The U.S. Army is nearing completion on a project to eliminate its dependency on foreign countries for a critical energetic component in artillery and mortar ammunition, officials said. Because of changes in the global cotton industry, the United States no longer has a domestic source of quality raw material for manufacturing nitrocellulose for combustible cartridge cases that are used extensively by the military. A domestic source is necessary to ensure a sufficient supply of quality cartridge cases, which is vital to maintaining readiness of the armed forces, according to Army experts.
Kristy Klein, project officer, Office of the Project Manager for Combat Ammunition Systems, and her colleagues immediately began to investigate possible technology solutions to meet the military's operational needs. "The American cotton industry has changed from producing raw material that is a loose fiber to a pressed stock material," Klein said. "The processes downstream in our manufacturing facilities are not capable of handling the physical change. The pressed stock material could not meet the Army's needs for combustible case materials."
Since foreign companies are the only source of nitrocellulose from baled cotton linters, the Army needed a solution that will allow the use of domestically produced nitrocellulose from pressed stock, which is readily available from domestic sources.
"The problem in the manufacturing of the combustible cases using pressed stock nitrocellulose is that cutting or shredding the material using the existing process results in tight clumps of cotton fibers," Klein said. "Several attempts at breaking up these clumps were unsuccessful. In fact, a study by a leading pressed stock producer showed that cutting actually welded the fibers together."
Klein explained that these clumps inhibit achieving a homogeneous composition of the slurry used to manufacture combustible cases, thus causing variations in energetic composition throughout the product. This non-homogeneity caused by the clumps of pressed stock within the combustible case results in burning residue in the gun chamber after firing. This burning residue could ignite the next round being inserted into the chamber.
Another major concern is the poor performance in terms of muzzle velocity variation, she said. Production data have shown the muzzle velocity variance to be four times greater when using nitrocellulose with clumps.
To establish a manufacturing process using domestic pressed sheet and alleviate these performance and safety issues, the Army turned to the Office of the Secretary of Defense Comparative Technology Office's Foreign Comparative Testing, or FCT, program, in 2010. FCT's mission is to find and evaluate "here and now" solutions to meet operational needs, regardless of the origin of that technology. The U.S. Army Research, Development and Engineering Command, known as RDECOM, manages the FCT for the Army.
"FCT provides foreign companies with the 'on ramp' to Army acquisition," said William "Randy" Everett, FCT project officer at RDECOM headquarters. "When a foreign company has a mature technology or product the U.S. Army has a requirement for, FCT allows program managers to leverage [Office of the Secretary of Defense] funds for test and evaluation."
The Army leveraged FCT funds to review foreign nitrocellulose manufacturers' processes that utilize pressed stock. Klein's team evaluated technologies from companies in France and the Czech Republic.
"How are they breaking down the pressed stock? That is, taking something like pressed cardboard and fluff it again into loose fibers? What processes are they using, and what can we do to bring it to the U.S.? We tested their processed material through the FCT program, and we specifically used a domestic source for the pressed stock," Klein said. "Their nitrocellulose worked in our combustible cases, eliminating the safety and performance issues."
The key to the process was a hammer mill machine, which fluffed the pressed stock without major damage to the fibers. The tests of these technologies were successful, and the Army has subsequently purchased a hammer mill machine that will enable this manufacturing process for nitrocellulose to be transitioned to the United States. Two Program Executive Office Ammunition offices, PM-CAS and Project Manager for Maneuver Ammunition Systems, are working closely with BAE Systems, the operating contractor of the Radford Army Ammunition Plant, to install, prove-out and commission the hammer mill.