17 replies to this topic

[Robbie414]

The epoxy propellant is probrably the easiest prop to make, as per Mr Nakka's instructions. You do need the iron oxide though!

Leni if you have your component compounds ground finely it is an excellent prop, however there is a fairly large difference in the thrust depending on the epoxy brand that you use! These prop's also rely on a fairly high pressure being developed in the motor, this may be why your rockets did not develop full thrust and as for lighting you should be making up some BP paste to be applied to a ignition disc, and painted around the base of the grain. Another way to ignite the grain, although not practical for fireworks is a top ignitor. Basically you make a mini fountain that sticks in the top of the core of the grain in the motor housing....instant complete ignition!

What makes epoxy grains so safe is the fact that they cast with practically no internal faults so explosions caused by cracks in the grain are rare. Plus it is cold cast.

Casting the sugar propellants is also pretty safe as long as you avoid flames at all cost. As Richard Nakka shows in his 'effect of overheating SU/KN' experiment it is practically impossible to actually get this stuff to ignite without flame, it goes black and charred and cracks up well before ignition.....you would have to be pretty stupid to allow it to do that! Besides if the sugar so much as turns golden you have the temp too high and lose performance. When you get it right boy these things fly....and for a couple of pence a shot they have to be one of the cheapest ways of getting your display in the air?

[Stuart]

A little note on melting sugar and KNO3 together, I read somewhere that heating normal cooking oil up to a high temp and then putting the container of KNO3 and sugar would melt and its quite safe. Cant remember where I read it though.

[Robbie414]

Thats right, as I put in an earlier post you can use an old deep fat fryer and a container that will withstand the temperature (ie not plastic) to melt the sugar/KNO3 mix. The sugar will melt at around 193 degrees celcius. You should try and get hold of a high temp thermometer to check that the thermostat on your fryer is working properly! The KNO3 has a much higher melting point so it will not melt, which is why it must be as fine as possible to get a well mixed slurry!

The longer you keep the propellent mix at high temperature the less powerful it will become so try and do the whole operation fairly quickly. If the sugar starts to turn golden your heat is to high and all you will get is fairly flammable toffee! You only want it to melt, nothing else! I use a cast iron pot which helps keep the slurry warm whilst casting.

Have fun, like I say READ ALL OF Richard Nakka's pages on casting etc...consider this the bible!