Aircraft Maintenance: Coating Removal and Advanced Composites Repairs

Coating Removal

• TO 1-1-8 is for removal of applications of organic coatings and PPE
• Mechanical Compatibility: using the right tool for the right job
• Material Compatibility: using compatible materials for a job, including using similar metals in repairs
• Removal Prep: cleaning and inspecting the area, allowing the area to dry, protecting/masking off special areas, and positioning aircraft in a sheltered area
• Types of paint removal: chemical and mechanical
• 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, with different grades of abrasive for topcoat and primer removal
• Plastic Media Blasting (PMB): preferred method of paint removal for advanced composites, using TYPE V: Acrylic plastic
• Dry abrasive blasting: rapid paint removal, but only down to primer on advanced composite surfaces

Plastic Media Blasting (PMB)

• Cleaning up: using a HEPA vacuum or compressed air with no more than 30psi
• Blasting Cabinet: three major components - cabinet/glove box, blast/reclaimer assembly, and dust collector
• Reclaimer: separates debris and good media, recycling good media back into the cabinet
• Dust collector: collects all debris, with collector drum replaced at 90% capacity
• Blasting Booth: similar to blasting cabinet, but larger and with a different volume of media output

Theory of Operation

• Clean and dry compressed air mixed with clean and dry media
• Blasting Parameters:
  • Substrate (metallic or non-metallic)
  • Type of media (Acrylic Plastic)
  • Nozzle pressure (25-40 psi)
  • Standoff distance (12-24 inches)
  • Angle of impingement (30-90 degrees)
  • Dwell time (how fast or slow the nozzle should be kept moving)

HVLP Spray Equipment

• High Volume Low Pressure (HVLP) spray gun: uses 1-10 psi
• Benefits: less overspray, waste, danger, and atomizing
• Three classes of guns: suction feed, pressure feed, and gravity feed
• HVLP Breakdown/Parts:
  • Fluid Cup: typically holds one quart, for small area painting, with limited spray time
  • Nose Assembly: air cap and fluid tip, with air cap pushing air out and fluid tip pushing coating material out
  • Fluid Needle: must be the same diameter as fluid tip, with needle moving back and releasing fluid when trigger is pulled
  • Spray Pattern Adjustment Screw: adjusts width of spray pattern
  • Fluid Needle Adjustment Screw: adjusts flow of fluid

Pressure Pots

• Large Volume Painting: uses 2 quarts to 120 gallons
• Parts: pressure regulator, material regulator, safety valve, and agitators
• Agitators: mix paint and are either electrically or pneumatically powered, keeping paint suspended and must be explosion-proof

Passivation Coating

• Treating/coating 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, with three forms (liquid concentrate, powder, and pre-mixed)
• Application of passivation coating: apply immediately after corrosion removal, using immersion/submersion/dunking, with proper color being a brassy yellow

Coating Defects

• Paint Terms:
  • Adhesion: adhesion is when the surface is roughened or cleaned to promote adherence
  • Coating: coating generally consists of a primer and topcoat
  • Vehicle: vehicle is the liquid portion of the coating, consisting of volatiles and non-volatiles
  • Viscosity: viscosity refers to a liquid's resistance to flow, measured with a viscometer
• Improper Surface Treatment Defects:
  • Pinhole Cavities: "solvent pop" due to insufficient primer dry time and painting over volatile gases
  • Peeling: due to improper roughing or moisture removal
  • Blistering: due to moisture resembling water blisters
  • Fish eyes: due to silicon left on the surface
  • Pitting/cupping: due to corrosion left on the surface
  • Crazing/mudcracking/checking: due to painting over a hard glossy coat
  • Sandpaper Finish: due to insufficient scuffing, unsatisfactory primer, improper cleaning, and stroking gun too far away

Spray Gun Troubleshooting

• Paint don't spray: check for paint, blockage
• Paint don'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, may be damaged or needle and tip may be different
• If paint gun sputters: check fluid tip, may be loose, tighten all assemblies

Spray Booth

• Purpose: fireproof compartment built to confine and remove fumes and overspray during the painting process
• Design: two types of designs - partially enclosed booth (type 1) and fully enclosed booth (type 2)
• Filters: dry filters that collect and pull overspray into filters, then exhausted
• Air velocity: term used to describe the speed of air moving through the empty spray booth, typically 100 feet per minute
• Major Components: exhaust fans, air replacement unit, and manometer (draft gauge)

Surface Prep

• Preparing unpainted surfaces: solvent wipe, passivate, and tack rag
• Preparing painted surfaces: scuff, solvent wipe, re-passivate, and tack rag
• Preparing a primed surface: solvent wipe, scuff, solvent wipe, and tack rag

Coating Removal

• TO 1-1-8 is for removal of applications of organic coatings and PPE
• Mechanical Compatibility: using the right tool for the right job
• Material Compatibility: using compatible materials for a job, including using similar metals in repairs
• Removal Prep: cleaning and inspecting the area, allowing the area to dry, protecting/masking off special areas, and positioning aircraft in a sheltered area
• Types of paint removal: chemical and mechanical
• 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, with different grades of abrasive for topcoat and primer removal
• Plastic Media Blasting (PMB): preferred method of paint removal for advanced composites, using TYPE V: Acrylic plastic
• Dry abrasive blasting: rapid paint removal, but only down to primer on advanced composite surfaces

Plastic Media Blasting (PMB)

• Cleaning up: using a HEPA vacuum or compressed air with no more than 30psi
• Blasting Cabinet: three major components - cabinet/glove box, blast/reclaimer assembly, and dust collector
• Reclaimer: separates debris and good media, recycling good media back into the cabinet
• Dust collector: collects all debris, with collector drum replaced at 90% capacity
• Blasting Booth: similar to blasting cabinet, but larger and with a different volume of media output

Theory of Operation

• Clean and dry compressed air mixed with clean and dry media
• Blasting Parameters:
  • Substrate (metallic or non-metallic)
  • Type of media (Acrylic Plastic)
  • Nozzle pressure (25-40 psi)
  • Standoff distance (12-24 inches)
  • Angle of impingement (30-90 degrees)
  • Dwell time (how fast or slow the nozzle should be kept moving)

HVLP Spray Equipment

• High Volume Low Pressure (HVLP) spray gun: uses 1-10 psi
• Benefits: less overspray, waste, danger, and atomizing
• Three classes of guns: suction feed, pressure feed, and gravity feed
• HVLP Breakdown/Parts:
  • Fluid Cup: typically holds one quart, for small area painting, with limited spray time
  • Nose Assembly: air cap and fluid tip, with air cap pushing air out and fluid tip pushing coating material out
  • Fluid Needle: must be the same diameter as fluid tip, with needle moving back and releasing fluid when trigger is pulled
  • Spray Pattern Adjustment Screw: adjusts width of spray pattern
  • Fluid Needle Adjustment Screw: adjusts flow of fluid

Pressure Pots

• Large Volume Painting: uses 2 quarts to 120 gallons
• Parts: pressure regulator, material regulator, safety valve, and agitators
• Agitators: mix paint and are either electrically or pneumatically powered, keeping paint suspended and must be explosion-proof

Passivation Coating

• Treating/coating 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, with three forms (liquid concentrate, powder, and pre-mixed)
• Application of passivation coating: apply immediately after corrosion removal, using immersion/submersion/dunking, with proper color being a brassy yellow

Coating Defects

• Paint Terms:
  • Adhesion: adhesion is when the surface is roughened or cleaned to promote adherence
  • Coating: coating generally consists of a primer and topcoat
  • Vehicle: vehicle is the liquid portion of the coating, consisting of volatiles and non-volatiles
  • Viscosity: viscosity refers to a liquid's resistance to flow, measured with a viscometer
• Improper Surface Treatment Defects:
  • Pinhole Cavities: "solvent pop" due to insufficient primer dry time and painting over volatile gases
  • Peeling: due to improper roughing or moisture removal
  • Blistering: due to moisture resembling water blisters
  • Fish eyes: due to silicon left on the surface
  • Pitting/cupping: due to corrosion left on the surface
  • Crazing/mudcracking/checking: due to painting over a hard glossy coat
  • Sandpaper Finish: due to insufficient scuffing, unsatisfactory primer, improper cleaning, and stroking gun too far away

Spray Gun Troubleshooting

• Paint don't spray: check for paint, blockage
• Paint don'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, may be damaged or needle and tip may be different
• If paint gun sputters: check fluid tip, may be loose, tighten all assemblies

Spray Booth

• Purpose: fireproof compartment built to confine and remove fumes and overspray during the painting process
• Design: two types of designs - partially enclosed booth (type 1) and fully enclosed booth (type 2)
• Filters: dry filters that collect and pull overspray into filters, then exhausted
• Air velocity: term used to describe the speed of air moving through the empty spray booth, typically 100 feet per minute
• Major Components: exhaust fans, air replacement unit, and manometer (draft gauge)

Surface Prep

• Preparing unpainted surfaces: solvent wipe, passivate, and tack rag
• Preparing painted surfaces: scuff, solvent wipe, re-passivate, and tack rag
• Preparing a primed surface: solvent wipe, scuff, solvent wipe, and tack rag

This quiz covers the procedures and considerations for removing organic coatings and performing advanced composites repairs in aircraft maintenance. It includes topics such as mechanical and material compatibility, removal preparation, and tool selection.