ENVIROMENTAL CONDITIONS
Prior to PSP (primary surface preparation), we ensure that the relative humidity is above 85% or the surface temperature of steel is less than 3°C above the dew point. Environmental conditions and steel surface temperature are controlled with Elcometer-319, according to IMO PCPS (performance standard for protective coatings) in every shift.
HEATING SECTION
While applying heat to the profile, the humidity is removed, and the steel must be pre-heated to the appropriate temperature. To acquire appropriate drying, before applying the primer onto the surface of the steel, the recommended steel temperature should be between 30 °C and 40 ° C, depending on the primer type and thickness.
SHOTBLAST SECTION - STEEL CLEANLINESS
The shot blasting section ensures the steel surface is free from visible oil, grease, dirt, mill scale, rust, and foreign matter (ISO 8501-1: 2007 Sa 2½ -very thorough blast-cleaning). There is a cleaning unit and a blasting unit. These units are required for PSP (primary surface preparation) and the abrasives (grit, shot) sprayed on the surface of the material.
To achieve a good protection against corrosion after shop-primer, it is necessary that the material to be painted is applied Sa 2½ - very thorough blast-cleaning. During the preparations for Sa 2½, there will be no oil, grease, or dirt on the surface of the material; there will be no remnants of rust and paint or any other foreign matters.
PROFILE SURFACE
Applying the grit, shot will create the 30-75μm rough surface as per IMO PSPC (performance standard for protective coatings). This roughness will depend on the quality and dimension of the particles, such as grit, shot, etc. and on the grit, shot speed of the spraying. This roughness will create a good adhesive area for the primer, and therefore, the adhesiveness of the primer on the steel profile will be enhanced.
By examining the surface profile with Mitutoyo SJ-301 and Elcometer-224, the ideal surface profile Ry level (the spaciousness between the gorges and peaks) for the primer application should be between 30 and 75 μm.
WATER SOLUBE SALT LIMIT
Water soluble salt limit equivalent to NaCl should be ≤ 50 mg/m2 of sodium chloride as per IMO PSPC (performance standard for protective coatings). By examining the salt contamination with Elcometer-138 (Bresle Method) in every shift, according to ISO 8502-6 and ISO 8502-9.
APPLICATION OF PRIMER
After passing through the shot blast section, the steel proceeds to the priming centre, where the required prefabricated primer is applied through a vertical moving head comprising nozzles spraying the primer on both sides of the steel profile.
DRYING SECTION
The final part of the surface treatment process is for the steel to pass through the heated after dryer. It is advised to do this process in a closed environment for air pollution protection. DFT (dry-film thickness) is measured, according to paint manufacturer spec, with Elcometer-456 at final stage.
