Historical Overview of Explosive Transfer Line Technology

®detonating cord, but determined that core loads of 30 grains per foot or less were unreliable for propagation when wet. The importance of this new detonating cord in the mining industry came about as quarries wanted to bottom initiate explosives loaded in holes without detonating the material along the length of the detonating cord. The initial thought process was to make Primacord ® with less explosive core load, and then overbraid textile on the cord to approximately 0.5 inch diameter to decouple the resultant shock output along the length of the cord. With the failure of developing a reliable low core load product, efforts were devoted to ‘developing a radically new type of detonating fuse of low explosive energy’. Ensign-Bickford pioneered the development and production of metal clad low energy detonating fuse, now commonly known as mild detonating fuse (MDF) in 1955. At that time, Ensign-Bickford enjoyed a preeminent position as the producer of textile braid detonating cord for commercial mining, blasting, and seismic exploration. To insure the market position was not jeopardized by technology advancement, EB embarked on an ambitious research and development effort to look at different design and manufacturing approaches to develop a low core load explosive transfer mechanism. The military markets were considered ancillary and aerospace applications were not considered. The initial candidates for consideration were the drawing of explosively filled tubes, extrusion of thermoplastic explosives, coating of strings or wires with adhesive pastes, and the filling and wrapping of foils. Futile attempts of coating a string with lead azide paste resulted in trying low core loads wrapped in metal foils, at the suggestion of DuPont’s Eastern Laboratory. While this worked with small samples, it was not successful when producing long lengths of detonating fuse. In July of 1955, Ensign-Bickford determined that by filling and reducing a lead tube loaded with PETN or RDX it was possible to manufacture detonating fuse under 2 grains per foot that had satisfactory initiation and propagation characteristics. With these positive results, EB decided to concentrate efforts on development of a metal clad low energy detonating fuse. EB understood that the best method of manufacture was to load explosive material into a larger diameter tube and then reduce the tube diameter, driving the linear core load of the material down. This was in-line with the method of manufacturing rosin core tin/lead solder. Three methods (drawing, swaging, and rolling) for reducing the loaded tubes were investigated as part of the development of MDF and are still used today in the manufacture of