The Gimbal Cam Socket Story - development of tool for use in chemical-weapons disposal operations

CML Army Chemical Review, July, 2000 by William McLay, John Lambert

The end is in sight at the U.S. Army's Johnston Atoll Chemical Agent Disposal System (JACADS) where chemical-weapons disposal operations are in the final stages. The completion of disposal operations at JACADS will be a milestone event for the program manager for chemical demilitarization--the Army organization charged with the mission of destroying the nation's chemical-weapons stockpile. It is a milestone 10 years in the making and has significance not only for the team that has labored so long and hard to bring it about but for the country, as well as those who work to meet our international Chemical Weapons Convention Treaty obligations.

In May 1997, during the GB (sarin) nerve-agent campaign (the disposal of a specific agent and/or munition type), the Army faced a roadblock that threatened to delay the schedule at JACADS and cost the disposal program considerable time and money. The state-of-the-art machinery developed to disassemble the chemical weapons into separate parts for processing was rejecting 6 percent of a particular type of munition--155-mm projectiles--resulting in the need to process 6,402 munitions separately. Separate processing of munitions significantly increases both time and cost of disposal operations. With the prospect of facing the same challenge again during the final VX nerve-agent disposal campaign, the JACADS team, including Army and contractor personnel, resolved to find a permanent solution to the problem.

Identifying the Problem

The Army's chemical-weapons disposal facility on Johnston Island houses sophisticated equipment developed specifically for the purpose of processing a lethal chemical agent and munitions in all their various types and forms. The theory behind the process is simple: disassemble the munitions and distribute their parts and the chemical agent to appropriate high-temperature incinerators that decontaminate the metal and break down the composition of the agent. The sophistication of the equipment lies in its efficiency, adaptability and, especially, automation--it was designed to require as little human intervention as possible for safety purposes.

In the first step of the disposal process, where the munitions are introduced to the projectile mortar disassembly (PMD) machine, munitions are conveyed onto a round, slotted table that positions them into alignment with equipment engineered to unthread them. The unthreading equipment (at the center of a hydraulic chuck), grasps the nose of the munition (fuse adapter), exerts force, and spins to remove the fuse adapter, exposing the munitions' various parts for further disassembly. Once this operation is complete, the table rotates the munition around to the next operating station, which removes the miscellaneous parts from the munition body and places them on a conveyor to the deactivation furnace where they are thermally destroyed.

The table then moves the munition around to the burster-removal station where the projectile explosive is removed and also sent to the deactivation furnace. From the PMD machine, the projectile is conveyed to the multipurpose demil machine where the bursterwell is removed from the munition body and the chemical agent is drained from it. The agent is collected and sent to the liquid incinerator, which burns at 2,700 degrees Fahrenheit. Finally, the body and parts of the munition are sent to the metal-parts furnace where any remaining agent contamination is destroyed.

During the GB 155-mm projectile campaign at JACADS from May 1996 through May 1997, processing of the munitions was hampered occasionally when the fuse adapter on the projectile could not be removed. Inspection revealed that the fuse adapters were becoming seized to the projectile body during the unthreading cycle. The seizure was a result of the steel threads on the fuse adapter galling, or grating, against the mating steel threads of the projectile body. It was discovered that precise alignment between the hydraulic chuck, the clamp securing the projectile, and the table was critical and there was virtually no tolerance for any misalignment.

The jaws of the hydraulic chuck are designed to close symmetrically around the projectile to exert even pressure in removing the fuse adapter. When the centerline of the projectile is aligned properly with the unthreading equipment, the chuck is able to function as it was designed. However, the slightest misalignment of the projectile forces the chuck to close on the fuse adapter unevenly, thereby causing the threads to grate against each other. When this happens, the projectiles must be removed from the processing equipment and set aside for a separate cutting operation and disposal.

Finding the Solution

To resolve the problem of processing munitions separately, the Army initially focused its attention on finding a way to ensure proper munition alignment with the unthreading equipment. Various attempts were made to align the slots on the table with the unthreading equipment, but the alignment was difficult to set and hard to maintain. Because of this difficulty, it was decided to modify the PMD machine so that alignment was not critical. Several different modifications to the PMD were designed and tested. These designs were an attempt to overcome the force imparted by the chuck jaws onto the fuse adapter so that the threads would not gall. The methods included rubber chuck jaws, two-finger wrenches, and the socket and nut, which led to the development of the gimbal cam socket. Preliminary testing at the Army's Chemical Demilitarization Training Facility in Edgewood, Maryland, demonstrated that the gimbal cam socket was the most promising.