Lightened shank screws for rail transport

Lightened shank screws for rail transport

In the rail transportation sector, safety and reliability are essential requirements, especially when it comes to mechanical components subjected to cyclic stresses and extreme environmental conditions. In this context, lightened shank screws represent an advanced technical solution designed to ensure maximum fatigue resistance and durability.

EFS supports its customers in selecting and supplying these solutions, offering screws made to specific design requirements, carefully selecting the most suitable materials and finishes.

Case study: lightened shank screw made by EFS for railway applications

A significant example of technical support by EFS is the recent supply of screws destined for a major customer in the railroad industry. These are hexagon head screws, made to the customer’s design, ideal for critical applications where fatigue resistance and fastener stability are critical.

The technical features of this supply include:

• Type: hexagon head screw.
• Processing: hot stamped, with production in batches of 2000 pieces.
• Size: M10x65, with lightened shank to reduce weight without compromising strength.
• Material: 42CrMo4 steel hardened and tempered to class 12.9, with burnished finish.
• Certification with testing in the presence of DNV inspectors (certification 3.2)

The use of the material 42CrMo4 is a strategic choice for applications subjected to high loads. It is a quenching and tempering steel that combines excellent hardenability, mechanical strength and good machinability.

Class 12.9, which indicates a tensile strength of about 1200 N/mm², is one of the highest available for fasteners. It is therefore perfect for critical connections in rail vehicles.

To learn more, we recommend consulting the table of resistance classes.

What distinguishes a lightened-shank screw

But what makes these screws so special for use in the railroad industry?

The main feature is the presence of a shank with a smaller diameter than the threaded part. This design solution allows the screw to stretch elastically under load, improving stress distribution and reducing the risk of fatigue failure.

The presence of an unthreaded collar between the head and the discharged part facilitates assembly and disassembly operations, avoiding the risk of seizing in the bore. Overall, this results in a stronger and more durable fastening system that can effectively meet the maintenance and safety requirements of the railroad industry.

Typical applications in the railway industry

Lightened shank screws are widely used in all situations where components are subjected to cyclic vibrations and dynamic loads. In the railway industry, these screws are used for:

• Fasteners in wheel hubs and brake discs, where fatigue resistance is critical.
• Elastic joints and connections subject to continuous vibration.
• Drive systems and other mechanical components that require highly reliable fasteners.

In these contexts, the use of standard screws would provide inferior performance in terms of safety and durability. This is precisely where the added value of the lightened-shank screws provided by EFS becomes apparent.

Surface treatments for maximum durability: burnishing vs Geomet

To withstand the most aggressive environmental conditions, such as exposure to moisture, salt spray or chemicals, specific surface treatments can be applied.

At the request of our customer, this screw was subjected to burnishing. Burnishing is a chemical treatment that gives the steel a dark color and protection against oxidation, while also improving the aesthetic appearance of the component.

In other cases, the surface treatment indentified as Geomet®, a high-performance anticorrosive coating between 5 and 10 µm thick, is applied to the screws. This treatment, based on aluminum and zinc passivated in lamellar form, is particularly effective against salt spray corrosion, making it ideal for outdoor applications or in wet environments. Visually, it is distinguished by its characteristic silver color.

Reference standards: safety assurance

Safety is an indispensable principle in the world of rail transportation. For this reason, the use of lightened shank screws must meet strict technical and regulatory standards.

The main reference standards are:

• EN 15085: European standard defining requirements for the quality of welding of railway vehicles and their components.
• UIC 864-3: Specific international standard for fasteners used in railway applications.
• EN ISO 898-1: relating to the mechanical properties of steel fasteners.

The use of these screws should always be planned for at the design stage, with careful calculations taking into account the stresses to which the component will be subjected.

Conclusions

The lightened shank screws for rail transportation supplied by EFS represent the perfect synthesis of technology, safety and mechanical strength. With in-depth knowledge of industry regulations and the ability to provide customized solutions, EFS serves as a strategic partner for companies operating in the railway industry.

Choosing EFS means counting on an experienced interlocutor, capable of supporting the customer at every stage: from the selection of the most suitable material, to the choice of finishes, to the timely delivery of batches that meet the most stringent technical specifications.

References:

EN ISO 898-1 – Mechanical properties of steel fasteners: BS EN ISO 898-1:2013