Test design and control of compressive strength of

2022-08-04
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The test, design and control of the compressive strength of corrugated boxes

the test and analysis of the compressive strength of corrugated boxes

the compressive strength of corrugated boxes refers to the maximum load and deformation of the box under the dynamic pressure uniformly applied by the pressure testing machine

the compression test process is divided into four stages: the first is the preloading stage to ensure that the carton is in contact with the compression machine pressing plate; The second is the stage when the transverse pressure line is pressed down. At this time, the load increases slightly and the deformation changes greatly; The third is the compression stage of the side wall of the carton. At this time, the load increases rapidly and the deformation increases slowly; Fourth, when the carton is completely damaged, this is the crushing point of the carton. Because the four corners of the carton are mainly stressed during the whole pressure bearing process, accounting for about two-thirds of the total stress, we should try to reduce the damage to the corrugation around the four corners of the carton during the production process

the compressive strength of cartons is divided into effective value and final value. During the compression test, the force value sometimes changes from slow to fast directly to the collapse point, and some increase steadily to the collapse point. In the long-term compression test, we found that the change of force value sometimes has a certain buffer: that is, when the force value and deformation increase to a certain extent, the force value stops and the deformation continues to increase. After a period of time, the force value continues to increase until the carton collapse point. We can call the force value before buffering as effective value, and the deformation before buffering as effective deformation. After buffering, although the force value can continue to increase, the carton has begun to deform and cannot meet the use requirements. Therefore, the standard for judging the compressive strength of the carton should be the effective value during the compression test

generally, the deformation of three-layer a-box is less than 10mm, the deformation of three-layer b-box is less than 7mm, the deformation of three-layer C-box is less than 9mm, and the deformation of five-layer BC box is less than 18mm. The test force value should reach the effective value of compressive strength

the better the quality of the carton, the higher the effective value of the compressive strength, and the smaller the deviation between the effective value and the final value. The analysis of the compressive strength of corrugated boxes is generally expressed by the average value of a group of multiple experiments (≥ 3). The smaller the deviation between each experimental data, the more stable the compressive performance of corrugated boxes. We can further analyze the quality of cartons through the change process of force value and deformation, combined with various factors affecting the compression resistance of cartons

Rapid design of compressive strength of 0201 corrugated box

China's corrugated box packaging industry has made great progress in the past 20 years, and the changes in recent years have changed with each passing day. Some sophisticated science and technology have been applied to the industry. However, due to the late start, some of the corrugated box design processes we use still use foreign ones, especially the calculation method of the compressive strength of empty corrugated boxes. Foreign formulas are too cumbersome and difficult to understand. It is difficult to combine the price design of domestic cartons with the compressive strength design of empty cartons, which is easy to cause waste of raw materials or quality problems in the compression resistance of cartons after forming

in order to make up for these shortcomings and enhance the predictability of the compressive strength before making cartons, after long-term calculation and verification, I have found a simple and effective calculation method for calculating the compressive strength of empty cartons by using the physical properties of base paper, that is, the calculation formula for the compressive strength design of corrugated cartons, which can be expressed by tensile breaking force (n) or tensile strength (MPA). This paper only discusses the compressive strength design of 0201 three-layer corrugated box in this method

corrugated box is composed of corrugated base paper at all levels. The compressive strength of corrugated box not only has the function of microcomputer control, full digital closed loop and graphic display lamp, but also has the function of calculating the compressive strength of the box according to the physical properties of the base paper to see whether it can meet the requirements; The appropriate corrugated base paper can also be selected according to the compressive strength requirements of the predetermined corrugated box

p = px.k

p -- the empty box compressive strength of the corrugated box (unit n)

px -- the transverse comprehensive ring compressive strength of the base paper (unit n/cm)

the comprehensive ring compressive strength of the three-layer corrugated board base paper = (the ring pressure value of the face paper R1 + the ring pressure value of the lining paper R2 + the ring pressure value of the corrugated paper R3 × Corrugating corresponding shrinkage C)/15.2

the ring pressure values mentioned in this paper refer to the horizontal ring pressure values (unit: n/0.152m), which can be obtained by testing, or by checking the national standard of 55 lightweight aggregate concrete small hollow blocks according to the grade of the base paper and calculating through the ring pressure index

ring pressure value r = quantitative w (unit: g/m2) × Ring pressure index R (unit: N.m/g) × 0.152 (unit: m). There are some differences between the test value and the calculated value of the pressure value of the same paper ring. Generally, the test value is larger than the calculated value. This is because the internal control standard of each paper factory is higher than the national elevation. Both data can be used to calculate the compressive strength

k - the effective value of the comprehensive ring pressure in the empty carton compressive strength, The calculation formula is:

three-layer a-beam k = 30.3 + 0.275z-0.0005z2

three-layer C-beam k = 27.9 + 0.265z-0.0005z2

three-layer B-BEAM k = 24.6 + 0.235z-0.0005z2

the product of the comprehensive ring crush strength and its effective value in the carton is the compressive strength of the carton. C stands for the shrinkage rate. The shrinkage rate of the A-line is C = 1.532, the shrinkage rate of the B-line is C = 1.361, and the shrinkage rate of the c-line is C = 1.477. Z represents the perimeter of the carton (value range 70cm ~ 200cm)

example 1 a three-layer C-shaped corrugated box has a circumference of 125cm, the surface paper and the lining paper are grade a 250G/m2 box board paper, and the corrugated paper is grade a 170g/m2 high-strength corrugated base paper. Calculate the compressive strength of the box

solution: the shrinkage rate of c-ridge C = 1.477; According to the national standard, the ring pressure index of face paper and lining paper is 10.6, and the ring pressure index of corrugated paper is 9.2; Z=125。

r1 = R2 = operation No. 250 × 10.6 × 0.152=403

R3=170 × 9.2 × 0.152 = 238n

is substituted into the formula to get

(R1 + R2 + R3 × C)/15.2 × (27.9+0.265Z-0.0005Z2)=(403+403+238 × 1.477)/15.2 × (27.9+0.265 × 125-0.0005 × 1252)=76 × 53.2 = 4043n

the corrugated box can reach the compressive strength of 4043n

example 2 the perimeter of a three-layer a corrugated box is 148cm, and the compressive strength is required to be 4500n. The surface paper and lining paper are Grade B 250G/m2 box board paper, and the corrugated paper is grade a high-strength corrugated base paper. Calculate the quantity of corrugated paper to be used

solution: the ring pressure index of the face paper and the lining paper is 9.2

let the quantitative w of the corrugated paper be an unknown number, and the shrinkage rate of the a corrugated paper c = 1.532, Z = 148, P = 4500

r1 = R2 = 250 × 9.2 × 0.152=350

(R1+R2+R3 × C)/15.2 × (30.3+0.275Z-0.0005Z2)=

P(350+350+R3 × 1.532)/15.2 × (30.3+0.275 × 148-0.0005 × 1482)=4500

R3=287

R3=W × 9.2 × 0.152 = 287

w = 205g/m2

205g/m2 grade a high-strength corrugated base paper shall be selected for the corrugated box

I have verified the Kelly Carter formula for a long time in my work, and found that there is a certain relationship between the calculated compressive strength and the measured compressive strength after the carton is formed through testing in the production process of other companies. Compared with Kelly Carter's formula, the set of compression calculation formulas I have calculated are in good agreement

it should be noted that even if the same kind of paper is used for matching, due to different production processes of various companies, the compressive strength of cartons of the same specification after forming is also different. Some are close to or lower than the compressive strength calculated by the calculated value of ring pressure, and some are close to or even higher than the compressive strength calculated by the test value of ring pressure. Theoretical calculation can guide the work of controlling the compressive strength of cartons in each process of production, eliminate various factors affecting the compressive strength, improve product quality and reduce production costs

factors affecting the compressive strength of corrugated boxes

1. cartons are composed of paper at all levels, and the reasonable allocation of paper is the basic condition to ensure the compressive strength of cartons

by testing the physical properties of the paper at all levels, we can preliminarily calculate the compressive strength of the carton, and then control the compressive strength of the carton in each process in the production process through the calculated compressive strength

2. the annular compressive strength of the paper is the key to ensure the compressive strength of the carton, but other physical properties of the paper can not be ignored

when the tensile strength of the paper, especially the corrugated paper, is not enough, the force and deformation of the carton will increase steadily in the compression test, the final value is very high and the effective value is very low, and the deformation of the box after the test is like an accordion. The waterproof performance of paper is also very important. In particular, refrigerated containers have higher requirements on the waterproof performance of paper. Sometimes, although the compressive strength of cartons is very high, because the paper is not waterproof, cartons are easy to absorb moisture when stored in the cold storage, resulting in the collapse of the storage

3. the production process of cartons will also affect the compressive strength

according to the test, under the same conditions, the compressive strength of the carton will decrease by 90N ~ 130n and the deformation will increase by about 2mm when the transverse pressing line of the carton is widened by 1mm. If the pressing line is too wide, the force value of the carton will increase slowly during the compression test, the effective value will be small, and the final deformation will be large. In order to ensure the compressive strength, we should try our best to improve the production process and reduce the impact of each process on the compressive strength of cartons

4. it is also crucial to select the appropriate ridge type according to the carton type

in people's consciousness, it is often thought that the larger the ridge, the higher the compressive strength of the carton, and it is easy to ignore the influence of the ridge on the deformation. The larger the ridge, the greater the compressive strength and deformation of the carton; The smaller the ridge, the smaller the compressive strength of the carton and the smaller the deformation. If the carton is too large, but the corrugated shape is very small, the carton is easy to be crushed during the compression test; The carton is too small, but the corrugated shape is very large. During the compression test, the deformation will be too large, the cushioning process will be long, and the deviation between the effective value and the final force value will be too large

5. the influence of moisture on the compressive strength of cartons should not be ignored

the production environment, storage environment, use environment, weather, climate and other factors of the carton will affect the moisture content of the carton. In order to ensure the compressive strength of the carton, try to avoid the impact of the external environment on the moisture content of the carton and keep the carton dry

there are many factors that affect the compressive strength of cartons. I will not discuss them one by one here

control of compressive strength of corrugated box

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