Anticake resulting in poorly bound stars?

[AdmiralDonSnider]

I have rolled dextrin bound stars using a formula containing about 50% potassium perchlorate and 4% dextrin. The stars were sized to 6mm and set to dry.

 

The result is disappointing. The stars, even though clearly fully dry based on ambient humidity and drying time (several days), crumbly quite easily when compressed between two fingers. They are much less hard than stars of similar size and similar formula I have produced earlier.

 

I ask myself if it is worth to enlarge them, as intended, into round stars of 9mm for use in shells, since there is quite a chance they will crumble under the break forces.

 

What I really wonder about is what caused the weak adhesion. There are two factors that might have caused the effect.

 

- One is the white dextin I was using. I´m pretty sure though I have used it before to consolidate stars and they came out well.

- Secondly I recently started to use potassium perchlorate with anticake. It comes as a very convenient fine powder and clearly has some cabosil addition. Pretty standard pyro grade though. Are there known problems concerning the binding of mixes linked with anticake chems?

Edited December 25, 2013 by AdmiralDonSnider

[psyco_1322]

I can't say anything on the anticake causing issues, though I know sometimes the excess coating on bright Al can cause that issue.

 

I have had this same issue with some colored comps, like emerald green and a purple formula I use. It might be enough dextrin to bind if pressing stars, but with cut or rolled stars, they don't come out hard enough. I've just bumped the dextrin percent up a few percent and it usually fixes the issue.

 

With some colored stars I have rolled that came out weak, I spray then with lacquer thinner, to a good soaking. It will dissolve some of the parlon, with out turn the star to mush, then after it dries, they are hard enough to be usable in shells. If you can crumble then with your fingers, they will not hold up in a shell.

[FlaMtnBkr]

I know there are a ton of stars rolled with perchlorate that contains anti cake without issue. I would say your issue is with the dextrin. Either it isn't any good for some reason or you just didn't use enough? Have you ever tried using dextrin liquor to roll with? That way you know there is enough water to activate the dextrin? Did you use water and alcohol to roll with? Could there have been too high a percentage of alcohol since it won't activate the dextrin and there isn't a particularly high amount of liquid when rolling? Just a thought.

[dan999ification]

I'm having similar issues with mine, the perc is not white and feels greasy.

My other 'white' perc which cakes a bit does not have this problem of not adhering.

Some Blue cores cracked and felt wet and crumbly although perfectly dry, the same comp with different perc they dried fine.

 

Trying to coat graphite lubed seed is fun with this greasy perc aswell

 

Dan.

[AdmiralDonSnider]

Thank you for your input.

 

In rolling I used 25% alc in the water, which is pretty standard. With non-water-sensitive mixes I also used to spray more water to activate the binder.

 

Since I am pretty sure I have used the dextrin before, I was blaming the anticake perc. But then, since it is a pyro grade from a pyro supplier, like FlaMtnBkr I can´t imagine that it poses a problem in production.

 

4% dextrin also seems a pretty standard amount to me, and should result in hard stars. I am really clueless. More thoughts appreciated!

Edited December 26, 2013 by AdmiralDonSnider

[pyrojig]

Could you post the comp ?

The use of anti cake has not posed a prob for me in the past. It sounds like a binder issue. Do you have and tan or yellow grade dex. ? If so, try a controlled batch to test against. I had a similar prob recently with some glitter . I used 5% dex and never had a issue before , but my speculation was there wasnt enough water to activate the dex , and the pumped 1/2" stars suffered the same fate( crumbly).

Edited December 26, 2013 by pyrojig

[dan999ification]

It was pyro science blue, there was plenty of water used. Different perc.. Hard stars.

The dextrin is homemade and has given good strength in other comps for years even with high %'s charcoal.

For me it's the perc, the dextrin and methods are fine with my other perc.

 

Dan.

[AdmiralDonSnider]

The problem initially described seems to have been caused by a combination of factors. I have seeked help in other communities as well as have been told that anticake oxidizers do not render binders useless, but do in fact adversely affect adhesion, thus require more attention to a good binder amount and activation.

 

The formula I was using came from the spanish script posted on APC. Those color formulas all contain as little as 4% dextrin, which does not seem to be an issue if caking perchlorate is used and if the binder is activated with plenty of solvent. I sometimes tend to roll on the dry side though, especially if the stars are still small.

 

To sum up, the poor adhesion was not caused by the anticake alone, but also by a comparably small amount of binder and rather little activation due to the use of little solvent.

 

I was also told that yellow dextrin is better than the white variety I am using, as well as that the american pyro industry usually includes about 6% dextrin in their color formulas, which also is expected to eliminate soft star problems.

Edited December 28, 2013 by AdmiralDonSnider

[pyrojig]

Hey , It sounds like you nailed it!! It is nice to have the resources and great minds at work to help figure out these annoying probs.

Good Job, and thanks for sharing . Im sure that your not the only one that has dealt with this, and you sharing will save another pyros the headache of figuring out what went wrong.

Edited December 29, 2013 by pyrojig