Binding comps

[loaded4bear]

Hopefully someone can fill in some gaps in my knowledge. I see somewhat frequently the phrase "red gum bound" referring to star comps. My general rule of thumb was if you see dextrin or SGRS in the comp, you activate with water (or water/alc). If I saw no dextrin and the comp had parlon, I would bind with acetone. I was under the impression that red gum was basically a fuel and that the acetone melts the parlon thus binding the whole star together. Will red gum bind a comp by itself? Someone please straighten me out.

[LTUPyro]

Red gum in star comps is usually fuel, but in some cases you can use it as binder aswell. Red gum is activated by acetone or alcohol. Dextrin can be added to most of star comps and using parlon as binder is not nessesary. Edited August 13, 2013 by LTUPyro

[PyroCube]

You may like to know that red gum isn`t a very strong binder, in my experience dextrin works much better.

[nater]

What solvent are you using with red gum? My last batch of red stars bound with red gun were just as strong as other binders.

[PyroCube]

I used 98% Ethanol for binding them. They really were quite crumbly, maybe I did something wrong.

[Mumbles]

For me red gum is a decent binder, but the stars are still softer than when using dextrin or SGRS. They generally hold up to shell bursts at least.

[nater]

When pressing stars, I found I could only dampen enough comp at a time to fill and press the plate 3 times. Otherwise the stars came out crumbly. The good stars were nice and hard when dry, but I don't break shells that hard. Dextrin bound stars may be a little harder, but both types clink like glass after drying.

[loaded4bear]

So is it safe to say, if the comp has parlon, use acetone to melt the rubber binding the components regardless if it has red gum in it or not. If the comp has no parlon (or calls for a small percentage), or you just dont want to mess with acetone, it makes sense to add dextrin or SGRS and activate with water. Is this a sensible approach?

 

Is dextrin and SGRS interchangeable? Used in the same general percentages (3-5%)? I have some SGRS and have yet to try it. Thanks for your comments.

[nater]

Dexrin and SGRS are interchangable, but don't use any alcohol with SGRS. Use water only.

 

For comps with plenty of parlon and red gum, use your choice of solvent to activate one or the other as a binder. When pressing stars, I use alcohol / red gum in order to press a drier comp and avoid the stringy half dissolved parlon. You will just need to see what you like the best.

[Mumbles]

Making substitutions between dextrin and SGRS will probably change the appearance a little, but the overall effect will be the same. Some are of the opinion that SGRS give a bushier charcoal streamer for instance.

 

As a fair warning, SGRS takes a little getting used to, especially if you're planning on cutting the stars. It generally takes more water than dextrin, and also can take longer to fully activate.

 

Personally, the only thing I ever bind with acetone are go-getters. If there is substantial (over 15% or so), parlon in a composition it can generally be bound with acetone without any issues. From what I've gathered, it's really best to make cut or screen sliced stars if going this route. Pressing and rolling has additional complications, though can be done.

[loaded4bear]

OK so is this a good summary about binders and activators:

 

Dextrin - water or water and alcohol

 

SGRS - water only

 

Red Gum - Alcohol or Acetone

 

Parlon - Acetone

 

*********

 

Pumped stars - best to use dextrin or SGRS, red gum is ok but may be somewhat softer. Parlon/acetone would be messy.

 

Screen slice or cut stars - acetone for high parlon content, otherwise dextrin or SGRS

 

Rolled stars - anything but acetone to avoid a huge mess.

 

Have I got the right. Sorry, I am an engineer and like to nail things down with hard rules.

 

Also, does alcohol by itself activate dextrin? I noticed that Veline says to use 100% alcohol for his comps. I thought this was weird since it has dextrin. Why not just use water or the usual 75%-25% water/alcohol?

 

BTW - thank you Mumbles for all of your dedication to helping others learn pyrotechnics on this site. I have read hundreds of your posts and have enjoyed them all!