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one or more of the other materials in the mixture to flame, friction and static electrical discharges from the cause detonation. Some pyrotechnic compositions human body.

(mixtures) may become more sensitive because of exposure to moisture. Mixtures are sensitive to heat,

Section IV. HIGH EXPLOSIVES

2-15. General

High explosives are usually nitration products of such organic substances as toluene, phenol, pentaerythritol, amines, glycerin, and starch. Otherwise, high explosives may be nitrogen-containing inorganic substances or mixtures. A high explosive may be a pure compound or an intimate mixture of several compounds with additives, such as powdered metals (aluminum), plasticizing oils, waxes, etc., which impart desired stability and performance characteristics. A high explosive is characterized by the extreme rapidity with which its decomposition occurs. This is known as detonation. When initiated by a blow or shock, high explosives will decompose almost instantaneously, either in a manner similar to extremely rapid combustion or with rupture and rearrangement of the molecules themselves. In either case, gaseous and solid products of reaction are produced. The disruptive effect of the reaction makes some explosives valuable as a bursting charge but precludes their use as a propellant. This is due to the fact that the gases formed would develop excessive pressures that might burst the barrel of the weapon.

a. Terms and Definitions.

(1) Primer. A primer is a relatively small and sensitive initial explosive train component which, on being actuated, initiates functioning of the explosive train. The primer itself will not reliably initiate highexplosive charges. In general, primers are classified by method of initiation, such as percussion, stab, electric, friction, chemical, etc.

(2) Detonator. A detonator is an explosive train component that can be activated by a nonexplosive impulse or action of a primer. A detonator is capable of reliably initiating secondary high explosive charges. When activated by a nonexplosive impulse, a detonator includes the function of a primer. In general, detonators are classified, according to the method of initiation, as percussion, stab, electric, friction, flash, chemical, etc.

(3) Igniter. An igniter is definable as follows:

(a) A device containing a composition, usually in the form of black powder, which burns readily. Such an igniter is used to amplify initiation of a primer in functioning of a fuze.

(b) A device containing a spontaneously combustible material, such as white phosphorus, used to ignite fillings of incendiary bombs and flamethrower fuels at the time of dispersion or rupture of the bomb casing.

(c) A device used to initiate burning of the fuel mixture in a rocket combustion chamber.

(4) Delay. A delay is an explosive train component that introduces a controlled time delay in functioning of the train.

(5) Relay. A relay is an element of a fuze explosive train that augments an otherwise inadequate output of a prior explosive component. Thus, a relay reliably initiates a succeeding train component. Relays, in general, contain a small single explosive charge, such as lead azide, and are not usually employed to initiate high-explosive charges.

(6) Lead. A lead is an explosive train component that consists of a column of high explosive, usually small in diameter. A lead transmits detonation from one detonating component to a succeeding highexplosive component. It is generally used to transmit detonation from a detonator to a booster charge.

(7) Booster charge. A booster charge is the final high-explosive component of an explosive train that amplifies the detonation from the lead or detonator. Thus, a booster charge reliably detonates the main highexplosive charge of the munition.

(8) Fuze explosive train. A fuze explosive train is an arrangement of a series of combustible and explosive elements consisting of a primer, a detonator, a delay, a relay, a lead and a booster charge, one or more of which may be either omitted, or combined. The explosive train serves to accomplish controlled augmentation of a relatively small impulse into one of sufficient energy to cause the main charge of the munition to function.

(9) Primer compositions. A primer composition is an explosive that is sensitive to a blow, such as that imparted by a firing pin. A primer composition transmits shock or flame to another explosive, a time element or a detonator. Most mil itary priming compositions consist of mixtures of one or more initial detonating agents, oxidants, fuels, sensitizers and binding agents. Many compositions contain potassium chlorate, lead thiocyaate, calcium silicide, antimony sulfide, lead azide, lead styphnate, mercury fulminate and a binding agent. The potassium chlorate acts as an oxidizing agent; the lead thiocynate and calcium silicide act as the fuel, and as desensitizer to the chlorate; and the explosive acts as the detonating agent. Other materials, such as ground glass and carborundum, may be added to increase sensitivity to friction. Priming compositions for electic primers and squibs may contain barium nitrate as the oxidizing agent instead of potassium chlorate, and lead styphnate or DDNP (diazodinitrophenol) as the initiating explosive. Primer mixtures are used in percussion elements of artillery primers, in fuzes and in small-arms primers, and as the upper layer of a detonator assembly.

(10) Bursting charge. This is an encased explosive designed to break the metal casing into small fragments.

b. High-Explosive Train. An explosive train is a means by which a small amount of energy is built up sufficiently to assure a high-order detonation for a bursting charge. Fundamentally, an explosive train consists of a detonator, booster and bursting charge. This sequence is often interrupted by a delay or relay. The example of a 2,000-pound bomb filled with TNT, with a fuze of the firing pin type, illustrates the principle of the explosive train. The TNT by itself will not detonate from release of the firing pin. This is so because the initial source of energy, a friction or percussion effect of the firing pin, is insufficient and must be stepped up to where it will detonate the TNT. This is always accomplished by means of an explosive train, as follows:

(1) When initiated by stab action of a firing pin or by a flame, the detonator sets up a high-explosive wave. This wave is so small and weak that it will not initiate a high-order detonation in the bursting charge unless a booster is placed between the two. The booster picks up the small explosive wave from the detonator and amplifies it. The bursting charge is thus initiated and a high-order detonation results (fig. 2-6 and 2-7).

(2) To gain control of the time and place at which an explosive will function, it is necessary to

detonator

bursting charge detonator booster detonator booster

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detonating wave amplified by use of booster Figure 2-7. Detonating wave amplified by use of a booster.

Incorporate other components in a high-explosive train. The action desired may be a burst in the air, a burst instantly upon impact with the target, or a burst shortly after the projectile has penetrated the target. The components to give these various actions may be a primer, a black powder delay pellet or train, an upper detonator or any combination of these components. Arrangement of the components does not change the basic chain. Other components are simply placed in front of the basic chain (fig. 28).

(3) Placing a primer and a black powder time train in front of the basic chain causes a projectile to burst in air. When the projectile leaves the weapon (or the bomb is dropped), the primer ignites the time-train rings. After the time-train rings burn the requisite time, the primer initiates action of the detonator, booster and bursting charge (schemes A and C, fig. 2-8).

(4) To burst the projectile promptly upon impact with the target, a superquick or instantaneous action is necessary. This action is usually obtained by placing an upper detonator in the extreme front of the fuse, and lower detonator in the body near the booster charge. The detonating wave is thus transmitted instantly to the bursting charge (scheme D, fig. 2-8).

(5) To permit the projectile to penetrate the target, a delay action is necessary. This is obtained by placing a primer and delay element ahead of the detonator. In some cases, this combination of primer and delay is inserted between an upper and lower detonator (scheme E, fig. 2-8).

(6) A variation of the high-explosive train is found in chemical projectiles In this train, there s no large bursting charge " in high-explosive project It is only necessary to rupture the projectile and allow the chemical contents to escape. Actual bursting of the projectile is accomplished by an enlarged booster, known as a burster charge, contained in a tube running through the center of the projectile.

2-16. Classification

High explosives are classified according to their sensitivity as initiating, booster and bursting explosives a. Initiating. Initiating high explosives are extremely sensitive to shock, friction and heat. Under normal conditions, they will not burn, but will detonate if ignited. Their strength and brisance are inferior, but are sufficient to detonate high explosives Because of their sensitivity, they are used in munitions for Initiating and intensifying high-order explosions. Mercury fulminate, lead azide, lead styphnate and diazodinitrophenol are examples of such explosives.

b. Booster. Explosives of this type include tetryl, PETN and RDX. They have intermediate sensitivity between initiating explosives and explosives used as bursting charges. Booster explosives may be ignited by heat, friction or impact and may detonate when burned in large quantities.

c. Bursting. Bursting explosives include explosive D, amatol, TNT, tetryl, pentolite, picratol, tritonal, composition B, DBX, HBX and others.

2-17. Demolition and Fragmentation Explosives a. Tetryl.

(1) Characteristics. Tetryl 2, 4, 6 -trinitrophenylmethylnitramine is a fine yellow crystalline material. When heated, it melts, decomposes and then explodes. It burns rapidly, is more easily detonated than TNT or ammonium picrate (explosive D) and is much more sensitive than picric acid. It is detonated by friction, shock or spark. It is insoluble in water, practically nonhygroscopic. Tetryl is stable at all temperatures that may be encountered in storage. It is toxic when taken internally; on contact, it discolors skin tissue (resembles tobacco stain) and causes dermatitis.

(2) Detonations. Brisance tests show tetryl to have a very high shattering power. Tetryl is greater in brisance than TNT and is exceeded in standard military explosives only by PETN and RDX.

(a) Charges. Tetryl is the standard booster explosive and is sufficiently insensitive when compressed to be used safely as a booster explosive. Violence of its detonation assures a high-order detonation of the bursting charge. Tetryl is used in the form of pressed pellets. It is the standard bursting charge for small-caliber (20-mm and 87mm) projectiles. It produces appreciably better fragmentation of these projectiles than TNT. It is also more readily detonated, and yet, in small-caliber cartridges, withstands the force of setback in the weapon. It is also a constituent of tetrytoL

(b) Detonator. When it is used in detonators, tetryl is pressed into the bottom of the detonator shell and covered with a small priming charge of mercury fulminate, lead azide or other initiator.

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