What is the primary purpose of the EN 12081 standard?

The primary purpose of EN 12081 is to define the quality requirements, testing methods, and approval procedures for lubricating greases used in railway vehicle axleboxes. It ensures these greases provide reliable performance, protect bearings from wear and corrosion, and contribute to the overall safety and efficiency of railway operations.

What key performance criteria does EN 12081 evaluate for axlebox grease?

EN 12081 evaluates several key performance criteria, including: Mechanical Stability (resistance to softening or hardening), Thermal Stability (performance at high and low temperatures), Water Resistance, Corrosion Protection, and Load-Carrying Capacity (anti-wear and extreme pressure properties).

Is compliance with EN 12081 mandatory?

While EN 12081 is a European Standard, its application is often made mandatory through contractual agreements between railway operators and suppliers, or by national and international railway safety regulations. For operations within the European Union, compliance is generally considered a requirement for ensuring interoperability and safety.

How does EN 12081 relate to EN 12080 and EN 12082?

These three standards form a complementary set for railway axleboxes. EN 12080 specifies the requirements for the rolling bearings themselves. EN 12081 specifies the requirements for the lubricating grease used in those bearings. EN 12082 defines the performance testing method for the complete axlebox assembly (bearing, grease, and housing) on a rig to simulate real-world service conditions and validate the performance of the entire system.

EN 12081: Securing European Rail Safety & Reliability

December 15, 2024 2:02 am

What is EN 12081? The Standard for Axlebox Lubricating Greases

EN 12081 is a European Standard that specifies the quality requirements and approval procedures for lubricating greases intended for use in railway vehicle axleboxes. This standard is critical for ensuring the safety, reliability, and operational efficiency of rolling stock by defining the precise performance characteristics that axlebox greases must meet under demanding railway conditions.

The standard establishes a common technical language and a set of rigorous test methods for grease manufacturers, rolling stock producers, and railway operators. By adhering to EN 12081, stakeholders can be confident that the grease will perform consistently, protecting the axlebox bearings from wear, corrosion, and premature failure, which is paramount for the safety of the entire railway system.

Core Objectives and Scope of EN 12081

The primary goal of EN 12081 is to ensure that lubricating greases used in the axleboxes of all types of railway vehicles, from high-speed trains to heavy-freight wagons, meet a high and consistent standard of quality. Its objectives include:

Ensuring Operational Safety: To prevent axlebox bearing failures caused by inadequate lubrication, which could lead to catastrophic derailments.
Defining Performance Benchmarks: To provide a clear set of measurable physical and chemical properties that a grease must possess.
Standardizing Testing Methods: To create a uniform framework for evaluating and comparing different greases, ensuring that test results are repeatable and reliable.
Facilitating Interoperability: To allow for the use of approved greases across different European railway networks, simplifying procurement and maintenance for cross-border operations.
Extending Component Lifespan: To guarantee that the grease provides long-term protection against wear and corrosion, thus maximizing the service life of axlebox bearings and reducing maintenance costs.

Key Technical Requirements and Performance Characteristics

EN 12081 outlines a comprehensive list of technical properties that a grease must exhibit. These are tested through a series of laboratory procedures designed to simulate the harsh operating environment of a railway axlebox.

Mechanical Stability

A crucial property of grease is its ability to maintain its consistency under the constant shear and vibration experienced in an axlebox. EN 12081 specifies strict limits on how much the grease’s consistency (measured by cone penetration) can change after being mechanically worked. If a grease is not mechanically stable, it can soften and leak out of the bearing or harden and fail to lubricate effectively.

Thermal Stability and Operating Temperature Range

Axleboxes are exposed to a wide range of temperatures, from sub-zero winter conditions to the high heat generated during braking and high-speed operation. The standard mandates tests to verify:

Dropping Point: The temperature at which the grease becomes fluid enough to ‘drop’. A high dropping point is essential to prevent the grease from melting and leaking out at high operating temperatures.
Low-Temperature Performance: The grease must not become so stiff at low temperatures that it impedes bearing rotation or fails to flow into lubricating zones.
Oxidation Stability: This measures the grease’s resistance to chemical degradation at high temperatures over long periods. Poor oxidation stability leads to the formation of sludge and varnish, which can block lubrication pathways and cause bearing failure.

Water Resistance and Corrosion Protection

Railway vehicles operate in all weather conditions, making water ingress a significant risk. EN 12081 requires greases to demonstrate excellent resistance to water washout and to provide robust protection against rust and corrosion. This is verified through tests that expose lubricated bearings to water and assess the level of corrosion on the metal surfaces.

Load-Carrying Capacity and Wear Protection

Axlebox bearings are subjected to immense static and dynamic loads. The grease must form a durable lubricating film that separates the rolling elements from the raceways, preventing metal-to-metal contact. The standard includes tests to evaluate the grease’s anti-wear (AW) and extreme pressure (EP) properties, ensuring it can protect the bearing under heavy and shock-loading conditions.

Mandatory Testing Procedures within EN 12081

To qualify a grease according to EN 12081, it must pass a battery of standardized laboratory tests. The following table summarizes some of the most critical tests and their significance.

Test Parameter	Typical Test Method (Reference)	Purpose and Significance
Consistency / Cone Penetration	ISO 2137	Measures the stiffness of the grease. Ensures the grease is not too hard to lubricate or too soft to stay in place. Tested before and after mechanical working.
Dropping Point	ISO 2176	Determines the temperature at which the grease loses its structure. A high value is required to ensure thermal stability at peak operating temperatures.
Oxidation Stability	ISO 14619 / ASTM D942	Assesses the grease’s resistance to aging and degradation due to heat and oxygen, which is critical for long-life lubrication.
Corrosion Protection	ISO 11007 (EMCOR Test)	Evaluates the grease’s ability to protect steel bearings from rusting in the presence of water. A low corrosion rating is mandatory.
Water Washout	ISO 11009 / ASTM D1264	Measures the percentage of grease lost from a bearing when exposed to a jet of water. A low value indicates good resistance to being washed away by rain or spray.
Oil Separation	DIN 51817	Checks the tendency of the base oil to “bleed” from the thickener. A controlled amount of bleed is necessary for lubrication, but excessive separation is a failure.
Mechanical Stability (Roll Stability)	ASTM D1831	Provides an aggressive mechanical working test to assess the shear stability of the grease over a long duration, simulating in-service conditions.

The Role of EN 12081 in the Railway Ecosystem

This standard serves as a fundamental link between different players in the railway industry, ensuring a common understanding of quality and performance for a critical component.

For Grease Manufacturers: It provides a clear target for product formulation and a standardized procedure for product approval, enabling access to the European railway market.
For Rolling Stock Manufacturers: It simplifies the specification and sourcing of axlebox grease, guaranteeing that the chosen lubricant is fit for purpose and compatible with the bearing design.
For Railway Operators and Maintenance Depots: It ensures that the grease used during maintenance will deliver reliable, long-term performance, reducing the risk of in-service failures and optimizing maintenance intervals.

Conclusion: Ensuring Reliability on the Rails

EN 12081 is more than just a technical document; it is a cornerstone of railway safety and reliability. By establishing stringent, verifiable requirements for axlebox lubricating greases, the standard ensures that bearings—one of the most critical components of a rail vehicle—are adequately protected. This leads to longer component life, lower maintenance costs, and, most importantly, a safer railway network for passengers and freight alike.