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

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.

The Gimbal Cam Socket

The gimbal cam socket was the brainchild of the Army's operating contractor at JACADS--the Raytheon Demilitarization Corporation. It is a direct replacement assembly for the hydraulic chuck. Like the hydraulic chuck it replaces, it is designed to engage the projectile fuse adapter and provide rotational force to unthread the fuse adapter from the nose of the projectile. Unlike the hydraulic chuck, the gimbal cam socket is designed to allow for some side-to-side movement (compliance) of the fuse adapter while it is being unthreaded from the projectile body. Compliance is required to allow for any misalignment between the projectile and the unthreading equipment. The lack of compliance during the unthreading cycle was the cause for the high number of rejects during the 155-mm GB projectile campaign at JACADS.

The gimbal cam socket assembly consists of a set of three eccentric (not centered on the same axis) cams designed to tightly grip onto the fuse adapter, similar to the rubber pad used to twist the lids off stubborn jars. Their eccentric design and mounting locations cause them to grip progressively tighter onto the fuse adapter as resistance to unthreading increases. This arrangement of the gimbals allows the cam ring to move and wobble continuously throughout the unthreading cycle without causing any stress on the fuse-adapter threads due to noncompliance. As a result, the fuse adapter and the projectile body easily unscrew, whether the munition is precisely aligned with the unthreading equipment or not.

The entire gimbal assembly is one complete unit that is mounted inside a large, cylindrical steel-socket housing. The housing contains rails on the inside that line up with slots machined into the outer ring. These rails allow the gimbal assembly to slide (front to back) inside the housing, while the gimbal assembly rotates. The gimbal assembly is held in the housing by a retainer plate, which closes the front of the socket housing after the gimbal cam is installed against a large compression spring.

Performance Excellence

In January 1998, the gimbal cam socket was installed at JACADS for prototype testing during the GB 8-inch projectile campaign. During that testing, approximately 5,000 projectiles were processed. While reject projectiles were virtually eliminated, lessons learned from the testing resulted in the need for several changes to the gimbal cam socket, and it was modified and rebuilt. Once again, the tool was sent to the facility in Edgewood, Maryland, for pilot testing where it functioned with great success. Several units were built and sent to JACADS for full-scale testing during the VX nerve-agent 155-mm projectile campaign in December 1999.

The VX 155-mm projectile campaign was completed on 10 March 2000 -- six days ahead of schedule. During this campaign, 42,678 projectiles were disassembled using the gimbal cam socket, which performed flawlessly. The gimbal cam socket simplified the unthreading operation, reduced the cycle time, reduced maintenance time, and virtually eliminated munition rejects. Of the 42,678 projectiles processed, only 2 were unable to be processed using the gimbal cam socket.

Programmatic Impact

As of April 2000, the gimbal cam socket is being used to process 8-inch projectiles at JACADS. After this munition campaign, only two more remain--VX land mines and VX ton containers--accomplishment of which will take the facility from 93 percent completed disposal operations to 100 percent. The gimbal cam socket has greatly contributed to successful operations at the Johnston Atoll Chemical Agent Disposal System and helped the Army to maintain its disposal schedule. The tool has been so successful that, as a programmatic lesson learned and solution, it will be used at the Army's chemical-agent disposal facilities in the continental United States to process all nerve-agent (GB and VX) 155-mm and 8-inch projectiles, resulting in significant schedule and cost savings. The gimbal cam socket, and the story surrounding its development and use, is a perfect example of the Army's commitment to innovation and excellence in its mission to dispose of the U.S. chemical-weapons stockpile.

Mr. William McLay currently is the Process Improvement Team Leader for all chemical demilitarization operations. In this capacity, Mr. McLay manages the campaign process for the gimbal cam socket. Previous employments include 22 years at the Kaiser Aluminum and Chemical Corporation, retiring in 1989. During his years with the Kaiser Corporation, he held a variety of industrial engineering and management positions. His career with Kaiser culminated with an appointment as operations manager of a hard alloy extrusion plant. He has a bachelor of science degree in industrial engineering and electrical engineering from the University of Washington.

Mr. John Lambert is currently the Test and Evaluation Group Leader for the General Physics Corporation at the U.S. Army's Chemical Demilitarization Training Facility. His previous employments include the Flair Corporation Research and Development Department where he primarily was involved with the design and development of industrial machinery. During this time, he obtained his professional engineering registration both in Maryland and Delaware. Mr. Lambert has a bachelor of science degree in mechanical engineering from the University of Delaware.

                   The original stockpile of chemical
                   weapons stored on Johnston Island
                      consisted of the following:
AGENT       ITEM                QUANTITY  POUNDS   STATUS
HD-blister  155-mm projectiles  5,779     66,340   Destroyed
HD-blister  105-mm projectiles  46        140      Destroyed
HD-blister  M60 projectiles     45,108    133,971  Destroyed
HD-blister  4.2 mortars         43,600    261,960  Destroyed
HD-blister  Ton containers      68        116,294  Destroyed
GB-nerve    M55 rockets         58,353    624,377  Destroyed
GB-nerve    155-mm projectiles  107,197   696,780  Destroyed
GB-nerve    105-mm projectiles  49,360    80,460   Destroyed
GB-nerve    8-inch projectiles  13,020    188,800  Destroyed
GB-nerve    MC-1 bombs          3,047     670,340  Destroyed
GB-nerve    MK 94 bombs         2,490     268,920  Destroyed
GB-nerve    Ton containers      66        101,158  Destroyed
VX-nerve    M55 rockets         13,889    141,770  Destroyed
VX-nerve    155-mm projectiles  42,682    256,100  Destroyed
VX-nerve    8-inch projectiles  14,519    210,520  In progress
VX-nerve    Land mines          13,302    139,680  Remaining
VX-nerve    Ton containers      66        97,360   Remaining
NOTE: For information on what the
facility has destroyed to date, please
refer to the JACADS Processing Status on
the Web at http://www.-pmcd.apgea.army.mil/

aag_jacads.html

COPYRIGHT 2000 U.S. Army Maneuver Support Center
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