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Low Emissivity Coating Options for the HET Enclosure

Low Emissivity Coating Options for the HET Enclosure. 18 September 2002 John Good. Choices Available. Aluminized Mylar (3M product #8437) Emissivity = 0.03 Solar Absorption = 0.15 Aluminum Foil (3M product #427, 2.8 mil. Thick, Compac #804 – Bron Tapes, Inc.) Emissivity (new) = 0.03

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Low Emissivity Coating Options for the HET Enclosure

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  1. Low Emissivity Coating Options for the HET Enclosure 18 September 2002 John Good

  2. Choices Available Aluminized Mylar (3M product #8437) Emissivity = 0.03 Solar Absorption = 0.15 Aluminum Foil (3M product #427, 2.8 mil. Thick, Compac #804 – Bron Tapes, Inc.) Emissivity (new) = 0.03 Emissivity (heavily oxidized) = 0.20 Solar Absorption (new) = 0.15 LO/MIT I/II Emissivity = 0.21 Solar Absorption = 0.22 TiO2 (White Paint) Emissivity = 0.87 Solar absorption = 0.25

  3. Where they are in use (an incomplete list). • Aluminized Mylar • SPIE technical papers. • Medical Imaging Equipment • Aluminum Foil • WIYN, LBT, IRTF, Magellan, CTIO? • LO/MIT I • Gemini, GTC

  4. Method of application. • Aluminum Foil • Clean surface with 50/50 alcohol/water solution and allow to dry. • Prime with 3M product #94 primer. • Wet surface with rag and let dry for 5 minutes. • Cut to shape • Paper linered acrylic adhesive. • Peel and stick. • Smooth with squeegee. • LO/MIT I • Water blast. • Dry. • Roll-on (2 coats).

  5. Longevity and Maintenance • Aluminum Foil • No problems reported from facilities using foil. • WIYN – 8 years old. • Failure mode: Adhesive failure (de-lamination). • Replacement: Remove, Clean, & Re-apply. • LO/MIT I • Company line: 6-7 Years • “Coating on steel roof still good after 14 years.” • Failure mode: Abrasion. 100% silicone binder is very soft, flexible and thin (1/2 to 1 mil.). • Replacement: Light water blast, recoat with roller.

  6. Cost (very preliminary) • Dome, CSB roof, GTAG roof • Aluminum Tape: $58-60k • $38,000 + Labor (~8-12 man-weeks) + $7k to $10k (125ft. Manlift) + $1,500 (Misc. Supplies). • LO/MIT I: $19-21k • $5.5k (paint) + Labor (~6-8 man-weeks) + $7k (125ft. Manlift) + $1,500 (Misc. Supplies).

  7. Test plan. • Materials • Aluminum Tape • Does the primer attack the present finish on the dome? • Ease of Application. • Day/Night thermal performance. • LO/MIT I • Ease of application. • Adhesion. • Day/Night thermal performance. • Location • Upper right hand corner of dome aperture (looking out of the dome).

  8. Information Sources • Chas Cavedoni – Gemini • Bob Aresty – SOLEC (manufacturer of LO/MIT) • Dan Neff – M3 Engineering & Technology, Inc. • http://www.electro-optical.com/ • Don Ketchem (Chemical Engineer) - 3M Corporation • George Kuenig – Superintendent IRTF • Bron Tapes of Nevada, LLC • http://www.ctio.noao.edu/telescopes/opteng/dome.html

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