Research on Testing Method of Corrugated Crush Test (CCT)

Corrugated cardboard boxes are gradually replacing wooden boxes and other transport packaging containers with their superior use performance and good processing performance, becoming the most widely used packaging material. Compressive strength is a vital performance index of corrugated cardboard boxes. Too high or too low compressive strength of cardboard boxes is not allowed. Too high will inevitably increase the cost of packaging, and if it is too low, the function of protecting the goods will be lost. The corrugated cardboard box is made of corrugated cardboard. From the structural analysis of corrugated cardboard, the corrugated cardboard is composed of inner liner, liner, flute paper and medium paper. Corrugated paper plays a supporting role like bones, it has more influence on the strength than liner and inner liner, so the Corrugated Medium Test(CMT) and Corrugated crush test(CCT) of base paper have become very important. CMT affects the cushioning performance of corrugated box, and CCT mainly affects the compressive performance of corrugated box. As so far there is currently no testing method for Corrugated Medium Test(CMT) in China. The relevant international standard is ISO 16945 "Corrugating medium --- Determination of the edge crush resistance after laboratory fluting "and the American standard TAPPI T824 and TAPPI T843. In the ISO 16945 standard, there are two different methods for testing the crush strength of corrugated medium.
The first one is to place the corrugated medium on the CCT sample holder immediately after corrugation, and start the compression strength tester for testing. The time from corrugating to applying pressure is 20s to 25s, referred to as CCT0.
The second is place the corrugated medium on the CCT sample holder after corrugation, and process it in standard atmospheric environment (temperature 23 ℃, relative humidity 50%) for 30min ~ 35min, and then test it, referred to as CCT30.
The test result obtained by the first method is higher than the result obtained by the second one, the difference is the influence of humidity after temperature and humidity treatment. These two methods have their own advantages, and both are widely used. The test results are not comparable, like ring crush test (RCT) and short span test (SCT).
CCT test principle: After a certain size of sample (152mm × 12.7mm) is corrugated on the medium fluter, the sample holder is used to fix the sample state, and then placed on the compressor to perform the compression test until the corrugated medium is crushed, and the maximum compressive force per unit length is measured and expressed in kN/m.

  • Testers and accessories needed
Crush tester, CCT/RCT sampler, Medium fluter, CCT sample holder and base paper
  • Testing procedure
1. Sample preparing and pre-treatment
According to the national standard GB/T 450 and GB/T 10739, the samples are taken and processed.
2.  Sampling
Use a CCT/RCT sampler to accurately cut a sample with a width of 12.7mm ± 0.1mm and a length of 152mm ± 0.5mm. The number of samples is at least 10 pieces. The long side is the longitudinal direction of the sample, and the parallelism of the long side direction of the sample is within 0.01mm , and smooth, without defects.
3.  Parameter setting
Now switch the test mode to CCT mode, and then set the test speed to 12.5mm / min, and set the platen spacing slightly higher than the sample height 12.7mm, such as 14 ~ 15mm, waiting for the test.
4. Corrugation
Start the Medium fluter. When the pressure roller is heated to (175 ± 8) ℃, insert the long side of the sample vertically into the feed port to make the sample corrugated. Place the corrugated sample in the holder.
5. Test
 There are two methods of testing: immediately after corrugation and after 30 minutes of temperature and humidity treatment.
 5.1 Test immediately after corrugated. If the compression test is performed immediately after the sample is corrugated, the time from corrugation to the application of pressure should be within 20 to 25 s, that is, the sample should be tested immediately, known as CCT0.
5.2 Test after 30 minutes of temperature and humidity treatment. If the sample is corrugated and subjected to temperature and humidity treatment, it should be treated in an environment of temperature (23 ± 1) ° C and relative humidity (50 ± 2)% for 30 to 35 minutes, which is CCT30.

6. Result calculation
6.1 Corrugated medium edge crush strength
CCT is calculated according to the formula (1), Unit kN/m
F——The average value of the maximum compression force, unit N;
l—— Sample length (before corrugated), unit mm.
In order to quickly identify the method used for the testing result, the following format can also be used to show the result more conveniently.
    CCT0=x.xx kN/m
    CCT30=x.xx kN/m
CCT represents the corrugated medium edge crush strength, and the subscript represents the temperature and humidity treatment time, in units of min.
6.2 Index of corrugated medium edge crush strength
      CCT index is calculated according to the formual (2), unit N.m/g
g——The sample grammage, unit g/m2

  • Comparison of CCT0 and CCT30 test results
CCT results of three kinds corrugated medium, each sample test 20 data, and then average, the test results are shown in Figure 3.
As can be seen from Figure 3, the test results of the three samples are all CMT0 is greater than CMT30.
Conclusion: This article introduces the test method of CCT in lab. This test method requires sampling, corrugation and flute fixing, and temperature and humidity treatment, which is complicated to operate. At present, China domestic users are less used, but foreign users are doing more, we need to learn advanced foreign technology to make up for our deficiencies. This is my personal understanding of this advanced technology, and if there are errors, please criticize and correct.

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