SIST EN 3726:2005

Overview

SIST EN 3726:2005 is a European standard that specifies the technical requirements and characteristics for self-locking clip nuts used in aerospace applications. These nuts are manufactured from heat-resisting steel grade FE-PA2601 (A286) and are coated with molybdenum disulphide (MoS2) to enhance performance under extreme conditions. The standard ensures that the nuts meet stringent mechanical and thermal classifications, specifically maintaining performance up to 1,100 MPa tensile strength at ambient temperature and functional integrity at temperatures as high as 425 °C.

Issued by the European Committee for Standardization (CEN), this standard is integral for aerospace manufacturers and suppliers aiming to achieve reliability and safety in high-temperature aerospace environments.

Key Topics

• Material Specifications: The nuts must be made from heat-resisting alloy FE-PA2601 (commonly known as A286), known for its strength and corrosion resistance at elevated temperatures. The clip component also derives from this material.

• Coating: A molybdenum disulphide (MoS2) dry lubricant coating, as per EN 2491, is applied to reduce friction and wear during assembly and operation.

• Mechanical Strength: Classified to withstand a minimum tensile load of 1,100 MPa at room temperature, ensuring robust locking performance under mechanical stress.

• Thermal Resistance: Capable of enduring operational temperatures up to 425 °C without degradation, suitable for aerospace engine and structural applications exposed to heat.

• Design and Dimensions: The standard provides defined maximum dimensions and tolerances to guarantee interchangeability and proper fit with related aerospace fasteners. Although a sample configuration is illustrated, manufacturers may produce alternate forms within specified dimensional limits.

• Marking and Identification: Marking in accordance with EN 2424 requirements ensures traceability and conformity, critical for aerospace quality assurance.

• Related Technical Specifications: Compliance with EN 3752 provides further technical requirements on specifications for self-locking nuts using FE-PA2601 steel with MoS2 coating.

Applications

SIST EN 3726:2005 self-locking clip nuts are primarily used in:

• Aerospace fasteners for high-temperature areas: Such as engine housings, exhaust assemblies, and other components exposed to extreme heat.

• Structural aerospace joints: Where vibration resistance and secure locking prevent loosening during long-term service.

• Aerospace manufacturing and maintenance: Used by manufacturers and maintenance engineers to ensure fasteners meet international aerospace standards for safety and reliability.

• Other high-performance engineering sectors: Though designed for aerospace, these nuts can be applicable in automotive racing, power generation, or chemical industries where heat-resistant fastening solutions are required.

Related Standards

• EN 3752 – Specifies technical requirements for nuts with self-locking features in FE-PA2601 (A286) with MoS2 coating, closely linked to EN 3726.

• EN 2491 – Covers the coating methods and standards for molybdenum disulphide dry lubricants applied to aerospace fasteners.

• EN 2424 – Defines marking rules for aerospace products, ensuring proper identification and traceability of fasteners under EN 3726.

• ISO 5855-2 – Pertains to limit dimensions for aerospace bolts and nuts with MJ threads, referenced for sizing validity within EN 3726.

By adhering to SIST EN 3726:2005, aerospace manufacturers ensure that their self-locking clip nuts deliver optimum performance in demanding temperature and mechanical load environments, upholding safety and quality in critical aerospace assemblies.