EN 4011:2004

Overview

EN 4011:2004 is a European aerospace standard that specifies requirements for self-locking bihexagonal nuts made from the heat-resistant nickel base alloy NI-PH2601 (Inconel 718). These nuts are silver-plated and designed for high-performance aerospace applications, offering exceptional strength and temperature resistance. The nuts are classified to withstand a minimum tensile stress of 1,550 MPa at ambient temperature and maintain performance up to 600 °C.

Developed under the auspices of CEN and the European Association of Aerospace Manufacturers (AECMA-STAN), EN 4011:2004 sets strict guidelines for the dimensions, material properties, surface treatment, marking, and mechanical characteristics of these specialized aerospace fasteners.

Key Topics

• Material Specification
  The nuts are manufactured from NI-PH2601 alloy, commonly known as Inconel 718. This nickel base alloy offers excellent heat resistance and mechanical strength, suitable for aerospace environments subject to thermal stress and vibration.

• Design and Dimensions
  The bihexagonal nut design features twelve sides to facilitate torque application and enhanced self-locking behavior. Dimensions and tolerances comply with ISO 4095 and ISO 5855-2, providing consistent fit and performance throughout aerospace assemblies.

• Surface Coating
  Silver plating is applied electrolytically according to EN 2786, with a thickness range between 5 µm to 15 µm on external surfaces. Complete thread coverage is mandatory-threads sized MJ6 and above require a minimum of 5 µm plating to ensure corrosion resistance and maintain conductivity.

• Classification and Performance
  These nuts are classified as capable of withstanding 1,550 MPa tensile stress at ambient temperature and functional stability up to 600 °C. This classification suits parts exposed to elevated temperatures in aerospace engines and structural components.

• Marking and Traceability
  Marking conforms to EN 2424 style A, ensuring clear identification on the nut head. This facilitates traceability and compliance verification in manufacturing and maintenance.

Applications

EN 4011:2004 nuts serve critical roles in aerospace sectors, including:

• Aircraft Engines
  Used in high-temperature zones within gas turbines, where mechanical reliability and heat resistance are crucial.

• Structural Assemblies
  Applicable in airframe connections requiring self-locking fasteners that resist vibration-induced loosening.

• Spacecraft Components
  Suitable for spacecraft and satellite assemblies subjected to extreme temperature cycles and mechanical stresses.

• High-Performance Mechanical Systems
  Utilized wherever lightweight, durable, and heat-resistant fasteners are required under rigorous aerospace standards.

By adhering to this standard, aerospace manufacturers ensure interchangeability, safety, and performance reliability of fasteners in demanding environments.

Related Standards

• EN 2786 – Specifications for electrolytic silver plating of aerospace fasteners, ensuring corrosion resistance and consistent surface quality.
• EN 2952 – Material specification for heat-resisting alloy NI-PH2601 (Inconel 718), covering mechanical properties and treatment.
• EN 4047 – Technical specifications for self-locking nuts with MJ threads in NI-PH2601 alloy, complementing EN 4011 for variations in fastener types.
• ISO 4095 – Defines wrenching configurations for bihexagonal drives, ensuring standardized tool compatibility.
• ISO 5855-2 – Sets limit dimensions for aerospace bolts and nuts with MJ threads to maintain assembly integrity.
• EN 2424 – Marking requirements for aerospace products, providing uniform traceability practices.

Leveraging EN 4011:2004 facilitates standardized, high-strength, heat-resistant self-locking nuts essential for modern aerospace engineering, improving safety, durability, and operational efficiency across the aviation and space industries.