protective coating for steel structures

8/2/2019 Protective Coating for Steel Structures

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Defined as a material which isapplied to a surface as a fluid andwhich forms, by chemical and/orphysical processes, a solidcontinuous film bonded to thesurface.


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Pigments Non-Volatile Vehicles (Binders)

Volatile Vehicles (Solvents)

Additives


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Pigments are included in coatings to performany of the following functions:

! Add colour

! Adjust the flow properties of wet coatings ! Resist light, heat, moisture, chemicals

! Inhibit corrosion

! Reflect light for opacity or hiding

! Contribute mechanical strength


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The binder or resin portion(polyurethane, epoxy, etc.) of the coatingis the "glue" that holds the coating

together and onto the substrate.

The physical properties of the coatingare mainly derived from the physicalproperties of the solid resin, butpigments and additives can affect the

final properties.


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A solvent is used to dissolve the resinsand additives in order to reduce theviscosity of the mixture to provide

application consistency .

And allow the paint to flow out properly.In every case, it is designed to evaporatefrom the film during or after application.


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Additives make up only a smallproportion of any paint.

Yet without these chemicals the paintcould not deliver all of its potentialperformance.


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Zinc-Rich Primers Epoxy

Acrylics

Polyurethane Alkyds


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Intumescent Paint Hot-Dip Galvanizing


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Inorganic zinccoatings Powdered metallic zinc mixed into a reactive

silicate solution

Organic zinc-richprimers

The binders of which are based on organic orcarbon-based compounds.(phonoxies,catalyzed epoxies, urethanes, chlorinated

rubbers, vinyls).


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Epoxy binders are available in three types:epoxy ester; epoxy lacquer resin;and two-component epoxy.

The two-component epoxies are mostcommonly used for painting structural steel

The epoxy is generally combined with either

of two types of hardeners (polyamine orpolyamide) to form epoxy-polyamineandepoxy-polyamide.


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Acrylics can be supplied as solvent- or water-based coatings with varying performancecharacteristics.

Exhibit good color and gloss retention, aresingle package, relatively low in cost and easyto apply.

Solvent and chemical resistance, however, is

lacking. They are best for interior, non-corrosive environments.


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Moisture-cure polyurethane Two-component polyurethane


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Reacts with air moisture to cure. Theyproduce the hardest, toughest coatingsavailable in one package, and are

increasingly popular due to the wide range ofapplication


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! Can be applied to cold damp surfaces ! Can be applied at temperatures below

freezing

! No dew point restriction

! Year round application season

! Excellent recoatability

! Single component


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Polyurethanes can also be reacted with

products such as polyols, polyethers,

polyesters or acrylics to produceextremely hard, resistant durablecoatings.

These are commonly used as topcoats


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Alkyds are available in both water dispersionand solvent-based formulations.

Alkyd-oil vehicles can be formulated in flatand semi-gloss finishes over a widecompositional range.

Generally, alkyds have poor color andretention properties and tend to chalk when

exposed to sunlight. Their primary advantageis low cost.


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Intumescent paints are examples ofspecial purpose coating systems.

They can provide fire ratings for exposedsteel for up to three hours


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Hot-dip galvanizing is a process in which asteel article is cleaned in acid (pickled) andthen immersed in molten zinc that is heatedto approximately 850 Fahrenheit.

This results in formation of a zinc and a zinc-iron alloy coating that is metallurgicallybonded to the steel.

The galvanized member is then cooled in airor quenched in water.

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The zinc coating acts as a barrier thatseparates the steel from the environmentalconditions that can cause corrosion


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Thank u!!

protective coating for steel structures

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