IEC 60068-2-75 Test Eh: Simulating Real-World Impacts with Spring Impact Hammers

IEC 60068-2-75 Test Eh: Simulating Real-World Impacts with Spring Impact Hammers

Introduction

In the realm of product design and validation, ensuring mechanical robustness is non-negotiable. Products, from consumer electronics and industrial controls to automotive components, must withstand the inevitable bumps, knocks, and impacts of their operational life. While drop tests simulate one type of accident, they don't cover the full spectrum of mechanical abuse a product might encounter. How do you simulate a tool being dropped on a control panel, a knee bumping into a device under a desk, or the sharp impact of a thrown object?

The answer lies in a highly specific and repeatable test method defined by the international standard IEC 60068-2-75: Environmental testing - Part 2-75: Tests - Test Eh: Hammer tests. This standard, and particularly its use of spring-operated impact hammers, provides a scientific framework for replicating these real-world impact events in a controlled laboratory environment. This article provides a comprehensive guide to Test Eh, moving beyond the basic specification to explore its practical application, the physics behind the spring hammer, and strategies for designing products that pass with confidence.

Understanding the Standard: IEC 60068-2-75 Test Eh

IEC 60068-2-75 is an umbrella standard that covers several hammer test methods, including pendulum hammers, swing hammers, and vertical impact hammers. However, Test Eh specifically refers to tests carried out using spring-operated impact hammers. This method is prized for its simplicity, reproducibility, and ability to deliver a known, consistent energy level to a test sample.

The fundamental purpose of Test Eh is to assess the ability of a product's enclosure and internal components to withstand specified severities of impact. The test evaluates:

   Structural Integrity: Cracking, fracturing, or permanent deformation of housings.

   Safety: The integrity of protective covers and barriers, ensuring live parts are not exposed.

   Functionality: The product must continue to operate normally after impact without performance degradation.

   Stability: For equipment stands or covers, the test can verify they don't become unstable or hazardous.

The Tool: Deconstructing the Spring Impact Hammer

The heart of Test Eh is the spring hammer, often referred to by its historical namesakes like the "ESD Simulator Impact Hammer" (though not for ESD testing) or generically as an "IK test hammer" (relating to the IK code for mechanical impact protection).

A standard spring hammer consists of three main components:

1.  Hammer Head: The striking element. The standard defines specific head geometries to simulate different real-world contact points:

       Hemispherical Head: (Radius 10mm) Simulates rounded, blunt impacts (e.g., a tool handle, a knee).

       Conical Head: (Radius 10mm, 150° angle) Simulates sharper impacts (e.g., a corner of a falling object).

       Spherical Head: (Radius 50mm) Simulates larger, more distributed impacts.

2.  Spring-Driven Mechanism: This is the core of the system's repeatability. The hammer is cocked against a pre-calibrated spring to a specific energy level. When released, the spring propels the hammer head forward in a linear motion, ensuring the same energy is delivered every time for a given setting.

3.  Release and Guidance System: This ensures the hammer travels in a straight line towards the impact point without deviation, which is critical for accurate and consistent results.

The Physics of the Impact: Energy, not Force

A key conceptual shift when working with Test Eh is to think in terms of impact energy (joules), not force (newtons). The standard specifies test severities based on the kinetic energy of the hammer at the moment of impact. Common energy levels are derived from the IK Code (IEC 62262):

   0.14 J (IK03)

   0.35 J (IK04)

   0.70 J (IK05)

   1.00 J (IK06)

   2.00 J (IK07)

   5.00 J (IK08)

   10.00 J (IK09)

   20.00 J (IK10)

The product specification or relevant safety standard (e.g., IEC 61010-1 for lab equipment, IEC 60529 for IP enclosures) will dictate the required energy level and number of impacts. The force exerted on the product is a result of this energy being dissipated over a very short time and distance. It is influenced by the hardness and deformation characteristics of both the hammer head and the product surface.

Executing Test Eh: A Step-by-Step Methodology

Simply hitting a product with a hammer is not a compliant test. A rigorous procedure must be followed:

1.  Sample Conditioning: The product is typically stabilized at standard atmospheric conditions (e.g., 23°C ± 2°C, 50% RH ± 5%) to ensure material properties are consistent.

2.  Mounting/Fixturing: The sample is mounted on a rigid surface in its "worst-case" orientation for each impact point. This simulates the product being installed in its final location. Poor fixturing can absorb energy and invalidate the test.

3.  Selection of Impact Points: Impacts are applied to every likely point of weakness on the enclosure. This includes:

       Seams and joints between parts.

       Windows, displays, and lenses.

       Ventilation grilles.

       Operator controls, buttons, and switches.

       The centers of large, unsupported surfaces.

       Anywhere a label specifies a warning or instruction.

4.  Applying the Impacts: For each selected point, a series of impacts (typically 3 or 5) are applied. The hammer must be released perpendicular to the surface at the point of impact. The hammer is re-cocked to the same energy level for each strike.

5.  Post-Test Evaluation: After testing, the unit undergoes a thorough inspection:

       Visual Inspection: For cracks, breaks, or permanent deformation >1mm.

       Safety Check: Using a standard test finger (as per IEC 61032) to verify no hazardous live parts are accessible.

       Functional Test: The product is powered on and verified to operate within its specified parameters.

From Laboratory to Real World: Translating Test Parameters

The true engineering challenge is not just running the test, but correctly interpreting the standard for your product.

   Choosing the Right Energy Level: A medical device used in a calm hospital lab may only require 1 J (IK06), while a circuit breaker in a factory hallway might need to withstand 20 J (IK10). Consider the product's environment. What objects could hit it? With what force? A 2 J impact simulates the energy of a 1kg mass dropped from 200mm—a common scenario for a hand tool slipping from a bench.

   Selecting the Hammer Head: Use the conical head for vulnerable thin parts or sharp edges on other objects. Use the hemispherical head for general robustness testing on thicker housings.

   The Myth of "Passing IK10": Simply stating a product is "IK10 rated" is an oversimplification. The rating must be defined in context: "The front panel, when mounted per the manufacturer's instructions, can withstand five 20 J impacts with a hemispherical hammer head without exposing live parts or impairing functionality." The rating may not apply to other surfaces like plastic side panels.

Designing for Impact Resistance: A Proactive Approach

Passing Test Eh is not about building a tank; it's about intelligent design.

1.  Material Selection: Use materials with high impact strength and good toughness. Polycarbonate blends are often superior to ABS for enclosures. Consider glass-filled polymers for added stiffness and strength.

2.  Geometry and Ribbing: Avoid large, flat, unsupported surfaces. Use strategic ribbing, corrugation, or curved geometries to stiffen walls and dissipate impact energy over a larger area.

3.  Managing Weak Points: Reinforce areas around mounting holes, seams, and openings. Use overmolding or soft-touch materials in high-impact zones to absorb energy.

4.  Protecting Critical Components: Ensure a clear gap between the inside of the enclosure and internal PCBs or fragile components. Use shock-absorbing mounts for sensitive displays.

Common Pitfalls and How to Avoid Them

   Under-testing: Only testing the strongest part of the enclosure. Be ruthlessly thorough in identifying every potential weak point.

   Incorrect Fixturing: Mounting the product in a way that doesn't represent real-world use, leading to false passes.

   Ignoring Cold Temperatures: Materials become brittle at low temperatures. If your product ships or operates in cold environments, consider performing Test Eh after conditioning the sample to a low temperature (e.g., -25°C) as a type test.

   Overlooking Post-Impact Functionality: A housing might not crack, but the impact could dislodge a connector or crack a solder joint on an internal board. Full functional testing is mandatory.

Conclusion

IEC 60068-2-75 Test Eh is far more than a simple "hammer test." It is a sophisticated simulation tool that bridges the gap between theoretical design and real-world durability. By understanding the principles behind the spring hammer's calibrated energy delivery and applying the test method with a rigorous, forensic approach, engineers can move beyond compliance checklists.

This method empowers designers to create products that are not only safe but also inherently reliable, building user trust and reducing warranty claims. In a competitive market, the ability to confidently validate a product's robustness against mechanical impacts is a significant advantage, proving that a product is built not just to specification, but for the realities of its working life.

References & Further Reading:

   IEC 60068-2-75:2014 - Environmental testing - Part 2-75: Tests - Test Eh: Hammer tests

   IEC 62262:2002 - Degrees of protection provided by enclosures for electrical equipment against external mechanical impacts (IK code)

   IEC 61010-1:2010+AMD1:2016 CSV - Safety requirements for electrical equipment for measurement, control, and laboratory use