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Coating Technique, application • Adhesion of paint or other organic…

- - - - Process:
        
        Immersion: The substrate is immersed in the solution of the coating material at a constant speed
        
        Start-up: The substrate has remained inside the solution for a while and is starting to be pulled up.
        
        Deposition: The thin layer deposits itself on the substrate while it is pulled up. The withdrawing is carried out at a constant speed to avoid any jitters. The speed determines the thickness of the coating (faster withdrawal gives thicker coating material).
        
        Drainage: Excess liquid will drain from the surface.
        
        Evaporation: The solvent evaporates from the liquid, forming the thin layer. For volatile solvents, such as alcohols, evaporation starts already during the deposition and drainage steps.
      - Application
        Coated fabrics
        Biomedical products(eg: gloves, etc)
    - - Application
        To apply paints, inks, adhesive or other coatings material onto:
        paper, textiles, leather, floor tiles, test charts.
    - - It is distinguished from other roll coating methods by having two reverse-running nips. The metering roll and the applicator roll contra-rotate, with an accurate gap between them. The surface of the applicator roll is loaded with an excess of coating prior to the metering nip, so its surface emerges from the metering nip with a precise thickness of coating equal to the gap. At the application nip, the applicator roll transfers all of this coating to the substrate, by running in the opposite direction to the movement of the substrate, wiping the coating onto the substrate.
      - magnetic tapes
        
        coated papers
        
        pressure sensitive tapes
    - - The excess coating material that drips off is then collected, filtered and automatically reintroduced to the lacquering system. The application performance is high in comparison with spraying (approximately 90 per cent) and there is almost no loss of lacquer.
        In order to obtain a homogeneous layer the coating must be able to flow freely over the surface and so thorough
      - Advantages
        
        dust particles on the surface to be coated can be swept away by the coating.
        
        saving of coating materials as any excess materials recirculate within the system.
        
        ~ can be applied to just one side.
- - - - Must have an autocatalytic substrate – To allow deposition to initiate and continue
      - • Constant deposition rate with time – Typically 10-15 micron per hour
      - • Uniform deposit thickness – Even on complex shapes
      - • Baths require good analytical control – To maintain deposit thickness and composition
      - • Baths have a short lifetime – Can be < 5 metal turnovers – Spontaneous decomposition can occur – ‘bombing out’
- - - - Ø Formed in near neutral electrolyte solution (eg. Ammonium borate)
      - Ø Al2O3 does not dissolve in solution
      - Ø Max 1µm thick
      - -Forms oxide on both sides
        -Dielectric, which supports up to 1 V/nm
        -Thickness of film is determined by the voltage applied between the anode and cathode
        -Too thin for most mechanical applications
    - - Acidic electrolyte solution (eg. diluted sulfuric acid)
      - Ø Al2O3 not only grows but also
      - dissolves in solution. Ø Can be several hundred µm thick
      - Cellular (porous) structure of the oxide layer is a result of fluctuations on the metal surface causing local concentrations of the electric current and enhanced oxide film growing.
  - - - degreaser
        
        rinse
        
        anodize
        
        rinse
        
        neutralize
        
        rinse
        
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- - - - advantagaes
        • Corrosion protection (when oiled)
        • Good paint and oil base
        • Protects base steel for top coat applications
        • Holds lubricants in place
      - application
        • Retain oil on parts such as gun triggers and barrels
        • Adhesion of paint or dry lube on steel parts
        • Lubrication during drawing or shaping
        • Gears and cam shafts during break-in periods
    - - Similar to phosphate coatings
      - processes of chemical conversion.
        But the chromate coatings are formed by the reaction of water solutions of chromic acid or chromium salts.
    - - advantages
        • Corrosion Resistance (when oiled/waxed)
        • Appearance
        • Cost Competitive
        • Dimensional Stability
      - application
        • Model railroad track • Firearm components • Precision bearings • Tooling
  - - - rinsing
        
        acid cleaning
        
        rinsing
        
        conversion coating
        
        rinsing
        
        drying
- - - - washing
        
        drying and cooling
        
        coating
        
        drying
        
        firing
        
        controlled cooling
        
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- - - - melted coating obtained through heating by plasma, flame and arc
      - method
        
        flame powder method
        
        https://www.youtube.com/watch?v=4QWxzGND8xc&ab_channel=SkandYtforadling
        
        detonation powder
        
        rod
        
        arc spraying
        
        plasma powder
        
        https://www.youtube.com/watch?v=sfbfObSU1V0&ab_channel=MTUAeroEngines
    - - Trowelling process
        Troweling is usually used in inaccessible areas or where it is
        necessary to produce a very heavy coating in one application.
      - spraying process
        
        Substrate preparation by chemical cleaning and sand paper grinding.
        Spray the coating on to the substrate surface
        Water is added for better spraying process.
        Heat the object for strong binding coating.
        Fine-grinding the ceramic material.
        Thickness of 1-250 mils are obtainable.
- - - - Deposition of a material in the vapour phase onto a solid in a vacuum via evaporation.
        Usually no chemical reactions take place.
        Carried out in a vacuum atmosphere.
      - Principle of PVD
        
        Source(solid/liquid)
        
        gas phase
        
        solid phase
      - Ø Ev a p o r a ti o n r e li e s o n thermal energy supplied to the crucible or boat.
        Ø Electrical resistance or electric beam can be used as source of heat.
        Ø Source materials melts and vaporizes which is then deposited on the substrate placed directly above.
        Ø A shield is usually provided between source metal and substrate.
      - advantages
        
        harder and corrosion resistant
        
        abrasion resistance
        
        durable
        
        perfect adhesion
        
        good color consistency
        
        process is enviromentally friendly
      - disadvantages
        
        dificult to coat undercuts
        
        high capital ost
        
        need skilled operator
        
        require large amount of heat for cooling system
    - - CVD is a chemical process used to high-purity, high-performance solid materials or coatings. In a typical CVD process, the substrate is exposed to one or more volatile precursors which react and decompose on the substrate surface to produce the desired deposit.
        Precursors include halide (e.g. TiCl4), hydrides (e.g. SiH4)
      - principle of CVD
        
        Transport of reactants by forced convection to the deposition region
        
        Transport of reactants by diffusion from the main gas stream to the substrate surface
        
        Adsorption of gaseous reactants onto the heated wafer (substrate) surface
        
        Chemical decomposition and other surface (heterogeneous) reactions take place at the gas- solid interface (heated substrate). Produce deposits & by-product
        
        Deposits diffuse along the surface forming the crystallization centre and growth of the film. Desorption of by-products from the surface.
        
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      - advantages
        
        versatile
        
        produce highly dense and pure material
        
        uniform film with good reproducibility
        
        reasonable procesing cost (economical)
      - disadvantages
        
        chemical and safety hazard
        
        dificult to deposit multi components mateials
        
        use of more sophisticatd reactor and vacuum system