Priming troubles...

[mabuse00]

Hi,

 

I just tried out some recently made barium nitrate strobes in a stargun and they failed.

The Pinball prime lights rather easily, but in this case it just burnt on the fast moving star without the least effect... The prime layer was not to thick, about 1mm.

 

They would work in a rocket with a dump header for sure, or when coated with another layer of TT on top, but I want them to light under any circumstances, and immediately, not seconds later until the TT burned off and they slowed down.

 

Since I'm allready using +8% silicon and +2% MgAl I wonder what you would do to make it even hotter.

 

 

Also I wonder what's the best high temperature fuel, people often mention MgAl, Al or Si at once. At the moment I prefer Si, because it does not produce so much light. But I does not burn very fast.

 

MgAl burns faster, but I would expect MgAl to be inferior because the Mg vaporises before burning, thus much energy is carried away...

 

Pure Al would be better, hot and fast, but it has to be the dusty dark stuff, and I hate working with that.

 

That's why I settled on the 8% silicon and 2% MgAl. My next step would be using less charcoal and more metal... This will make the prime itself less ignitable but since it lights very easy now I think there is some margin...

 

Do you have an opinion on that? What kind of prime do you use on very fast flying stars?

Edited September 11, 2012 by mabuse00

[Potassiumchlorate]

What about using NC-lacquer? It "sticks" very good to the stars.

 

What do you mean with dusty dark stuff? German Black? It's not that dusty, though a simpler filter mask is recommended when working with any bigger amounts.

[Mumbles]

You might need to step prime your stars. Lloyd alludes to this on occasion when talking about the Pinball prime he developed. It will light nearly anything, but it has to be applied properly. He claims that even without metals or silicon, it will light just about everything except for things like white mag stars. I have a quote from him below that describes how he tends to do it.

 

 

 

 

 

I might add that there's a technique to applying a prime to hard-to-light

stars. Merely "pasting" on a layer on the outside may not do the trick.

 

The proper way to do it is to use a common solvent to both the star and

the prime's binding system, then to significanly over-wet the stars

before the first prime layer, so they begin to "slime" themselves in a

dissolved layer of star composition.

 

To that wet slurry is added an amout of prime estimated to be about 25-

50% of the amount of slurry. With that you've built a mixed layer of

prime and star composition.

 

Then you begin to apply one or two more layers, slightly over-wet again,

but not to the degree of the first layer.

 

Finally, apply a layer of prime with the stars only just wet enough to

take it up.

 

I like, then, to apply a thin but dusty layer of rough hand-made powder

as an outer take-fire layer.

 

What you've done with all this is to build a step-prime system without

mixing star composition and prime before applying it.

 

LLoyd

[mabuse00]

That's about what I did allready.

 

Perhaps I should mention that I used Polyvinylbutyral as the binder for both the prime and the stars. I'm quite happy with it, as the stars are rock-hard, including the prime. Also the prime is impossible to blow of by hard breaks. As alcohol is used for the binder, the redgum is also dissolved.

 

Thing about PVB is, that it seems to inhibit the burn a little - maybe that's the problem here. On the other hand I consider that an advantage for strobes.

 

I slurry primed them this time, what means I made a slurry of prime, wetted the stars until the outer layer became soft, dumped them in the primeslurry and let the suplus prime drop off. I also gave them a dusting with H3, as I use H3 in the stargun.

 

Maybe the prime was just to thin...

The stars where 12mm pumped, and they had to fit in a 14mm stargun

How much do you usually use?

Edited September 12, 2012 by mabuse00

[AdmiralDonSnider]

Mumbles, I have been searching for this post by Lloyd for quite a while now. It´s excellent info - once read it on rec.pyro I think but then lost the link and failed to find the post again. Thank you!

 

mabuse: A thin layer of super hot prime just might not do the trick. I once was really suprised when a hot military type Si based igniter failed to light ruby red stars in a canister shell. The layer was rather thin. Step priming is better, as already suggested. Sometimes it´s also unclear what is meant by a "1mm" layer. A round star will actually grow 2mm in diameter by such a layer of prime, but people often apply what makes up a 1mm growth only. That is a thin layer of 0.5mm of prime, which simply fails to transfer enough heat. Step priming is necessary but takes up space in stars; methods like the one mentioned by Lloyd help save diameter.

[dan999ification]

i dont use barium so did not reply to be wrong but can you cut these strobes? It would be easier to apply the prime by overwetting the pattie applying lots of prime to both sides and pushing it in with gloved hands or a rolling pin between two shims, then cut and dust with the same prime ( i leave them in there until dry) all my solvent stars are primed this way but they are quite easy to light anyway so may not help you.

What about a cavity pump, you could get quite a bit of prime in the cavity and you are giving the prime less work by giving it the circumference to light then the face, some primes will obviously ruin the effect used this way but the idea im sure can be tweaked.

 

Dan.

[mabuse00]

A round star will actually grow 2mm in diameter by such a layer of prime, but people often apply what makes up a 1mm growth only. That is a thin layer of 0.5mm of prime, which simply fails to transfer enough heat

I mean 1mm layer. Almost. Maybe 0,8mm or so as they fit in the pipe.

 

can you cut these strobes?

Of course. But in this case I wanted to compere some modifications with each other, and I prefer the stars to be as identically as possible.

 

What about using NC-lacquer? It "sticks" very good to the stars.

I only use NC laquer in small amounts, not for stars. Also it dries to fast. Stickyness is not the problem here.

What do you mean with dusbonds perfectly to the starty dark stuff? German Black?

"Black000". I do not like the dust flying around, a mask does not solve that. And larger aluminium seems to fly away before it is consumed, it burns rather with a tail.

 

 

I'll try a thicker prime and see what happens. I was just puzzled, because that was the first time that pinball prime failed for me. I never had that before.

Edited September 12, 2012 by mabuse00

[Potassiumchlorate]

Pinball with both dextrin and red gum in it and then double priming it is what I do. I always use H3 as burst in my bigger shells. Only in the smallest I use flash as burst, and only then I prime with a BP layer as well.