Delay composition, also called delay chargeordelay train, is a pyrotechnic composition, a sort of pyrotechnic initiator, a mixture of oxidizer and fuel that burns in a slow, constant rate that should not be significantly dependent on temperature and pressure. Delay compositions are used to introduce a delay into the firing train, e.g. to properly sequence firing of fireworks, to delay firing of ejection charges in e.g. model rockets, or to introduce a few seconds of time between triggering a hand grenade and its explosion. Typical delay times range between several milliseconds and several seconds.
A popular delay charge is a tube of pressed black powder. The mechanical assembly prevents the outright detonation of the charge.
While delay compositions are principally similar to other fuel-oxidizer compositions, larger grain sizes and less aggressively reacting chemicals are used. Many of the compositions generate little or no gas during burning. Typical materials used are:
The burn rates are dependent on: [1]
Examples of some compositions are: [2]
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