How do fireworks explode at intevals?

[Paul87]

How do fireworks explode at different times,

For example we had a few rockets fireworks at new years and Im wondering how the rocket fires up dips out then explodes a couple seconds later.

Also them fireworks that explode then little bits explode after how do they explode with out exploding the little bits inside?

Thanks

[Buenchico]

Take a look at these sites:

http://www.pyrouniverse.com/manufacture.htm (Plenty of detail about the physical construction of fireworks).

http://science.howstuffworks.com/fireworks1.htm (Good for information about the chemicals used).

http://www.nationalgeographic.com/ngkids/0007/fireworks/ (Designed for kids but still informative).

Hoping this helps,

Chris

[Mortartube]

The rockets appear to burn out for a small interval before exploding, as they have a delay composition in the top. The rocket motor is a tube containing gumpowder that is restricted by a nozzle at the bottom end (this is called the choke). This restriction helps to keep up gas pressure in the tube. Once the propellant is burnt out, the rocket still has forward motion which drops off rapidly. The ideal time for a rocket to burst is just as it begins to turn over before heading downwards under the force of gravity. This enables the stars to burst in a regular pattern and not be affected by momentum.

The little bits that explode either in bangs or smaller starbursts, are cardboard tubes containing the stars and/or composition, plugged at one end (usually by cork or clay). The other end has a delay fuse glued in it (often visco fuse which is a gunpowder fuse contained in wrapped textile yarns. Visco fuse burns at a reliable regular rate e.g 1 inch a second, so to get a half second delay, use half an inch etc). This visco fuse is primed at each end with a slurry of gunpowder often made with gum arabic solution.Once dry, this prime ensures ignition. These little units are then put into the heading of a rocket for example. Once the rocket has gone into the air, the small delay at the top burns and this in turn ignites gunpowder or flashpowder which explodes. This explosion blows all of the little inserts outwards into the air. At the same time, the flash from the blowing charge ignites the gunpowder prime on the units and sets the visco delay fuse burning. Once the visco has burnt inside of the units, there is another blowing charge that will blow stars in the little units outwards, or a flashpowder charge that will make a bang from each unit. And all of that work is over in a very short time indeed. But good fun to make. I must point out that I worked in a firework factory and it's illegal to make them on unlicensed premises).