How to prepare a metal surface for industrial painting?

In the field of anti-corrosion protection, a key aspect is the appropriate preparation of steel surfaces before applying paints and protective coatings. This process is aimed not only at removing unwanted substances, but also at creating optimal conditions for the adhesion of primer paints or primer enamels. The importance of this process is emphasized by the PN-EN ISO 8501-1 standard, which is a benchmark in assessing surface preparation in terms of cleanliness and appropriate profile.

Why is it worth preparing the surface for painting?

It is necessary to emphasize that without proper preparation of the substrate, even the best anti-corrosion paint will not be able to fully fulfill its function.

This applies in particular to high-tin primers, heat-resistant paints and thermally sprayed zinc. These products require not only the removal of all mineral and organic contaminants, but also corrosion products that are not strongly bonded to the steel.

It is worth noting that some paints advertised as “anti-rust” also require careful preparation of the substrate, often to the purity level of Sa 2 in accordance with the PN-EN ISO 8501-1 standard, in order to fully demonstrate their anti-corrosion properties.

PN-EN ISO 8501-1 standard: Basis for preparing surfaces for painting

The PN-EN ISO 8501-1 standard is a fundamental document referred to by paint manufacturers in the context of surface preparation. It contains standards that enable a visual assessment of the cleanliness of steel surfaces before and after the cleaning process.

There are four basic initial states of steel, from “straight from the steelworks” covered with mill scale, to steel with partially fallen scale and corrosion coating. Unfortunately, due to high costs, access to the standard is limited, especially for smaller enterprises.

Methods of cleaning the surface before painting

Surface preparation includes various cleaning techniques, including abrasive blasting, which affects the roughness of the substrate, increasing the adhesion of paints. Before the painting process, assess the degree of cleanliness in accordance with the standard, and check the preparation of joints, edges and other potentially problematic areas.

The presence of dust residues and other contaminants that may negatively affect the durability of paint coatings should be assessed.

The most popular methods of cleaning surfaces as preparation for painting

Mechanical cleaning:

  • Mechanical brushing (using wire brushes) – removes loose rust, paint and other contaminants.
  • Shot blasting (sandblasting, abrasive blasting) – use of a high-pressure abrasive stream for cleaning and roughening.
  • Grinding – using sandpaper or sanding discs to smooth the surface.

Dry cleaning:

  • Degreasing – the use of solvents or alkaline agents to remove fats, oils and other organic contaminants.
  • Phosphating – a chemical process that applies a light layer of phosphate to the metal to provide better paint adhesion and protection against corrosion.
  • Passivation – mainly used to increase corrosion resistance by creating a protective oxide layer.

Thermal cleaning:

  • Incineration – removal of organic pollutants by burning at high temperature.
  • Plasma treatment – using plasma to clean and activate the surface before painting.

Laser cleaning – removal of contaminants using a concentrated laser beam, which allows for very precise cleaning without contact with the surface.

Ultrasonic cleaning – immersing an item in a bath of cleaning solution and using ultrasound to remove contaminants from hard-to-reach places.

To sum up: The process of preparing a steel substrate for industrial painting is complex and multi-stage, requiring not only compliance with strictly defined standards, but also understanding the impact of each stage on the final quality and durability of anti-corrosion protection. Despite challenges related to access to standards and costs, appropriate surface preparation is necessary to ensure high adhesion and effectiveness of the applied coatings.

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