Analytical Determination of the Bending Stiffness of a Five-Layer Corrugated Cardboard with Imperfections

Bending stiffness (BS) is one of the two most important mechanical parameters of corrugated board. The second is edge crush resistance (ECT). Both are used in many analytical formulas to assess the load capacity of corrugated cardboard packaging. Therefore, the correct determination of bending stiffness is crucial in the design of corrugated board structures. This paper focuses on the analytical determination of BS based on the known parameters of the constituent papers and the geometry of the corrugated layers. The work analyzes in detail the dependence of the bending stiffness of an asymmetric, five-layer corrugated cardboard on the sample arrangement. A specimen bent so that the layers on the lower wave side are compressed has approximately 10% higher stiffness value. This is due to imperfections, which are particularly important in the case of compression of very thin liners. The study showed that imperfection at the level of a few microns causes noticeable drops in bending stiffness. The method has also been validated by means of experimental data from the literature and simple numerical finite element model (FEM). The obtained compliance of the computational model with the experimental model is very satisfactory. The work also included a critical discussion of the already published data and observations of other scientists in the field.

Influence of the surface characteristics of corrugated cardboard on the quality of inkjet printing

This paper investigates the quality of inkjet printing on corrugated cardboard with various characteristics such as the presence of surface coating, the type of cardboard structure, the corrugated layer profile, and the corrugated cardboard height. The color characteristics of the corrugated board surface of studied samples were analyzed in the CIE Lab system; the value of the discrepancy in the shade of white was established when compared with the reference values of the ISO 12647 standard. During the study, the main criteria for assessing the quality of color reproduction of inkjet imprints were analyzed: an indicator of the general contrast level (K), the value of color differences for the basic tone shades (ΔE), and the volume of the body color coverage (ΔE2). It was found that when printing on various types of corrugated cardboard, there is a general decrease in the overall contrast value. The actual level of color differences is ΔE=10...45 and exceeds the permissible standards for the color reproduction quality. This adversely affects the reproduction of different color tones in the printed image. In general, the quality of color reproduction differs for the test samples of corrugated cardboard in terms of the magnitude of the spread in the values of color distortions on the tone shades. The influence of the main characteristics of the investigated samples of corrugated cardboard on the quality indicators of inkjet printing has been analyzed. In particular, a significant influence of the index of color characteristics of the surface of corrugated cardboard L* and the type of corrugated board structure on the quality of color reproduction has been established. The study results reported here could make it possible to reasonably approach the selection of the corrugated board structure that is optimal in composition, increase the productivity of the technological process for manufacturing containers, and stabilize the quality of printing on corrugated cardboard

Geometrical properties of underutilized cereal varieties of Himalayan origin for the development of future processing equipments.

This paper presents the database of physical and engineering characteristics of grains and flours of five underutilized cereal varieties viz sorghum, buck wheat, pearl millet, proso millet and barley of Himalayan origin. The results revealed a significant difference in width, length and breadth of these cereals. The sphericity value of cereal grains showed significant difference (p≤0.05) in the range 97.42 to 137.25.84% which was found to be highest for sorghum grain while as aspect ratio was found highest for proso millet grain. The static coefficient of friction samples was found maximum on corrugated board for the flour and grain. The hausner ratio and compressibility index indicated poor flowability of the sorghum flour. The bulk density, tapped density and porosity values of cereal grains varied significantly for cereal grains as well as flours. ATR-FTIR (attenuated total reflectance-Fourier transform infrared spectroscopy) confirmed the different types of linkages present in the flour samples found within the absorption bands of 3500-993 cm-1.

New Edge Crush Test Configuration Enhanced with Full-Field Strain Measurements

The standard edge crush test (ECT) allows the determination of the crushing strength of the corrugated cardboard. Unfortunately, this test cannot be used to estimate the compressive stiffness, which is an equally important parameter. This is because any attempt to determine this parameter using current lab equipment quickly ends in a fiasco. The biggest obstacle is obtaining a reliable measurement of displacements and strains in the corrugated cardboard sample. In this paper, we present a method that not only allows for the reliable identification of the stiffness in the loaded direction of orthotropy in the corrugated board sample, but also the full orthotropic material stiffness matrix. The proposed method uses two samples: (a) traditional, cut crosswise to the wave direction of the corrugated core, and (b) cut at an angle of 45°. Additionally, in both cases, an optical system with digital image correlation (DIC) was used to measure the displacements and strains on the outer surfaces of samples. The use of a non-contact measuring system allowed us to avoid using the measurement of displacements from the crosshead, which is burdened with a large error. Apart from the new experimental configuration, the article also proposes a simple algorithm to quickly characterize all sought stiffness parameters. The obtained results are finally compared with the results obtained in the homogenization procedure of the cross-section of the corrugated board. The results were consistent in both cases.

Geometrical properties of underutilized cereal varieties of Himalayan origin for the development of future processing equipments.

This paper presents the database of physical and engineering characteristics of grains and flours of five underutilized cereal varieties viz sorghum, buck wheat, pearl millet, proso millet and barley of Himalayan origin. The results revealed a significant difference in width, length and breadth of these cereals. The sphericity value of cereal grains showed significant difference (p≤0.05) in the range 97.42 to 137.25.84% which was found to be highest for sorghum grain while as aspect ratio was found highest for proso millet grain. The static coefficient of friction samples was found maximum on corrugated board for the flour and grain. The hausner ratio and compressibility index indicated poor flowability of the sorghum flour. The bulk density, tapped density and porosity values of cereal grains varied significantly for cereal grains as well as flours. ATR-FTIR (attenuated total reflectance-Fourier transform infrared spectroscopy) confirmed the different types of linkages present in the flour samples found within the absorption bands of 3500-993 cm-1.

Estimation of the Compressive Strength of Corrugated Board Boxes with Shifted Creases on the Flaps

In the modern world, all manufacturers strive for the optimal design of their products. This general trend is recently also observed in the corrugated board packaging industry. Colorful prints on displays, perforations in shelf-ready-packaging and various types of ventilation holes in trays, although extremely important for ergonomic or functional reasons, weaken the strength of the box. To meet the requirements of customers and recipients, packaging manufacturers outdo each other with new ideas for the construction of their products. Often the aesthetic qualities of the product become more important than the attention to maintaining the standards of the load capacity of the packaging (which, apart from their attention-grabbing functions, are also intended to protect transported products). A particular flaps design (both top and bottom) and its influence on the strength of the box are investigated in this study. An updated analytical–numerical approach is used here to predict the strength of packaging with various flap offsets. Experimental results indicated a significant decrease in the static load-bearing capacity of packaging in the case of shifted flap creases. The simulation model proposed in our previous work has been modified and updated to take into account this effect. The results obtained by the model presented in this paper are in satisfactory agreement with the experimental data.

New Edge Crush Test Configuration Enhanced with Full-Field Strain Measurements

The standard edge crush test (ECT) allows to determine the crushing strength of the corrugated cardboard. Unfortunately, this test cannot be used to estimate the compressive stiffness, which is an equally important parameter. It is because, any attempt to determine this parameter using current lab equipment quickly ends in a fiasco. The biggest obstacle is obtaining a reliable measurement of displacements and strains in the corrugated cardboard sample. In this paper, we present a method that not only allows to reliably identify the stiffness in the loaded direction of orthotropy in the corrugated board sample, but also the full orthotropic material stiffness matrix. The proposed method uses two samples: (a) traditional, cut crosswise to the wave direction of the corrugated core, and (b) cut at an angle of 45 degrees. Additionally, in both cases, an optical system with digital image correlation (DIC) is used to measure the displacements and strains on the outer surface of samples. The use of a non-contact measuring system allows to avoid using the measurement of displacements from the crosshead, which is burdened with a large error. Apart from the new experimental configuration, the article also proposes a simple algorithm to quickly characterize all sought stiffness parameters. The obtained results are finally compared with the results obtained in the homogenization procedure of the cross-section of the corrugated board. The results were consistent in both cases.

Estimation of the Compressive Strength of Corrugated Board Boxes with Shifted Creases on the Flaps

In the modern world, all manufacturers strive for the optimal design of their products. This general trend is recently also observed in the corrugated board packaging industry. Colorful prints on displays, perforations in shelf-ready-packaging and various types of ventilation holes in trays, although extremely important for ergonomic or functional reasons, weaken the strength of the box. To meet the requirements of customers and recipients, packaging manufacturers outdo each other in new ideas for the construction of their products. Often the aesthetic qualities of the product become more important than the attention to maintaining the standards of the load capacity of the packaging (which, apart from their attention-grabbing functions, are also intended to protect transported products). The particular flaps design (both top and bottom) and their influence on the strength of the box is investigated in this study. The updated analytical-numerical approach is used here to predict the strength of the packaging with various flap’s offsets. Experimental results indicated a significant decrease in the static load-bearing capacity of packaging in the case of shifted flap creases. The simulation model proposed in our previous work has been modified and updated to take into account also this effect. The results obtained by the model presented in the paper are in satisfactory agreement with the experimental data.

Crushing of Double-Walled Corrugated Board and Its Influence on the Load Capacity of Various Boxes

As long as non-contact digital printing remains an uncommon standard in the corrugated packaging industry, corrugated board crushing remains a real issue that affects the load capacity of boxes. Crushing mainly occurs during the converting of corrugated board (e.g., analog flexographic printing or laminating) and is a process that cannot be avoided. However, as this study shows, it can be controlled. In this work, extended laboratory tests were carried out on the crushing of double-walled corrugated board. The influence of fully controlled crushing (with a precision of ±10 μm) in the range from 10 to 70% on different laboratory measurements was checked. The typical mechanical tests—i.e., edge crush test, four-point bending test, shear stiffness test, torsional stiffness test, etc.—were performed on reference and crushed specimens. The residual thickness reduction of the crushed samples was also controlled. All empirical observations and performed measurements were the basis for building an analytical model of crushed corrugated board. The proven and verified model was then used to study the crushing effect of the selected corrugated board on the efficiency of simple packages with various dimensions. The proposed measurement technique was successfully used to precisely estimate and thus control the crushing of corrugated board, while the proposed numerical and analytical techniques was used to estimate the load capacity of corrugated board packaging. A good correlation between the measured reduced stiffness of the corrugated cardboard and the proposed analytical predictive models was obtained.