The main components of double-base propellants are nitrocellulose and nitroglycerin, and their properties determine the performance of the double-base propellant. The outstanding advantages of double-base propellants are their uniform texture, uniform structure, and good reproducibility, meeting the needs of tactical rockets and missiles. Double-base propellants possess the general properties of solid propellants, meeting the general requirements for solid propellants, namely high energy (density generally between 1.54 and 1.65 g/cm³, actual specific impulse generally between 1666 and 2156 N·s/kg); good combustion performance (burning velocity generally between 5 and 40 mm/s (6.86 MPa), with a burning velocity-pressure index approaching zero); good mechanical properties; good internal ballistic performance; good processability; good stability; wide availability and low price of raw materials, resulting in good economic efficiency; and other special requirements, such as low smoke or no smoke, low detonation temperature, and low burning velocity.
Classification
Double-base propellants can be classified into different types based on variations in the addition of combustion catalysts, manufacturing processes, combustion performance, and the properties of solvents or additives.
Based on the addition of combustion catalysts: They can be classified into different grades: those with graphite added are called double-graphite propellants (SS); those with lead oxide added are called double-lead propellants (SQ); those with cobalt oxide added are called double-cobalt propellants (SG); and those with magnesium oxide added are called double-aryl magnesium propellants (SFM). These propellants are collectively referred to as ordinary double-base propellants.
Based on the molding process: They can be divided into two types: one is propellants manufactured by extrusion molding or stretching molding (using a screw-type stretching machine or a plunger-type stretching machine), called stretched double-base propellants; the other is propellants manufactured by casting molding, called cast double-base propellants.
According to combustion performance:
Propellants that achieve a burning rate pressure index of less than 0.2 and close to zero within an irregular pressure range, producing plateau combustion, are called dual-base plateau propellants. As engine operating time increases, the propellant burning rate decreases, and its pressure decreases within a certain range, resulting in smoldering combustion; these propellants are called smoldering dual-base propellants.
According to combustion speed:
Propellants with a combustion speed of 25 mm/s or higher under normal temperature and 6.68 MPa pressure conditions are called high-burning-speed propellants; propellants with a combustion speed of less than 5 mm/s under normal temperature and 6.68 MPa conditions are called low-burning-speed propellants.
According to the presence or absence of volatile solvents: Propellants with volatile solvents such as acetone are called Kodak-type dual-base propellants or dual-base propellants containing volatile solvents; those without volatile solvents are called Balestier dual-base propellants or solvent-free pressure-stretching dual-base propellants. Propellants with Gina added to the two components are called Gina dual-base propellants, such as my country's 171 propellant.
