Definition
A paper folding meter is a specialized inspection device used to evaluate the resistance of paper or cardboard materials to breakage under repeated folding conditions. This indicator reflects the mechanical durability of materials during simulated long-term use or processing, and is one of the important parameters to measure their service life and suitability.
Principle
The device works based on material fatigue theory by clamping the specimen between two opposed chucks and subjecting it to a reciprocating folding motion at a specific angle under constant tension. When the specimen is stressed and eventually breaks due to repeated bending, the instrument automatically records the number of folds. This number is the bending resistance value, which is usually expressed as a bifold value, and its relationship can be expressed as:M = N, where M is the folding resistance and N is the number of folds when the specimen breaks. During the test, some models will use the adjustment mechanism to keep the tension of the specimen stable to ensure data consistency.
Measurement method
The standard measurement process follows domestic and foreign norms such as ISO 5626 and GB/T 457. First, the specimen is cut to the specified size, usually in a long strip. The specimen is then mounted flat in the instrument's clamping device and a defined initial tension is applied. After starting the device, the specimen is folded back and forth at a set speed until it breaks completely. The instrument automatically records the number of folds, and a single test often repeats multiple specimens to calculate the average. Test conditions such as folding angle, speed, and ambient temperature and humidity need to be strictly controlled according to standards to ensure comparable results.
Influencing factors
The flexural resistance of a material is influenced by various factors. The type and length of fiber raw materials directly affect the flexibility and bonding strength of the paper. Slurry treatment processes such as pulping degree will affect the bonding state of fibers. The quantitative and thickness of paper is usually related to fold resistance, but not linearly. Humidity conditions significantly changed the flexibility of fibers, and most materials exhibited higher folding resistance in moderately humid environments. In addition, the filler content, surface treatment and calendering process during production also play a role in the final performance.
Application:
This test is widely used in the quality control process of the paper industry, especially for materials that need to be folded frequently, such as map paper, banknote paper, book cover paper, securities paper and some packaging cardboard. In the printing industry, bend resistance data helps predict adaptability in finishing processes such as folding and binding. The data can also be used as a reference for product development to optimize formulations or improve production processes.
Selection
Equipment selection involves considering compliance with testing standards to ensure that the instrument meets the standard requirements of the target region or industry. The measurement range should cover the expected number of folds of the material to be measured. The equipment should be able to accurately control the folding angle, tension and speed, and have stable counting capabilities. Clear user interface and easy maintenance are also considerations. For high-intensity testing needs, it is necessary to pay attention to the durability of the equipment structure. In addition, environmental simulation capabilities, such as whether or not they are equipped with temperature and humidity control units, can be determined based on actual test conditions.