Podcast
Questions and Answers
Why is compressed air not recommended for drying surfaces?
Why is compressed air not recommended for drying surfaces?
- Because it is too slow a process
- Because it may contain oil that can degrade the repair's durability (correct)
- Because it is not effective in removing moisture
- Because it can cause overheating of the surface
What is the main purpose of hand abrasion or grit blasting in surface preparation?
What is the main purpose of hand abrasion or grit blasting in surface preparation?
- To remove moisture from the surface
- To apply a subsequent treatment to the surface
- To roughen the surface for the adhesive to 'key' into it
- To generate a fresh, chemically active surface (correct)
What should be used to dry surfaces before bonding?
What should be used to dry surfaces before bonding?
- Compressed air
- Hot air from a handheld hot air gun or an external hot air blower
- A recirculating air oven
- All of the above except compressed air (correct)
Why is it important to apply subsequent treatments soon after hand abrasion or grit blasting?
Why is it important to apply subsequent treatments soon after hand abrasion or grit blasting?
What is the consequence of inadequate drying of the surface before bonding?
What is the consequence of inadequate drying of the surface before bonding?
What should be done after water break testing?
What should be done after water break testing?
What is the primary purpose of using Methyl Ethyl Ketone (MEK) in composite component repair?
What is the primary purpose of using Methyl Ethyl Ketone (MEK) in composite component repair?
What is a critical requirement for solvents used in repair surface preparation?
What is a critical requirement for solvents used in repair surface preparation?
Why should chlorinated solvents not be used on titanium alloys?
Why should chlorinated solvents not be used on titanium alloys?
What type of wipe cloths should be used for wiping the surface with solvents?
What type of wipe cloths should be used for wiping the surface with solvents?
Why must wipe cloths be changed frequently during solvent degreasing?
Why must wipe cloths be changed frequently during solvent degreasing?
What is the final step in the solvent wiping process?
What is the final step in the solvent wiping process?
What is the primary purpose of a hot patch bonding machine?
What is the primary purpose of a hot patch bonding machine?
What is the purpose of a temperature recording unit in hot bonding units?
What is the purpose of a temperature recording unit in hot bonding units?
Why is it crucial to control the temperature during the curing process?
Why is it crucial to control the temperature during the curing process?
What is the purpose of a thermocouple in the curing process?
What is the purpose of a thermocouple in the curing process?
What is the purpose of the controller in hot patch bonding equipment?
What is the purpose of the controller in hot patch bonding equipment?
Why is it necessary to include permanent records of the cure cycle in the aircraft log book?
Why is it necessary to include permanent records of the cure cycle in the aircraft log book?
What is the purpose of applying a special UV-blocking dark paint to a component?
What is the purpose of applying a special UV-blocking dark paint to a component?
What is the primary benefit of applying a white or light-coloured paint finish to fibreglass-reinforced plastics?
What is the primary benefit of applying a white or light-coloured paint finish to fibreglass-reinforced plastics?
What is necessary for polyurethane paint to provide effective protection against erosion?
What is necessary for polyurethane paint to provide effective protection against erosion?
What is the effect of UV radiation on cured epoxy?
What is the effect of UV radiation on cured epoxy?
Why is it recommended to keep an aircraft out of the sun while it is on the ground?
Why is it recommended to keep an aircraft out of the sun while it is on the ground?
What is the benefit of using an opaque paint with a UV barrier to protect composites?
What is the benefit of using an opaque paint with a UV barrier to protect composites?
What is the primary purpose of the water break test?
What is the primary purpose of the water break test?
What happens if the surface fails the water break test?
What happens if the surface fails the water break test?
What is the consequence of inadequate drying prior to application of adhesives?
What is the consequence of inadequate drying prior to application of adhesives?
How is the water break test performed?
How is the water break test performed?
What should be observed during the drying process after water break testing?
What should be observed during the drying process after water break testing?
Why is solvent degreasing repeated if contamination is detected on the final wipes?
Why is solvent degreasing repeated if contamination is detected on the final wipes?
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Study Notes
Solvent Properties
- Solvents used for repair surface preparation must meet specific requirements, including:
- Readily dissolve surface contaminants
- Have a rapid evaporation rate to prevent re-contamination
- Produce no residue on the surface
- Have no deleterious effect on the material being cleaned
- Be of a guaranteed high grade of purity
- Chlorinated solvents should not be used on titanium alloys to prevent stress corrosion cracking
Solvents Used
- Methyl ethyl ketone (MEK) is used for removing dust, grease, and mould release agents from composite components
- Acetone is used for general clean-up of tools and equipment and to clean composite parts after sanding as a pre-bond prep
Solvent Wipe Cloths
- Only clean, lint-free white facial tissues or approved aircraft wipes should be used for wiping the surface with solvents
- Wipe cloths must be changed frequently during solvent degreasing to prevent re-contamination
- The frequency of changing cloths increases as the degreasing process progresses
Water Break Test
- The water break test is used to evaluate the surface condition of prepared metals and composites
- The test assesses the surface tension of water placed on the surface
- The test is performed after solvent degreasing and prior to generating a fresh, chemically active surface
- If the surface is properly clean, the water break test should pass; if not, solvent degreasing must be repeated
Drying Procedures
- Drying is performed after water break testing and before application of adhesives
- Inadequate drying can lead to serious degradation of adhesive strength and durability
- Drying methods include:
- Using hot air from a handheld hot air gun or an external hot air blower fitted with air filters
- Placing the item in a recirculating air oven
- Compressed air must not be used, as it can degrade the repair’s durability
Exposing Fresh Material
- Following solvent degreasing, water break testing, and drying, surfaces are prepared for adhesive bonding by:
- Hand abrasion or grit blasting to generate a fresh, chemically active surface
- Applying subsequent treatment as soon as possible to prevent unwanted contamination or oxide formation
- The procedure must be thorough, and the exposure time during this step is critical to the bonding process
Hot Patch Bonding Equipment
- Hot patch bonding equipment applies atmospheric pressure and heat to the repair area
- Heat blankets are used to control the temperature, and the rate of temperature rise and fall is critical
- The controller allows for slow temperature rise, holds the temperature constant, and then allows a slow decline
- Recording the temperatures of the curing process is essential, and permanent records must be kept in the aircraft log book
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