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Edited by NeilB, 11 October 2017 - 06:50 PM.
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Posted 11 October 2017 - 06:48 PM
Edited by NeilB, 11 October 2017 - 06:50 PM.
Posted 11 October 2017 - 09:33 PM
What you really need is a drying box. There is a good description in lesson 3 of Ned Gorski's 'Fireworking 101' course, which is available - without subscription - at www.fireworking.com. An easy alternative which should solve most drying problems in our climate is to buy a fruit and vegetable dehydrator.
Posted 12 October 2017 - 09:07 AM
Posted 12 October 2017 - 02:48 PM
I use an electric fruit dehydrator for drying lots of different compositions including some solvent based ones and it's absolutely brilliant. They are pretty cheap for what you get too so highly recommended.
You may need to do a bit of work with it to establish your own drying times though, just weigh a star before you put it in and then take it out every so often and reweigh it. When the weight loss is insignificant, it's dry. You do need to let the star cool before you weigh it in order to get an accurate weight and also remember that different compositions will probably require different drying times.
Posted 12 October 2017 - 05:22 PM
........... You do need to let the star cool before you weigh it in order to get an accurate weight .......
Blimey, you work to fine tolerances
Posted 12 October 2017 - 10:01 PM
Posted 12 October 2017 - 10:35 PM
Posted 13 October 2017 - 06:50 AM
Edited by NeilB, 13 October 2017 - 06:55 AM.
Posted 13 October 2017 - 07:56 AM
In a dehydrator the contents are heated indirectly, by means of the hot air that flows over them. The amount of moisture that air can contain depends on the temperature; hot air can hold more. Even if the outside air is saturated, by the time it is heated (most food dehydrators go up to 70°C) it is capable of absorbing significantly more water. Blowing the hot air over the contents will dry them very effectively. A custom-made drying box works no differently.
Posted 13 October 2017 - 11:45 AM
Posted 13 October 2017 - 01:44 PM
Offhand, I don't know of any common pyrotechnic composition that is liable to ignite at that kind of temperature. In any case, most of these dehydrators have an adjustable temperature between 35 and 70°C, and that's the type I would recommend. Ned Gorski's article points out that the home-made version he describes will reach temperatures of around 140°F (=60°C) but I accept that he says he uses it outside the workshop, in a covered but otherwise open area.
Everyone has to decide on their own acceptable level of risk, but my feeling is that using a dehydrator at a low to medium temperature setting is unlikely to cause an unexpected ignition.
Posted 13 October 2017 - 03:03 PM
As Richard says, everyone has to decide on their own level of risk.
My dehydrator runs at a maximum temperature of 70 deg C and I've used this temperature several times for BP compositions wetted with water, including the standard 75:15:10 and I've never had a problem. I use 60 deg C for isopropanol wetted compositions and 50 deg C for acetone.
Drying times vary according to thickness but, as a guide, BP at about 12mm thick and soaking wet with water will be dry in about 5 hours. Isopropanol wetted materials about 10mm thick dry in about 3.5 hours and acetone wetted at 17mm inside a thin paper tube takes about 3 hours.
NeilB: Some charcoal based compositions can hold onto moisture for quite a while but, I think that whatever the composition, you'll find that drying times are hours rather than a week. Just play around a bit along the lines that I suggested before and determine the drying times you need for your compositions. You'll soon build up the experience to make a good guess at a likely drying time for any new composition.
There are lots of different models of dehydrator on the market and there are some that look rather like mine for about £30 on Amazon just search for dehydrator. I'd love to post a link but, unfortunately, I can't copy and paste into the forums.
Edited by BlackCat, 13 October 2017 - 03:11 PM.
Posted 13 October 2017 - 03:27 PM
I have used a food dehydrator for the last 8 years although I am now on my 3rd one, technology has moved very fast on this item hence the 3 to date.
If using a binder such as polyvinyl butyral (C8H14O2)n as your binder @ 2% you can fire the stars within 24hrs or less just let the wetting agent (IPA) flash off a little volatiles no problem what so ever.
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