REMOVING AND TREATING CORROSION, Non metallic and metallic components.pptx

Aircraft repair structure

1. REMOVING AND TREATING CORROSION

2. SURFACE PREPARATION CLEANING The first and most important step on corrosion control is a thorough cleaning of the airplane. An emulsion type cleaner that meets MIL-C-25769 specification does an excellent job of removing grime, dirt exhaust residue, and dried oil and grease deposits.

3. SURFACE PREPARATION PAINT REMOVAL Corrosion on a painted surfaces cannot be inspected thoroughly without first removing all of the paint. before using any paint remover with which you are not familiar, first test it on a piece of metal similar to that with which you will be working.

4. Caution must be observed whenever you use any paint remover. Many solvents used in paint removers attack rubber and synthetic rubber products. Tires, hoses, and seals must be protected from contact with paint removers.

5. TREATMENT OF ALUMINUM ALLOY

6. 1.MECHANICAL CORROSION REMOVAL After all the paint has been removed. all traces of corrosion products, the white powder, must be removed from the surface.

7. A very mild corrosion may be removed by using a household cleaner such as Bon- Ami. Be sure that the abrasive cleaner does not contain chlorine. Nylon scrubbers such as Scotch-Brite can be used to remove mild corrosion.

8. More severe, but not heavy corrosion can be removed by brushing with aluminum wool or an aluminum wire brush. CAUTION: Do not use a steel wire brush or steel wool, as traces of the steel will embed in the aluminum and can cause severe corrosion.

9. BLASTING the surface with glass beads smaller than 500 mesh can be used to remove corrosion from pits.

10. GLASS BEAD AND SAND BLASTING

11. Severely corroded aluminum alloys must be given more drastic treatment to remove all of the corrosion. Rotary files or power grinders may be used to grind out every trace of corrosion damage.

12. after an examination with 5 to 10 power magnifying glass shows no trace of corrosion remaining, remove about two thousandths inch more material to be sure that the ends of intergranular cracks have been reached, then san the area smooth with 280 grit, then 400 grit abrasive sand paper and treat the surface with inhibitor such as Alodine ®.

13. 2.CHEMICAL NUETRALIZATION After removing all of the corrosion product possible, the surface should be treated with a 5% chromic acid solution to neutralize any remaining corrosion salts. After 5 minutes it should be washed off with water and allowed to dry. Conform to MIL-C-5541 ALODINE®

14. ALODINE Alodining (chemical conversion) is a coating method intended to provide corrosion prevention to aluminum products left unpainted, as well as to improve adhesion of painting processes. 

15. ALODINING

16. Unlike anodizing, aluminum parts are alodined in only two colors, clear and gold.  Unless specified, gold alodining is the standard and offers the most corrosion protection. It conforms to specification MIL-C-5541B.

17. 3. PROTECTIVE COATING A  protective coating  is a layer of material applied to the surface of another material with the intent of inhibiting or preventing corrosion. A  protective coating  may be metallic or non-metallic

18. CLADDING A method of protecting aluminum alloy from corrosion by rolling a coating of pure aluminum onto the surface of the alloy. This is done by rolling mill.

19. CLADDING In the manufacture of clad aluminum, pure aluminum is rolled into the surface of alloy. It actually penetrates to alloy and become part of it, 1.5 to 5% of the total thickness of the sheet.

20. this cladding is anodic to the core material, any corrosion that takes place will attack the coating rather than he core.

21. SURFACE OXIDE FILM a layer or coating of metallic oxide on the surface of the metal. Metallurgists have found ways of forming films on metal surface that are hard, decorative waterproof and air tight. ALODINING - chemical process ANODIZING - electrolytic(electrochemical) process.

22. ELECTROLYTIC PROCESS Anodizing  is an electrochemical  process  that converts the metal surface into a decorative, durable, corrosion-resistant, anodic oxide finish.  Aluminum  is ideally suited to  anodizing , although other nonferrous metals, such as magnesium and titanium, also can be  anodized

23. ORGANIC FILM COATING One of the most universally used corrosion control devices for metal surfaces is a good coat of “PAINT”. The surface of the aluminum must be prepared in order that the paint will have a rough surface on which to adhere. The surface must be roughened with mild etch or by either anodizing or alodining .

24. TERM MEANING PAINT Organic coatings in which the vehicle is usually a drying oil, such as linseed, soybean, tung , or dehydrated castor, or varnish the term paint is often used to cover all organic coating. PRIMER First coating, which is applied on surfaces to be painted before the painting schemes commences LACQUER a liquid made of shellac dissolved in alcohol, or of synthetic substances, that dries to form a hard protective coating for wood, metal, etc. VARNISH Clear unpigmented coatings made by dissolving a resin or the reaction products of a resin and drying a oil in suitable solvent ENAMEL Paint in which the pigment is very well dispersed and the vehicle is chosen to flow out to an extremely smooth finish, usually with a high gloss and semi-gloss enamels are also made.

25. WHAT IS SHOT PEENING IT ISA COLD WORK PROCESS USED TO FINISH MACHINE COMPONENTS TO IMPROVE FATIGUE AND STRERSS CORROSION FAILURE SMALL SPHERICAL SHOTS BOMBARDS THE SURFACE. DIMPLING THE SURFACE TO DEVELOP COMPRESSIVE STRESS.

26. SHOT PEENING CAN BE DONE WITHOUT CHANGING ITS DESIGN. MEDIA USED FOR SHOT PEENING STEEL CERAMICS GLASS

27. APPLICATION OF SHOT PEENING Gear parts cams and camshafts clutch springs connecting rods crankshaft gear wheels leaf and suspension springs turbine blades

28. METHODS USED FOR SHOT PEENING CONVENTIONAL (MECHANICAL) SHOT PEENING TWO METHODS OF MECHANICAL It involves the accelerating shot material with compressed air. shit introduced into a high velocity air stream that accelerates the shot to speed of up to 250 ft /s. accelerating the shot with a wheel

29. LASER-SHOT-PEENING laser-shot –peening utilizes shock waves to induce residual compressive stress. The primary benefit of the process is a very deep compressive layer with minimal cold working. Layer depths up to 0.040 on carburized steel and 0.100 on aluminum alloys have been achieved unlike mechanical peening method can only produce 35% of theses depths.

30. DUAL PEENING Dual peening further enhances the fatigue performance from a single shot peen operation by re-peening the same surface with smaller shot and lower intensity. Peening the surface a second time drives the peaks into valleys, further increasing the compressive stress at the surface.

31. ANTI CORROSION TREATMENT FOR FERROUOS METAL Abrasive blasting Chrome plating Galvanizing Organic coating Zinc chromate priming Enamels