Strength Under Pressure: The Principle of the Paper Ring Crush Tester

For users concerned with the edgewise compressive strength of paper and paperboard, particularly important for predicting the stacking strength of corrugated boxes, the Paper Ring Crush Tester is a vital instrument. This tester measures the resistance of a paper or paperboard ring specimen to crushing forces applied parallel to its edges. This article explores the unique principle behind the operation of a Paper Ring Crush Tester.
 

The Paper Ring Crush Tester operates on the principle of applying a controlled compressive force to a specifically prepared ring-shaped specimen of paper or paperboard until it collapses. The maximum force the ring can withstand before failure is recorded as the ring crush strength.
 

The typical Paper Ring Crush Tester setup involves:

Precision Sample Cutter: This cutter is used to prepare a precisely dimensioned strip of paper or paperboard. The dimensions (length and width) are critical and are specified in testing standards like TAPPI T 822 and ISO 12192.

Ring Forming Device: The cut strip is then formed into a ring of a specific diameter and held in place by a jig or holder. The accuracy of the ring dimensions is important for consistent test results.
 

Compression Plates: The ring specimen, held in the jig, is placed between two parallel compression plates of the tester.

Force Application System: A motor-driven or hydraulic system applies a controlled and steadily increasing compressive force to the ring specimen through the compression plates, parallel to the axis of the ring (and thus parallel to the edges of the paper).
 

Load Cell and Data Acquisition: A precision load cell measures the applied compressive force, and a data acquisition system records the force and the corresponding deformation of the ring specimen. The test continues until the ring collapses or a peak load is reached.
 

Microprocessor and Display: The tester calculates and displays the maximum compressive force (ring crush strength), typically expressed in units of force per unit width of the original strip (e.g., N/m or lbf/in).
 

The principle of measurement involves:

Preparing a paper or paperboard strip of precise dimensions.

Forming the strip into a ring of a specific diameter and securing it.

Placing the ring between the compression plates of the tester.

Applying a steadily increasing compressive force to the ring, parallel to its edges.

Measuring the force as the ring deforms.

Identifying and recording the maximum compressive force (peak load) before the ring collapses.

Calculating the ring crush strength by dividing the peak load by the width of the original paper strip.
 

The Paper Ring Crush Tester is an offline instrument crucial for predicting the compressive strength of corrugated board, as the edgewise compressive strength of the linerboard and medium is a primary factor determining the stacking strength of the final box.
 

While the core principle remains mechanical compression, modern automated instrument testing systems in paperboard mills might incorporate automated sample preparation and testing for continuous monitoring of this critical strength property.
 

In conclusion, the Paper Ring Crush Tester operates on the principle of applying controlled edgewise compression to a ring-shaped paper or paperboard specimen until failure. By accurately measuring the peak compressive force, it provides a critical indicator of the material's resistance to crushing forces parallel to its edges, essential for predicting the stacking strength of corrugated packaging and ensuring structural integrity.