SIST EN 4396:2008

Overview

SIST EN 4396:2008 is a European standard developed by CEN that specifies the technical requirements for aerospace-grade self-locking shaft-nuts made from heat-resisting steel FE-PA92HT (A286), with silver plating. These shaft-nuts are metric and primarily designed for the axial location of bearing inner rings on shafts in aerospace applications. The components are engineered to maintain performance at elevated temperatures, with a maximum test temperature of 450 °C.

This standard ensures uniformity in the dimensions, materials, surface treatment, and mechanical properties of the self-locking shaft-nuts, contributing to enhanced reliability, durability, and safety in aerospace assemblies.

Key Topics

• Material Specifications
  The shaft-nuts must be manufactured using heat resisting steel FE-PA92HT (A286), meeting the stringent mechanical and thermal performance criteria outlined in EN 2171 and related aerospace alloy standards.

• Self-Locking Feature
  The nuts include a self-locking mechanism designed to maintain secure fastening under vibration and thermal cycling, critical in aerospace environments where safety and integrity are paramount.

• Silver Plating Surface Treatment
  According to EN 2786, shaft-nuts are silver plated with an external coating thickness ranging between 5 µm and 15 µm, and a minimum of 5 µm on thread surfaces to provide enhanced corrosion resistance and electrical conductivity.

• Dimensions and Tolerances
  The standard provides detailed dimensional specifications and tolerances for various thread sizes, compliant with metric aerospace thread standards, specifically for use with 4g6g external threads. These dimensions apply post silver plating to ensure assembly compatibility.

• Marking and Designation
  The nuts are marked in accordance with EN 2424, facilitating proper identification, traceability, and quality assurance. The designation includes the standard number and thread code for easy reference.

Applications

• Aerospace Bearings Installation
  EN 4396 shaft-nuts are primarily used to axially secure bearing inner rings on shafts, ensuring stable and precise positioning critical for the performance and longevity of aerospace actuators, engines, and control systems.

• High-Temperature Environments
  Ideal for applications subjected to temperatures up to 450 °C, such as in jet engines or other thermal-intensive aerospace components, maintaining mechanical integrity and locking performance under thermal stresses.

• Vibration and Safety-Critical Fastening
  The self-locking feature makes these shaft-nuts suitable for use in high-vibration zones within aircraft and spacecraft where loosening could result in catastrophic failure.

• Replacement and Maintenance Components
  EN 4396 nuts are standardized parts that can be sourced and replaced in legacy systems, supporting consistent maintenance and interoperability across aerospace fleets.

Related Standards

• EN 2171 - Heat resisting steel FE-PA92-HT bars for aerospace applications, defines mechanical properties of the steel used.
• EN 2786 - Specification for electrolytic silver plating of fasteners, ensuring durability and corrosion resistance of coatings.
• EN 3299 - Technical specification for similar shaft-nuts and threaded rings made from heat-resisting steel FE-PA2601 (A286).
• ISO 5855-1 - General requirements for aerospace metric threads, guiding thread form and fit applicable for mating external threads in a 4g6g tolerance class.
• EN 2424 - Marking requirements for aerospace products, ensuring traceability and compliance with industry standards.

Utilizing shaft-nuts compliant with SIST EN 4396:2008 guarantees aerospace-quality fastening solutions that meet rigorous thermal, mechanical, and environmental demands, thereby enhancing the safety, reliability, and service life of critical aerospace systems.