EN 4594:2013

Overview

EN 4594:2013 is a European standard developed by CEN that specifies the requirements for a two component cold curing polyurethane finish designed for aerospace applications with a focus on supersonic rain erosion resistance. This coating is formulated to provide a durable, medium level of protection against erosion caused by high-speed rain impact, particularly on critical aircraft areas such as leading edges and air intakes. The standard ensures high performance and reliability of polyurethane topcoats used over aerospace primers on aluminium substrates.

The specification covers the technical and physical properties of such coatings, including their application, drying conditions, formulation, and testing methodologies to verify erosion resistance and other key parameters. EN 4594:2013 supports safety and longevity in the aerospace industry by setting stringent performance criteria for coatings exposed to extreme environmental stress.

Key Topics

• Scope and Application
  This standard applies to two component polyurethane topcoats used over primers on aluminium alloy substrates, designed specifically for aerospace parts exposed to supersonic rain erosion.

• Formulation Requirements

  • Base contains hydroxyl functional resin, solvents, pigments for color and gloss, and additives for erosion resistance.
  • Activator is a polyisocyanate solution.
  • Optional thinner to aid application.

• Physical and Chemical Characteristics

  • Dry film thickness around 250 ± 50 µm to ensure adequate protection.
  • Viscosity and pot life controlled to maintain application quality.
  • Compliance with specified density, VOC content, and flash point limits to meet safety and environmental standards.

• Mechanical and Optical Properties

  • Specified gloss levels to maintain surface finish aesthetics.
  • Colour consistency verified by colorimetry to prevent visual deviations.
  • Ultimate tensile elongation ≥ 400% to ensure coating flexibility.

• Erosion Resistance Testing

  • Utilizes whirling arm test rig simulating supersonic rain conditions (223 m/s velocity, 25 mm/h rain, 2 mm drop size).
  • Maximum erosion limited to less than 50 g/m² after exposure without pitting or film degradation.

• Standardized Testing Procedures
  EN 4594 requires strict adherence to supplementary aerospace standards for substrate preparation and primer application, such as EN 3837, EN 23270, and EN 2435, ensuring repeatability and reliability of test data.

Applications

EN 4594:2013 polyurethane finishes are primarily used in aerospace manufacturing and maintenance for:

• Leading Edges of Wings and Control Surfaces
  To protect these critical aerodynamic surfaces from rain erosion during supersonic flight.

• Air Intakes
  Coatings prevent erosion damage that can degrade aerodynamic efficiency and structural integrity.

• Other High-Speed Exposure Surfaces
  Aircraft components exposed to extreme velocities and weather conditions benefit from enhanced durability and longevity.

The coatings balance erosion resistance with aesthetic quality, maintaining color and gloss to comply with aerospace visual standards. Their medium resistance level makes them ideal for typical supersonic operational environments.

Related Standards

For comprehensive application and testing consistency, EN 4594 references several key standards:

• EN 3837 – Surface preparation of aluminium alloy test pieces for coating application.
• EN 2435 – Corrosion resistant chromated two component cold curing primers for aerospace use.
• EN 23270 – Conditioning and testing environments for paints and varnishes.
• EN 3840 – Technical specifications for aerospace coatings including relevant tests and requirements.
• EN ISO 1513, EN ISO 2813, EN ISO 9117-1 – Testing methods for coating sample preparation, gloss measurement, and drying time.
• EN ISO 11890-1 – VOC content determination ensuring environmental compliance.

These interconnected standards support the reliable implementation of EN 4594 coatings in aerospace manufacturing and quality assurance processes.

Keywords: EN 4594:2013, aerospace coatings, polyurethane finish, supersonic erosion resistance, rain erosion protection, two component polyurethane, aerospace paint standard, cold curing polyurethane, aircraft coating standards, aerospace surface protection.