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1
What is the purpose of conversion coatings?
“Alodine is an example and produces a golden brown finish on aluminum” 1. It is a protective coating formed on the surface of materials 2. Produces an aluminum oxide protective layer created by a chemical reaction between the metal and the chemical solution 3. Protects the metal from further oxidation 4. Excellent paint adhesion and corrosion resistance
2
What methods are used to identify aluminum?
You identify different alloys by using diluted hydrocloric acid 7075 - Will turn black 2024 - this alloy will not be affected
3
what is galvanic corrosion
Occurs between two dissimilar metals (anode & cathode) in the presence of an electrolyte “Pitting and surface corrosion can be caused from galvanic corrosion”
4
what is intergranular corrosion
Is an attack along the grain boundaries of an alloy “Results from a lack of uniformity in the alloy & during heating and cooling of the alloy”
5
what is galling?
caused by adhesion between SLIDING surfaces “Occurs when metal surfaces are in contact sliding against eachother”, especially with poor lubrication 1. Common in bearings, pistons, cylinders and also in screws and bolts causing the threads to seize
6
what is brinelling ?
Permanent indentation of a hard surface Named after the brinell scale of hardness
7
How are aluminum conversion solutions applied on aluminum parts?
1. Brushing 2. Spraying 3. Immersion
8
When applying conversion coatings, what is the purpose of the soaking period?
let the coating soak to perform
9
what is cladding?
1. They are extremely thin sheets of pure alumminum laminated onto each side of the aluminum alloy Improves the corrosion resistance with little impairment of strength 2. Trade name is Alclad
10
What is anodizing?
1. Electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts 2. Increases corrosion resistance & wear resistance 3. Provides better paint adhesion
11
Why is it important to use explosion proof lights, electrical wall sockets & cords and remove all sources of ignition like open flames?
The spray guns require a pressured air
12
What is the deciding factor in using an air purifying or atmosphere supplying mask?
1. Air-Purifying - used during exposure to specific chemicals described on the cartridge as well as sanding 2. Cartridges are only good for limited time and replaced when; You start to smell the vapors in the mask 3. They become difficult to breathe through They have exceeded their specific lifetime
13
List the three main types of guns used in a/c painting?
1. Siphon Feed 2. Gravity Feed 3. High Velocity Low Pressure Productin Gun
14
What is the purpose of viscosity measuring cups?
1. Viscosity is determined by measuring the efflux (drain) time of the liquid coating through the cup orifice 2. The measurement determines if the mixed coating meets the recommended viscosity for spraying
15
To obtain the correct spray pattern set the recommended air pressure on the gun too?
typically 40 to 50psi
16
The paint gun UPPER control knob proportions the?
Proportions the airflow Which adjusts the spray pattern of the gun
17
The paint gun LOWER knob adjusts the?
Fluid passing through the needle Controls the amount of volume of paint delivered through the gun
18
What is the distance you should hold the paint gun perpendicular to the surface of the part?
8-10 inches
19
What is the purpose of the tack coat?
Spray a light tack coat before spraying on the second coat “A tack coat holds the second coat from sagging and running”
20
To ensure an even amount of paint on the surface you repeat the sequence of the application, moving back in the opposite direction and overlapping the first pass by how much?
50% “Accomplished by aiming the center of the spray pattern at the outer edge of the first pass and continuing on”
21
Why would you want to release the trigger enough to stop the paint flow, but not the air flow?
“Because constant air flow through the gun maintains a constant pressure rather than buildup of pressure each time the trigger is fully released” 1. Not doing this could cause a build up of paint at the end of each pass causing runs and sags in the finish
22
what is corrosion?
the deterioration by chemical or electrochemical attack
23
what is direct chemical attack / pure chemical corrosion?
the result from direct exposure to caustic liquid or gaseous agents “ex. battery acid leaking”
24
surface corrosion
appears as general roughening, etching or pitting of surface, frequently accompanied by white powder. caused by direct chemical or electrochemical attack
25
dissimilar metal corrosion?
galvanic corrosion
26
stress corrosion
result of combined tensile stresses and a corrosive environment
27
fretting ?
two mating surfaces normally at rest subject to relative motion “characterized by pitting of the surfaces and debris”
28
plugs, sockets (explosive proof - lights & sockets must be approved for spray painting & flammable storage area). true or false?
true
29
air hose inspections should be done frequently for breaks. if damage detected, the hose must be replaced?
true
30
many paint coatings contain flammable substances, aerosolized when sprayed and without proper ventilation, vapours can build creating and explosion / fire
true
31
siphon feed gun
uses regulated air which passes the gun and draws/ siphons the paint from the cup
32
gravity feed gun
paint is located at the top of the gun and is supplied by gravity
33
conversion coatings created by chemical or electrochemical reaction between metal and conversation coating ?
true, created by either chemical or electrochemical
34
what is metalizing?
process of coating a surface with metal or alloy by spray equipment. “guards metals from corrosion”
35
shot peening
cold working process used to produce a COMPRESSIVE residual stress layer “used to relieve tensile strength, replaced with beneficial compressive strength”
36
flapper peening
1. used for peening small areas on new or repaired parts 2. can be done in field 3. developed by US army in Vietnam
37
zinc chromatic primer
refers to a protective coating, not paint colour “corrosion resistant agent called zinc chromate” highly toxic
38
expoxy primer
1. superior anti corrosive properties 2. exceeds one part zinc chromatic primers in terms of performance 3. “provides solvent proof barrier coat, protects from fabric cements and dope”
39
before you start doing the job, when cleaning the AC before painting, what kind of tools can be used to clean the A/C?
1. abrasive pads 2. don’t use same pad on different metals 3. aluminum wool / scotch brite
40
what test must be done to ensure the aircraft surface is clean?
water break test, ensures no debris on contamination on surface
41
what is another name used when doing chemical conversion coating?
blueing
42
steps to preparing plane to paint
READ WHIMIS and MSDS safety sheets first! 1. prepare / strip old paint from plane 2. scotch brite and water break test surface 3. acid etch plane 4. apply conversion coating “alodine” 5. apply primer 6. apply paint