too wet and too big, shrinkage problems occur.

[50AE]

There's the other problem we didn't discuss - why are they so crumbly, breaking into dust in my fingers like if there wasn't any binder at all?

[pyroguy1960]

If it were me, I'd want to eliminate the unknown variables here, get some parlon and some commercial dextrin. Then use one of those formulas I quoted or a more well known green formula. You don't seem to be having much luck going down the road you're on. Just what I'd do if I were in your situation....

 

 

 

[50AE]

I think I'll switch to another formula. It's a shame though, this one was a faster burning with pretty easy ignition.

Parlon formulas are not an option for me

[50AE]

I remember I have bound the following formuka with GA without any problems. I modified it a little by adding 10 parts potassium chlorate.

The main difference is that it doesn't contain sulfur.

 

Barium nitrate 56

Red gum 7

Magnalium -200 mesh 17

PVC 15

Dextrin 5

[Mumbles]

Unless you have some idea what difference sulfur would make, I think you're grasping at straws here. I would think that the biggest difference between that formula, and the first one you tried is the presence of dextrin. The facts in this thread point toward one thing to me, which I am sure you will argue with. That is that you have shitty gum arabic, or at least it is not as good of a binder as you believe. I know you'll disagree, but looking at the thread makes me lean that way. The first formula without dextrin doesn't bind with GA. The second formula with just dextrin and no GA doesn't bind, as it's possible the dextrin was never activated. The gum arabic solution could potentially act somewhat like wheat paste in that it could be breaking down surface tension from hydrophobic (PVC) components. This third formula using both seemed to bind fine.

 

As I've said before, I always use dex in combination with gum arabic. Perhaps there is some sort of mutually beneficial interaction. In my mind gum arabic solution on it's own introduces relatively small amounts of binder. The dextrin does the majority of the binding, but the GA just hardens the stars, probably not unlike certain additives in polymers. It could be totally off base, but I don't intend to change what is already working to prove/disprove that.

[50AE]

Thank you for the helpful answer. I'll assume the possibility of having shitty gum arabic, because I can't prove the opposite.

As a last thing, I'll try binding a small batch with dextrin and GA.

 

Edit: I noticed something weird. I have a habit that consist of taking the small residue of left composition and form it into big cubes, which will be used as comets for shells.

 

I have three cubes of comp 1 - bound with GA and comp 2 - bound with dextrin

They are all ROCK HARD.

I also remember that before priming the comp 1 stars, they were very hard as well.

So now I connect the problem with the priming.

But how does it come a layer of prime to ruin the whole star?

Edited May 16, 2011 by 50AE