Protective Coating L6- Surface preparation & Paint application - PowerPoint PPT Presentation

Protective Coating L6- Surface preparation & Paint application MM650/2 Prof. A.S. Khanna Corrosion Science & Eng. IIT Bombay & Prof Siva Bohm Honorary visiting scientist - IIT Bombay Principal scientist - Tata Steel Ltd

Contents  Revision of Surface preparation  Paint Applications  Reduced Solvent Technologies  High solid systems  Powder coatings

Surface Preparation Effect of Abrasive on Surface Profile Grit (Iron/Slag) Shot (Cast Steel)

Surface Preparation Effect of Abrasive on Surface Profile High Build Paints & Thin Film Paints Metal Coatings Grit (Iron/Slag) Shot (Cast Steel)

Surface Preparation – Grit Blast 3D map of Grit blast cleaned surface

Surface Preparation – Shot Blast 3D map of shot blast cleaned surface

Surface Preparation Measurement of Profile Shot Grit Comparator Surfaces – BS 7079 Part C1 / ISO 8503-1

Surface Preparation Measurement of Profile Replica Tape Method

The Specification • Main Purposes: • To ensure that the metalwork is protected for the required durability • To consider the appearance • To provide a basis for pricing and tendering

The Specification • What Should be Included? • Scope • Surface Preparation – Removal of Contaminants – Standard of Cleanliness – Profile and Amplitude – Additional Treatments – Pre-Coating Condition

The Specification • What Should be Included? • Scope • Surface Preparation • Protective Coatings & Application Method • Handling & Transport • Quality Control & Inspection – Materials, Application and Finished Job

The Structure • Design: • Corrosion Traps? – Retention of Water and Dirt • Provision for Inspection and Maintenance • ISO 12944: Part 3 ‘Design Considerations’

Surface Preparation Steel Condition Before Preparation – Rust Grades Pictorial Reference BS 7079: Part A1 / ISO 8501-1 B A D C

Surface Preparation • Cleaning Standards • BS 7079: Part A1 / ISO 8501-1 • Pictorial Reference • Abrasive Blast Clean (Dry & Wet), Sa • Sa1 Light • Sa2 Thorough • Sa2½ Very Thorough • Sa3 Visually Clean • Mechanical / Power Clean, St • St2 Thorough • St3 Very Thorough • Flame Clean, Fl • Acid Pickling

Surface Preparation Dry Abrasive Blast Cleaning Manual Compressed Air System

Surface Preparation Dry Abrasive Blast Cleaning

Surface Preparation Dry Abrasive Blast Cleaning Automatic Wheelabrator System

Surface Preparation Dry Abrasive Blast Cleaning Modern Automatic Blast Cleaning Plant

Surface Preparation Removal of Scale and Rust Method Effectivene Use ss (%) 25 Maintenance Manual Mechanical 30 Maintenance 35 Maintenance /New Work Flame Clean Dry Abrasive Blast Clean 100 Maintenance /New Work Wet Abrasive Blast Clean 100 Maintenance /New Work 100 New Work Acid Pickling High Pressure Water Jet 100 Maintenance /New Work ‘If the surface preparation isn’t correct, the best coating in the world will not protect the steel.’

Surface Preparation • Required Information: 1. Cleanliness • Removal of Oil, Grease etc.. • BS 7773 • Abrasive Blast Cleaning • BS 7079: Part A1 / ISO 8501-1 2. Profile & Amplitude • BS 7079: Part C1 / ISO 8503-1

Surface Preparation • Additional Surface Treatments: – Weldments • ISO/DIS 8501-3 – Joint Interfaces • Faying Surfaces – Slip Factors – Fasteners • Compatible Protection

Surface Preparation • Surface Contaminants: – Dust • BS 7079: Part B3 / ISO 8502-3 – Soluble Corrosion Products • Not Usually Found on New Steel – Rusting • Reformation (Flash Rusting)

Paint Applications 23

Main Coating Components • Four components of paint: – Additives (0 - 5%) – Solvent (30 - 80%) – Binder, resin, or polymer (20 - 60 %) – Pigment (2 - 40%) 24

Curing/ Drying Mechanisms • Solvent Loss • Air Reaction • Emulsion Drying • Radiation Curing • Chemical Reaction – Epoxy , Polyurethane 25

Types of Coatings • Conventional Solvent-borne • High-solids Solvent-borne • Water-borne • Plural Component • Powder 26

Classification of Paint Application Techniques • Manual Methods - Brush - Roller • Spray Techniques - Air Spray – HVLP – Airless – Air Assisted – Electrostatic • Airspray • Air Assisted • Alternative Coating Methods - Electroplating - Galvanizing - Powder Coating 27

Paint Application – By Brush • • Disadvantages Advantages 1. Very Slow Application 1. Applicable of Low 2. No Consistancy with film viscosities paints and thickness ( Non Uniform low volumes. coating thickness ) 3. High Fatigue to the applicator 2. Can reach any profile 4. Speeds of painting is 3. Least Expensive generally defined by the applicator 5. Applicator is in contact with harmful solvents for longer periods of time. 6. Not suitable for High solids and low pot life paints. 28

Paint Application – By Roller Advantages  Disadvantages  Slow Application 3-4 times faster than 1. 1. Brush High Fatigue to the applicator 2. Speeds of painting is generally Suitable for Low 3. 2. defined by the applicators viscosities skill. Best suited for low / Applicator is in contact with 3. 4. medium volumes harmful solvents for longer periods of time. Superior over Brush 4. Not suitable for High solids 5. finish and low pot life paints. Least Expensive Cannot be used on all profiles 5. 6. 29

Spray Application Atomization is:  Breaking up fluid into small particles  Collection of moving particles on surface is known as spray  Spray pattern can be created by variety of means 30

Fluid Properties & Particle Size  Fluid viscosity  Density  Surface Tension of the paint . 31

Adjusting Atomization  Viscosity  Quantity - fluid flow rate  Energy - air and/or fluid pressure required to atomize the paint. 32

Liquid Spray Application Types of Atomization Air Spray/ HVLP Airless Air Assisted Electrostatic 33

Low Pressure Application  Generally use Airspray Conventional or HVLP  Common applications:  Decorative coating  Primers  Top Coats  Clear Coats  Stains 34

Air Spray Atomization Ad dv va an nt ta ag ge es s Li im mi it ta at ti io on ns s A L Fi in ne e f fi in ni is sh h q qu ua al li it ty y. . Ea as sy y t to o o ov ve er r- -a at to om mi iz ze e a an nd d c ca au us se e F E ex xc ce es ss si iv ve e o ov ve er rs sp pr ra ay y. . e Fl F le ex xi ib bl le e - -- - o op pe er ra at to or r c co on nt tr ro ol l o of f T Ty yp pi ic ca al ll ly y, , t to oo o m mu uc ch h c co on nt tr ro ol l f fo or r al ll l a as sp pe ec ct ts s o of f a at to om mi iz za at ti io on n in ne ex xp pe er ri ie en nc ce ed d o op pe er ra at to or r. . T Ta ak ke es s a an n a i in i nc cl lu ud di in ng g p pr re es ss su ur re e, , f fa an n w wi id dt th h, , ex e xp pe er ri ie en nc ce ed d o op pe er ra at to or r t to o s se et t- -u up p t th he e an nd d f fl lu ui id d d de el li iv ve er ry y. . gu un n f fo or r o op pt ti im mu um m p pe er rf fo or rm ma an nc ce e a g In ne ex xp pe en ns si iv ve e e eq qu ui ip pm me en nt t Pu ur rc ch ha as se ed d d du ue e t to o p pr ri ic ce e t to oo o m ma an ny y I P re eq qu ui ir re ed d ti im me es s. . r t Ea as sy y t to o u us se e. . S Si im mp pl le e o op pe er ra at ti io on n e ea as sy y t to o o op pe er ra at te e o ou ut ts si id de e o of f t th he e g gu un ns s E de es si ig gn n l li im mi it ts s. . d Lo ow w p pr re es ss su ur re e s sa af fe et ty y. . N No ot t r re ec co om mm me en nd de ed d f fo or r p pr ro ot te ec ct ti iv ve e L co oa at ti in ng g a ap pp pl li ic ca at ti io on n, , c Ty yp pi ic ca al ll ly y t th ho ou ug gh ht t o of f a as s t th he e Tr ra an ns sf fe er r e ef ff fi ic ci ie en nc cy y i is s p po oo or r, , c ca an nn no ot t T T on nl ly y w wa ay y t to o g ge et t a a g go oo od d f fi in ni is sh h. . ha an nd dl le e h hi ig gh h s so ol li id ds s p pa ai in nt ts s. . o h 35

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Different Air Spray Applications Equipment • Gravity Feed system • Siphon Feed System • Pressure Pot Feed system • Low Pressure Pump feed system 37

Air spray, Theory of Operation  Air spray atomization is Air Pressure 20-60 psi created by air flow 1.5-3.5 bar disrupting a fluid stream .  Air spray gives the finest finish quality referred to as an Automotive finish or Class A Finish. Transfer efficiency = 20 - 30% 38