Chapter Explosive And Chemical Agents

Section I. SOLID PROPELLANTS

2-1. General

Solid propellants are low explosives used to propel projectiles, rockets, etc. Nitrocellulose, though unstable, is a general ingredient of propellants. Stabilizers are added to counteract acid breakdown products of nitrocellulose. Propellant compositions, generally referred to as smokeless powders (a misnomer), burn at characteristic, linear rates affected by initial temperatures and pressures. Propellants are identified by M or T numbers. See TM 9-1300-214 for specific coverage on United States propellants.

2-2. Classification a. From the viewpoint of composition, modern propellants are classified as follows:

(1) Single base. These compositions contain nitrocellulose as their chief ingredient. In addition to a stabilizer, they may contain inorganic nitrates, nitrocompounds and such nonexplosive materials as metallic salts, metals, carbohydrates, and dyes.

(2) Double base. A double-base composition contains nitrocellulose and a liquid organic nitrate, such as nitroglycerine, capable of gelatinizing nitrocellulose. Like single-base powders, double-base powders frequently contain additives in addition to a stabilizer.

(3) Composite. Composite propellants contain neither nitrocellulose nor an organic nitrate. Generally, they consist of a physical mixture of an organic fuel (such as ammonium picrate), an inorganic oxidizing agent (such as potassium nitrate) and an organic binding agent. A composite propellant has a heterogeneous physical structure.

b. Use of propellant compositions is not in accordance with the foregoing classification. While single-base compositions are used in cannon, small arms and grenades, double-base compositions are used in cannon, small arms, mortars, rockets and jet propulsion units. Composite compositions are used in rocket assemblies and jet propulsion units. Choice of propellant for a specific use is determined by ballistic and physical requirements, rather than on the basis of composition. As a given composition may be suitable for use in several different applications, it is not practicable to classify propellants on the basis of use.

2-3. Characteristics a. Form. Propellant grains take the form of strips, flakes, balls, sheets or cords; single-perforated or multiperforated cylinders; and rosette cylinders (fig. 21). Grains vary in size and form with the weapons. In rockets, for example, grains are considerably larger than those used for artillery. Figure 2-2 shows the relative size of grains used in some artillery propellants. Small grains require no perforation or a single perforation. Larger gains require more equally spaced perforations, usually seven, to provide a greater burning surface. The United States Army and Navy have favored the multiperforated grain form for use in weapons.

b. Burning.

(1) General. Unconfined, nitrocellulose propellant burns relatively slowly and smoothly but, when confined, its rate of burning increases with temperature and pressure. In order not to exceed the permissible chamber pressure of the weapon in which it is to be used, the rate of burning is proportional to the propellant free to burn (fig. 2-3). Therefore, propellants are made into accurate sizes and definite shapes.

(2) Degressive burning. As strips and cords burn, the burning surface decreases continuously until the grain is consumed. Such burning is characterized as degressive.

(3) Neutral burning. A single-perforated grain burns in opposite directions. By controlling the initial diameter of the perforation, the total burning surface hardly changes during burning. Such burning is characterized as neutral.

Degressive Grains

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SINGLE PERFORATED-IGNITER 6ND SÈQTO

Figure 2-1. Shapes and forms of propellant grains.

MULTI PERFORATED (SPECIAL)

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SINGLE PERFORATED-IGNITER 6ND SÈQTO

Figure 2-1. Shapes and forms of propellant grains.

MULTI PERFORATED (SPECIAL)

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