Ring Crush and Flat Crush Test Modes of Paper Compression Strength Tester

This article introduces two testing modes of the paper compression strength tester: ring crush test and flat crush test. The ring crush test is primarily used to measure the longitudinal compressive strength of paper, making it suitable for cylindrical structures like corrugated paper cores. It involves rolling a strip of paper into a ring and conducting a crushing test to calculate the ring crush strength. The flat crush test evaluates the compressive performance of paper in the planar direction and is commonly applied to materials such as boxboard. It involves compressing a flat sample and recording the maximum load to determine the flat crush strength. Each mode has its applicable scenarios and standards. During testing, attention must be paid to environmental conditions, instrument calibration, and sample preparation to ensure accurate results. These methods provide an essential basis for paper quality control.

Overview

Paper compressive strength tester is a key equipment for evaluating the compressive properties of paper products, and is widely used in packaging, printing, and materials research. Its core function is to simulate the pressure of paper during actual transportation, stacking or processing, and quantify the compressive strength and deformation characteristics of the material through two standardized test modes: ring pressure and flat pressure. These two modes correspond to different stress states, providing a scientific basis for paper quality control and performance optimization.

Ring pressure test mode

Ring pressure test is mainly used to evaluate the longitudinal compressive resistance of paper, especially for the strength analysis of corrugated cardboard core paper or paper tube-like cylindrical structures. During the test, the specimen is cut into rectangular strips of a specific size, curled into a ring shape and placed in the center of the lower platen of the instrument, and the upper platen is pressed down at a constant rate until the specimen collapses. The maximum pressure value is recorded, and the ring pressure strength is calculated in combination with the specimen size, and the formula is:

R = F / L

where R represents the ring compression strength (unit: kN/m), F is the maximum pressure (unit: N), and L is the length of the specimen (unit: mm). This mode follows standards such as GB/T 2679.8, ISO 12192, etc., emphasizing the parallelism and perpendicularity of the specimen edges to ensure uniform pressure distribution.

Flat pressure test mode

Flat pressure testing focuses on measuring the compressive properties of paper or cardboard in a flat direction and is commonly used to evaluate the rigidity of materials such as containerboard and cardboard. The specimen is usually a flat round or square sheet, placed on the lower platen, and the upper platen is applied vertically until the specimen is deformed. The test results are expressed in terms of breaking resistance index or compressive strength, calculated as:

C = P / A

where C represents the flat compressive strength (unit: kPa), P is the maximum load (unit: N), and A is the initial area of the specimen (unit: m²). This mode reference standards such as GB/T 22874 and TAPPI T825 pay attention to the flatness and clamping stability of the specimen to avoid errors caused by bias load.

Technical comparison

There are differences between the two modes in terms of application scenarios, sample preparation and mechanical meaning. The ring pressure test simulates the compressive behavior of the annular structure and is sensitive to the strength of the edge of the material. The flat pressure test reflects the uniform compressive performance of the plane and is more related to the overall rigidity of the material. The following table provides a brief comparison of its key parameters:

Test mode	Main application objects
Ring pressure test	Corrugated core paper, paper tubes, cylindrical components
Flat pressure test	Containerboard, cardboard, flat paper products
Specimen shape	Rectangular strips curl into rings
Specimen shape	Round or square flakes
Core standards	GB/T 2679.8, ISO 12192
Core standards	GB/T 22874, TAPPI T825
Strength calculation	Based on length and maximum pressure
Strength calculation	Based on area and maximum load

Influencing factors

To ensure the accuracy and repeatability of test results, it is necessary to control the ambient temperature and humidity conditions (usually 23°C±1°C, 50%±2%RH) to avoid moisture or dryness of the specimen. Instrument calibration should be carried out regularly, including accuracy verification of pressure and displacement sensors. Standard cutting knives should be used to prepare specimens to reduce edge burrs; The test rate should be set according to the standard, too fast or too slow may cause deviations in the intensity values. In addition, operators should record specimen failure modes, such as buckling or shear, to aid in material defect analysis.

Summary

The ring pressure and flat pressure test modes together constitute the basic method for determining the compressive strength of paper, which reveals the mechanical behavior of the material from different dimensions. In practical applications, users should choose the appropriate mode according to the product type and usage scenario, and strictly follow the standard process. As materials science evolves, these test methods will continue to be optimized to support performance improvements and innovative designs for paper products.

References

GB/T 2679.8-2016, Paper and cardboard - Determination of ring compressive strength

ISO 12192:2011, Paper and board — Determination of compressive strength — Ring crush method

GB/T 22874-2008, Determination of flat compressive strength of single-sided and single-corrugated board

TAPPI T825 om-22, Compression resistance of paperboard (ring crush test)