surface preparation

1. Surface Preparation

2. INTRODUCTION : To obtain the best results from a paint system the best possible surface preparation consistent with the degree of sophistication of the system is required. The quality of the paint and surface preparation (i.e. the removal of rust, scale, salt, grease, dirt and loose paint) are the most important factors in determining the lifetime of the paintwork, and therefore the length of time the surface will be protected. First class preparation has the potential to extend the protective life of any paint system.

3. What is surface preparation ? Coating performance is directly affected by surface preparation. Coating integrity and service life will be reduced because of improperly prepared surfaces. As high as 80% of all coating failures can be directly attributed to inadequate surface preparation that affects coating adhesion. The majority of paintable surfaces are concrete, ferrous metal, galvanizing and aluminum . They all require protection to keep them from corroding in aggressive environments. Selection of the proper method for surface preparation depends on the substrate, the environment, the coating selected and the expected service life of the coating system.

4. The greater the DFT the greater the Surface Profile

5. SURFACE CONTAMINANTS Mill Scale : The complete removal of mill scale and rust is critical in order to limit its corrosive properties. Mill scale is generally found on new steel as a hard brittle coating – it consists of distinct layers of various iron oxides and is formed during the hot rolling process in the manufacture of steel. Painting over mill scale is not satisfactory, as mill scale is not firmly or permanently bonded to the steel. Eventually the scale will lift off, causing paint coatings to flake and corrosion to occur. Rust: Rust is a form of hydrated ferric oxide formed by the action of water and oxygen on iron and steel surfaces and occupies a much greater volume than the original steel. It is for this reason that rust forming beneath a paint layer is able to rupture a coating. All areas of rust should be completely removed – any rust remaining will act as a nucleus for further rusting . Oil, Grease Fat and Perspiration : Oil , grease, fat and perspiration deposits cannot be removed by mechanical methods of cleaning. The simplest method of removal is to use a solvent emulsifiable degreaser or biodegradable detergent. Apply the degreaser liberally to the contaminated surface, allow to stand for a short time, then hose off with fresh water.

6. Prepare surface for subsequent processing, such as a coating application or adhesive bonding Improve hygiene conditions for workers and customers Remove contaminants that might chemically react with the surface Enhance appearance and performance of the product Reasons Why Parts Must be Cleaned

7. Factors in Selecting a Cleaning Method Contaminant to be removed Degree of cleanliness required Substrate material to be cleaned Purpose of cleaning Environmental and safety factors Size and geometry of the part Production and cost requirements

8. Various contaminants build up on part surfaces, either due to previous processing or factory environment Principal surface contaminants found in factory Oil and grease, e.g., lubricants in metalworking Solid particles such as metal chips, abrasive grits, shop dirt, dust, etc. Buffing and polishing compounds Oxide films, rust, and scale Contaminant to be Removed

9. What are Non-Ferrous Metals? Non-ferrous metals refer to metals that are not derived from iron ore, such as aluminium and its alloys, copper, brass and bronze. Whilst iron (mild steel) will readily oxidize to red rust (iron oxide), non-ferrous metals usually exhibit only tarnishing (surface corrosion). Aluminum finds ready use in window- and door-frames, handrails, balustrades and architectural work generally. Copper is used in water pipes and guttering.

10. . Primary Substrates Steel Carbon Steel – Easily attacked by the environment in which it is placed and will begin to revert back to iron ore. Stainless Steel - Stainless steel does not stain, corrode, or rust as easily as ordinary steel.

11. Non-Ferrous Metal Surfaces Aluminum Remove all oil, grease, dirt, oxide and other foreign material by cleaning per SSPC-SP1 , Solvent Cleaning. Galvanized Metal Allow to weather a minimum of six months prior to coating. Clean per SSPC-SP1 using detergent and water or a degreasing cleaner, then prime as required. When weathering is not possible or the surface has been treated with chromates or silicates, first Solvent Clean per SSPC-SP1 and apply a test area, priming as required. Allow the coating to cure at least one week before testing per ASTM D3359. If adhesion is poor, Brush Blast per SSPC-SP7/NACE 4 is necessary to remove these treatments.

12. Ductile Iron National Association of Pipe Fabricators, Inc. www.napf.com NAPF 500-03 Surface Preparation Standard for Ductile Iron Pipe and Fittings in Exposed Locations Receiving Special External Coatings and/or Special Internal Linings This standard summarizes the surface preparation requirements for ductile iron. Included within this standard are the following : NAPF 500-03-01 Solvent Cleaning NAPF 500-03-02 Hand Tool Cleaning NAPF 500-03-03 Power Tool Cleaning NAPF 500-03-04 Abrasive Blast Cleaning for Ductile Iron Pipe NAPF 500-03-05 Abrasive Blast Cleaning for Cast Ductile Iron NOTE: Recommended Coating Systems for Non-Ferrous Metals : A surface tolerant epoxy primer is the preferred primer for most non-ferrous metals.

13. Concrete Concrete - used more than any other man-made material in the world and is easily attacked when placed in chemical environments. PROPER SURFACE PREPARATION Proper surface preparation includes the following: Inspection of the concrete substrate Removal and replacement of non-durable concrete Decontamination of the concrete surface 4. Creation of surface profile 5. Repair of surface irregularities .

14. METHODS OF SURFACE PREPARATION Depending upon conditions of the concrete one or more methods of surface preparation may be required. It is common for decontamination to precede mechanical preparation, and if necessary a second decontamination to follow

15. Protection Mechanisms Barrier Protection The coating/lining isolates the electrolyte from the anode, cathode, and metallic pathway. Rust Inhibitive The slightly water-soluble pigments permeate to steel/coating interface and passivate the substrate. Sacrificial The coating/lining contains pigments that are more active than the metal and sacrifice themselves to protect the substrate.

16. Chemical Cleaning Processes Alkaline cleaning Emulsion cleaning Solvent cleaning Acid cleaning Ultrasonic cleaning

17. Alkaline Cleaning Uses an alkali to remove oils, grease, wax, and various types of particles (metal chips, silica, light scale) from a metallic surface Most widely used industrial cleaning method Alkaline solutions include sodium and potassium hydroxide ( NaOH , KOH), sodium carbonate (Na 2 CO 3 ), borax (Na 2 B 4 O 7 ) Cleaning methods: immersion or spraying followed by water rinse to remove residue

18. Emulsion Cleaning Uses organic solvents (oils) dispersed in an aqueous solution Suitable emulsifiers (soaps) results in a two‑phase cleaning fluid (oil‑in‑water), which functions by dissolving or emulsifying the soils on the part surface Used on either metal or nonmetallic parts Must be followed by alkaline cleaning to eliminate all residues of the organic solvent prior to plating

19. Solvent Cleaning Organic soils such as oil and grease are removed from a metallic surface by chemicals that dissolve the soils Common application techniques: hand‑wiping, immersion, spraying, and vapor degreasing Vapor degreasing (a solvent cleaning method) uses hot vapors of chlorinated or fluorinated solvents

20. Acid Cleaning Removes oils and light oxides from metal surfaces using acid solutions combined with water‑miscible solvents, wetting and emulsifying agents Common application techniques: soaking, spraying, or manual brushing or wiping carried out at ambient or elevated temperatures Cleaning acids include hydrochloric (HCl), nitric (HNO 3 ), phosphoric (H 3 PO 4 ), and sulfuric (H 2 SO 4 )

21. Acid Pickling More severe acid treatment to remove thicker oxides, rusts, and scales Distinction between acid cleaning and acid pickling is a matter of degree Generally results in some etching of the metallic surface which serves to improve organic paint adhesion

22. ©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e Ultrasonic Cleaning Mechanical agitation of cleaning fluid by high‑frequency vibrations (between 20 and 45 kHz) to cause cavitation (formation of low pressure vapor bubbles that scrub the surface) Combines chemical cleaning and mechanical agitation of the cleaning fluid Cleaning fluid is generally an aqueous solution containing alkaline detergents Highly effective for removing surface contaminants

23. Phosphating: Phosphating improves the adhesion of a the coating to the metal surface and can also improve the corrosion resistance of the painted surface. Iron, steel, zinc and hot galvanized surfaces are suitable for phosphating, and in some cases, Aluminium surfaces. During phosphating a thin, crystalline phosphate layer forms on the metal surface, which improves the adhesion. The most usual phosphating methods are iron and zinc phosphating.

24. Chromating Chromating is used as a pretreatment method for light alloys and galvanized surfaces. The treatment causes a thin colorless or yellowish coat. There are also chromating methods which form a substrate which is not suitable for painting. Chemistry:- Chromate coating on aluminium may contain the compound AL2O3.Cr(OH)3.CrOH.CrO4. On zinc as basis metal, ZnCrO4 has been claimed to appear

25. Mechanical Cleaning Physical removal of soils, scales, or films from the work surface by abrasives or similar mechanical action Often serves other functions also, such as deburring, improving surface finish, and surface hardening Processes: Blast finishing Shot peening Mass finishing processes

26. Blast Finishing High velocity impact of particulate media to clean and finish a surface Media is propelled at the target surface by pressurized air or centrifugal force Most well‑known method is sand blasting , which uses grits of sand as blasting media Other blasting media: Hard abrasives such as Al 2 O 3 and SiC Soft media such as nylon beads

27. Shot Peening High velocity stream of small cast steel pellets (called shot ) is directed at a metallic surface to cold work and induce compressive stresses into surface layers Used primarily to improve fatigue strength of metal parts Purpose is therefore different from blast finishing, although surface cleaning is accomplished as a byproduct of the operation

28. Surface Preparation Affects on System Selection SSPC-SP 1 “Solvent Cleaning” SSPC-SP 2 “Hand Tool Cleaning” SSPC-SP 3 “Power Tool Cleaning” SSPC-SP 11 “ Power Tool Cleaning to Bare Metal” SSPC-SP 7/NACE No. 4 “Brush-Off Blast Cleaning” SSPC-SP 6/NACE No. 3 “Commercial Blast Cleaning”

29. U ses of pretreatment:- To increase the long-life of a substrate. To increase the coating performance. To increase the surface area for good adhesion To remove all contamination from the metal surface and prevent their re-deposition.

30. Conclusion: Pretreatment is a part of surface coating technology therefore before application of protective coating pretreatment is must in order to have improved properties of the coating and the substrate. It is expected that technocrats in the finishing industry try to make use of it and upgrade it as per the requirement .