Why does the puncture-proof retort pouch burst?

First, we analyze the boiled bag, put the water into the bag according to the regulations, and vent the seal. After careful observation, we found that the air was not cleaned. The heating process before 100 ° C shows that the time-sealed glass ball represents a closed bag, and it can be seen that the expansion of the boiled bag during heating is normal. The reason for the analysis is that the water seal is filled at room temperature. At this time, the pressure inside and outside the bag is balanced. During the heating to 98 °C at room temperature, the liquid water itself is expanded, and the air in the bag is expanded. At this time, part of the water vapor is also occupied. Space, leading to expansion. At this time, the pressure inside the bag will increase. In order to support the above conclusions, we have conducted a test in which the pressure inside the bag is indeed raised during the heating process, and the degree of the increase is related to the ratio of the residual air to the maximum volume of the bag, and the amount of residual air. relationship. The ratio of water to bag is high, the pressure is high, and the residual air is high, and the pressure is high. The blasting of the bag is caused by the creep of the polymer material in the sealing part under such a hot state, which is insufficient to support the pressure. This strength is called thermal bursting strength. In order to compare the hot and cold blasting strength, we used the ZY-1 positive pressure tester to test the blasting intensity at different temperatures at room temperature and 95 °C respectively. The 2O group was found to compare the heat-sealed bags, and the bursting strength at room temperature was 95 °C. The difference is large. The reason for the analysis is the decrease in strength when heated. This is the normal situation encountered in our production. If the bag is not heat-sealed, the bursting strength is small at normal temperature, which is a defective product in production. Although there is no leakage, it is more likely to burst when heated.

Then let's take a look at the puncture-proof retort pouch. The puncture-proof retort pouch is the same as the boiled pouch before it is heated to 100 oC. We investigated the anti-puncture retort pouch when it was heated above 100 °C. Because there is no instrument in China that can observe the cooking process, we can only speculate that in the cooking pot, when the heating exceeds 100 °C, the pressure inside the bag is always higher than the pressure outside the bag. (This speculation is currently not supported by facts, we are developing a cooking pot with a transparent viewing window to solve this problem.

Can the explosion bag be avoided? The explosion bag is that the pressure inside the bag is higher than the bag. Is there any way to avoid this? From the boiling process, we know that the pressure in the bag is high and the pressure is constant. Bags, if you let the environment change synchronously can not be avoided. We closed the exhaust of the TS-25C back pressure cooker, and formed a closed environment from the sample. Set 115 °C (cannot be set higher because of the safety valve relationship), and test 30 punctures. The retort pouch did not see the blast bag. It is conceivable that this is equivalent to applying an external pressure to the bag from the start of heating to balance the internal and external pressures, so there is no bursting bag.

Conclusion: (1) The problem of cooking and blasting bags in high temperature anti-puncture retort pouch is actually the thermal blasting strength of the bag, which is generally caused by damage to the heat seal. (2) If an external pressure is added to the retort pouch in advance, and this relative external pressure is maintained during the heating process, the blast bag should not occur, but the pressure resistance of the pot body is high, such as 135 ° C, which requires normal working resistance. The pressure increased from 2.2 kg to 3.2 kg. In this way, the explosion bag is related to the test method and also related to the production mode. It is important to improve the high temperature sterilization process to reduce the explosion of the bag.