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Analysis of Compressive Strength and Influencing Factors of Carton in Jinan Carton Factory
The compressive strength of a cardboard box is one of the most critical quality indicators in packaging, especially for products that require strong protection during storage and transportation. During testing, the corrugated box is placed between two pressure plates, and the force at which the box collapses is measured as its compressive strength, typically expressed in kilonewtons (kN).
First, determining the required compressive strength of the carton.
Cardons stacked on the bottom layer must withstand the weight of the boxes above them. To prevent collapse, they need sufficient compressive strength. This strength can be calculated using the formula:
P = K × W × (n - 1)
Where:
- P is the compressive strength of the carton (in Newtons),
- W is the weight of the loaded carton (in Newtons),
- n is the number of layers in the stack,
- K is the safety factor based on storage duration.
The stacking height H and the height of a single carton h are used to calculate n: n = H / h.
According to national standards:
- For storage less than 30 days, K = 1.6
- For 30–100 days, K = 1.65
- For more than 100 days, K = 2.0
Second, Jinan Carton Factory calculates compressive strength based on materials. Once the required strength is known, appropriate corrugated board and paper are selected to avoid unnecessary waste. One commonly used formula for estimating compressive strength is the Kellicutt formula, which is particularly effective for 0201 type boxes.
Third, methods for determining compressive strength.
Due to variations in production, the actual compressive strength may differ from estimated values. Therefore, the most accurate method is to test the carton after it has been conditioned under controlled temperature and humidity using a compression testing machine. For small and medium-sized factories without such equipment, a wooden board can be placed on the carton, followed by an equal weight of objects to roughly assess whether the compressive strength meets requirements.
Fourth, factors affecting compressive strength.
1. **Raw material quality**: The base paper is the main determinant of compressive strength, as shown in the Kellicutt formula. However, other factors like adhesive amount, impregnation, coating, and composite processing also play a role.
2. **Moisture content**: High moisture in corrugated cardboard or long-term exposure to humid conditions can significantly reduce compressive strength. Paper is highly absorbent, so maintaining proper moisture levels is crucial.
3. **Box design**: The type and dimensions of the box have a major impact. Double-layer corrugated boxes generally offer better strength than single-layer ones. Taller boxes tend to be less stable and have lower compressive strength.
4. **Printing and cutting**: Printing and openings (like ventilation holes or handle cutouts) can weaken the structure, especially if large or unevenly distributed.
5. **Manufacturing process**: Issues like improper creasing, deep grooves, or weak joints can reduce the box's resistance.
6. **Dynamic performance testing**: For fragile items like glass, electronics, or instruments, dynamic tests such as drop tests, impact tests, vibration tests, and hexagonal drum rotation tests are essential to evaluate cushioning and durability.
These tests are destructive, but protective measures like padding, baffles, or shock-absorbing materials can help improve the carton’s resistance. Additional tests, such as weather resistance or spray tests, may also be required based on customer agreements.