Drying in the sun

[PyroCube]

I`ve heard that drying BP and stars in the direct sun is a bad idea.

I always dried my stars and shells in the sun until now and never had any problems, is there

anything likely to happen?

 

 

Greets

[schroedinger]

Depending on many factors.

 

Speccially riski if you have anything reflectiong near you`re stars, as this could givehot spots orif you got really high temperatures. Also you can get the problem with driven in stars.

 

But if you lock at movies from factories they all dry in the outside and even shimizu statesto do so.

 

But a fact is that dring in the shade is safer as you reduce sources of ignition

[LTUPyro]

I dry BP and every color star comp in direct sun and never had problems. I don't like to dry charcoal streamers in direct sun though because they usually get driven-in. Charcoal streamers I usually dry 2-3 days in breezy shadow place, and then 1 day in sun and have no problems.

[mabuse00]

That Driven-in phenomenon is your enemy here. The stars are hard on the outside but still wet inside.

The moisture trapped inside takes a very long time to get out through the hard dry outer layer (and has plenty of time to ruin your metal fuels ).

[schroedinger]

As i read often about the driven in phaenomena, did anyone ever tried to dry them complete by putting the driven in stars in vakuum with some dessificant, this should get them dry quite fast, as the watter would be quite near to start boiling

[mikeee]

If you have a vacuum setup it would surely work well for drying your materials.

Not too many people have these vacuum setups in a pyro shop area and the screens they put stars on are quite large.

This has been discussed on several other pyro websites.

[schroedinger]

Yeah, that`s wath i thought to, the biggest problem will be the Vacuum chamber, you propably need mutiple ones lined up in a row

[Arthur]

The usual reason for the lack of machinery is cost. Machines cost, the number of stars that could be dried in a vacuum chamber wouldn't make a box of shells.

 

Drying in warm daylight is great especially if there is a breeze. When there is full sunlight directly curved shiny things like bowls can focus enough light (and heat) to cause the whole lot to burst into flame.

 

Rolled stars can well be dried at 4mm. 8mm and 12mm especially if there are lots of them this makes complete drying easier and quicker.

Solvent stars using acetone usually cost too much and have the added flammable vapour problem too both of which limit their commercial use

[Mumbles]

Driving in stars really only is a problem if the wet layer is too thick. This can most prominently be an issue with large cut stars or pumped comets. If you roll in reasonable increments, or make smaller stars, force drying is fine.

 

Using a vacuum can make the driven in problem worse. Driven in stars, have dry outer layers, and sealed in wet layers inside from drying too fast. Using dessicants or vacuums in lieu of good airflow makes these issues much worse. The issue with vacuum chambers tends to be the complete lack of thermal conductivity. A vacuum is a great insulator. Vacuum chambers seem great in theory, but work poorly in practice. Under vacuum some overly wet stars have issues with swelling and cracking as the water comes off too fast. With drier stars, the stars end up getting very cold and the evaporation/sublimation of water slows down considerably. The way most vacuum chambers are constructed tends to not allow a lot of thermal contact, so even heating the chamber doesn't do a lot. I've been told that it can be done to some degree by using clear chambers to allow for light irradiation as the heat source, and trays that allow for stars to be rolled and shifted in position.

[NeuroticNurse]

What about one of those food-dessicators that you can buy from EBay for 45 bucks? Would they work to avoid that?

[Mumbles]

They can work. I'm still uneasy about them. I'd prefer an isolated heat/air source. Most food dehydrators have the heat source directly underneath the trays, which isn't ideal for us as flammable powders can and will fall directly into it. I'd suggest trying to modify it to prevent this if you want to use one. Drying chambers are easy to build. Take a look at the skylighter article for some ideas. I had one a lot like the top most picture. It took about 2 hour to build, and cost around $20. Most of the time was spent making the screens honestly. The chamber itself took about 5 minutes.

 

http://www.skylighter.com/fireworks/how-to-make/drying-chamber.asp

[50AE]

Also keep in mind that some compositions must not be under sunlight, such as chlorate containing ones, because UV rays tend to decompose them.

 

I've always feared driven in problems, so I used to dry my stars in a shade. If there's some wind, then great.