Surface Preparation – Dry Abrasive Blasting
- Dry abrasive blasting – grit blasting, more commonly referred to as sandblasting
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Pressurized air is used to transport the abrasive to the nozzle
Abrasive media being propelled into the surface at high-velocity to clean or etch the surface.
The performance of a coating system largely depends on bond strength between the clean steel substrate and the first coat, primer.
Abrasive blast cleaning is just about the only method that effectively removes millscale and provides a good surface profile.
For the reparation of aged coating systems our sandblasters focus on abrading the surface, feathering terminal edges, and removing and loosely adhered coatings.
The surfaces must be clean for good coating adhesion. Therefore it requires any oil, grease, chemicals, and particulate residues to be removed from the surface.
Mill scale should be removed prior to application of coating systems where long service lives are expected. It is electro-chemically cathodic to the underlying steel layers and as such will promote corrosion at varying rates depending on the prevailing environmental conditions.
Dry Abrasive Blasting
Thorough blast cleaning with the proper abrasive is generally considered to be the best method for preparing steel.
The governing standard for removing visible contaminants from steel surfaces is SSPC SP-1. This can be accomplished by several methods including wiping the surface with volatile solvents or power washing with or without emulsifying cleaners. Achieving an SSPC SP-1 criteria is a pre-requisite to any of the other SSPC surface preparation requirements.
Surface preparation is done to increase adhesion to coatings.
Without good quality surface preparation, meaning ultra-clean and a proper profile, all coating systems will fail.
It can be done mechanically or chemically, with different techniques, reaching different cleaning grades.
Surface preparation processes are used for clearing surfaces of coatings, imperfections, residue, organic matters, oxidation, and other contaminants like salts.
Abrasive is best used to create a surface profile needed for proper adhesion of coating systems.
Coating failure generally occurs at the steel – primer interface, hence the importance of a surface profile to maximise the bond area.
So, greater the profile, greater will be the surface area and the stronger the mechanical and chemical bond. If the steel is smooth, however, then adhesion of the coating is entirely dependent on a chemical bond, which can vary enormously from product to product.
The applicable standards for blasting area:
SSPC SP-5 / ISO 8501-1 Sa 3 / NACE 1 SSPC SP-5 / ISO 8501-1 Sa 3 / NACE 1 – White Metal Blast Cleaning
SSPC SP-10 / ISO 8501-1 Sa 2.5 / NACE 2 – Near White Metal Blast Cleaning
SSPC SP-6 / ISO 8501-1 Sa 2 / NACE 3 – Commercial Blast Cleaning
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