Paints & Painting Process

This presentation is tell about paints and painting process on steel surfaces. It also covers paint failures, surface preparation, type of painting process, etc.

1. By: Rahul Buswala Chemical Engineer PAINTS & PAINTING PROCESS Email: [email protected] Linkedin : www.linkedin.com/in/rahul-buswala-93123b40 Contact: [phone]

2. What is Paint? Paint is basically a s olution or suspension of pigment, binder, mineral solvent (or water ) and some additives that after application on a substrate forms an adhering film on it. Paints are required for: Protection of substrate against corrosion, weathering and mechanical damage. Decorative function like automotive coatings, household appliances, etc. Information signals like traffic signs, information signs, advertising. Specific applications like electrical conducting paints.

3. Composition of Paint Paint is a solution/suspension of following: 1. Binder Binders are usually resins or oils but can be inorganic compounds such as soluble silicates. The binder is the film forming component in the paint. 2. Pigment Pigments are finely ground inorganic or organic powders which provide colour , opacity, film cohesion and sometimes corrosion inhibition. 3. Solvent Solvents are used to dissolve the binder and to facilitate application at the paint. Solvents are usually organic liquids or water. 4. Additives They are added to paints to improve particular technical properties like leveling agents (butyl ether of ethylene glycol) to promote smooth, uniform surface on drying, wetting agents to prevent flocculation of pigments, antifoaming agents, thickening agents, etc.

4. Paint Film Formation Paint film formation can occur physically or chemically. Physical film formation from liquid coatings is known as drying whereas from powder coating is known as melting. Ex: High molecular mass polymer binders such as cellulose nitrate, chlorinated rubber, polyacrylates , stryrene copolymers, etc. Chemical film formation takes place by chemical reaction between components that react together on drying to form cross linked macromolecules. In single pack system: Reactive components are constituents of the coating and the reaction can be initiated by heat or radiation. In multi pack system: A reaction partner (hardener/catalyst) is added. Chemical film formation can also be done by oxidation of coating component(s) by atmospheric oxygen. Physical & Chemical film formation are often combined, ex: in solvent containing stoving paints, first stage is solvent evaporation and then film is cured by stoving .

5. Classification of Paints Paints can be classified on the basis of: Binder Diluent (Solvent) Sheen Task And so on…..

6. Classification of Paints Paints/Coatings classification on the basis of binder: Oil Paints Alkyd Silicone Cellulose Saturated Polyester Urea, Benzoguanamine and Melamine Chlorinated Rubber Unsaturated Polyester Phenolic Resins Vinyl Polyurethane Asphalt, Bitumen, and Pitch Acrylic Epoxy Silicate Paints/Coatings classification on the basis of diluent: Solventborne Paints Waterborne Dispersion Paints (Emulsion) Solvent Free and Low Solvent Paints Non-aqueous Dispersion Paints Waterborne Paints Radiation Curing Systems Coating Powders Electrodeposition Paints

7. Classification of Paints Paints/Coatings classification on the basis of sheen: Flat/Matte Eggshell Satin Semi Glossy Glossy Paints/Coatings classification on the basis of Task: Primer Sealer and Surfacer Undercoat Topcoat G loss

8. Painting Process for steel substrate

9. Why Surface Preparation Metal surfaces having contamination with oil , greases and having oxide film provide little or no adhesion to paints. Freshly prepared and roughened surfaces are active (have more surface energy) and provide better adhesion to paint film. Surface preparation affects the performance of the coating more than other variables. Surface preparation is to a coating system is just like a foundation to a building . The investment made in the purchase and application of best coating will be entirely lost if surface preparation is inadequate . Basic objective of surface preparation to attain the required cleanliness and surface roughness for adhesion of primary paint. Increasing surface energy and surface area to facilitate bonding Increase in life of paint film.

10. Methods of Surface Preparation Surface Preparation includes Removal of oil, grease, dirt and swarf followed by Removal of rust by means of mechanical or chemical treatment.

11. Methods of Surface Preparation Removal of Rust by Mechanical Cleaning

12. Methods of Surface Preparation Blasting White metal blast cleaning : A white metal blast cleaned surface when viewed without magnification shall be free of all visible oil, grease, dirt, dust, mill scale rust, paint oxides, corrosion products and other foreign materials . Near white blast cleaning : A near white blast cleaned surface, when viewed without magnification, shall be free of all visible oil, grease, dirt, dust, mill scale, rust, paint, oxide corrosion products and other foreign matter, except for shall be limited to no more than 5% of each square inch of surface area and may consist of light shadows, slight streaks or minor discolouration caused by stains of rust, stains of mill scale or stains of previously applied paint Commercial blast cleaning: A commercial blast cleaned surface when viewed without magnification shall be free of all visible oil, grease, dirt, dust, mill scale rust, paint oxides, corrosion products and other foreign materials . Staining shall be limited to no more than the 33% of each square inch of surface area and may consist of light shadows, slight streaks or minor discolouration caused by stains of rust. Stains of mill scale or stains of previously applied paint, slight residues of rust and paint may also be left in the bottom of the pits if the original surface is pitted . Brush - off blast cleaning : A brush -off blast cleaned surface when viewed without magnification, shall be free of all visible oil, grease, dirt, dust, loose mill scales, loose rust and loose paint. The entire surface shall be subjected to the abrasive blast. The remaining mill scale, rust or paint shall be tight. When painting is specified, the surface shall be roughened to a degree suitable for the specified paint system. Immediately prior to paint application, the surface shall comply with the degree of cleaning as specified .

13. Methods of Surface Preparation Blasting It shall also be ensured that the shot blasted surface should be subjected to\ phosphating or application of priming paint within 4 hours except the jobs which need pressure testing due to code requirements.

14. Methods of Surface Preparation Surface Finish Rust Grade

15. Methods of Surface Preparation Surface Finish Rust Grade

16. Methods of Surface Preparation Surface Finish Rust Grade

17. Methods of Surface Preparation Surface Finish Rust Grade

18. Methods of Surface Preparation Rust Removal by Chemical Cleaning Acid Treatment should be used only for parts that can be easily and thoroughly washed free from acid. It may thus be unsuitable for parts of complicated shape. Particularly those containing narrow channels or blind holes that cannot be properly washed out, or parts with porous surface layers. The following types of components , therefore, should not normally be treated with these acids : Parts built up by riveting, spot welding, or similar methods; 2. Cast-iron parts, owing to the possibility of occlusion of pickling acid in porous surface layers, or with machined cast iron in graphite pockets ; 3. Ferrous articles with associated non-ferrous or non-metallic parts because of the risk of attack of these parts due to electrolytic effects, and acid may be trapped at the joint; and 4. In case of high strength steel having strength more than 1 000 MPa, which are susceptible to hydrogen embrittlement and pickling may be avoided.

19. Methods of Surface Preparation Rust Removal by Chemical Cleaning Derusting solution shall be applied for light rust removal in a thin film, using brush or swab and left for 10 to 15 minutes followed to dry and be brushed down with a clean dry brush before painting. Pickling with Hydrochloric Acid (room temp), Sulphuric Acid (60-80 deg C) or Phosphoric Acid (60-85 deg C) can be used to remove heavy rust. Phosphating process includes degreasing by caustic, pickling by acid, phosphating and passivation with rinsing in between every stage (7 tank process). Electrochemical Cleaning can be done by any of the following way: 4a. Cathodic Treatment in Acidic Solution 4b. Cathodic Treatment in Alkaline Solution 4b. Anodic Treatment in Acidic Solution 4b. Anodic Treatment in Alkaline Solution Note: Within 8 hours of surface preparation, the job should be subjected to phosphating or application of priming paint.

20. Methods of Surface Preparation Inspection Quality control inspector shall inspect the prepared surface for Freedom from rust, stain, oil or grease before application of priming paint. Surface cleanliness. Profile measurement using profile gauges and appearance of surface to pictorial standards in case of blasting. Test for assessment of dust on steel surfaces prepared for painting can be carried out as per the Pressure-sensitive Tape method as per ISO 8502-3-1992(E ). Further, in case of chemical treatment the solutions concentration shall be examined periodically by shops to maintain them as per desired concentration.

21. Paint Application Methods of Painting Brushing/Rolling Conventional Spraying Airless Spraying Mode of Application Viscosity (FC 4 Cup) Brushing 40-60 seconds Spraying 28-32 seconds

22. Paint Application Preparation of Paint for Painting When the containers of air drying paints are opened, the material is observed for skin formation . The skin formed should be carefully removed and settled pigment has to be broken up and loosened by vigorous stirring preferably mechanically to ensure homogenous dispersion . Care should be taken to avoid air entrapment while stirring. The paint, if required may be strained through muslin cloth or 60mesh sieve. Maturation is an important criterion for two pack products where curing takes place through chemical reaction when the components are mixed before application. The mixed paint is normally matured for about 30 minutes to initiate the reaction process which ensures thickness build up and proper drying of the paint film unless otherwise specified. Maturation time is, however, to be adjusted depending on pot life and ambient temperature . Products having a short pot life should be allowed less maturation time as recommended by supplier to provide the adequate effect during film formation

23. Paint Application Points to remember before applying paint Painting shall not be performed when the temperature is less than 3°C above the dew point of the surrounding air. When the relative humidity of the air is greater than 85%. W hen the surface temperature is greater than 40°C (unless a higher temperature is recommended by the paint manufacturer ). When the air temperature is less than 10°C (depending on local conditions ). W hen there is the likelihood of an unfavourable change in the weather conditions within two hours after painting. When there is deposition of moisture in the form of rain, condensation, frost etc. on the surface.

24. Paint Application Points to remember before applying paint ( cont …) When the available light, ventilation is not adequate for painting . Paints shall not be applied within 50mm of edges which will later have to be welded. Such weld areas should be taped for a distance of 50mm on either side of the weld line. When zinc rich primers are used, care shall be taken to avoid any possibility of over spraying onto duplex or austenitic stainless steels, nickel alloys or 9% nickel steel components. Note : Zinc rich primers shall not be applied on equipment made from the above mentioned materials unless such equipment is located in a shielded position which will minimise the risk of molten zinc falling onto the equipment in the event of a fire . 10. Extra coats of paint shall be applied on the areas where the shape and/or plane of application result in thinly applied coatings etc., at edges, welds, corners etc. To compensate for these effects, stripes coats of paints shall be applied (normally applied first so that they will be covered by the full coat).

25. Paint Application Points to remember before applying paint ( cont …) Surfaces not to be painted shall be properly masked . Surfaces shall be cleaned by solvent cleaning method to remove oil, grease,dirt , cutting fluids and other contaminants . Surfaces to be coated shall be blast cleaned with suitable abrasive to the required surface finish for operating temperatures above 120° C i.e at least near white metal blast cleaning and a minimum of a commercial blast cleaning for operating temperatures below 120° C . The average maximum blast profile shall be between 3.5 to 6.0 mils or as per requirement. All traces of abrasive and other debris shall be removed by brushing, sweeping, blowing with clean compressed air, and vacuuming before the application of any coating

26. Paint Application Painting Process Ensure that after thorough mixing of the product of two component systems, the maturation time as indicated in the manufacturer’s product data sheet is to be allowed before applying the paint.

27. Paint Application Quality Check Following points shall be ensured to achieve overall quality of the job : (a) Compressed air used for spray application shall be free from oil, moisture and other contaminants. (b) Steel surfaces to be painted shall be free from burrs, sharp edges, lamination, surface imperfections and any other contamination detrimental to paint adhesion finish or appearance . (c) S urfaces to be coated have been cleaned. (d) All surfaces to be coated shall be completely dry before paint application . (e) Paint components shall be mixed as prescribed / recommended and mixed paint shall be consumed with in specified pot life . (f) Drying / curing requirements shall be fully satisfied . (g) Damaged paint coating shall be properly touched up before another coating application .

28. Paint Application Quality Inspection Dry film thickness DFT. A dhesion by cross cut test. G loss level. Finish. S hade: as per IS: 5 unless otherwise specified. C oated surfaces are smooth and uniform in coverage. T here is no visible porosity or pot holes. U nacceptable defects such as peeling, blistering cracking and damage caused by external sources are clearly marked with a mark-free chalk and with in the specification requirements. R uns and sags, dry spray and over spray are not present in excess of 5% in any given square foot and cumulatively not in excess of 2% of any surface, unless otherwise specified D rying time/curing time requirements have been satisfied.

29. Paint Failure Skinning: Formation of a layer of skin on paint surface in the container.

30. Paint Failure Settlement: The sedimentation of the solid constituents comprising pigments and extenders from the binder and solvent while standing in a container. Settlement that occurs after mixing and during application can result in different shades and performance in different areas.

31. Paint Failure Sagging: Sags are caused by the downward movement of a coat of paitn that appear soon after application before setting, resulting in an uneven area with thick lower edge. They are usually apparent on local areas of vertical surface and in severe situation may be described as curtains.

32. Paint Failure Adhesion Failure: Paints fails to adhere to substrate or underlying coats of paint.

33. Paint Failure Blistering: Dome Shaped projections or blisters in the dry paint film through local loss of adhesion and lifting of the film form the underlying surface. Blisters may contain liquid, vapour, gas or crystals.

34. Paint Failure Bubbles: Bubbles within a paint film appear as small blisters. They may be intact or broken (leaving a crater). Can be found in excessively thick paint films, especially if spray applied and also with roller application.

35. Paint Failure Chalking: A friable, powdery layer on the surface of a pint film. A change of color or fading is also seen. Chalking rates vary with pigment concentration and choice of binder. Chalking is known characteristics of certain paints ex: epoxy paints.

36. Paint Failure Cissing: Surface breaks in wet paint film, where the paint has receded to expose the underlying substrate. The paint is unable to wet out the substrate. It can be very large.

37. Paint Failure Orange Peeling: A uniform pock marked appearance in particular of a spray applied coating in which the surface of the paint film resembles the skin of an orange.

38. Paint Failure Crocodiling : Very large crazing/cracking that resembles the skin of a crocodile. Cracks may penetrate through to the undercoat or down to the substrate .

39. Paint Failure Bleeding: Staining of a paint film by diffusion of a soluble colored substance from the underlying paint to give undesirable discoloration or staining. Often seen where bituminous or tar based products are over coated with topcoats in which the tar or bitumen is soluble. Also occurs with emulsion paints.

40. Paint Failure Bloom (Blush): A hazy deposit on the surface of the paint resembling the bloom on a grape, resulting in a loss of gloss a dulling colour.

41. Paint Failure Bridging: The covering over of unfilled gaps such as cracks or corners with a film of coating material. This introduces a weakness in eh paint film which may crack or flake off.

42. Paint Failure Cobwebbing: The production of the fine filament instead of normal atomized particles when some solutions of high molecular weight polymer are sprayed. Traditionally when applying chlorinated rubber coating by conventional spray.

43. Paint Failure Cracking: The splitting of a dry paint film through at least one coat to form visible cracks, which may penetrate down to the substrate. Cracking comes in several forms from minute cracking to severe cracking.

44. Paint Failure Cratering: The formation of small bowl shaped depressions in the paint film. Not to be confused with cissing.

45. Paint Failure Crazing: Cracks are generally wider and penetrate deeper into the film.

46. Paint Failure Crowsfooting : Development of small wrinkles in the paint film in a pattern resembling a crow’s foot.

47. Paint Failure Delamination: Loss of adhesion between coats of paint.

48. Paint Failure Fading: Discoloration or gradual decrease in color of paint when exposed to sunlight/weather. May be accompanied by loss of gloss. In some situations it may resemble chalking but without the powdery surface. Fading tends to accelerate in the presence of moisture.

49. Paint Failure Flaking: A form of adhesion failure.

50. Paint Failure Grinning: The underlying surface is visible through the paint film due to inadequate hiding power of the coating material. This is sometimes called grinning through. Often seen when dark colours are overacted with light colours.

51. Paint Failure Heat Damage: Discolouration, detachment and/or blistering and general degradation of paint film.

52. Paint Failure Impact Damage: cracks that radiate form the point of impact.

53. Paint Failure Intercoat Contamination

54. Paint Failure Mud Cracking: The dried paint film has appearance of a dried out mud flat. The cracks appear as a network that can vary in size and amount.

55. Thank You