Application Method of "METSOL" Coating on Heat Exchanger Finned Tubes.
It is mandatory to clean “Finned Tube” surface to get rid of oil, dirt etc, for proper binding of METSOL to the tube surface. Uniform thickness and strong binding of coating is very essential. Therefore following coating procedure is to be followed.
Wash the tubes by dipping them in plain cold water. Keep the tubes for 20 to 25 minutes in water and wait so that the oil will float on the surface of water. Ensure oil is removed from the tube surface.
Prepare alkaline water solution of N/1000 strength by dissolving Caustic Soda (NAOH) in hot water and keep solution temperature at 80 to 85 Deg C. Immerse the tubes for 10 to 15 minutes in alkaline solution. Ensure oil is removed from the tube surface and rinse the tubes again with hot water.
Dry the tubes at room temperature.
Now the surface preparation is complete and dry tubes are ready for coating.
METSOL” can be coated by spray or by dipping the tubes in METSOL solution. Apply “METSOL” on finned tube surface and let the excess “METSOL” drain 2 -3 min.
Tap the coated tube 3-4 times gently to remove excess “METSOL”.
Keep coated tubes for air drying in dust free atmosphere and wait till it becomes touch dry. This is the “GREEN” stage of coating. In this stage coating can come under the influence of moisture/vapors. To avoid influence of any kind of atmospheric conditions on coating, coated tubes are kept on elevated temperature (>100degC) for 8-10 hrs or (140degC) till golden color turns into reddish-brown. In this stage coating is NEUTRAL against condensate, acidic vapors or any type of moisture and gases. Generally slow temperature picked up by coating is preferred for the development of strong binding. Looking to this property of coating, generally long duration air drying (14-16hrs at 30DegC room temperature) in GREEN stage is preferred at the time of assembly of the tubes. Reddish brown color of coating is an indication of strong and neutral condition of coating.
“METSOL” coating is lasts quite long (more than 10 years) in air after proper application and curing.
Film thickness of the coat is recommended for long life is 18-20 micron.
As compared to Phenolic resin, Metsol coated surface can stand better in corrosive atmosphere
Metal surface coated with Phenolic resin base coating develops micro cracks on surface due to mismatch between their coefficients of thermal expansion. This problem does not arise on METSOL coated surface.
Lots of other benefits are there after by application of “METSOL” which other coatings cannot offer. Anti oxidation/Anti corrosion/High Thermal conductivity/etc are unique properties to maintain high working efficiency for long time period.