Spring impact strength testing, commonly performed with a spring-operated impact hammer, verifies the mechanical robustness of product enclosures and external components against defined impact energies. This guide explains the testing principle, applicable standards such as IEC 60068-2-75 and IEC 62262, typical sample types, test procedures, and how accredited third-party laboratories help manufacturers achieve compliance and IK code certification.
Technical Overview
Spring impact strength testing, widely known as the spring hammer test, is a mechanical robustness test in which a spring-operated impact hammer delivers a calibrated kinetic energy blow to the surface of a specimen. The purpose of the test is to evaluate whether enclosures, covers, operating parts, and other externally accessible components of a product can withstand mechanical stresses that may occur during transportation, installation, and normal use without creating a safety hazard. The test is a fundamental requirement in product safety standards for electrical and electronic equipment and forms the basis of the IK impact protection rating system defined in IEC 62262.
The test device consists of a striking element with a hemispherical polyamide head that is propelled against the specimen surface by releasing a compressed spring. By adjusting the spring compression, the hammer delivers discrete impact energies in the range of approximately 0.14 J to 1.0 J. For higher energy levels, pendulum hammers or vertical free-fall hammers are used as specified in the relevant standards. The specimen is struck perpendicularly at predefined points, after which it is inspected for damage that could impair safety or functionality.
Spring impact strength testing is governed by several international and national standards, the most important of which include:
- IEC 60068-2-75 / EN IEC 60068-2-75 - Environmental testing, Part 2-75: Test Eh - Hammer tests, which defines the spring hammer apparatus, calibration, and test procedure
- IEC 62262 / EN 62262 - Degrees of protection provided by enclosures for electrical equipment against external mechanical impacts (IK code)
- IEC 60529 - IP code testing, which includes an impact verification component for enclosure integrity
- GB/T 2423.55 - Chinese national standard equivalent to IEC 60068-2-75
- GB/T 20138 - Chinese national standard equivalent to IEC 62262 for IK ratings
- UL 746C - Polymeric materials, which includes mechanical impact requirements for enclosure materials
- JIS C 60068-2-75 - Japanese industrial standard adopting the IEC hammer test method
The IK code classifies enclosures from IK00 (no special protection) to IK10 according to the impact energy they can withstand. The corresponding energy levels are summarized below:
- IK01 - 0.14 J impact energy
- IK02 - 0.2 J impact energy
- IK03 - 0.35 J impact energy
- IK04 - 0.5 J impact energy
- IK05 - 0.7 J impact energy
- IK06 - 1 J impact energy
- IK07 - 2 J impact energy (pendulum or free-fall hammer)
- IK08 - 5 J impact energy (pendulum or free-fall hammer)
- IK09 - 10 J impact energy (pendulum or free-fall hammer)
- IK10 - 20 J impact energy (pendulum or free-fall hammer)
Testing Samples
Electrical and Electronic Equipment Enclosures
Complete enclosures or enclosure subassemblies of electrical equipment, including plastic and metal housings, terminal covers, and inspection windows, are the most common test specimens. The enclosure is tested in its intended mounted condition to reproduce real-world support conditions.
Household Appliances
Kitchen appliances, cleaning appliances, heating appliances, and personal care devices are tested at externally accessible surfaces such as housings, control panels, knobs, and covers protecting live parts, in accordance with the requirements of the applicable household appliance safety standards.
Lighting Products and Luminaires
Lamp enclosures, diffusers, shades, and luminaire housings for indoor and outdoor use are subjected to spring hammer blows to verify mechanical strength, particularly for street lighting and industrial luminaires that must also meet elevated IK ratings.
Switches, Sockets, and Wiring Accessories
Wall switches, socket outlets, plugs, junction boxes, and control devices are struck at covers, actuating members, and enclosure walls to confirm that insulation barriers and live-part protection are not compromised by impact.
IT, AV, and Communication Equipment
Enclosures of information technology equipment, audio-video products, network devices, and outdoor communication cabinets are tested to confirm enclosure integrity and continued protection against access to hazardous live parts after impact.
Medical Devices and Laboratory Equipment
Housings of medical electrical equipment and laboratory instruments are evaluated to ensure that impacts during handling and use do not damage enclosures in a way that could affect electrical safety, operator protection, or measurement reliability.
EV Charging and Energy Storage Equipment
Charging stations, charging connectors, battery enclosures, and outdoor power cabinets are increasingly required to demonstrate elevated IK ratings because they are exposed to public access and potential vandalism, making spring hammer and higher-energy impact testing essential for market acceptance.
Testing Items
Spring impact strength testing encompasses several distinct test items, depending on the purpose of the evaluation:
- Spring hammer impact test at specified energy levels from 0.14 J to 1.0 J
- IK code determination and verification in accordance with IEC 62262 and GB/T 20138
- Enclosure mechanical strength verification required by product safety standards
- Post-impact integrity assessment, including verification of IP code maintenance after impact
- Post-impact electrical safety checks, such as earthing continuity, dielectric withstand, and accessibility of live parts
- Verification of impact resistance of components such as displays, lenses, actuating members, and cable glands
- Spring hammer apparatus calibration and energy verification to traceable standards
For each test item, the laboratory documents the striking points, the number of blows, the applied energy, and the resulting condition of the specimen, providing manufacturers with objective evidence for design validation, certification, and quality control purposes.
Testing Methods
Test Apparatus
The standard spring hammer consists of a cylindrical body containing a spring-driven striking element terminated in a hemispherical head of radius 10 mm made of polyamide. The compression of the spring is adjustable, allowing the impact energy to be set to discrete values between 0.14 J and 1.0 J. A release trigger fires the striking element, which transfers its kinetic energy to the specimen surface in a single, controlled blow.
Calibration Requirements
The spring hammer must be calibrated at regular intervals on a calibration device compliant with IEC 60068-2-75, which measures the velocity of the striking element and calculates the delivered impact energy. Accredited third-party laboratories maintain strict calibration schedules and traceable calibration records to ensure that every blow delivered during testing corresponds to the specified energy within the permitted tolerances.
Test Procedure
The specimen is secured on a rigid support or mounted in its intended installation position. Striking points are selected at the most vulnerable locations, typically including enclosure walls, corners, covers, and areas adjacent to live parts as specified by the relevant product standard. The hammer is positioned with its nose resting against the surface and oriented perpendicular to the plane of impact. The trigger is then released to deliver the blow. Most product standards require three consecutive blows at each selected point, although the exact number and energy level are defined by the applicable specification.
Test Conditions
Testing is normally performed at an ambient temperature of 15 to 35 degrees Celsius and a relative humidity of 25 to 75 percent, unless the product standard specifies conditioning at extreme temperatures. For thermoplastic enclosures, some standards require the test to be carried out after thermal conditioning to account for material behavior at low temperatures.
Acceptance Criteria
After the impact blows are applied, the specimen is examined visually, mechanically, and electrically. The test is considered passed if the specimen shows no damage that impairs safety or functionality, typically including:
- No cracks or openings that allow access to hazardous live parts
- No degradation of the enclosure protection rating, such as the IP rating
- No impairment of the continuity of protective earthing connections
- No detachment of covers, actuators, or insulating barriers
- No sharp edges or protrusions created by the impact that could injure users
- Continued normal operation of the equipment where the standard requires a functional check
Applications
Spring impact strength testing serves a wide range of engineering and commercial purposes across industries:
- Product safety certification and compliance demonstration for market access in regions requiring conformity with IEC, EN, GB, UL, or JIS based standards
- IK rating verification for outdoor enclosures, public infrastructure equipment, and vandal-resistant products
- Design validation and comparison of enclosure materials, wall thicknesses, and structural reinforcements during product development
- Quality control and incoming inspection of enclosure components in serial production
- Failure analysis and root cause investigation of field damage or transit damage claims
- Supporting technical documentation for tenders and customer specifications that specify mechanical robustness requirements
Manufacturers working with accredited third-party laboratories benefit from internationally recognized test reports that can be submitted to certification bodies, regulators, and customers worldwide, reducing duplication of testing and accelerating time to market.
FAQ
What is the difference between the spring hammer test and the IK code test?
The spring hammer test is a test method defined in IEC 60068-2-75 that delivers impact energies up to approximately 1 J using a spring-operated device. The IK code test defined in IEC 62262 is a rating system that classifies enclosures from IK00 to IK10; the lower energy levels are verified with the spring hammer, while the higher energy levels above 1 J are applied with pendulum or free-fall hammer apparatus.
Which impact energies can a spring hammer deliver?
A calibrated spring hammer typically delivers discrete impact energies of 0.14 J, 0.2 J, 0.35 J, 0.5 J, 0.7 J, 0.75 J, and 1.0 J, corresponding to the lower range of the IK classification. Energies of 2 J and above require alternative impact apparatus as specified in the standards.
How many blows are applied during the test?
Most product safety standards require three consecutive blows at each selected striking point, with the points chosen at structurally vulnerable locations and positions adjacent to hazardous parts. The exact number, energy, and locations are always governed by the applicable product standard.
Is spring impact strength testing destructive?
The test is potentially destructive because the specimen is subjected to real impact blows that may leave marks or cause damage. Samples tested for certification are generally not returned to production, and manufacturers are advised to submit dedicated test samples representing the final production design.
What samples and information should be submitted for testing?
Manufacturers should provide complete samples with final enclosure materials and construction, installation or mounting instructions, the applicable product standard or required IK rating, and any specific striking points of concern. Accredited third-party laboratories can also assist in determining the appropriate energy level if the requirement is unclear.
How often must a spring hammer be calibrated?
Spring hammers must be calibrated periodically according to the requirements of IEC 60068-2-75 and the laboratory quality system, typically at intervals not exceeding twelve months or after any repair or suspected deviation. Calibration verifies striking velocity and delivered energy against traceable reference measurements.