Passivation Coating: Metal Surface Treatment

Surface Defects

• Pinhole cavities: Caused by insufficient primer dry time and painting over volatile gases
• Peeling: Due to improper roughing or moisture removal
• Blistering: Caused by moisture, resembling water blisters
• Fish eyes: Caused by silicon left on the surface
• Pitting/cupping: Caused by corrosion left on the surface
• Crazing/mudcracking/checking: Caused by painting over a hard glossy coat
• Sandpaper finish: Due to insufficient scuffing, unsatisfactory primer, improper cleaning, or stroking gun too far away

Surface Defects due to Improper Use of Technique Applications

• Runs and sags: Caused by too heavy of a paint application due to spraying too close at uneven angles
• Streaks: Caused by improper overlapping and air pressure being too high
• Orange peel: Caused by insufficient thinning due to the coating being too thick

Defects due to Equipment and Need for Adjustment

• Heavy center: Caused by low atomizing pressure, fluid pressure too high (air low)
• Split spray: Caused by atomizing pressure high, air pressure high, and fluid low
• Heavy top/bottom & heavy left/right: Caused by air cap clogged (check for dirt/burr)
• Wrinkling: Caused by coats applied fast, humidity, and rising temperatures
• Blushing: Caused by moisture condensation from the atmosphere

Faulty Finishing Material

• Faulty finishing material: Caused by coating/paint being stored improperly or material being expired

Spray Gun Troubleshooting

• Paint doesn't spray: Check for paint, blockage
• Paint doesn't transfer: Check for dirty tool or clogged air vent/cup cover
• Excessive fog: Check for pressure being too high
• If paint leaks: Check fluid tip, tip may be damaged or needle and tip may be different
• If paint gun sputters: Check fluid tip, may be loose, tighten all assemblies

Passivation Coating

• Passivation coating: Treats/coats metal to reduce chemical reactivity of its surface
• Surface prep/prior coating: Cleaning surface, solvent wipe, and water break test
• Chromate conversion coating (alodine): Used on aluminum and alloys
• Application of passivation coating: Apply immediately after corrosion removal, immersion/submersion/dunking is the best method

Coating Defects

• Adhesion: Surface is roughened or cleaned to promote adherence/stick
• Coating: Consists of a primer and topcoat
• Primer: Promotes corrosion protection for metal and is an adherent for the top coat
• Top coat: Provides toughness, outdoor durability, and good chemical resistance
• Vehicle: Liquid portion of the coating, consisting of volatiles and non-volatiles
• Volatile: Solvents and dilutants lost through evaporation in curing
• Non-volatile: Pigments and resins that form and leave an actual film on the surface
• Viscosity: Liquid's resistance to flow, measured with a viscometer

Improper Surface Treatment Defects

• Block 8: Improper surface treatment defect

Coating Removal

• TO 1-1-8: Removal of applications of organic coatings, and PPE
• TO 1-1-690: General Advanced composites repairs
• Mechanical Compatibility: Using the right tool for the right job
• Material Compatibility: Using compatible materials for a job
• Removal prep: Includes cleaning and inspecting the area, allowing the area to dry, protecting/masking off any special area, and positioning aircraft in a sheltered area
• Types of paint removal: Chemical and mechanical paint removal
• Chemical paint removal: Fastest and easiest method, but hazardous, and not authorized on advanced composites
• Mechanical paint removal: Includes abrasive cloths/paper and abrasive mats, top coat removal requires a courser grit (grade C), and primer removal requires a finer grade (grade B)

Plastic Media Blasting (PMB)

• PMB: A form of paint removal, preferred method for advanced composites
• Cleanup: HEPA vacuum, or compressed air with no more than 30psi when unavailable