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Strength is the life of corrugated box

strength is the life of corrugated box, which is particularly important for transportation packaging box. Here are some experiences and understandings about the strength of corrugated boxes

I. strength standard of corrugated boxes

strength standard of corrugated boxes. Appendix g of GB national standard stipulates that the compressive strength value p of corrugated boxes should not be less than the value calculated by the following formula: p=k · g (h-h/h · s) (kgf/cm2)

where: k-strength insurance coefficient; Although the charge can reduce the use of plastic bags

g-The weight of goods in corrugated boxes, KGF

h-stacking 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 layers

k- it depends on the storage time:

<30 days 1.6, days 1.65, more than 100 days 2

but some textbooks set it as 3, so the safety factor is greater

if a certain instant noodle box has a gross weight of 3.5kgf and is stacked for 16 layers, the strength (pressure resistance, the same below) standard of corrugated boxes should be:

p=2 × 3.5（16－1）

=7kgf × 15

=105kgf

some large box users also have their own strength standards. For example, Nanfeng chemical group stipulates that the strength standard of its washing powder packaging box is 350kgf. To make a box for it, the strength must meet this standard

II. Strength design of corrugated boxes

the strength of corrugated boxes is determined by raw materials and manufacturing processes. The so-called strength formula calculation is mainly based on the performance index of the material used and the strength formula. If the calculation result is not lower than the strength standard, it can be put into production. The design strength can be filled in the quality assurance seal and printed on the relevant position of the carton as a commitment to the user

The strength calculation ofo2 corrugated box is generally carried out according to the internationally commonly used Kelly Carter formula. In order to facilitate operation, we use its simple formula: p=px · f... (1)

where: p-compressive strength of corrugated box (n/m2)

px- comprehensive ring crush strength of corrugated paper base (n/cm)

f-kelly Carter simple constant is obtained by looking up the table according to the perimeter length (z) of the corrugated box

calculation formula of comprehensive ring crush strength of corrugated paper base (taking double corrugated paper as an example):

px=r1+r2+rm+ (c1+c2+c3)/15.2... (2)

where: R1 - ring crush strength value of face paper

r2- ring pressure strength value of lining paper

rm- ring compression strength value of corrugated core paper

c-corrugated shrinkage, that is, the ratio of the length of corrugated core paper to that of face paper, varies according to the equipment state. Generally, the length of A-line (C1) is 1.43, that of B-line (C2) is 1.36, and that of sandwich (C3) is 1

15.2-the length of the sample when testing the ring compression strength of the base paper (CM)

set the corrugated board as AB corrugated structure, and the paper used is 250g/140g × 3/250g, all C-grade paper. Since the national standard (GB, gb13024 - 91) only stipulates that the horizontal ring pressure index (R) needs to be converted into ring pressure strength, the conversion formula is: r=0.152rw

where: r-ring pressure strength (n/0.152m) r-ring pressure index (n · m/g) w-quantitative (g Jinan experimental machine factory Jinan new era Gold Testing Instrument Co., Ltd. friction and wear experimental machine is different from other places/m2)

r1.2=0.152 × six × 250=228

Rm=0.152 × four × 140=85

is substituted into formula (2):

px=228+228+85 (1.43+1.36+1)/15.2

=228+322/15.2=778/15.2

=51

f value is obtained by looking up the table of the perimeter length (z) of the carton

the perimeter length (z) of the carton in the design is: z=2 (l+b) l=44cm b=29cm

then z=2 (44+29)

=146cm

look up the table and get f=75.6 (omitted in this table)

substitution formula (1)

p=51 × 75.6=3855 (n) ≈ 385kgf

the above calculation instructions: the structure is 250g/140g × 3/250g double corrugated board can be made into cartons with L (length) =44cm and B (width) =29cm, and its compressive strength can reach 385kg

III. technological guarantee of corrugated box strength

in addition to the guarantee of raw materials, the manufacturing process plays a very important role in the strength of corrugated boxes. Because corrugated board is a clever combination of face paper and core paper, from the perspective of structural mechanics, its structure is very scientific and reasonable, and its mechanical structure is completed by the manufacturing process. Therefore, the manufacturing process plays a decisive role in the strength of corrugated boxes

1. Quality of base paper. It is mainly that the tightness, quantity, strength, moisture content, folding resistance, paper surface and rewinding end face of the base paper should meet the specified quality indicators. In this way, the strength of the corrugated box has a material basis

2. Quality of corrugated board. It must be high-quality paperboard, with good molding, regular corrugation, firm bonding, flat surface, etc; The paperboard is neat, without lack of materials, neat cutting edges, etc; The moisture content is appropriate. High quality paperboard should start from single-sided paperboard, and the compounding and shearing process should also be appropriate

3. Printing quality assurance. The main thing is that the stamping force should be appropriate, and the corrugation should not be depressed or collapsed. The inspection method is: first, the image and text edges cannot have thick ink watermark; The second is the feeling of hand. There should be no depression when touching the cardboard; There should be no extra indentation on the cardboard

4. Processing and molding quality. Such as indentation, slotting, nailing, etc., must be just right, in line with the process regulations. Otherwise, it will have a negative effect on the strength of the carton

5. Other artificial influences. Such as stepping, stepping, squeezing, pressing, bumping, and hurting cardboard and cartons in the process of handling and loading and unloading will damage their strength

IV. verification of the strength of corrugated boxes

whether the strength of corrugated boxes will reach the predetermined goal after design and manufacturing, it must be verified by inspection. The ideal inspection method is to test the carton with a press after constant temperature and humidity treatment. The simple verification method is to cover a wooden board on the carton after it is found by Chinese enterprises that their plastic extrusion machinery has been shaped by temperature and humidity, and then press the weight according to the design strength to verify whether it meets the design requirements. If it fails to meet the requirements, it must be analyzed, studied and improved. Until it meets the requirements, it is considered that the restenosis rate after vascular stent implantation reaches ≈ 10%

from China Packaging Yearbook, 1999

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