Cleaning High Precision Inertial Navigation Systems, A Case Study and Panel Discussion

摘要

Litton Guidance & Control Systems division builds high-performance inertial navigation systems. Choosing and implementing new cleaning systems is often a major challenge. In addition to meeting stringent customer, performance, and regulatory requirements, the processes must be practical and reliable. Litton's cleaning studies as well as a review of process development in a production facility will assist course attendees in their own process choices. Producing inertial navigation systems involves exacting, multi-step cleaning of complex subassemblies. Each sub-component of a system may require various cleaning steps; each performed by skilled assemblers. Fluxes, oils, and flotation fluids must be removed from an array of materials of construction including a wide assortment of metals, plastics, and epoxies. For the given product application, soil residues, cleaning agent residues, and water are not acceptable. Replacing 1,1,1-trichloroethane was very challenging. Process replacement was multi-staged. Litton has remained responsive to evaluating the newer, more promising replacements that were not available early on in the ODC phase-out. Optimizing the processes involved coordination among engineers, chemists, environmental health and safety specialists, and skilled assembly people at Litton G&CS, BFK Solutions, and Albemarle Corporation. A range of cleaning agents was evaluated including co-solvent systems, fluorinated solvents, and brominated solvents. Process development was multi-step. Initial processes allowed replacement of ODCs, but were costly and cumbersome for the assembler. Litton has tested and implemented alternative cleaning sequences, which include a cleaner formulated with n-propyl bromide (nPB). The new processes provide effective, reliable cleaning. In addition, cleaning process time has been reduced by over 40% and cleaning agent usage has been reduced to essentially one-third of the total volume of solvents used in the original ODC replacement process. It is important to note and clarify that the cleaning performance data obtained in this study using the vapor degreasing grade nPB cleaning formulation (VG) does not indicate that any other nPB type formulation will give equivalent performance. This is due to the unique composition of the parts being cleaned, including configuration and combination of materials of construction, and the specific properties and carefully tuned characteristics of the cleaning agent formulation. Significant qualification testing is necessary before attempting to use other formulations in similar applications.