Corrugated cardboard box compressive strength calculation and paper testing

The corrugated box is composed of various layers of corrugated paper. The corrugated box's compression formula is based on the physical properties of the paper board to calculate the compressive strength of the corrugated box. We can select a certain corrugated board base paper according to the predetermined corrugated box compressive strength requirements. . Only with a clear understanding of the various properties of the base paper, can the papers of various types and sizes be combined and configured in accordance with the needs of production in the next step, and products that meet the needs of users will be produced.

In fact, the compressive strength of corrugated boxes is a more complicated issue because the baseboard and corrugated base papers that make up the corrugated board are anisotropic, non-uniform, and the fibrous material is also viscoelastic in the making of boxes. In the process of the board, the original paper is subjected to different temperatures, adhesives and external forces, and many changes have taken place in itself. Therefore, the change from the base paper to the corrugated board and the physical properties of the corrugated box is irreversible. The physical properties of base paper to calculate the physical properties of paperboard and cartons have been the subject of research in the carton research and manufacturing industry. In order to better produce various types of cartons, it is necessary for us to understand some of the paper paper's performance testing knowledge.

Compression strength calculation

The existing compressive strength calculation formulas are many, but most of them are based on foreign countries, and they are difficult to understand and remember. It is difficult to grasp the existing corrugated cardboard box designers in China. Among companies, due to the difficulty of the design of compression, the price design is often decoupled from the design of the compressive strength of the carton, which may easily lead to waste of raw materials or insufficient quality of the pressure. The resistance formula in the design and production of the convergence, to avoid blindness in the design, increase the production of the compressive strength of the carton at the beginning of the predictability.

Corrugated cartons are made of corrugated paper of various layers. The anti-cotton formula calculates the compressive strength of the cartons based on the physical properties of the cardboard base paper to see whether it can meet the requirements; it can also choose certain according to the compressive strength requirements of the predetermined corrugated cardboard boxes. Corrugated paper base paper.

P=Px·K

P—the compressive strength of the empty box of the corrugated box (units N),

Px—The transverse composite crush strength (in N/cm) of the corrugated paper base paper.

Among them, the calculation formula for the integrated ring pressure strength of the three-layer corrugated paperboard paper is:

Px=(R1+R2+RmC)/15.2

The formula for calculating the composite ring pressure strength of the five-layer corrugated paper base paper is:

Px=(R1+R2+R3+Rm1C1+Rm2C2)/15.2

Rn --- test value of cross-pressure strength of lateral paper (N/0.152m)

Rmn---The test value of the lateral crushing strength of crape paper (N/0.152m)

C---Corrugated shrinkage, that is, the ratio of the length of the corrugated core paper to the face paper. (CA=1.532, CC=1.477, CB=1.361)

K—The effective value of the integrated ring pressure in the compressive strength of the empty carton. The formula is:

K3A=30.3+0.275Z-0.0005Z2

K three C=27.9+0.265Z-0.0005Z2

K three B=24.6+0.235Z-0.0005Z2

K Five AA=41.7+0.355Z-0.0005Z2

K Five BB=33.2+0.305Z-0.0005Z2

K Five CC=38.1+0.345Z-0.0005Z2

K Five AB=38.2+0.335Z-0.0005Z2

K 5 AC=40.2+0.355Z-0.0005Z2

K Five BC=35.7+0.325Z-0.0005Z2

Three A---three-layer A box, three-layer box perimeter value range: 70-200cm

Five AC --- five-layer AC box, five-layer box perimeter value range: 70-300cm

In the production process, each company will only be involved in part of the production process, so it is only necessary to select the corresponding anti-Kai formula according to the company's model. According to the enthalpy and base paper ring pressure value to calculate the comprehensive ring pressure, and then the carton perimeter into the formula corresponding to the K value of the formula, the product of comprehensive ring pressure and K value is the compressive strength of the carton. We can also choose the right cardboard base paper according to the compressive strength and perimeter of the predetermined carton, and can also use the calculated compressive strength to guide the production process.

In most of the compressive strength calculation formulas, most use the base paper crushing strength to calculate, but in fact the impact on the carton compressive resistance is not only the raw paper's ring crush strength. There are many factors that affect the compressive strength of corrugated carton, but For paper, it should include the paper's ring pressure strength, tensile strength, tightness, and the paper's water and water absorption.

The fiber arrangement of the fourdrinier paper machine is different from that of the circular paper machine. The paper produced by the rotary paper machine has an orderly arrangement of the fibers due to the mechanical process. The pulp is not easy to be evenly distributed. The paper looks like a cotton wool through strong light. , uneven texture, prone to light transmission; and the long-grid paper machine on the contrary, the arrangement of fibers is complicated, tending to disorder, hanging pulp evenly, the paper through the light looks uniform texture, no obvious light transmission Due to the different arrangement of fibers, various physical indexes of the base paper of the long web and the paper of the rotary screen are affected.

Paper test

In the ring pressure test, the ring pressure test of corrugated medium base paper is divided into longitudinal ring pressure strength and horizontal ring pressure strength. It is necessary to pay attention to the ring pressure test sampling test. The vertical ring pressure strength sampling needs to be consistent with the paper width direction. The lateral crush strength should be sampled in the same direction as the length of the web. During the test, we will find that although the fiber arrangement of the long web machine tends to disorder, the transverse crush strength is always higher than the longitudinal crush. The strength is low, and as a 0201 corrugated box, the horizontal ring pressure strength is consistent with the direction of force of the corrugation, that is to say, when the grade of the paper is judged or the compressive force is calculated, the corrugated paper is horizontally looped. Compression strength is the effective strength of the test. The fourdrinier paper machine has increased the number of fibers in the transverse ring pressure test while performing disordered arrangement of the fibers, thereby enhancing the lateral crushing strength of the corrugated paper, and at the same time enhancing the interfiber fibers due to disordered arrangement of fibers. The firmness, in turn, ensures the stability of the compressive strength of the corrugated carton, which results in a reduction in the drop in the pressure resistance value between the individual carton boxes.

Regarding the value of the ring pressure in the compression formula, we should follow the test results of the standard environment to reduce the error between the test values ​​due to changes in the test environment. We all know that the humidity of the air will have a certain impact on the crushing strength of the corrugated paper and the pressure resistance of the carton. If we test the base paper in a too dry environment, the force value of the ring pressure test will be higher than it actually is. If the use environment is too humid, we use this higher force value to carry out the compression design, which will inevitably cause unsafe quality risks; conversely, if the test environment is too humid and the use environment is too dry, the paper will experience a ring pressure test. It will be very low, and we use this very low force value to design the compressive strength, which is bound to waste raw materials. When using the test value for pressure calculation, we first need to verify it within our company. Under normal circumstances, we should guarantee a safety factor for the calculated value. Generally, we choose 1.2, that is, the calculated value is 1, and the actual compression should be Can reach 1.2 times the calculated value to prevent the difference between carton individuals or some external environment changes caused by insufficient pressure.

Tensile strength, the tensile strength of corrugated base paper depends on the fiber structure of the base paper and the binding force between the fibers. The tensile strength not only affects the resistance of the base paper in the machine during use, but also affects the tensile strength of the base paper. After the carton is formed, the compressive quality, usually, if the paper's ring crush strength is very good, but the cracking length and tensile strength are not good, it will often cause the carton deformation in the compression test, the final edge shape Such as the accordion, this is because when the carton is subjected to the pressure test, due to the poor texture or structure of the fiber or the poor connection between the fibers, the fiber at the edge of the pressure line is first stressed, and this weak fiber is not very good. The force exerted on the carton is conveyed to the entire carton, except that the passive part is under pressure. With the local collapse of the edge, the force part gradually moves toward the middle of the box, and a deformation test is formed like an accordion. . However, if the tensile strength is good, no such situation will occur. The carton will bear a great deal of pressure under very small deformation. If it is overweighted, the carton will collapse from the center of the box face because the whole cannot withstand the pressure.

The tightness of the paper tests the pressing effect of the base paper during the production process. The closeness of the tightness will affect the tightness between the fibers and then affect the ring-press strength and tensile strength of the base paper, and ultimately affect the compressive strength of the carton. Because the tightness of the paper is not enough, it also affects the moisture absorption of the carton, which makes the carton excessively absorb moisture during use or storage and reduces the compressive strength of the carton itself.

The determination of the quality of paper is not determined by a single physical index. The physical properties of paper should be a comprehensive indicator. Occasionally, the customers of carton use to prevent carton companies from cutting corners and materials, and at the same time put forward requirements for the pressure resistance index of the carton, they also put too high weight requirements on the matching of the base paper. In order to meet the customer's request, the carton company only needs to increase paper grams. Reducing paper grades to ensure cost. This kind of requirement of customers has rejected the low-heavy and high-strength corrugated paper. In fact, considering the overall performance, the low-strength and high-strength corrugated base paper is much more stable than the low-grade and high-weight corrugated base paper. Because the stability of the base paper reduces the individual differences in the physical properties of the carton, the safety of the use of the carton is increased, and low-grade, high-weight paper is difficult to achieve this effect. In the compression design, due to the instability of the low-grade primary paper, it is difficult to accurately perform anti-pressure estimation. The physical properties of the carton after the completion of the individual differences are very large, and the poor quality of the doping, in the use or transport of the carton The process will become the first point of damage affect the use of the entire carton.

In the pressure resistance of the carton, the base paper plays a decisive role. We need to pay a certain amount of effort to detect and determine various kinds of base papers. We must rationally configure all kinds of papers to produce cartons that meet the physical performance requirements. The carton pressure resistance is a comprehensive control process. In the production process, the impact on the carton compression caused by the irrational process should be minimized. The loss of the compressive strength of the carton is equivalent to a waste of the original paper. This is the biggest hidden waste. It will inevitably create a vicious cycle, which will greatly increase the production cost of the carton. At the beginning of production, it will be well aware of the performance of various base papers. In actual production, paper can be dispensed as required.

Reprinted from: Industry Technology (Carton)