Definition
The cardboard stiffness meter is a special testing equipment used to determine the bending resistance of cardboard materials. The measurement results are usually expressed in terms of the torque required to bend a certain angle or the bending angle generated under a specific moment, which reflects the ability of the material to resist deformation and is one of the key parameters for evaluating the applicability and performance of cardboard processing.
How it works:
The instrument is designed based on the principle of cantilever bending principle. The rectangular specimen is clamped in the fixed grip so that part of its length becomes a free cantilever. The end of the cantilever is bent at a constant speed to a set angle by means of a driving device, and the applied torque is measured at the same time; or apply a constant torque, measuring the resulting bending angle. The mechanical relationship can be expressed as:
M = k × θ
where M is the bending moment, θ is the bending angle, and k is the stiffness coefficient of the specimen. This relationship is established within the elastic deformation range of the material.
Measurement method
The standard measurement process typically includes four stages: sample preparation, instrument calibration, test execution, and data processing. Specimens are cut to standard size and pre-treated to equilibrium in a constant temperature and humidity environment. Adjust the clamping distance and bending angle parameters during the test to ensure that the center line of the specimen is aligned with the grip. Each sample needs to be measured multiple times, and the statistical results are taken as the final stiffness value. The measurement method must comply with ISO 5628, GB/T 22364 and other standards.
Influencing factors
The stiffness of the material is affected by multiple factors. In terms of substrate, fiber type, pulping degree and slurry ratio determine fiber bonding strength. Quantitative and thickness increases usually increase stiffness, but have a nonlinear relationship. In terms of process, calendering pressure and drying curve affect fiber binding density and stress distribution. In terms of environment, increased temperature or increased relative humidity can reduce fiber stiffness, resulting in a decrease in stiffness. In addition, the angle between the cutting direction of the specimen and the fiber orientation can also lead to measurement differences.
Applications:
This instrument plays an important role in the evaluation of packaging materials. In carton manufacturing, stiffness data is used to predict the passability and forming stability of cardboard on automated packaging lines. In the printing industry, stiffness affects the transfer performance and overprinting accuracy of paper in high-speed presses. Special paper fields such as insulation materials and filter substrates also need this parameter to evaluate the support performance. In addition, stiffness measurement provides data support for product development and helps optimize the production process and raw material ratio.
Equipment selection
When selecting a model, it is necessary to comprehensively consider the measurement range, accuracy level and functional configuration. The measurement range should cover the expected stiffness value of the sample to be tested with an appropriate margin. In terms of accuracy, it is recommended to choose a model with higher resolution for scientific research purposes, and the production control can be appropriately relaxed. In terms of function, it is necessary to pay attention to whether the clamping system supports multiple specimen sizes and whether it has a temperature and humidity compensation module. The operation interface should be ergonomically designed, and the data output format should be compatible with the laboratory information management system. Ease of maintenance and calibration intervals are also important considerations for long-term use.