Corrugated cardboard box compressive strength test analysis
The compressive strength of a corrugated carton is the maximum load and the amount of deformation that occurs when the pressure tester uniformly applies dynamic pressure to the housing.
The compressive test process is divided into four stages: the first is the preloading stage to ensure that the carton is in contact with the press platen; the second is that the transverse pressure line is pressed down and the load is slightly increased at this time, and the deformation amount varies greatly; The third is the stage of pressure on the side wall of the carton. At this time, the load increases rapidly and the deformation increases slowly. Fourthly, when the carton is completely destroyed, it is the crushing point of the carton. Because in the entire pressure-bearing process of the carton, mainly the four corners are stressed, which accounts for about two-thirds of the total force, we should minimize the damage to the corrugations around the four corners of the carton during the production process.
The compressive strength of the carton is divided into effective and final values. The change of force during the compressive test is sometimes from slow to fast to the point of collapse, and some of it is gradually increased to the point of collapse. In the long-term compressive tests, we found that the change in the force value sometimes has a certain buffer: that is, when the force value and the deformation amount increase to a certain extent, the force value stops and the deformation amount continues to increase. After a period of time, the force value continues. Increase until the collapse of the carton. We can refer to the force value before buffering as the effective force value, and the deformation amount before buffering is called the effective deformation amount. After buffering, although the force value can continue to increase, but the carton has begun to deform, can not meet the requirements for use, so the standard for determining the compressive strength of the carton should be the effective value of the compressive test.
Generally, the deformation of the three-story A-case is below 10mm, the deformation of the three-story B-case is below 7mm, the deformation of the three-layer C-case is below 9mm, the deformation of the five-story BC is below 18mm, and the test force value should reach Effective 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. Analysis of the compressive strength of corrugated boxes is generally expressed by the average value of a set of multiple experiments (≥3). The smaller the deviation between each experimental data, the more stable the compression resistance of the carton. We can further analyze the quality of the carton through the process of changes in force and deformation, combined with various factors affecting the carton pressure resistance.
Rapid Design of Compressive Strength of Corrugated Box 0201
China's corrugated carton packaging industry has made great progress in more than 20 years. The changes in recent years are even more rapid. Some sophisticated science and technology have been applied to the industry, but due to the late start, we used corrugated paper. Some of the box design processes are still used abroad, especially the calculation method of the compressive strength of the corrugated box empty box. The foreign formulas are too cumbersome and difficult to understand. It is difficult to combine the price design of domestic cartons with the design of the compressive strength of empty containers. This can easily lead to the waste of raw materials or the quality problems in the compression resistance of cartons.
To compensate for these deficiencies and enhance the predictability of compressive strength before carton production, after a long period of measurement and verification, I have found a simple and effective method for calculating the compressive strength of empty carton boxes using the physical properties of the base paper. The formula for calculating the compressive strength of the box is written and discussed with everyone. This article only discusses the design of the 0201 type three-layer corrugated cardboard box compressive strength in this method.
The corrugated carton consists of various layers of corrugated paper. The formula for calculating the compressive strength of corrugated cartons is based on the physical properties of the original paper to calculate the compressive strength of the carton to see if it meets the requirements. It may also be based on the compressive strength requirements of the corrugated box. Select the appropriate corrugated paper.
P=Px. K
P - the empty box compressive strength of corrugated boxes (units N)
Px - the transverse integrated crush strength of base paper (units N/cm)
Three-layer corrugated board raw paper composite ring crush strength = (paper ring pressure value R1 + paper ring pressure R2 + paper ring pressure R3 x corrugation shrink rate C) / 15.2
The ring pressure value in this paper refers to the horizontal ring pressure value (unit: N/0.152m), which can be obtained through testing, or can be calculated according to the level of the base paper and the ring pressure index.
Ring pressure value R = quantitative W (units g/m2) × ring pressure index r (units N.m/g) × 0.152 (units m). There are some differences between the test value and the calculated value of the same kind of paper ring pressure value, and the general test value is larger than the calculated value. This is because the internal control standards of each paper mill are higher than the national standard, and both data can be used for compressive strength. The calculation.
K - The effective value of the integrated ring pressure in the compressive strength of the empty carton. The formula is:
Three layers A楞K=30.3+0.275Z-0.0005Z2
Three layers C楞K=27.9+0.265Z-0.0005Z2
Three layers B楞K=24.6+0.235Z-0.0005Z2
The product of the combined ring crush strength and its effective value in the carton is the compressive strength of the carton. C represents the shrinkage rate, the shrinkage ratio of A楞C=1.532, the shrinkage ratio of B楞C=1.361, and the shrinkage ratio of C楞=1.477. Z represents the perimeter of the carton (ranging from 70 cm to 200 cm).
Example 1 A three-layer C-paper box with a circumference of 125cm, A-level 250g/m2 board paper for face paper and back paper, and A-grade 170g/m2 high-strength corrugated paper for pick-up paper were used to calculate the compressive strength of the carton. .
Solution: The shrinkage of C楞 is C=1.477; the national index, the ring pressure index of surface paper and liner paper is 10.6, and the ring pressure index of 楞 paper is 9.2; Z=125.
R1=R2=250×10.6×0.152=403
R3=170×9.2×0.152=238N
Substitute into the formula
(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
This corrugated box can achieve a compressive strength of 4043N.
Example 2 The length of a three-layer A cardboard box is 148cm, the compressive strength is 4500N, the surface paper and the inner paper use the B-level 250g/m2 boxboard paper, and the paperboard uses the A-grade high-strength corrugated paper. The calculated paperboard should be selected. Quantitative.
Solution: The ring pressure index of paper and paper is 9.2
Let the quantitative W of the crepe paper be unknown, A-collapse rate 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
The corrugated carton should use 205g/m2 A-grade high-strength corrugated paper.
I worked on the long-term verification of the Kelly Carter formula, and through testing in other companies' production processes, I found that there is a certain relationship between the calculated value of compressive strength and the measured compressive value after carton forming. The set of compressive formulas I calculated was compared with the Kelly Carter formula. The calculated values of the two formulas are very consistent.
It is worth noting that even with the use of similar papers, the compressive strengths that can be achieved after molding the carton with the same specifications are different due to the differences in the production processes of the companies. Some of them are close to or lower than the calculated value of the ring pressure. Some of the compressive strengths are close to or even higher than the compressive strengths calculated using the ring pressure test values. The theoretical calculation can guide the work of controlling the compressive strength of the carton in each process of the production process, eliminate various factors that affect the compressive strength, improve the product quality, and reduce the production cost.
Factors affecting the compressive strength of corrugated boxes
1. The carton is composed of various layers of paper. Reasonable matching of paper is the basic condition for ensuring the compressive strength of the carton.
Through the testing of the physical properties of various layers of paper, we can initially calculate the compressive strength of the carton, and then use the calculated compressive strength to control the compressive strength of the carton during each process in the production process.
2. The ring pressure strength of the paper is the key to ensure the compressive strength of the carton, but the other physical properties of the paper can not be ignored.
When the tensile strength of the paper, especially the crepe paper, is not enough, the force and deformation of the carton during the compression test will increase steadily. The final value will be high and the effective force value will be low. The case will be deformed like an accordion after the test. . Waterproof performance of paper is also very important. In particular, the refrigerated box has higher requirements on the waterproof performance of paper. Sometimes, although the compressive strength of the carton is high, because the paper is not waterproof, the carton is easy to absorb moisture when it is stored in the cold storage, resulting in a .
3. The carton production process also affects the compressive strength.
Through experiments, under the same conditions, the width of the transverse pressure line of the carton is increased by 1 mm, the compressive strength of the carton is reduced by 90 N to 130 N, and the deformation amount is increased by about 2 mm. If the pressure line is too wide, the force value of the carton during the compression test will increase slowly, the effective force value will be small, and the final deformation will be large. In order to ensure the compressive strength, we should try to improve the production process and reduce the impact of various processes on the compressive strength of the carton.
4. It is also critical to choose the right type based on the type of carton.
In people's consciousness, it is often believed that the larger the carcass type is, the higher the compressive strength of the carton is, and it is easy to overlook the influence of the carp type on the amount of deformation. The larger the carcass type, the greater the compressive strength of the carton and the greater the amount of deformation; the smaller the carp type, the lower the compressive strength of the carton and the smaller the amount of deformation. If the carton is too large, the carp type is very small, and the carton is easily crushed during the compression test; the carton is too small, the carp type is large, and the deformation is excessively large during the compression test, and the buffering process is long and effective. The force value deviates too much from the final force value.
5. The effect of moisture on the compressive strength of the carton is even more negligible.
Carton production environment, storage environment, use of the environment, weather, climate and other factors will affect the moisture content of the carton, in order to ensure the compressive strength of the carton, should try to avoid the impact of external environment on the carton moisture content, keep the carton dry.
There are many factors that affect the compressive strength of cartons, and I will not discuss them here.
Corrugated cardboard box compressive strength control
The key to controlling the compressive strength of the carton lies in the quality management of the system. Careful study and strict control are required for all aspects of the pressure-resisting problem. First of all, to understand the environment in which the carton is used and to use the standard higher than the customer's requirements as its own internal control standard, this will leave room to solve the problem when there is a problem of compressive strength. Secondly, according to the internal control standards, select the appropriate type and production process, and draw up inspection standards for raw materials. Finally, according to internal control standards, raw materials and various production processes are strictly controlled, and records of relevant data are made to ensure traceability of product quality so that problems can be solved in a timely manner, and such problems can be prevented from happening again.
