Calcium Stearate Arms Amunation

A— UNBURNED GRAIN

Multiperforated Propellant

B —BURNING GRAIN

A— UNBURNED GRAIN

B —BURNING GRAIN

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Figure 2-4. Progressive burning of propellant grains (multiperforated).

(4) Progressive burning. A triperforated grain can be so designed that the burning surface actually increases until burning is nearly completed and slivers are formed. Such a grain is said to burn progressively. This characteristic can be made more pronounced if the grain is multiperforated (fig. 2-4). When a multiperforated grain is not completely consumed, portions of the grain remain in the form of slivers. These may be ejected as such from the weapon. The rosette or Walsh grain, with a scalloped periphery, reduces the amount of slivers produced by a multiperforated grain.

2-4. Single-Base Propellants a. Pyrocellulose Powder. The first nitrocellulose propellant standardized by the U.S. Army and Navy was termed pyrocellulose powder. As first manufactured, pyrocellulose powder consisted only of carefully purified nitrocellulose gelatinized in a mixture of ether and ethanol and extruded in the form of a cord with one or more perforations.

b. E.C. Powder. This partially colloided propellant was one of the earliest nitrocellulose compositions developed. Because it contains some ungelatinized nitrocellulose, E.C. powder is distinctly more sensitive to friction than completely colloided powders. Data indicate that the composition is sufficiently sensitive and powerful to be used as a high explosive as well as a propellant. For this reason, the powder has been used in hand grenades as well as in blank ammunition.

c. Flashless and Smokeless Compositions. The class of propellants known as flashless and smokeless (formerly designated as FNH and NH) comprises compositions used chiefly in artillery. Whether a composition is flashless depends upon the gun in which it is used. For example, the M1 composition is flashless when used in a 75-mm gun, but not in the 8-inch gun.

d. Small-Arms Powders. Both single-base and double-base propellants now are used in small arms. The earlier type of single-base powder for this purpose was known as IMR.

2-5. Double-Base Propellants a. Prior to World War II, double-base propellants were used in the United States for mortar and small-arms ammunition but not in cannon. Since then, double-base compositions have been standardized for use in the smaller guns. Requirements for rocket propellants have resulted in standardization of a number of such compositions.

b. Standard double-base cannon powders are used in the form of perforated grains. Although these propellants have considerably greater ballistic potential than the single-base compositions, they are less stable.

c. Double-base mortar powders include those used for propellant charges and those used in the ignition cartridges, both being in the form of flakes. In general, high nitroglycerine content gives double-base mortar propellant compositions very high ballistic potential values. These compositions, however, are the least stable of the standard propellants. This is due, in part, to the small grain size. Powders having large specific surfaces have been found to give lower test values than those in large grains.

d. Double-base propellants for small arms have been used for many years. At one time, these were of the ballistite type, in flake, disk, and grain forms. However, these compositions have been replaced by double-base compositions containing less nitroglycerine. The single-perforated grains having these compositions are coated with dinitrotoluene or centralite and glazed with graphite. Although they have some that less ballistic potential than the ballistite type of powders, they are more stable, cause less erosion of rifles, and have less tendency to flash.

e. Standardization of the caliber .30 carbine permitted use of a double-base composition in the form of spheres 0.02 or 0.03 inch in diameter, instead of flakes or grains (fig. 25). Commonly called ball powder, this composition is produced by dissolving wet nitrocellulose in a solvent (e.g., ethyl acetate), adding diphenylamine and chalk, and then nitroglycerine. Upon agitation and addition of a protective colloid, the solution is dispersed in the form of small globules. When the volatile solvent is removed by heating, the powder solidifies in the form of spherical pellets. A wide variety of single-base or double-base compositions may be produced by this process.

f. Essentially all propellants for rockets are of the double-base or composite type, as are those for rocket motors. Rocket propellants are manufactured in much larger grains than the largest cannon powder grains, and rocket motor grains are manufactured in very large sizes. The smallest rocket powder is 0.37 inch in diameter and 4.15 inches long. Rocket motor grains may exceed 12 inches in diameter and 6 feet in length. The smaller grains of rocket powder are manufactured by the solvent process. The larger grains are produced by rolling sheeted powder into a carpet roll, which is then extruded.

(1) Solid propellants for rockets are primarily of two types. The more common type is a double-base composition consisting principally of

(1) Solid propellants for rockets are primarily of two types. The more common type is a double-base composition consisting principally of

Figure 2-5. Ball powder, X25.

a colloided mixture of nitrocellulose and nitroglycerine. The other type consists of a mixture of an organic fuel, an inorganic oxidizing agent and a binding agent. In either case, the mode of burning and the limitations under which the compositions are used are the same.

(2) Most rocket motors accommodate maximum pressures developed by the propellants of the order of 3,500 psi. When the propellant charge is ignited, pressure within the rocket chamber generally increases within 0.0005 to 0.05 second. Maximum value of this pressure is determined by burning rate of the propellant and diameter of the nozzle orifice. Thereafter, the charge burns at a nearly constant rate. Steady-state pressure is maintained constant or decreases very slowly until the propellant is completely consumed.

2-6. Composite Propellants a. Difficulty In manufacturing double-base rocket and rocket motor propellants in large grains coupled with undesirable ballistic effects with change in initial temperature have led to the development of composite propellant. Containing no nitrocellulose or

Section II. LIQUID PROPELLANTS 2-7. General

Liquid propellants, which can be better controlled in combustion than solid propellants, have been developed for large rockets, missiles and projectiles. Such propellent compounds are either composite (fuel and oxidizer combined) or independent (fuel and oxidizer in separate containers). The propellant reacts rapidly to produce gaseous products which can propel the rockets at supersonic velocities

2-8. Classification

Liquid propellants are classified by the type of reaction system, as follows:

a. Monopropellant. This system consists of fuel and oxidizer stored in one tank, and delivered by a pump or pressurized tank for eventual reaction in the chamber of a rocket. To initiate, a separate source of ignition is required.

b. Bipropellants. These systems consist of an organic fuel and an oxidizer, in separate containers, for dual feed, carburetion and combustion within the reaction chamber. Reaction may be initiated by contact nitroglycerine, composite propellant is a mixture of an organic fuel, an inorganic oxidizing agent and an organic binding agent.

b. A representative composite propellant is the T9 composition, which consists of the following:

Ammonium picrate 40.7

Potassium nitrate 40.8

Ethyl cellulose 4.6

Chlorinated wax 4.6

Calcium stearate 0.5

Such a composition can be manufactured by a simple mixing operation and can be molded in the desired form by pressing. While it has a desirably low temperature sensitivity, with respect to the burning rate, the composition tends to become brittle and crack when subjected to low temperatures. It therefore cannot be used safely at temperatures below -12° C. (10° F.). A further disadvantage is the relatively large amount of white smoke produced when the propellant is burned.

of the fuel with the oxidizer (hydrazine with nitric acid, for example) or by such external influences as electrical spark ignition or catalysts.

2-9. Characteristics

Burning rate and specific impulse of solid propellant are controlled by propellant composition and grain design In liquid propellant rockets, however, the fuel/oxidizer mix can be adjusted in flight to regulate the burning rate and specific impulse. Like some chemical agents and explosives, liquid propellants are hazardous, toxic, flammable, sensitive and inherently dangerous.

2-10. Materials

Listed below are the most common combustible and flammable materials used as fuels and oxidizers with liquid propellants:

a. FueI-alcohols (ethyl, methyl, furfural); hydrocarbons (kerosene, aviation gasoline, octane, heptane, pentane); aniline, monoethylaniline, hydrazine, diborane, pentaborane, liquid hydrogen and anhydrous ammonia.

b. Ozidizer-white fuming and red fuming, nitric acids (WFNA and RFNA); oxygen, hydrogen peroxide, chlorine trifluoride and dinitrogen tetroxide.

Change 4 2-5

Section III. LOW EXPLOSIVES

2-11. General

Rates of transformation of explosives have been found to vary greatly. One group, which includes smokeless and black powders, undergoes combustion at rates that vary from a few centimeters per minute to approximately 400 meter per second. These are known as low explosives. Some high explosives (e.g., nitrocellulose) can, by physical conditioning, be rendered capable of functioning as a low explosive when ignited.

a. Definition. An explosive is a material that can undergo very rapid self-propagating decomposition, with formation of more stable materials, liberation of heat, and development of a sudden pressure effect. An explosive may be solid, liquid or gaseous. It may be a chemical compound, a mixture of compounds, or a mixture of one or more compounds and one or more elements. Military explosives are chiefly solids or mixtures formulated to be solid at normal temperatures.

b. Deflagration. If a particle of an explosive reaches a temperature at which the rate of decomposition becomes significant, deflagration or spattering of the particles from the surface occur prior to decomposition. At a characteristic temperature, heat output is sufficient for the reaction to proceed and be accelerated without input of heat from another source. At this temperature, called the ignition temperature, deflagration, a surface phenomenon, begins. Gaseous reaction products flow away from the unreacted material below the surface. Deflagration of all the particles in a mass of finely divided explosive occur almost simultaneously. In a confined space, pressure increases, which, in turn has the effect of increasing the rate of reaction and temperature. The final effect of deflagration under confinement is explosion, which may be violent deflagration or even detonation. In the case of low explosives, such as loose black powder and pyrotechnic compositions, only violent deflagration can take place. Nitrocellulose propellants can burn, or if confinement is sufficient, deflagrate so rapidly as to detonate.

c. Characteristic. To qualify for military use, a low explosive (propellant) must evidence the following:

(1) A controlled burning rate.

(2) Capability for instant ignition and combustion.

(3) Stability over extended periods of storage under normal conditions.

(4) Balance for complete combustion, producing a minimum amount of residue and weapon-bore erosion.

(5) Minimal toxic and explosive hazard.

(6) Capability of withstanding mechanical shock incident to loading, transportation and handling by commercial and military carriers.

d. Low-Explosive Train. An explosive train consists of combustibles and explosives arranged according to decreasing sensitivity. This arrangement serves to transform a small impulse into one sufficiently large to function a main charge. A fuze explosive train, for example, may consist of primer, detonator, delay, relay, lead and booster charge, one or more of which may be omitted or combined. Addition of a bursting charge renders such a train a bursting charge explosive train (fig. 2-6). A propelling charge explosive train (fig. 2-6), on the other hand, may consist of primer, igniter (or igniting charge-usually black powder) and some type of propellant.

(1) Small-arms ammunition (cartridges) explosive trains have percussion primers, relatively small propelling charges and no igniter. Initially, the firing pin explodes the primer. The flame then passes through the vent leading to the powder chamber and ignites the propelling charge. Expansion of the resultant gases ejects the bullet.

(2) In artillery ammunition, the low explosive train includes an auxiliary charge of black powder, called the primer charge or igniter charge. The auxiliary charge between the primer and the propelling charge is necessary to intensify the small flame produced by the primer composition sufficiently to initiate combustion of the large quantity of propellant. As in fixed ammunition, the primer or igniter charge may be contained in the body of the primer. This makes one assembly of the percussion element of the primer and the primer charge. Otherwise, the primer or igniter charge may be divided between the primer body and the igniter pad attached to separate-loading propelling charges.

(3) In jet propulsion weapons (rockets and rocket motors), the low-explosive train consists of propelling charge (single-perforated or multiperforated grain of double-base or composite propellant), igniter (usually a black powder mixture) and initiator (electric squib or squibs).

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