Optimising Line Manufacturing Painting for Long-Term Performance

Painting is far more than a finishing touch in the line manufacturing of metal products such as machinery and equipment. It is a critical stage of production that defines brand appearance, protects against corrosion and wear, and significantly influences lifecycle cost.

A recent expert article by Nor-Maali featured in Protective Coatings Expert Magazine highlights the key considerations for designing and optimising an in-line industrial painting process, from surface preparation through to final quality control.

Surface Preparation: The Foundation of Performance

As with all protective coating systems, performance begins with preparation. Effective cleaning removes salts, grease, oils and particulates that compromise adhesion. Alkaline water-based detergents are commonly used in modern production environments.

For steel components, abrasive blast cleaning to Sa 2½ – and in demanding cases Sa 3 – remains the benchmark. Where blasting is unsuitable, chemical pre-treatment methods such as iron or zinc phosphating may be used, with careful verification of coating adhesion, particularly when passivation layers are involved.

The higher the corrosion class defined under ISO 12944, the more critical surface preparation becomes, especially when using waterborne coatings, which are generally less tolerant of residual contamination than solvent-based systems.

Selecting the Right Coating System

Coating selection depends primarily on service environment — corrosion exposure, UV radiation, mechanical stress and chemical contact.

The guidance in ISO 12944-5 provides a framework, although many manufacturers work to internal specifications based on field experience.

Common industrial coating options include:

• Epoxies – excellent corrosion and chemical resistance; widely used as primers in C4–C5 environments. Zinc-rich epoxies provide sacrificial protection in highly corrosive settings.

• Polyurethanes – superior gloss and colour retention under UV exposure; commonly used as topcoats and suitable for single-coat systems up to C3 environments.

• Acrylics and alkyds – generally limited to lower corrosion categories (C1–C2) and increasingly restricted by environmental legislation.

Single-Coat vs Multi-Coat Systems

Single-coat (Direct-to-Metal) systems offer efficiency and reduced process time, but demand precise film thickness control. Multi-coat systems provide greater tolerance for variation and often deliver higher corrosion protection levels, albeit with longer cycle times.

Wet-on-wet application — where primer and topcoat share compatible chemistry — can improve productivity in multi-coat systems.

Environmental Compliance and Safety

Environmental regulation plays an increasingly influential role in coating selection. EU Directive 1999/13 limits VOC emissions from production facilities, encouraging adoption of waterborne and high-solids systems. These can reduce VOC emissions to a fraction of traditional solvent-based alternatives.

In addition, EU Commission Regulation 2020/1149 imposes restrictions on products containing more than 0.1% isocyanate monomers. Many manufacturers also apply internal chemical compliance standards aligned with REACH and SVHC listings.

Process Efficiency in High-Speed Lines

High production speeds and limited drying time demand careful process engineering. High-pressure airless spraying remains the dominant application method, often supported by electrostatic or air-assisted systems. For complex geometries and high volumes, dip coating may also be considered.

Drying efficiency is increasingly optimised through electric or gas ovens, with infrared (IR) systems gaining popularity due to improved energy transfer efficiency. Waterborne coatings require particular attention to humidity control and evaporation management.

Quality Control and Long-Term Value

Final inspection – including adhesion testing such as cross-cut testing to ISO 2409 ensures both aesthetic and technical compliance.

When surface preparation, coating selection, and curing conditions are properly aligned, manufacturers can significantly extend service life, reduce maintenance repainting, and lower total lifecycle costs, even where premium coatings are used.

For a detailed technical breakdown of best practices in in-line product painting, read the full article from Nor-Maali here: Optimising Painting in Line Manufacturing – Full Article