The invention is directed to providing a delay mechanism for an explosive projectile. In particular, the invention is directed to providing an inertial delay fuse for use in explosive projectiles.
In many explosive projectile applications, such as projectile based drilling or excavation, the detonation of an explosive payload carried by the projectile preferably occurs after the projectile strikes and penetrates the target. The delay in detonating the explosive payload allows the projectile to penetrate into the target a prescribed distance before detonation, thereby allowing a greater amount of material to be excavated as opposed to having the projectile detonate upon impact. Due to the velocity of the fired projectile, the delay in detonation must be short (on the order of tens or hundreds of microseconds) to allow for the delivery of the explosive payload at an appropriate depth within the target.
Conventional chemical delay elements are not precise enough to be utilized for explosive projectile drilling applications. Chemical delay elements generally provide delays on the order of milliseconds with variances on the order of hundreds of microseconds as opposed to tens of microseconds. In addition, very sensitive primary explosives are required when chemical delay elements are used. The use of such sensitive primary explosives for chemical makes the handling and firing of projectiles fitted with chemical delays inherently dangerous.
Electronic delays can also be utilized in projectiles. Electronic delay elements can be very precise and flexible, however, they also require complex and fragile circuitry that is relatively expensive. In addition, electronic delays require that an energy storage device be incorporated into each projectile. Available energy storage devices are relatively bulky and heavy and are not particularly well suited for use in the relatively small projectiles used for excavation. In addition, energy sources may degrade over time causing problems in the reliability of projectiles that have been stored for long periods
In view of the above, it would be desirable to provide a delay mechanism that can be readily incorporated into an explosive projectile without requiring very sensitive primary explosives of conventional chemical delay devices or the circuitry of conventional electronic delay devices. Accordingly, such a delay mechanism would be less expensive to manufacture, safer to handle and more reliable.