How to test the burst resistance of cardboard
The burst resistance and burst index of cardboard are commonly used indicators to evaluate the strength and durability of cardboard.
Bursting Strength: Bursting strength measures the ability of cardboard to withstand internal pressure and external forces to break. It refers to the maximum pressure that cardboard can withstand under gradually increasing pressure. Burst resistance is usually expressed in terms of pressure per unit area, such as kilopascals (kPa) or pounds per square inch (psi).
Bursting Strength Index: The Bursting Strength Index is the ratio of bursting strength to the reference weight of cardboard. It represents the burst resistance of cardboard per unit weight. The calculation formula for burst index is: burst index=burst degree/reference weight. Usually expressed in kilopascals per gram (kPa/g) or pound force per pound (psi/lb).
The measurement of burst strength and burst index is usually carried out using a burst strength tester, which applies pressure gradually by increasing the internal air pressure until the cardboard ruptures. This can determine the burst performance of the cardboard and calculate the burst index.
The burst resistance and burst index are very important for the quality control and evaluation of cardboard. A higher burst strength and burst index mean that cardboard has better strength and durability, which can provide better performance in transportation, packaging, and product protection. These indicators are widely used in the cardboard manufacturing and packaging industry to ensure that the quality of the cardboard meets the requirements and meets the needs of specific applications.
Predicting the ability of corrugated cardboard to resist external pressure by detecting its burst resistance is a reflection of its static resistance to compression. The burst strength reflects the maximum pressure that cardboard can withstand uniformly in the vertical direction per unit area, and reflects the ability of cardboard boxes to protect products under static conditions during transportation and compression.
Factors affecting burst strength:
1. The breaking strength of corrugated cardboard boxes is determined by the breaking strength of the inner layer, outer layer, and intermediate paper that make up the cardboard, and is independent of the corrugated core paper.
2. The breaking strength of the base paper itself is mainly determined by the fibers of the base paper. The burst resistance is related to the fiber length and the bonding strength between fibers. As the fiber length increases, the bonding strength between fibers also increases, which improves the burst resistance. The paper made from wood pulp has higher breaking resistance than recycled pulp, while the paper made from coniferous forest pulp has higher breaking resistance than broad-leaved pulp. In addition, adding some additives appropriately during the process of making base paper can also help improve the breaking strength of the base paper.
3. When the moisture content of cardboard is between 5% and 6%, the maximum burst resistance value is achieved. When the moisture content varies within the range of 8-14%, the change in burst resistance value does not exceed 5%, but when the moisture content reaches 18%, the decrease in burst resistance value can reach about 10%. That is to say, when corrugated cardboard boxes are stored in an environment with a relative humidity of 50% RH to 80% RH, the change in their breaking strength is very small, so the temperature and humidity balance treatment process of the samples can be avoided, greatly reducing the testing time. From Zhongbao Testing Equipment Co., Ltd
4. The storage environment for raw paper or cardboard boxes should be 25 ± 5 ℃ and 55 ± 5% RH.
5. Long term stacking of roll paper in the warehouse can cause fiber fatigue of the raw paper, resulting in a decrease in its durability. Experiments have shown that if the original paper is stacked for more than 3 months, its breaking strength will decrease by 5-8%; If the stacking time exceeds 6 months, the breaking strength will reach more than 10%. Therefore, cardboard box factories should strive to achieve first in, first out when using raw paper.
