News - To Learn More About Round Link Chains Breaking Force Testing

Breaking force testing is a fundamental and mandatory quality control procedure for round link chains used across industrial and lifting applications. This paper outlines the methodology, significance, and key considerations for performing accurate breaking force tests, with a focus on high-grade lifting chains (e.g., G80, G100), coal mining chains, bucket elevator chains, and lashing chains. The goal is to verify both ultimate strength and elongation, ensuring compliance with international standards such as ISO 1834, DIN 5684, and ASME B30.9.

Introduction

Round link steel chains are critical components in material handling, lifting, mining, and marine applications. Their failure in service can lead to catastrophic accidents, making rigorous destructive testing essential. Breaking force testing not only determines the maximum load a chain link can withstand before fracture but also assesses its elongation behavior, which indicates ductility and material quality. This test is universally required for certification and routine batch inspection.

Testing Equipment and Setup

Breaking force testing machines can be oriented vertically or horizontally. Horizontal machines are often preferred for longer chain assemblies, while vertical machines may suit shorter samples or limited floor space. The test involves a sample length typically comprising 5, 7, or more links, depending on link diameter/link inner length and standard specifications. The chain is gripped at each end by specialized shackles or clamping jaws designed to apply tension purely axially, avoiding bending moments. Proper alignment is critical to prevent premature failure at the grips.

Key Testing Parameters

- Force Application Speed: The load must be increased steadily and continuously. Standards often prescribe a stress rate (e.g., 10 MPa/s) or a machine-controlled speed to ensure reproducible results. Too rapid loading can lead to inaccurate force readings, while too slow speeds may affect material behavior observations.

- Measurement: The machine records the peak force (breaking force) and often the elongation at break. Elongation is measured between specific points on the chain (usually two or three links apart) and indicates ductility—a vital safety attribute, especially for lifting chains.

- Clamping Tools: Grips must match the chain size and geometry to avoid slippage or notch effects. For high-grade chains like G80 and G100, careful attention is paid to preventing damage to the link surface during clamping, which could influence results.

round link chains breaking force testing

Application to Specific Chain Types

- G80 and G100 Lifting Chains: These are high-tensile steel chains, heat-treated for strength and wear resistance. G80 has a minimum breaking force of 800 MPa, and G100 of 1000 MPa. Testing verifies that each batch meets these minimums, with elongation typically required to be ≥12% for G80 and ≥10% for G100.

- Coal Mining Chains: Used in conveyors and powered roof supports, these chains operate in extremely abrasive and high-tension environments. Breaking force tests ensure they can withstand dynamic loading and shock forces underground.

- Bucket Elevator Chains: These chains handle bulk materials; testing confirms fatigue resistance and strength under continuous loading, often with additional emphasis on elongation to avoid brittle failure.

- Lashing Chains (Tie-down chains): Used for securing cargo, they must meet specified grades (e.g., Grade 8, Grade 10). Breaking force tests validate working load limits and safety factors, usually 4:1 or higher.

Importance of Accurate Testing

Reliable breaking force data ensures that chains perform safely under their rated working load limits. Inconsistent speed, poor clamping, or incorrect measurement can lead to false passes or failures, compromising safety and leading to liability. Regular calibration of testing machines and adherence to documented procedures are mandatory for accredited testing.

Breaking force testing remains the definitive method for validating the mechanical integrity of round link chains. For manufacturers and users of G80/G100 lifting chains, mining chains, elevator chains, and lashing chains, strict compliance with standardized testing protocols guarantees that chains meet the required strength and ductility criteria. Investing in precise testing equipment and trained operation not only fulfills regulatory obligations but also upholds the highest safety standards in industrial operations.

The elongation of a chain link during a breaking force test is a critical measure of its quality, revealing more than just ultimate strength. It acts as a key indicator of material ductility, manufacturing consistency, and overall structural integrity.

Elongation Measurement Methods

Elongation is measured as the permanent increase in the chain's length after it fractures, expressed as a percentage of the original length. There are two primary measurement approaches:

i) In-Laboratory Destructive Testing (During Manufacture & Certification)

This is the primary method for final quality control and type approval.

A pre-determined length of chain (e.g., 5 or 7 links) is mounted in a tensile testing machine. A laser displacement sensor or extensometer precisely measures the distance between two marked points on the chain as force is applied to destruction.

It captures the total (plastic) elongation at breaking force, providing the definitive value for quality certification. Advanced machines generate a complete force-elongation curve, showing both elastic and plastic deformation stages.

ii) In-Field & In-Process Measurement (For Monitoring & Maintenance)

These non-destructive methods check elongation during use to predict failure.

Image Analysis Method: An image of chain links is analyzed. The system calculates the different pitches (lengths) of inner and outer links. Wear and elongation primarily occur in the inner links; the elongation is calculated by comparing the increased inner link pitch to the stable outer link pitch.

Signal Pulse Counting Method: Used for continuously moving chains. Two sensors are placed a fixed distance apart. A marker on one link passes the first sensor, starting a counter that tallies pulses from markers on subsequent links until the original marker passes the second sensor. An increased count indicates the chain has stretched.

For High-Grade Lifting Chains (e.g., G80, G100), elongation is a strict quality gate:

G80 Chains: Minimum elongation at break is typically 15%.

G100 Chains: Minimum elongation at break is typically 12%.

These high minimums ensure exceptional toughness and energy absorption. A chain that meets the breaking force but has low elongation is brittle and prone to catastrophic, sudden failure under shock loads—a major safety hazard.

For applications like coal mining or bucket elevators, chain links elongation analysis is diagnostic:

Target Range: Acceptable elongation is often between 10% and 15%.

Too Low (<10%) elongation suggests material or heat-treatment issues, leading to brittle fractures. Research on mining chains indicates that poor elongation often correlates with undesirable fracture patterns at the weld zone, a critical weak point.

Too High (>18-20%) elongation may indicate softer material or inadequate hardening, compromising wear resistance and allowing the chain to permanently deform ("grow") excessively under normal load, causing operational issues like poor engagement with sprockets.

Post time: Jan-13-2026