Homemade Visco Fuse leaves lots of residue problem

[T1st]

Hi,

 

I am almost done with my homemade visco fuse machine, I solved most of the issues i had previously with some research and the help of members from this forum, now there is only one problem left, the fuse burns very well but it leaves a burning residue that lasts for long, the residue looks very similar to senko hanabi fireworks, it looks like a side reaction that keeps burning and bubbling and shooting sparks, this issue bothers me because one time the fuse was burning vertically and the residue fell on the bottom and burned the fuse from a different location wich made the firework go off much quicker than intended.

 

The composition i use is homemade BP, it is the regular 75/15/10 composition with 5% dextrin, it is then granulated and crushed again to get the right consistency for the powder to be used in the machine.

The strings i use are all 100% cotton.

I am confident that all my ingredients are pure.

 

Here is what i tried and non of it worked:

1- using sulfur from a different supplier.

2- adding more KNO3.

3- adding more sulfur.

4- adding more charcoal.

5- using different NC lacquers.

6- adding mgal to the mix.

6- adding flash powder to the mix.

I attached a video of how the fuse burns, i appreciate any help or suggestion that i may try, thanks!.

[cmjlab]

I don't know much about making visco, there used to be a guy here not long ago that did know all about it.

That bubbling is interesting, based on your description I initially thought maybe too much KNO3, or maybe you added more to help burn away the string and added too much by accident.  But after watching the video, that doesn't look at all like excess nitrate burning away - the times I've messed up with excess nitrate it was always more of a white bubbling. 

It appears to burn perfectly in my book, then the part right before the end seems to form some weird molten bubble.  Does dextrin do that?

[Carbon796]

Are you sure it's 100% cotton. It clearly looks like the string residue is reacting. Quite often cotton string/twine is sold as being cotton. But, in reality, its a 60/40 blend with polyester. 

The fuse also looks like it starts out really good. Then gets smothered some when it gets further in.

[T1st]

Not sure if dextrin is the issue, i don't think so since i did try changing the dextrin ratio with no luck.

 

The strings are labeled "100% cotton", i did a burn test for the string alone and it burned just like pure cotton with only some carbon and no residu or black smoke.

I forgot to mention i also tried to soak the strings with a concentrated solution of KNO3, this made the strings burn almost completely, but the moment the strings are woven to a visco fuse this problem keeps happening.

 

Don't get me wrong, i am very happy with how the fuse burns, its just this tiny issue that keeps bothering me, i want to solve it mainly for safety.

 

I read somewhere on this forum that straight BP is not good for visco fuses and that there are special compositions for different types of fuses, only thing is that i didn't find any good source for fuse compositions and all commercially ones keep their composition as a trade secret, i will keep trying different compositions until i find one that works good, unfortunately i don't have access to chlorates

 

[Zumber]

2 hours ago, T1st said:

Not sure if dextrin is the issue, i don't think so since i did try changing the dextrin ratio with no luck.

 

The strings are labeled "100% cotton", i did a burn test for the string alone and it burned just like pure cotton with only some carbon and no residu or black smoke.

I forgot to mention i also tried to soak the strings with a concentrated solution of KNO3, this made the strings burn almost completely, but the moment the strings are woven to a visco fuse this problem keeps happening.

 

Don't get me wrong, i am very happy with how the fuse burns, its just this tiny issue that keeps bothering me, i want to solve it mainly for safety.

 

I read somewhere on this forum that straight BP is not good for visco fuses and that there are special compositions for different types of fuses, only thing is that i didn't find any good source for fuse compositions and all commercially ones keep their composition as a trade secret, i will keep trying different compositions until i find one that works good, unfortunately i don't have access to chlorates

 

 

One of experienced member in visco fuse has posted formula here in this forum he said for visco fuse he mentioned blend of 70 percent 7F with 30 percent mead D.

You should really stay away of chlorate.

Have you tested your fuse before it passes through NC?

Is your NC of good fireworks grade?

You may also study what kind of NC is needed for visco fuse coating or other ingredients in it as I don't have that much experience in visco fuse.

[Carbon796]

If you're making ball milled BP ? That's a lot of Dex, just for granulating. But, just about right if you're pressing stars. Might not really change much. But, it's probably slowing your BP down some at a minimum.

[mx5kevin]

some visco compositions:

 

KP, BP, H3, BP from KClO4, some FP, modified WM, worth trying several things from visco. It is better to do it hotter at home, but not aggressively burning, so that can not move when burning. Aluminum increases the temperature, sulfur increases reactivation. More reactive active compositions can be prepared from KClO4 for more stable and hotter burning. Those that burn stably and are hot when stretched out in a very thin strip for a long, and are not absorbent, are good. It is worth testing small pices in a humid environment, after wetting, let it stand for a few months and dry in oven. It is not good if it burns with large sparks or starts to move while burning.

Edited November 1 by mx5kevin

[Mumbles]

Just checking, but the BP itself burns fairly cleanly, right? That's the first thing to check.

My initial thoughts also go to the NC lacquer. If the solution is too thin, I could see it soaking into the core more than you expect. A thicker solution may prevent as much migration. If the NC is lower nitration, I could see it not burning as cleanly and maybe interfering or consuming some of the fuel or oxidizer in the BP making residue like that. This is kind of a tough problem.

I know it's not as robust, but if your process supports it, have you tried burning a portion of uncoated fuse? It might help narrow it down to see if it's the string/construction that's the issue or the coating.