Ring Crush (RCT)

The ring crush test (RCT) is a key method for determining the edgewise compression strength of paper and paperboard. This property is directly related to the material’s ability to withstand the forces it experiences during stacking, storage, and transportation.

In the RCT, a paper or paperboard specimen is formed into a ring and subjected to a compressive force applied perpendicularly to its surface. The resulting measurement reflects the material’s resistance to crushing along its edge. For manufacturers, packaging engineers, and quality control teams, RCT provides a reliable indicator of structural integrity before materials enter the supply chain, reducing the risk of packaging failure.

Paperboard packaging must combine cost-efficiency with protective performance. The RCT is an essential quality measure for predicting in-plane crush resistance, helping manufacturers confirm that their material will perform under real-world conditions.

Key benefits include:

• Predicting packaging performance, with higher RCT values indicating the ability to support heavier loads
• Meeting compliance requirements for ISO and TAPPI standards
• Detecting process variations early through consistent quality checks
• Reducing waste by identifying substandard batches before production or distribution

In corrugated packaging manufacturing, for example, RCT is often used to confirm that a board meets stacking strength requirements before conversion into cartons.

Two principal methods are recognised for RCT, each with specific advantages:

TAPPI T 818 - Flexible beam method

This approach supports the specimen in a way that allows slight bending during compression. It can simulate more realistic loading conditions and is well-suited to materials with lower stiffness, though results can be more variable.

TAPPI T 822 - Rigid support method

In this method, the specimen is fully supported to prevent bending. It produces highly repeatable results and is ideal for comparative quality control. However, it may slightly overestimate strength in applications where bending is likely.

The main recognised standards for ring crush testing are:

• ISO 12192 - Standard method for RCT of paper and board
• TAPPI T 818 - Flexible beam support method
• TAPPI T 822 - Rigid support method

Each standard specifies apparatus requirements, sample dimensions, conditioning parameters, and load application speeds to ensure accurate and repeatable results across different facilities.

Prepare the sample

Cut samples to the required size specified by the relevant standard, typically corresponding to a circumference of 152 mm. Condition the samples at the specified temperature and humidity.

Set up the apparatus

Use a calibrated compression tester with the correct support fixture for the chosen method.

Position the sample

Form the sample into a ring shape without overlaps or gaps, then secure it in the fixture.

Apply the load

Apply compression at the specified rate, usually 12.5 mm per minute, until the sample fails or the peak load is reached.

Record results

Note the maximum load (in newtons) sustained before failure.

Repeat for consistency

Conduct multiple tests to confirm result reliability.

Results are expressed as the maximum load sustained by the sample. This can be converted into a ring crush index by dividing by the specimen width.

• Higher values indicate strong edgewise compression performance, suitable for heavy-duty packaging
• Lower values suggest possible structural weaknesses and may lead to adjustments in fibre composition or manufacturing processes
• Trend analysis over time can help detect material variability or process drift

Mecmesin designs and manufactures precision testing systems that meet ISO 12192 and TAPPI requirements for RCT. Our solutions provide repeatability, accuracy, and flexibility for both laboratory and production environments.

Technical advantages include:

• Compatibility with both TAPPI T 818 and T 822 support fixtures
• High-precision load cells to ensure measurement accuracy
• Configurable test stands such as the OmniTest and MultiTest-dV for different sample sizes and force ranges
• VectorPro software for digital data capture, analysis, and reporting
• Durable construction for consistent performance in demanding environments

With Mecmesin’s equipment, operators can perform reliable RCT in line with industry standards, supporting quality control and product performance assurance.

To discuss your ring crush testing requirements and identify the most suitable Mecmesin system for your application, speak to one of our technical experts today.