Elements of Explosive Trains

Ohart (Ref 17, p 20) gives a diagram of elements of explosive trains, both of low-and high-explosive, which are reproduced here as Fig l-21a 

In Fig l-21b is shown a complete explosive train (comprising both low- and high-explosive trains) in fixed round of artillery ammunition 

In order to understand clearer the function of elements in HE trains of fuzes, a description and sectional views of US Naval Base Fuze Mk21 are given. This information is derived from the comprehensive Ordnance Explosive Train Designers Handbook , 

FIRING PIN PRIMER UPPER DETONATOR DELAY ELEMENT 

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This starts the action of other elements of explosive train which consists of a Tetryl "lead", a relay detonator, and a booster charge. The stab detonator consists of a cup, which is made of A1 or A1 base alloys if LA is one of the expl ingredients, whereas Cu or Cu base alloys are used for detonators contg MF. The cup might have any one of several designs of its sensitive end closures, such as two disk-closed ends one disk-closed end one coined end one coined end one open end and one disk-closed end one open end... 

China Lake, Calif (1952), pp 2-23 to 2-32 (Characteristics of Explosive Train Materials) 3-1 to 3-53 (Characteristics of Primers) 4-1 to 4-22 (Characteristics of Detonators) 5-1 to 5-61 (Characteristics of Delays and Delay Elements) 6-1 to 6-11 (Characteristics of Leads) 7-1 to 7-25 (Characteristics of Boosters) 8-1 to 8-37 (Interaction of Explosive Train Materials) ... 

Cups, Percussion or Primer and Cops. They are small metallic cups (or caps) contg primer compositions which are covered with ap er disc, and a metallic anvil" (See Vol 1, p A473-L). These cups are part of "explosive trains". On firing a weapon, the base of the cup is struck by the firing pin of the percussion lock. This action ign ites by impact the primer mixt in the ci ) producing a flash, which in turn ignites either the proplnt (if the cup is part of a primer used in a propellant train), or the primer mixt of a detonator or delay element (if the cup is part of a primer used in an artillery ammunition train)... 

The need for data on the parameters is neither unique to the application of azides and solid explosives nor to the design of explosive-train elements, and numerous references to measurement techniques and relevant data are to be found throughout these two volumes and in standard handbooks [ 1 ]. However, the data on functional parameters, particularly within the constraints of element designs, represent a unique requirement, particularly because of the hazardous nature of the materials, the rapidity of the reactions involved, and the small quantities and dimensions available for measurement probes. In Section D of this chapter some recent techniques of measurement or observation are presented to illustrate current trends. One of the important parameters affecting the initiation and growth of reaction in the explosives is their vulnerability to shocks. Some recent techniques for quantifying these parameters are given in Section E below. 

Detonators are used to detonate high explosives. Stab detonators are initiated by sharp firing pins and are used in explosive trains of different types of fuses. Flash detonators are initiated by flames produced by safety fuses, primers, or delay elements. A special type of flash detonator ignited by the flame of a safety fuse is called a blasting cap. Detonators are primarily composed of three types of explosives including sinoxid mixtures, lead azide-based mixtures, and mercury fulminate-based mixtures. 

Detonation (and Explosion) by Priming and Boostering. These are means of building up a detonation from an initiating shock (Ref 2, p 294). The detonator, the first element in an explosive train or "explosive chain , may have three parts. 

Relay. A component of a high-explosive train that provides the required energy to reliably initiate the next element in the train. Specifically applied to small charges that are initiated by a delay element and, in turn cause the functioning of a detonator (Ref 40a, p 120)(See slso in this Volume, Section 4, Part F (Compare with Lead)... 

Since in the anvil-type of primer the cup is not pierced, obturation (sealing) is obtd after the primer is fired, because the entire cup is pressed into cartridge cavity. Such primers are also known as obturated type, to distinguish them from the unobturated type, which is usually employed as an "explosive-train element" in fuzes. This type and some obturated types employed in fuzes are described in Ref 4, Part F... 

Accdg to definition given in Ref 23, p 3-22 (slightly reworded) It is an initiating explosive - train component fired by an electrical impulse supplied by the energy either stored within the fuze before release of the missile, or generated within the fuze system just prior to or at impact of the fuze. An electric primer serves to initiate the next component of the train which can be either a detonator or delay element... 

Definition of a relay as given by Odierno of PicArsn (Ref 45d, p I) is An element of a fuze explosive train which augments an outside and otherwise inadequate output of a prior explosive component so as to reliably initiate succeeding train component. Relays, in general, contain a small single charge such... 

Delays may be incorporated into an explosive train in the form of a unit called delay element or delay element assembly. 

Fuze Body. The part of a fuze which houses the majority of the functioning parts, and to which small parts are attached. It also houses elements of an "ignition train "or of an "explosive train "(See Section 4, Part C, Item b)... 

Fuzes contain safety devices that tend to prevent functioning until after the fuze has been subjected to centrifugal and setback forces, after the round is fired. In the so-called bore-safe fuzes, the path of the explosive train is interrupted so that, while the projectile is still in the bore of the weapon, premature expln is prevented should any of the more sensitive fuze elements (such as primer and/or detonator) start to function. Interruption is usually achieved by inserting out-of-line components or interrupter blocks or slides. Although this leaves the fuze in an unarmed position, it would not be considered safe in handling or shipping, unless the fuze was not provided with safety devices such as safety wires or cotter pins. These outside devices must be removed prior to inserting the fuzed round of ammunition into gun barrel, but the fuze will still be unarmed because some of its inside parts are not free to move to their proper positions so that the fuze may operate in its intended manner... 

Nose Fuze AN-M103A1, shown in Fig 4-1, is cylindrical in shape, ca 2-inches in diameter and 7.23-in long (including the vane assembly). The fuze contains two explosive trains one for delay action, and another for instantaneous action. The "delay action train" consists of a primer, a delay element,... 

The fuze body assembly consists of metallic body which contains index lock pin, stop screw, index stop, striker assembly, rotor release assembly, delay lock pin, and rotor assembly. The explosive train consists of delay element M9, relay XM9 (2.31 grains of LA), detonator M35 (in rotor assembly) and a booster cup assembly. 

The arming vane may drive a gear train which, after a definite interval, removes safety blocks or aligns the detonator with the next element in the explosive train. Standard arming vanes have blade pitches of 30°, 60°or 90°, but there are also "special" vane assemblies with different blade pitches (Ref 51a, p 5-38)... 

Explosive Trains. An expl train is an assembly of elements arranged in order of decreasing sensitivity. The function of the train is to accomplish controlled augmentation of a small impulse into one of suitable energy to cause the main chge of the munition to function... 

All persons should be properly trained before they are assigned any explosive-related operation. Training for explosive-related work results in awareness and also helps in conducting the work safely. The essential elements of training are ... 

A pyrotechnic, mechanical, electronic, or explosive train component that introduces a controlled time delay in some element of the arming or functioning of a fuze mechanism. 

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