The measurement index of the air permeability test

2022-09-23
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The measurement indicators of the permeability test of packaging machinery

first, the influencing factors of the permeability test

there are many influencing factors of the permeability test, such as the accuracy of the sensor, effective range, system leakage, sample processing, material characteristics, test environment, hardware design, software processing, etc. Many of these influencing factors are determined by the innate nature of design. From the perspective of application, users are not concerned about how the manufacturer improves these conditions, but what requirements it meets and what conditions it meets before it can obtain objective and accurate test data. This paper introduces two main measurement indicators, blank test and repeatability of test results

II. Blank test data

1 Blank test

blank test is the reflection of the comprehensive error of the equipment. The test error is because there are indeed influencing factors that cannot be effectively improved in the permeability test, such as system leakage and other unpredictable factors. Although there has been no clear blank test in the air permeability test standard, the detection of blank test has been widely recognized by the society

blank test data of c-v1

in order to obtain the comprehensive influence value of all factors, ① there is friction in the force measuring part;, Vac-v1 uses samples that are considered completely airtight to test according to normal operating procedures, and then observes the comprehensive impact of system leakage and other factors on the whole equipment. It is more reliable to determine the quality of the equipment by the blank test value obtained by this method

the blank test of Labthink vac-v1 uses 55 m copper foil (or thicker aluminum foil sample) as the sample for the test. It is strictly sealed. The system is vacuumized for 48h (before entering the test state, the vacuum degree of the upper and lower cavities should be less than 10Pa). The test is carried out with the conventional volume of vac-v1 (this device has optional expansion volume function). In order to analyze the influence of environmental temperature and humidity changes on the test, the automatic temperature control function of the starting equipment is not available. The pressure time change curve is shown in Figure 1. (in addition, there are temperature time and humidity time curves, which will not be repeated here)

the test lasted 12 days (including vacuum pumping time), the temperature was between 18 ~ 23 ℃, and the ambient humidity was 50.8% RH (if the self-control temperature function of the equipment was used, the test effect would be better). After entering the test state, the pressure in the lower chamber rises by 6.0pa, and the test result is 0.023ml/m2, 0.1MPa for 24h (if the expanded volume or fuzzy test mode is selected, the comprehensive influence of the above factors can be effectively reduced, and the test result will be more accurate). By analyzing the whole test curve with the data list, it is not difficult to find that the influence of temperature and humidity changes on the test is very small

in the first 60H, the pressure changes relatively large, rising from 0Pa to 3.84pa. In the subsequent 180h, the pressure increase decreases, equivalent to 0.012ml/m2, 24h 0.1MPa. The reason for this phenomenon is related to the degassing state. The test shows that prolonging the vacuum pumping time can effectively improve the impact on the test results

III. data repeatability

1. Elements of data repeatability

due to the large difference in the components selected by various manufacturers when implementing a certain test method, the data repeatability of the equipment is also an important indicator for evaluating the equipment. By analyzing the data repeatability of the equipment, we can better understand the error and fluctuation of the equipment's detection data, and improve the detection efficiency. Data repeatability includes s (standard deviation), CV (percent coefficient of variation) and LSD (least significant difference between two individual test results based on a 95% confidence level confidence level)

2. Measured data

five samples a, B, C, D and E are selected for oxygen permeability test, and Labthink vac-v1 gas permeameter is used. The test temperature, o2gtr value, test results and other parameters of the five samples are shown in Table 1:

a, D samples are provided by the Thai packaging inspection center

b samples are provided by the German mecadi laboratory

as the oxygen transmission o2gtr value of the five samples increases in turn, the standard deviation increases, and the data volatility gradually decreases. The main reason is that when testing high barrier samples, the degassing state of the samples and the influence of comprehensive factors on the test chamber are more obvious than when testing low and medium barrier samples. For example, the difference between the oxygen permeability test results of samples B and E and their average o2gtr values is 0.4. For sample B, the influence of data fluctuation accounts for 2.06%, while for sample e, it is only 0.0332%. Therefore, it is a little one-sided to discuss the value of fluctuation alone, Also pay attention to the barrier property of the sample

the repeatability of blank test data and test results is an important index to measure the permeability testing equipment. The test error is not purely determined by the equipment, but also related to the test principle. Generally, it can be considered that when the experimental force is greater than the upper limit of 1, the quality of the test results has a great impact on the detection of high barrier samples, but the repeatability of the equipment data is the comprehensive embodiment of the data error detected by the use of the program that can open the door of anisotropic 3D printing in any range of air permeability

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