22 replies to this topic

[pritch]

I basically would like some information regarding methods of melting chemicals such as kno3 with sugar and im sure I will need to melt others. At the moment I only have my stove but I think regardless of what some have said, thats a bit risky. I would like to try and keep my costs for this under ?30 and im only making small amounts so I wont be needing anything heavy duty.
From what i've read so far I think maybe a cheap gas stove would be best but it's more the matter of monitoring the temperature so I can make sure it's only enough to melt and not ignite.

Thanks very much!
Pritch

[Stuart]

I have used a deep fat fryer to melt Potassium Nitrate and Sugar as sugar melts at 185*C and a deep fat fryer can go up to 190*C. I don't know what else it could be used for or what else you would want to melt but I have also had a reasonable amount of success by pressing a Potassium Nitrate and Sugar mix in my press and that produces good results. I should have a page about that up at the weekend so you can have a look at what I mean in detail then

Edited by Stuart, 21 April 2004 - 04:36 PM.

[chim-chim]

I've read all I can find on sugar rockets and everyone who seems to know what they're doing would second Stuart on the fryer idea. Many metion that the thermostats on fryers usually aren't that accurate and you will still probably want to get a candy thermometer. I think I remember you mentioning sorbitol in another post, it melts at about 111*C and dextrose at about 146*C, making a fryer more than suitable for sugars, which is all expect you trying to melt, except maybe sulfur, very low at about 112*C. KNO3 at 334*C and fuel metals range in the 600's (Al, Mg, and Sb anyway) put us at dutch oven or kiln.

As for portable gas stoves, many people use them, but I'd feel safer with an electric. A lot of this is just psycological I suppose, a red hot element isn't much slower than a flame for lighting spilled powder (not that any of us ever spill things), but still, why add propane or natural gas to the mix?

From my reading, I'd estimate that melt casting probably improves performance 10-15% over well mixed rammed powder. I considered the increased risk, and the effort/mess, and decided it wasn't worth the mess Not yet anyway, I'm sure I'll try it sooner or later. Let me know how it works out either way you go. You seem to be one of few others doing rockets at present.

Remember, ignitability increases with temperature. Be careful, as always.

[EDIT/ADD ON: The fryers are often used as a double boiler with Crisco (shortening) or something similar that will harden between uses for easy storage.]

Edited by chim-chim, 22 April 2004 - 05:00 PM.

[Demented Ferret]

From first hand experience, I'd say that placing the two ingredients over an electric heat source (in a saucepan!) on very low and move up slightly every 10 minutes until the compounds melt together is the best and cleanest way really. This only needs to be done once, as once they melt - you know exactly what temperature to set them at at for other times. The decomposition point of Potassium Nitrate is about 80 degrees above the melting point (I think) so as long as you're slow and careful you won't have a problem (I've done it loadsa times without fail, and it gets easier every time).

Edited by Demented Ferret, 22 April 2004 - 03:43 PM.

[chim-chim]

Demented Ferret is correct on having a good melting/decomposition temp. range for KNO3, (334*C MP, 400*C Decomp, for 66*C or 118*F), which is good to know if your mixing it with anything with a higher MP or too low a volume to effectively bind the mix, so you need the Nitrate to melt, but you don't need the Nitrate to melt (assuming it's reasonably fine, if not mill) for rocket fuel and it's a lot safer working in the 112*C-185*C range you need for the sugars.

[PanMaster]

My first attempt at melting sugar and KNO3 in a pan over gas made a very sticky mess that burnt like a smoke mixture but took a bit of starting. During my second attempt the mix became like caramel, while holding it, then I turned away for a second and looked as it burst into flame, I panicked dropping the burning mix on the worktop burning the it. Never try heating such mixtures, I nearly burnt the ceiling once hehe.

[adamw]

Yes even though it is just sugar and KNO3, when it wants to go by heck doesn't it just! When it starts turning dark brown you know there is a problem... So safety first - I would only recommend this is done outdoors.

[Matt]

One rule, keep stirring. I cook this stuff over a bloody fire no temp control whatsoever. I have had 2 batches go up as they were my first. If there is any on the walls of the pan darkening, scrape it off and strir it around.

Just keep it moving and you will be just fine

-Matt

[BigG]

One rule, keep stirring. I cook this stuff over a bloody fire  no temp control whatsoever. I have had 2 batches go up as they were my first. If there is any on the walls of the pan darkening, scrape it off and strir it around.

Just keep it moving and you will be just fine

-Matt

U do not melt over direct open fire, stiring or not, you do not do it. Please visit Richard Nakka site for safety issues and the two possible ways of doing it correctly.

[adamw]

BigG is correct. Using a direct flame creates hot-spots in the mixture and will cause it to go up. That is why the melting should be done with oil or water since the heat can be spread proportionately around the container.

[Demented Ferret]

Yeah, a safer way to do this is to heat the sugar until it melts, TAKE IT OFF OF THE HEAT and then add the Pot. Nit. - although the quality of the composition is a fair bit worse.

[Matt]

I really dont like trying to justify myself but... here I go.

It isnt on a direct flame as such, we put a 3mm steel plate on a grid above the flame, I suppose it still heats up more in some spots but the pan I use is kinda small so the general heat is ok, but I tell ya stirring reduces risk of going up due to hot spots! ya just gotta beleive me!

-Matt

[BigG]

I really dont like trying to justify myself but... here I go.

It isnt on a direct flame as such, we put a 3mm steel plate on a grid above the flame, I suppose it still heats up more in some spots but the pan I use is kinda small so the general heat is ok, but I tell ya stirring reduces risk of going up due to hot spots! ya just gotta beleive me!

-Matt

Matt, It still does not matter. What you suggest is putting a naked flame in a close proximity to a pyrotechnic composition. This is not safe. It does not matter how much inches of plate you got between the two. Let say that because of some silly breeze the flame escape from under the plate and touch the upper side of your pan? It does not matter how much unlikely it is, you don?t take the chance.

Electric or Enclosed flame (such device does exists), or hot oil are still safer by far, (although 100% safe does not really exists).

I understand some members consider naked flame on small quantities with good personal understanding of what you are doing represent small danger ? but they should not advise is to others who might not understand the level of procedural safety required.

[Matt]

Whoa ho ho ho I did not suggest it. Anyway notes taken.
Back to the melting......

-Matt

[pritch]

Some usefull information here thanks. I will be all kitted up this time next week so I might give the sugar rocket a blast