Strength is the life of corrugated boxes, which is especially important for shipping containers. Here are some issues related to the strength of corrugated cardboard boxes, and some experiences and understandings.
First, the strength of corrugated boxes Standard corrugated box strength standards, GB6543-86 National Standards Appendix G: corrugated box compressive strength value P should not be less than the value calculated by the following formula: P = K · G (H-h / h·s) (kgf/cm2)
Where: K-intensity insurance factor;
G - Weight of cargo loaded in corrugated boxes, kgf;
H-stack height, cm;
H-box height, cm;
S-box bottom area cm2.
This formula can be simplified in practice as: P=K·G(n-1)
Where: n-stacking number;
K- depends on the length of storage:
<30 days 1.6, 30-100 days 1.65, more than 100 days 2.
However, some textbooks set it as 3, so that the safety factor is greater.
If the weight of a certain type of instant noodle box is 3.5kgf and the stacking number is 16 layers, then the strength of the corrugated box (pressure resistance, the same below) should be:
P=2×3.5 (16-1)
Some large boxes, as well as their own strength standards, such as the Nanfeng Chemical Group specifies that its detergent powder box strength standard is 350kgf. To make a box for it, the strength must meet this standard.
Second, the strength of corrugated box design Corrugated box strength is determined by the raw materials and manufacturing processes. The calculation of the so-called strength formula is mainly based on the performance indicators of the materials used, and is calculated according to the strength formula. The calculation result is not lower than the strength standard, and the production can be carried out. The design strength can be filled in the quality assurance chapter, printed in the relevant position of the carton, as a commitment to the user.
The strength calculation of O2 corrugated carton is generally based on the commonly used Kelly Carter formulae in the world. To facilitate the operation, we use its simple formula: P=Px·F... (1)
In the formula: P-corrugated box compressive strength (N/m2);
Px-corrugated board raw paper composite ring crush strength (N/cm);
F-Kelly Carter simple constants, based on the long (Z) look-up table around the corrugated box.
Corrugated paper base paper composite ring crush strength calculation formula (in double corrugated cardboard as an example):
In the formula: R1-face paper ring pressure strength value;
R2-in paper ring pressure strength value;
Rm - corrugated core paper ring pressure strength value;
The C-corrugation shrinkage ratio, which is the ratio of the length of the corrugated medium to the length of the tissue paper, varies depending on the equipment state. Typically, A楞 (C1) is 1.43, B楞 (C2) is 1.36, and the sandwich (C3) is 1.
15.2 - Test sample length (cm) at the base crush strength.
The corrugated cardboard is designed as an AB crucible structure, and the paper is: 250g/140g×3/250g, both of which are Class C paper. As the national standard (GB13023-91, GB13024-91) only stipulates that the lateral ring pressure index (r) needs to be converted into the ring pressure strength, the conversion formula is: R=0.152rw
Where: R-Cylindrical strength (N/0.152m) r-Critical pressure index (N·m/g) W-Quantitative (g/m2)
Substituting formula (2):
The value of F is obtained from the long (Z) table around the carton.
The carton perimeter (Z) in the design is: Z=2(L+B) L=44cm B=29cm
Then Z=2(44+29)
Check table to obtain F = 75.6 (Table omitted)
Substitution formula (1)
The above calculations show that with a double corrugated paperboard with a structure of 250g/140g×3/250g, a carton with L (length) = 44cm and B (width) = 29cm can have a compressive strength of 385kg.
Third, the corrugated carton strength process guarantee corrugated box strength In addition to raw material guarantees, the manufacturing process plays a very important role. Because the corrugated paperboard is formed by the ingenious combination of face paper and core paper, the structure is very scientific and rational from the perspective of structural mechanics. Its mechanical structure is completed by the manufacturing process. Therefore, the manufacturing process has a decisive effect on the strength of corrugated boxes.
1. The quality of the base paper. Mainly, the tightness, basis weight, strength, moisture content, folding endurance, paper surface, rewinding end surface, etc. of the base paper must reach the specified quality index. Thus, the strength of the corrugated paperboard has the material basis.
2. The quality of corrugated board. Must be high-quality cardboard, well-formed, regular corrugated, firm bonding, smooth surface, etc.; cardboard neat, no shortage of material, trimming and trimming; moisture content is appropriate. High-quality cardboard from the single-sided cardboard, composite, cutting process should also be just right.
3. Print quality assurance. The main reason is that the embossing force should be appropriate and the corrugated can't be pressed down or collapsed. One test method is that the edge of the picture can not be printed with thick ink; the second is the feel, and the hand can not have depressions on the cardboard; the cardboard can not have any excess indentation.
4. Processing and molding quality. Such as indentation, slotting, nailing, etc., must be just right, in line with process regulations. Otherwise it will have an adverse effect on the strength of the carton.
5. Other artificial effects. For example, stepping, stepping, squeezing, pressing, bumping, injuring cardboard and carton during handling, loading and unloading will damage its strength.
Fourth, the corrugated carton strength verification Corrugated carton strength after design, manufacture, whether it will achieve the target, but also through the test proved. The ideal test method is to test the carton after constant temperature and humidity treatment. The simple verification method is that after the carton has been set in temperature and humidity, a wooden board is covered on the carton, and then a heavy object is pressed according to the design strength to verify whether it meets the design requirements. If it does not meet the requirements, it must be analyzed, studied and improved until it is up to the requirements.
Excerpted from China Packaging Yearbook 1999