Corrugated box compressive strength compressive test article

Four carton compression test

The carton compression test method is to place the carton on the pressure tester and apply pressure evenly at the top (or bottom) of the carton at a certain speed, thereby assessing the ability of the carton to withstand external pressure, that is, the ability of the carton to protect the contents. Carton pressure test, also known as compression test, is the most basic test of carton performance. This test can also determine the carton compression resistance under different conditions.

1. Carton compression test method

The equipment used in the carton pressure test is a carton special pressure tester. This tester has two large area pressurizing plates. The area of ​​common upper and lower platens is 1.5mx 1.5m or 1m x 1m. One of the two pressure plates is a support plate, the position of which can be adjusted according to the size of the sample, so that it has a suitable height, and then it is fastened; the other is a pressure plate, which can be along the guide rod ( Column) Slide to apply pressure to the specimen.

The maximum working capacity of the testing machine is 50 KN (5000 kgf), the moving speed of the pressure plate is 10 mm/min, and 1 in/min is also used. Equipment should be accompanied by a displacement indicating device with a measurement accuracy of not less than ±0.5 mm. Some testing machines have an automatic recorder that records the load-deformation curve on its own.

Cartons are sensitive to temperature and humidity, and have different temperature and humidity. The moisture content of cartons is also different. Moisture exerts a great influence on the compressive strength. Even if the moisture content of the same carton varies greatly, the measured compressive strength also differs greatly. Therefore, in order to ensure the objective and real test results, the test sample must be subjected to temperature and humidity balance before testing. The specific operation method is to place the sample in a standard temperature and humidity environment of 23±1° C. and 52±2% RH until the moisture content of the sample does not change. The processing time of the general sample needs more than 12 hours.

The entire compression test is broadly divided into three stages. The first is the preloading stage. A pressure of 220N is applied to the carton first to ensure that the pressure plate of the carton is fully in contact; the second is the stage of the carton compressive deformation, at which time the carton is under pressure. Under the slow deformation, the pressure value displayed by the testing machine increased steadily, but there was no sign of damage to the carton. The third stage was the crushing stage of the carton. The main characteristic of this stage was the momentary drop in the pressure value and the sudden increase in the deformation of the carton. The pressure value displayed at this time is the compressive strength of the carton.

Compressive test specimens are generally not less than three, and the specimens shall not have defects such as breakage, creases, and degumming. The test result is the average of each test value, but if there is a significant deviation in the test value, it should be pre-eliminated and then averaged.

2, the rapid and accurate measurement of the carton pressure value skills

The pretreatment time of the sample for the compression test is very long, and the shorter and shorter delivery time requires the carton to know the exact test result immediately after it is produced. Many carton manufacturers feel a headache. Herein, the author provides a method for quickly and accurately measuring the pressure resistance of a carton without temperature and humidity balance treatment. After practice tests, the results obtained are very close to those obtained after the temperature and humidity balance treatment.

To make a quick calculation, the required equipment must be equipped with a digital moisture tester in addition to the carton compression tester. The tester must be able to obtain test results immediately and the accuracy is within ±0.5°C.

The test method is to measure the compressive strength of the carton and the moisture content of the paperboard, and then calculate the compressive value of the carton according to the “Contrast Table of Moisture Content and Compression Resistance” (see Exhibit 5).

The test proved that the carton is in the standard; the moisture content in the temperature and humidity environment after balance is 8%, so it can be determined that when the carton moisture is 8%, the measured compressive value is the real value (reference value). If the moisture content of the cartons exceeds 8%, the compressive strength of the cartons will decrease in varying degrees, and the extent of the decrease will have a corresponding relationship with the moisture content. Therefore, after we measured the compressive value and the moisture content, we can calculate the compressive value after the balance according to the corresponding relationship in the comparison table.

Examples

There is a carton that has not been subjected to a temperature-humidity balance treatment. The compressive strength of the empty container is measured to be 6250N, and the moisture content of the paperboard is 10%. The correct compressive value of the sample is calculated.

Through the look-up table, the moisture content of the carton is 10%. At this time, the test value of the compressive strength is 81% of the true value.

Let the true value of compressive strength be R.

Then R=6250/81%

=7716N

It can be inferred that the compressive strength of the sample after temperature and humidity balance treatment is 77 76N

3, carton compression and high temperature and humidity

In the Pearl River Delta region of China, due to the way most containers are loaded with containers and exported by sea, the temperature and humidity inside the container can reach as high as 45°C and 93% RH during the tens of days of sea transport. The bearing pressure drops by more than 60% from the normal condition and it is easy to cause the carton to collapse. The main reason for this is the fact that the paste is prone to emulsification under high temperature and high humidity. Because the corrugated paperboard is made of glued paste, usually the paste of the corrugated paperboard paste line is solid, but if the paperboard box is stored for a long time in a high-temperature and high-humidity environment, the paste will emulsify and cause the corrugated board to stick. The disengagement of the combined position resulted in a sharp drop in the compression resistance of the carton.

In order to ensure that the export cartons still have adequate compressive strength under high temperature and high humidity conditions, some paper mills began to increase the high-temperature and high-humidity performance of the cartons under the promotion of customers. The test method for high temperature and humidity of the carton is to place the carton in the high and low temperature alternating damp heat box after sealing and set the temperature and humidity to 45°C and 93% RH. Stack the weight on the top of the box. The weight is the empty box resistance. The pressure value is 1/4 to 1/6, and the time it takes to bear the heavy pressure is observed.

Some cartons are forced to use the method of pulling out the compressive strength of cartons to ensure that the cartons can withstand a certain stacking weight under high temperature and high humidity, resulting in a substantial increase in the cost of paper. In the past two years, the practice of adding cross-linking agents and stabilizers to improve the high temperature and humidity resistance of cartons has been widely recognized. The cross-linking agent is a high-molecular polymer. After the paste is added, the molecules replace the hydroxyl groups in the starch molecule to form a stable cross-linking. Because the reaction process of the crosslinker molecule is relatively slow and the process is irreversible, its adhesion and moisture-proof effect will gradually increase after the cardboard leaves the production line. After the reaction is complete, it will be completely hydrophobic and form a strong and moisture-proof plasma film, thus giving the paperboard Good resistance to high temperature and humidity.

In addition, the starch molecules are surrounded by the cross-linker molecules, which enhances the resistance to heat and shear and thus maintains the stability of the viscosity during the cycle. Because the hydroxyl group in the starch molecule is substituted and changed from hydrophilic to hydrophobic, it is easy to be dehydrated during drying, and the drying speed is increased, thereby increasing the vehicle speed. The cross-linker molecules are easily affiliated with the fiber molecules and can also help increase the bond strength.

In the past three years, paste additives for improving the performance of paperboard have been released and rough estimates have been made. At present, there are no less than 20 varieties in the market, but the quality is uneven. As an example, resin additives that are water- and moisture-repellent have been used as examples. There are nearly 10 brands with different prices. Some inexpensive additives have a solid content of only 30%, and the gelatinization time is as long as several minutes. Some imports The brand, although the price is higher, but the solid content of more than 50%, the gelatinization time is less than? Minutes, the fastest or even just 40 seconds. In addition, the carton factory must consider what kind of additives should be selected according to customer needs, equipment conditions, raw paper specifications and employee quality, and also consider the supplier's professional level and after-sales service, because if you want to add an additive The role of the product is brought into full play. It is not simply "pour in and use it," it contains a considerable amount of expertise.

(Author / Guan Guoping: Shenzhen Liyang Packaging Technology Co., Ltd.)

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