Original Date: 04/26/2004
Revision Date: 01/18/2007
Best Practice : Parts Preparation
United Defense, L.P. Armament Systems Division Aberdeen developed innovative and effective equipment and processes for preparing individual machined piece parts and complete assemblies for final finishing and painting. These processes and equipment enabled the facility to reduce product through-put time, while increasing the safety of its workforce.
Machined products and items being returned from field service must be cleaned and neutralized to be free of oil, contaminants, and foreign residue prior to subsequent processing. Before the mid 1990s, machined parts were traditionally cleaned in a vapor degreaser containing 1-1-1 trichloroethylene to remove grease, oils, and contaminants. With trichloroethylene being phased out of manufacturing processes due to the environmental hazards created by its use, manufacturing companies had to find alternative cleaning methods. One of the most commonly used methods today is a wash using a caustic wash solution with a final rinse with reverse osmosis treated water. The wash water used in this process is normally heated to an elevated temperature to assist in the cleaning process.
United Defense, L.P. Armament Services Division (UDLP ASD) Aberdeen was faced with a peculiar process requirement. Many of its new manufacture and repair products are missile canisters, which are generally up to 24' long and approximately 24" square. Manually scrubbing these assemblies using the caustic wash solution and brushes was not a long term option as the assemblies had to be cleaned inside and outside of the canisters a time consuming process. Additionally, there were no commercially available parts washers on the market that could handle the size of the parts and clean both the inside and outside of the canisters.
To mitigate the problem, UDLP ASD Aberdeen personnel designed and built a parts washer that met the facility’s needs. The wash cabinet is located in a vertical position to allow an immediate deluge of the wash water in a drain off. A boom and winch system is used to orient the canister from a horizontal position to a vertical position. The load boom is designed to double as a boom, and an internal wash lance with spray nozzles is strategically located along the length of the boom. The cabinet has high pressure nozzles strategically located within it which effectively washes the outside of the canister (Figure 2-3). Utilization of this wash cabinet to clean missile canisters has enabled UDLP ASD Aberdeen personnel to reduce cleaning time by a factor of ten to one over manual scrubbing. In addition, the use of the cabinet enabled the process to produce consistent and predictable results.
Another method of preparing large missile canisters for finish paint is to grit blast previously painted canisters that are being refurbished or re-manufactured. Traditionally, this was accomplished by placing the unit in a large blasting room where the operator was in full suit personal protective equipment with breathing air. The operator manipulated large, heavy blasting hoses with nozzles to direct the blast pattern against the work surface. Because it was operator dependent, this yielded variations in process results. As operators performed this task, they suffered fatigue which resulted in lost productivity and uncontrolled processes. In addition, the safety of the operator was and is always a concern.
As a process improvement effort and, in an effort to remove operators from the harsh environment, Aberdeen personnel developed an automated blast process to pre-blast painted canisters. The facility purchased a commercial blast cabinet of sufficient size to meet its needs. The internal components of the cabinet were then modified to allow a canister to be crane-loaded into a work fixture. The fixture and canister are then placed into the blast cabinet. The system uses an internal lance blasting arrangement to blast the inside of the canisters and an external blast ring, which supports four rotary blast heads. The blast ring traverses the length of the canister while spinning the blast heads for a spread blast pattern. The system is automated, reducing the need for operator intervention.
The "Auto Blaster" demonstrated a 95% clean up of canisters with no operator interface, eliminating operator safety concerns and ergonomic problems, produced controllable results of the finished product, and reduced operator touch time for canister blasting by approximately 80%.
Figure 2-3. Loaded Wash Cabinet
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