In the highly demanding sectors of papermaking, commercial printing, and packaging converting, the structural integrity of flat materials is an uncompromising metric. The rigidity and stiffness of paperboard directly influence runnability on high-speed folding carton machines, the stacking strength of finished packaging, and the tactile quality experienced by the end consumer. To accurately quantify this physical property, industry professionals rely on the Paper Bending Resistance Tester, a highly specialized instrument engineered to execute the strict testing protocols outlined in the ISO 2493-1 international standard.
Unlike legacy mechanical pendulums, our state-of-the-art constant rate of deflection paper tester digitizes the evaluation process. By employing a motorized drive and a high-precision load cell, it eliminates human error and provides unparalleled repeatability. This article provides an in-depth exploration of the ISO 2493-1 testing framework, the two-point loading principle, and how this equipment serves as the definitive ISO 2493-1 two-point loading stiffness tester for global quality control laboratories.
| The ISO 2493 standard is divided into distinct parts based on measuring principles. While Part 2 covers Taber-type testers, ISO 2493-1 specifies procedures based on the two-point loading principle for determining the bending resistance of paper and board. It is crucial to understand that results obtained from testers using the principle of constant rate of deflection (Part 1) and Taber-type testers (Part 2) do not give comparable results due to their fundamentally different mechanical interactions with the substrate. | Understanding the ISO 2493-1 Standard and Testing Principle |
| At the heart of the automatic paperboard bending resistance testing machine is the two-point loading mechanism. The principle involves the measurement of the force required to bend a test piece clamped securely at one end through a specified angle, where the force is applied at a specified bending length. The bending resistance is subsequently calculated as the mean of these measured forces. | The Two-Point Loading Principle |
| This method is highly sensitive and is specifically designed to apply to the measurement of bending resistance within the broad range of 20 mN to 10,000 mN. While it is not applicable to fully assembled corrugated boards, it is highly applicable to the individual paper components (liners and fluting) that make up such boards. |
| Equipment Model: | WEW-PBR-2493-01 |
| Equipment Name: | Paper Bending Resistance Tester |
| Measurement Range: | (0~500) mNm or (0~10,000) mN |
| Accuracy Notification: | ±0.1% |
| Span Range: | Adjustable across 8 settings (5, 10, 15, 20, 25, 30, 40, 50 mm) |
| Specimen Dimensions: | Compatible with both old standard (38 × 70 mm) and new standard (38 × 80 mm) |
| Actual Measurement | Dimensions: 38 × 50 mm |
| Test Resolution: | 0.01 mN |
| Self-Calibration: | Supports self-calibration; standard calibration tools and weights included |
| Angular Velocity Control: | Adjustable from 0.5 to 1000°/min |
| Bending Time: | User-configurable (5~35 s) based on material elasticity |
| Bending Angle: | Continuously adjustable (1~92°); common angles include ±7.5° or ±15° (accuracy ±0.3°) |
| Operation Interface: | 5/7-inch touchscreen with visual menu-driven operation |
| Sensor Replacement: | Quick-change Sensor Capability |
| Print Output: | Integrated Modular Thermal Printer |
| Machine Dimensions: | 350 mm × 325 mm × 350 mm |
| Power Voltage: | AC 220V, AC110V, 50Hz, 60Hz, 1 Phase |
| Equipment Weight: | 105.0 KGS |
This paper bending resistance tester from Wewon Environmental Chambers Co., Ltd. is engineered to serve as the definitive laboratory solution for evaluating the bending stiffness of paper, paperboard, and a diverse range of sheet materials. By adhering strictly to the ISO 2493-1 constant rate of deflection method, the instrument accurately quantifies the resistance to bending, providing critical mechanical data for materials such as flexible polymer films, mica sheets, graphite composites, and various multi-layer laminates.
Beyond simple stiffness measurement, this equipment is instrumental in simulating the real-world performance of materials under stress, allowing quality control professionals to predict how substrates will behave during high-speed converting, automated folding, and final-product assembly.
Apparatus Architecture: How the Machine Works｜To achieve compliance with ISO 2493-1, the digital cardboard bending force gauge must be constructed with highly specific, calibrated components. The tester consists of several critical interactive parts that guarantee the constant rate of deflection:
| The clamp must be not less than 38 mm wide and not less than 20 mm long, and it must be adjustable in the direction perpendicular to the plane of the test piece. In its starting position, it holds the test piece in a strict vertical plane. The clamp is capable of being rotated about its axis at a highly controlled, constant speed of 5.0 ± 0.5 °/s. | The Precision Clamp: |
| The clamping pressure must be high enough to hold the test piece firmly without slippage, ensuring the measured bending force is insensitive to the clamping pressure itself. | |
| A specially designed knife is mounted perpendicular to the initial movement of the test piece, applying a centrally placed bending force with respect to the width of the specimen. The length of the knife edge is 16 ± 2 mm, and the edge is blunted to prevent cutting or damaging the paper matrix. | The Deflection Knife: |
| The device measures the force exerted on the knife edge by the test piece when it is bent through the specified angle. The accuracy requirements are incredibly strict: for readings from 0 mN to 100 mN, accuracy must be within ±5%, and for readings exceeding 100 mN, it must be within ±2%. | Force Measurement Device (Load Cell): |
| Furthermore, the movement of the sensor in its response direction shall be less than 0.05 mm over the full range of measurement, ensuring low sensitivity to lateral forces. |
Critical Testing Parameters: Angles and Lengths｜The versatility of the paper bending stiffness tester lies in its adjustable parameters, which accommodate materials ranging from thin copy paper to rigid folding boxboard.
| The standard bending angle for general paper and board testing is 15° (specifically 15.0 ± 0.3°). However, the standard accounts for thick, rigid boards that tend to be permanently deformed or suffer structural failure if bent through a full 15°. | 1. The Bending Angle |
| For such brittle or thick materials, the half bending angle of 7.5° (7.5 ± 0.3°) can and should be used. If a break, kink, or crease is observed before 15° is reached on more than 10% of the test pieces, the 7.5° angle must be adopted and noted in the test report. | |
| The bending length is defined as the constant radial distance between the clamp and the position on the test piece at which the force is applied. The primary, standardized bending length is 50.0 ± 0.1 mm. | 2. The Bending Length |
| However, for samples having a bending resistance that is too low to measure accurately with a 50 mm length (such as very thin tissue or film), a shorter 10 mm bending length (10.0 ± 0.1 mm) can be utilized. It is important to note that results obtained using different bending lengths will not be comparable. |
Testing Procedure & Data Analysis
Precision clamping and constant rate deflection mechanism.
Accurate evaluation demands strict environmental control (ISO 187). Test pieces must be cut to a precise width of 38.0 ± 0.2 mm, completely free of visible creases. To prevent localized moisture distortion, operators must never touch the clamping area with bare hands.
- Zero Pre-Load Contact: The knife edge contacts the specimen’s surface without applying initial force.
- Constant Deflection: The instrument rotates the clamp at a highly stable rate of 5.0 °/s.
- Peak Measurement: The load cell automatically captures the peak bending force exactly at the 15° or 7.5° angle.
- Single-Use Rule: Because continued flexing progressively weakens the material, no specimen is ever pre-flexed or reused.
Bending Resistance & Stiffness Index
Upon completion, the Bending Resistance (B) is calculated as the mean of all valid peak force readings (in mN) across the principal directions.
For advanced material comparison, quality control labs utilize the Bending Resistance Index (BI). This normalizes stiffness data against the paper’s weight using the formula: BI = B / g3 (where g is grammage per ISO 536). This index is exceptionally useful for comparing papers with minor basis weight variations, helping manufacturers optimize raw material costs without sacrificing structural rigidity.
