TO 1-1-700 - Robins Air Force Base

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TO 1-1-700 8.8.2 Protective Coatings. Protective coatings are susceptible to damage by handling, accidental scratching, and corrosion. The functions of boxes, chassis, housings, and frames are to enclose, protect and secure the vital internal components of any electronic assembly. Therefore, it is important that this structural integrity be maintained. Painted surfaces will withstand a normal amount of abrasion from handling and hand tools. However, chipped, scrapped, scratched, and scuffed surfaces of protective paint will cause the base metal of the structure to become corrosion prone. The electronic technician shall pay particular attention to the mishandling of hand tools and avionic equipment. A few minutes of extra time spent in the careful use of tools will save hours of paint touchup and corrosion removal work. Any painting operation involves three basic steps: surface preparation; application of primer and/or undercoat; and application of one or more finish/topcoats. Guidance regarding the application of protective coatings can be found in Chapter 7 of this manual. 8.8.3 Encapsulates. Encapsulates are materials used to cover a component or assembly in a continuous organic resin. Encapsulates provide electrical insulation, resistance to corrosion, moisture, fungus, and mechanically support the components. In military electronic equipment, encapsulates are classified as follows: 8.8.3.1 Potting Compounds. Potting compounds are used to seal electrical connectors, plugs, and receptacles. Potting compounds are used for their moisture-proof and reinforcement properties. They are used on electrical connectors to protect against fatigue failures caused by vibration and lateral pressure at the point of wire contact with the pin. Potting compounds also protect electrical connectors from corrosion, contamination, and arcing by the exclusion of moisture, stray particles, and liquids (hydraulic fluid, fuel, and oil). 8.8.3.1.1 Materials. The following materials shall be used for “potting” electrical connectors: MIL-A-46146, ADHESIVE/SEALANT, SILICONE RTV, NON-CORROSIVE, GROUP I/II/III, TYPE I OR GROUP I, TYPE II 19 8.8.3.1.1.2 MIL-A-46146 RTV is used for sealing electrical connectors electronic components where a more flowable, one-part material is required. This material is also used as a conventional sealant. MIL-PRF-81733, SEALING AND COATING COMPOUND, CORROSION INHIBITIVE 48 8.8.3.1.1.3 MIL-PRF-81733, Sealing and Coating Compound, is used to prevent entry of corrosive environments. This material is also used as a conventional sealant. MIL-M-24041, SEALING COMPOUND 33 8.8.3.1.1.4 MIL-M-24041 Sealing Compound, is a two-component polyether polyurethane system consisting of a prepolymer and a curing agent before mixing. These compounds are flexible cold-flow and cold-resistant materials with excellent electrical properties and are intended for use in a seawater environment. This compound will adhere to metal, rubber, or polyvinylchloride, and may be used for the sealing and reinforcement of electrical connectors, wiring and other electrical apparatus. This compound is used to seal connectors located in areas where the temperature range is -80 °F to +300 °F. 8.8.3.1.2 Precautions. When using potting compounds, the following precautions shall be observed: MIL-PRF-8516, TYPE II, SEALING COMPOUND, POLYSULFIDE RUBBER 49 8.8.3.1.1.1 MIL-PRF-8516 Sealing Compound, Synthetic Rubber, Accelerated, is a two-part synthetic rubber compound. It consists of a base and an accelerator (curing agent) packaged together. It is used for sealing low voltage electrical connectors, wiring, and other electrical apparatus, where temperature does not exceed 200 ºF (93 ºC). 8.8.3.1.2.1 Apply potting compounds only to clean surfaces. 8.8.3.1.2.2 Follow instructions carefully when mixing the base compound and accelerator. Substitution, partial mixing, or incorrect proportions of base compound and accelerator may produce a sealant with inferior properties. 8.8.3.1.2.3 Do not mix base compounds and accelerator components of different batch numbers because substandard electrical properties may result. 8-34
TO 1-1-700 8.8.3.1.2.4 Potting compounds may contain small quantities of flammable solvents and/or release by-products on curing. Adequate ventilation and fire precautions are required during mixing, curing, and/or storage of potting compounds. 8.8.3.1.2.5 Potting compounds that have exceeded normal shelf life are not to be used. 8.8.3.1.2.6 Avoid the use of masking tape and fiberboard molds. If potting molds are not furnished with connector or are not available, a plastic sleeve should be constructed. This will aid in forming the potting compound around the connector shell. 8.8.3.1.2.7 Allow potting compounds to cure until firm prior to installing connectors or components in equipment. 8.8.3.1.2.8 Frozen, premixed potting compounds should be used as soon as possible after the removal from the deep freeze or a significant (approximately 50%) reduction in work life can be experienced. 8.8.3.1.2.9 Remove reverted potting compounds as soon as possible. 8.8.3.1.3 Reverted Potting Compounds. Depending on the environment, potting compounds, such as Pro-Seal 777 (green) and EC-2273 (black), are known to revert to a liquid after a year or two. Compounds that revert exhibit a sticky, oozing consistency that flows out of the connector. In some cases, the reverted potting compounds flow around through the pins and receptacles, insulating the connections where continuity is required. 8.8.3.2 Conformal Coatings. Conformal coatings are used to encapsulate PCBs and modules. Guidance for using conformal coatings can be found in TO 00-25-234 or in equipment system specific technical manuals. 8.8.3.3 Fungus-Proof Coatings. Fungus proof coatings, usually varnish, used to encapsulate certain electronic circuit components in a thin protective film that is impervious to fungus attack. Usually used in older macro electronic and electrical components. Fungus-proof coatings should not be applied indiscriminately to all electronic components. Treat only those components that have been treated or are specified in the applicable equipment system specific technical manuals. Fungus-proof coatings can, in some instances, be detrimental to the function/maintenance of equipment. For example, it deteriorates wire insulation and its removal is labor intensive. The entire surface shall be retreated only when touch-up procedures will not provide protection to the item. Considering the difficulties of applying a fungus-proof coating, it is important to recognize that if the coating is not properly maintained; many hours of additional repair time will be required. ASTM D 3955 (MIL-V-173), VARNISH, ELECTRICAL INSULATING 12 A-A-3007, THINNER, PHENOLFORMALDEDYDE AND MEDIUM OIL AND STYRENATED ALKYD PAINTS AND VARNISHES 1 The authorized fungus-proof coating is Varnish, ASTM D 3955. If it is found necessary, the varnish may be thinned with A-A-3007 Thinner. 8.8.3.3.1 Items to be Protected Against Fungus-Proof Varnish. Varnish shall not be applied to any surface where it interferes with the operation/performance of the equipment. Such surfaces shall be protected against varnish application by masking with Pressure Sensitive Tape, SAE-AMS-T-22085, Type II. The following items shall be protected from fungusproof varnish: 8.8.3.3.1.1 Components and materials: • Cable, wire, braids, and jackets that are flexed during operation of the equipment. • Cables where treatment would reduce the insulation resistance below, or increase the loss factor above, the acceptable values. These values are specified in the applicable service directives. • Variable capacitors (air, ceramic, or mica). • High wattage and wire-wound resistors. • Ceramic insulators that are subject to an operating voltage of over 600 volts and in danger of flashover. • Painted, lacquered, or varnished surfaces, unless otherwise specified. • Rotating parts such as dynamotors, generators, motors, etc. However, electronic components associated with these parts shall be treated in accordance with procedures outlined in this manual. • Waveguides (working surfaces). • Electron Tubes. Change 1 8-35
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TO 1-1-700 TECHNICAL MANUAL CORROSI
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TO 1-1-700 TABLE OF CONTENTS Chapte
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TO 1-1-700 TABLE OF CONTENTS - CONT
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Page 13 and 14:
TO 1-1-700 LIST OF ILLUSTRATIONS -
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TO 1-1-700 FOREWORD 1. PURPOSE. The
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TO 1-1-700 List of Related Publicat
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TO 1-1-700 SAFETY SUMMARY 1. GENERA
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TO 1-1-700 AMS-G-6032, GREASE, PLUG
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TO 1-1-700 MIL-DTL-64159, COATING,
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TO 1-1-700 MIL-PRF-27617, GREASE, A
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TO 1-1-700 O-L-164, DRESSING, LEATH
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TO 1-1-700 MIL-T-81772, THINNER, PO
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TO 1-1-700 tronics equipment and th
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TO 1-1-700 cleaning situation, syst
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TO 1-1-700 c. Riveted joints shall
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TO 1-1-700 c. Remove and replace an
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TO 1-1-700 MIL-L-87177, LUBRICANT,
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TO 1-1-700 Figure 3-1. Simplified C
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TO 1-1-700 resistant, and also at t
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TO 1-1-700 is first noticeable as a
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TO 1-1-700 3.7.8 Oxygen Concentrati
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TO 1-1-700 Figure 3-14. Concentrati
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TO 1-1-700 Figure 3-17. Galvanic Se
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TO 1-1-700 Figure 3-20. Aluminum Su
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TO 1-1-700 3.8.7 CRES/Stainless Ste
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TO 1-1-700 3.9.10 Climate. Warm, mo
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TO 1-1-700 3.11 PREVENTATIVE MAINTE
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TO 1-1-700 CHAPTER 4 COMPOSITE AND
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TO 1-1-700 4.4.4.4 Glass parts shal
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TO 1-1-700 CHAPTER 5 PACKAGING (STO
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TO 1-1-700 extent of damage dependi
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TO 1-1-700 5.15 PRECAUTIONS FOR VCI
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TO 1-1-700 c. Secure the desiccant
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TO 1-1-700 Figure 5-8. Shock Isolat
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TO 1-1-700 Figure 5-9. Examples of
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TO 1-1-700 5.24.10 Rigid or Flexibl
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TO 1-1-700 CHAPTER 6 MOISTURE AND F
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TO 1-1-700 c. 6.2.6 Felt. Examine f
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TO 1-1-700 a. After first directing
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TO 1-1-700 6.4.5.14 Terminals, scre
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TO 1-1-700 NOTE • Authorized clea
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TO 1-1-700 Table 7-1. Cleaning of S
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TO 1-1-700 7.3.1.2.3 Portable, 45 g
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TO 1-1-700 Table 7-2. Common Milita
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TO 1-1-700 inactivity, storage, or
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TO 1-1-700 7.5.6.5.1 Grade 1 - A th
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TO 1-1-700 Table 7-4. Corrosion Pre
Page 112 and 113: TO 1-1-700 Table 7-5. Preservation
Page 114 and 115: TO 1-1-700 either case, MIL-PRF-269
Page 116 and 117: TO 1-1-700 MIL-PRF-85285, COATING,
Page 118 and 119: TO 1-1-700 c. Cadmium plated surfac
Page 120 and 121: TO 1-1-700 a. Scuff sand and feathe
Page 122 and 123: TO 1-1-700 7.7.7.2 If surface is no
Page 124 and 125: TO 1-1-700 7.7.9.2 Where only parti
Page 126 and 127: TO 1-1-700 7.8.1 Type I Application
Page 128 and 129: TO 1-1-700 Extend (Loctite) 32150 J
Page 130 and 131: TO 1-1-700 There are three ways to
Page 132 and 133: TO 1-1-700 vulnerable surfaces clea
Page 134 and 135: TO 1-1-700 Table 8-2. Materials, Th
Page 136 and 137: TO 1-1-700 Table 8-4. Electronic Cl
Page 150 and 151: TO 1-1-700 Table 8-5. Accessories o
Page 152 and 153: TO 1-1-700 Table 8-5. Accessories o
Page 154 and 155: TO 1-1-700 f. Devices with permanen
Page 156 and 157: TO 1-1-700 Table 8-7. Cleaning and
Page 158 and 159: TO 1-1-700 MIL-PRF-87937, CLEANING
Page 160 and 161: TO 1-1-700 of contamination). Maint
Page 164 and 165: TO 1-1-700 • Tube clamps. • Min
Page 166 and 167: TO 1-1-700 a. For bonding/grounding
Page 168 and 169: TO 1-1-700 vertently destroy the mo
Page 170 and 171: TO 1-1-700 doors, and other corrosi
Page 173 and 174: TO 1-1-700 CHAPTER 10 CORROSION PRO
Page 175 and 176: TO 1-1-700 MIL-PRF-81733, SEALING A
Page 177 and 178: TO 1-1-700 d. After corrosion is re
Page 179 and 180: TO 1-1-700 (3) Stainless/CRES steel
Page 181 and 182: TO 1-1-700 10.9 WATER ENTRAPMENT AR
Page 183 and 184: TO 1-1-700 f. Shield equipment from
Page 185 and 186: TO 1-1-700 b. Use e-inch rivnuts of
Page 187 and 188: TO 1-1-700 10.17.3 If the plating s
Page 189: TO 1-1-700 Figure 10-16. Dissipatio
Page 192 and 193: TO 1-1-700 (2) If allowable damage
Page 194 and 195: TO 1-1-700 Table 11-1. Recommended
Page 196 and 197: TO 1-1-700 11.6 3M CO. SCOTCH-BRITE
Page 198 and 199: TO 1-1-700 11.11.2 Control of Mecha
Page 200 and 201: TO 1-1-700 11.12.2 Mechanical Damag
Page 202 and 203: TO 1-1-700 MIL-DTL-81706 (ALODINE),
Page 204 and 205: TO 1-1-700 11.13.2.3 Application of
Page 206 and 207: TO 1-1-700 only when there is no da
Page 208 and 209: TO 1-1-700 NOTE SEMCO PASA-JELL 101
Page 210 and 211: TO 1-1-700 (CRES), lead, ceramic, g
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TO 1-1-700 11.13.7.2 Treatment of C
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TO 1-1-700 MIL-A-46106, ADHESIVE/SE
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TO 1-1-700 Table 12-1. Sealing Comp
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TO 1-1-700 used to apply sealants i
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TO 1-1-700 Figure 12-2. Sealant App
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TO 1-1-700 Figure 12-4. Rivet Appli
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TO 1-1-700 Figure 12-6. Sealant Inj
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TO 1-1-700 below and adhere very po
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TO 1-1-700 Table 12-2. Time Require
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TO 1-1-700 Table 12-2. Time Require
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TO 1-1-700 of 20 to 25 seconds in a
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TO 1-1-700 d. Remove all uncured se
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TO 1-1-700 MIL-PRF-81733, SEALING A
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TO 1-1-700 MIL-PRF-81733, SEALING A
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TO 1-1-700 Figure 12-12. Typical Me
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TO 1-1-700 may be used for low temp
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TO 1-1-700 Figure 12-14. Sealing Pr
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TO 1-1-700 - Robins Air Force Base

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