Notes

Details You Have To Have Knowledge Of Corrosion Control & Protection




Protective Coatings

Anti corrosive pigments are:-

a) Red Lead

b) Zinc Chromate

c) Zinc Phosphate

d) Zinc Dust

Preventing corrosion involve minimizing the flow of corrosion current to ensure that if negligible current, negligible corrosion result. Resins with highest electrical resistance are, catalyzed epoxy, phenol, vinyl and chlorinated rubber. Inclusion of pigments for example talc, china clay, mica and iron oxide also help out with increasing the resistance.

Removing soluble deposits on the steel surface is critical his or her presence will short circuit the resistance of the paint film to stage where rusting can take place. The thicker the coating the bigger could be the electrical resistance. Coatings limit the access of oxygen, water and salts and therefore control corrosion this way by the purely barrier effect. Catalyzed epoxies, coal tar epoxies, polyurethane, vinyl's and chlorinated rubber coatings have the lowest permeability to water and oxygen.

Alkyd and oil based coatings tend to be permeable to corrosive agents than top rated coatings specified to be sure all corrosive substances are removed from the steel surface and maximum adhesion is achieved relating to the coating and steel. The coatings chosen or specified ought to be ideal for the planet, characteristic and purpose the substrate is subjected.

For purpose in order to avoid and resist causes by:-

a) Chemical spillage

b) Chemical fumes

c) Temperature

d) Skid resistance

e) Abrasive resistance

f) Oil resistance

g) Fire retardant

Varieties of Coatings

Normally coatings these are known as conventional coating systems or high end systems. The decision on the coating to use depend upon the fee and budget one have and also the expected life or duration of the coatings as well as the required reason for the coatings, with either the protection, decoration or coding purposes, etc.





For coding and decorative purposes, conventional systems are usually recommended but also for protection purposes, high performance systems are suggested. Conventional coatings usually are one pack product whilst high end coatings can be found in two packs. Single pack product are usually air drying, two pack products normally cure by chemical reaction for the base by the catalyst or hardener.

For the best results, it is best to consult the designers who're specialised in manufacturing certain selection of coatings. Some are specialised in decorative coatings for houses, or protective coatings for industrial purposes or marine coatings vessels and ships or automotive coatings for vehicles or special coatings for appliances or air crafts. Visit the right manufacturer for the best sort of coatings needed.

Kind of Application

Application is possible by brush, roller, conventional spray or airless spray. Brush and roller are utilized where condition will not allow air or airless spray. Not suitable for top build coatings or achieve high film thickness. Slow in process and coverage is about 180m2 to 380m2 per man day. Conventional spray works for decorative and coding as only thin film is possible.

For defense purposes, airless spray is mandatory and it is the quickest technique of application. Covers 750m2 to 1100m2 per man day. Control of application is simply by tip size and input and output pressure. Can be used most paint types and will achieve high film thickness.

Application Condition

Paint really should not be applied in adverse conditions, like temperature below 5 degrees C and never above 35 degrees C. Not in a windy condition or when surfaces are wet because of rain, snow, ice, fog or condensation. Allow painting only once surface temperature is 3 degrees C higher than the dew point.

Paint Mixing

Every new tin of paint opened should be mixed thoroughly with a stirrer to disperse the solids. In two pack products, to make sure that the base and hardener can chemically react together and cure, only use an analog mixer. Always mix base and hardener within the correct ratio.

Paint Thinning

Use thinners only when necessary. Make use of the correct thinner for that product. Don't use more than 5% by number of thinners. Too much use will cause solvent entrapment, runs, sags, slumping, retard cure and affect wet film thickness and dry film thickness ratio.

Pot Life

All two pack products have a very pot life. That's time frame between mixing and curing once the paint is workable and can be applied. Pot life's temperature related. Never mix a lot more than may be used before pot life expires. Exceeding pot life will waste paint and will block up airless spray equipment.

Airless Spray Procedures

Check tip size and output pressure. Hold spray gun 30 cm to 45 cm through the surface. spray gun to be parallel to surface 90 degrees as a result. Horizontal pass 50 cm to l meter. Overlap previous pass by 50% if at all possible to ensure even film thickness. Trigger to be released after each pass. Cross hatching appropriate for even film thickness.



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