EN 3912:2007

Overview

EN 3912:2007 is a European aerospace standard that specifies the technical characteristics and classification of pan head bolts featuring a six lobe recess, relieved shank, and long thread. These bolts are manufactured from the heat-resisting steel FE-PA2601 (also known as FE-PA92HT or A286) and are silver plated. The standard establishes a tensile strength classification of 1100 MPa at ambient temperature with resistance up to 650 °C, specifically targeting aerospace industry applications where both mechanical strength and thermal endurance are critical.

This standard is maintained by CEN (European Committee for Standardization) and ensures uniformity and reliability of aerospace fasteners, facilitating their use across multiple European aerospace manufacturers and suppliers.

Key Topics

• Bolt Configuration and Dimensions: EN 3912:2007 provides precise specifications on bolt design including pan head shape, six lobe recess geometry per EN 3911, relieved shank, and long thread length. Dimensions and tolerances are specified in millimeters and apply after the silver plating process.

• Material Requirements: Bolts must be manufactured from heat-resistant steel grade FE-PA2601 (FE-PA92HT / A286), complying with relevant material standards EN 3761 or EN 2399, with specific heat treatments to achieve the required tensile strength and thermal resistance.

• Surface Treatment: Silver plating is mandated by EN 2786, ensuring corrosion resistance and surface durability crucial for aerospace environments. The plating thickness ranges from 3 µm to 6 µm on threads, with complete coverage required elsewhere.

• Mechanical Classification: The strength class is classified at a minimum tensile strength of 1100 MPa at room temperature, with operational temperature capability up to 650 °C. For seating torque calculations, the relevant strength class is limited to a maximum of 900 MPa due to recess geometry constraints.

• Designation and Marking: A standard coding system is outlined for bolt identification including thread and length codes. Markings should comply with EN 2424 style A, allowing traceability and conformity in aerospace assemblies.

• Referenced Standards: EN 3912 depends on several related standards such as ISO 3353-1 for thread profiles, ISO 5855-2 for limit dimensions, and EN 3905/EN 3911 for six lobe recess specifications.

Applications

EN 3912:2007 bolts are designed specifically for aerospace applications requiring reliable high-strength fasteners that maintain integrity under elevated temperatures and stress conditions. Key application areas include:

• Aircraft Structures: Fastening critical structural components where high tensile strength and heat resistance are necessary.

• Aerospace Engines and Systems: Components exposed to high thermal environments benefit from the heat-resistant steel and silver plating to resist corrosion and mechanical fatigue.

• Defense Aerospace Equipment: High-performance bolts ensuring safety and performance consistency in military aerospace hardware.

• Spacecraft Assemblies: Where materials must withstand extreme temperature variations and mechanical loads.

The silver plating additionally provides enhanced corrosion protection in varying climatic conditions encountered in aviation and space environments.

Related Standards

EN 3912:2007 is part of a broader suite of aerospace fastener standards ensuring compatibility and quality consistency across the industry:

• EN 3685: Technical specification for bolts in heat resisting steel FE-PA92HT with similar classification.

• EN 3905 & EN 3911: Detailed specifications and geometrical definitions for the six lobe recess design.

• EN 3761: Defines materials and heat treatments for FE-PA2601 heat-resistant alloys used in aerospace fasteners.

• EN 2786: Outlines the electrolytic silver plating process for aerospace fasteners.

• ISO 3353-1 and ISO 5855-2: Standards covering thread profiles and dimensional limits for aerospace bolts and nuts.

Compliance with EN 3912:2007 ensures that aerospace bolts meet stringent European aerospace industry requirements for mechanical strength, thermal resistance, and corrosion protection, thus supporting safety and durability in critical aerospace systems.

Keywords: EN 3912:2007, aerospace bolts, pan head bolt, six lobe recess, heat resisting steel, FE-PA2601, A286, silver plated bolts, aerospace fastener standards, high temperature bolts, tensile strength 1100 MPa, aerospace industry bolts, EU aerospace standard, aerospace bolt classification.