Supercritical CO2 (SCCO2) Cleaning of Space Precision Assemblies at Raytheon Missile Systems Hunter L. Rosen, Presenter (1) Paul W. Fecsik (2) 1 M&P Engineer Raytheon Missile Systems M&P Engineering Manufacturing Support Tucson, Arizona 520-794-0481 hlrosen@raytheon.com 2 Project Manager Raytheon Missile Systems EH&S Pollution Prevention Tucson, Arizona 520-794-4105 pwfecsik@raytheon.com
Project History Demanding cleanliness requirements leading to: Excessive solvent usage High cost for specialty solvents Time consuming (4 hours) cleanliness verification Experience with supercritical carbon dioxide: Raytheon (legacy Hughes Aircraft Company) Numerous patents US Air Force Plant (AFP) 44 Pollution Prevention (P2) Project ACHA02PV05 Supercritical Cleaning. : Funded purchase of SCCO2 Cryostat Cleaning System 12/15/2003 Page 2
Carbon Dioxide Phase Diagram Log Pressure, bar absolute 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 Solid-Liquid Solid-Gas Liquid-Gas SC-Liquid SC-Gas Gas-Plasma Triple Point Critical Point 1.E-03-150 -125-100 -75-50 -25 0 25 50 75 100 125 Temperature, C Diagram courtesy of Nelson Sorbo, Raytheon Electronic Systems 12/15/2003 Page 3
Supercritical Carbon Dioxide Properties Dense Phase Carbon Dioxide Physical Properties Solvent Surface Tension (Dynes/cm) Density (g/cm 3 ) Viscosity (centipoise) Perchlorethylene 32 1.6 0.9 (20 C) 1,1,1-Trichloroethane 26 1.4 1.2 (20 C) Freon 113 20 1.6 0.7 (20 C) Petroleum (C12-C18) 28 0.8 ~2.0 (20 C) Water 72 1.0 0.9 (20 C) Liquid CO 2 ~5 0.8 0.08 (~15 C) Supercritical CO2 1 0.7 0.03 (38 C/~300atm) Table courtesy of Nelson Sorbo, Raytheon Electronic Systems 12/15/2003 Page 4
Supercritical Carbon Dioxide Properties Excellent solvent for complex geometries Penetrates into blind holes like a gas Holds contaminants like a liquid Co-Solvents provide wide range of solubilities Silicones Hydrocarbons Fluorinated greases Ionics Ester Oils Provides easy drying Density improves particle removal 12/15/2003 Page 5
Critical Hardware Cleanliness Cryostats Small heat exchangers used to cool detectors Highly sensitive to residues Optics Thin films reduce performance Precision Parts and Assemblies Potential source of out-gassing residues 12/15/2003 Page 6
Cryostats Small heat exchangers used to cool detectors Extremely sensitive to residues left in gas path As gas cools and expands, residues can collect at the outlet of the cryostat and impede gas flow High Pressure Gas In Rapidly Expanding Gas Cools Detector Diagram courtesy of Rick Kundrat, Raytheon Missile Systems 12/15/2003 Page 7
Cryostats Pictures to show relative size of cryostat components 12/15/2003 Page 8
SCCO2 Cryostat Cleaning System P Heater Test coupon Tubular Reactor Additive injection system T From LCO2 Source Screen filter Piston pump To LCO2 recovery Flow Diagram Diagram courtesy of Thar Technologies, Pittsburgh, PA 12/15/2003 Page 9
SCCO2 Cleaning System Back Pressure Regulator In-Line Cleanliness Verification (ELSD) Cyclone Separator Co-Solvent Pump High Pressure Vessel Heat Exchanger SCCO2 Pump FTIR (not shown) Recycle Unit (not shown) Equipment photo courtesy of Thar Technologies, Pittsburgh, PA 12/15/2003 Page 10
ELSD In-Line Cleanliness Verification Nebulization: Supercritical carbon dioxide containing soils is throttled through a needle and forms a dispersion of droplets. Evaporation: Droplets pass through heated tube where SCCO2 flash evaporates, leaving a fine mist of soils. ELSD (Evaporative Light Scattering Detection): Mist of soils pass to detection cell and scatter light from laser beam. The scattering light produces a signal on the detector. 12/15/2003 Page 11
Fourier Transform Infrared Spectroscopy Used in conjunction with ELSD to determine the mass of residue Serves as check to determine vendor compliance Are vendors using unapproved lubricants and cutting oils? 12/15/2003 Page 12
Results Implementation of SCCO2 cleaning process resulted in: 85% reduction in cycle time for cleaning cryostats. $30,000 per year cost savings for solvent purchases. $107,000 per year overall cost savings. 12/15/2003 Page 13
Moving Forward Implement an in-line FTIR View Cell Spread SCCO2 technology to other areas requiring ultra high precision cleaning. Investigate SCCO2 for accelerated out gassing Implement vacuum vapor degreasing for all other hardware. 12/15/2003 Page 14
Acknowledgements USAF/ASC/ENVC (Wright Patterson AFB, Ohio) Dick Lantis Thar Technologies, Inc, Pittsburgh, PA Harbaksh Sidhu Todd Palcic Raytheon Electronic Systems, Los Angeles, CA Nelson Sorbo 12/15/2003 Page 15