Metal food cans are recognized as the safest and environmentally friendly products in the world. The metal material has good airtightness and opacity, and can effectively prevent the contents from being oxidized by light and secondary intrusion of pollutants, and has the characteristics of safety, health and health. In addition, the metal packaging recycling cycle has the highest recycling rate, in line with the national energy conservation and environmental protection requirements.
However, with the development and use of some new technologies, new materials, and people's new understanding of some of the characteristics of the original packaging materials, the food can production industry has encountered some new problems. How to make food cans become the safest food packaging, eliminate and avoid some obvious or invisible hazards, make new technology, new materials and traditional production processes more suitable, can really produce the expected business Economic benefits are issues that must be addressed and resolved in the industry today.
Beware of the generation of low vacuum tanks
At present, under the new situation of reducing costs and increasing efficiency and increasing attention to the concept of environmentally friendly low-carbon, the gradual thinning of tinplate thickness for food cans is inevitable. However, if other production process parameters and production equipment do not change, a slight vacuum tank will be produced without paying attention, which makes many food tank manufacturers confused.
The vacuum of the can is formed after the venting and sterilizing cooling. When the residual gas pressure in the tank is lower than the atmospheric pressure outside the tank, the pressure difference is the vacuum of the can.
In the production process of food cans that affect the abnormal change of vacuum degree, when the exhaust gas process parameters are constant or the vacuum degree of the sealing equipment is set to a certain value, and the quality of the can lid sealant is normal, the food can can be formed in the tank after sealing. Effective vacuum. In the subsequent high temperature sterilization process, due to the sudden change of the pressure inside the tank, when the sealing capacity of the container is insufficient to resist the pressure change in the tank, the vacuum in the tank will be reduced or even disappeared, which is an abnormal change in the degree of vacuum in the tank. The main reason (also detailed in the chapter).
The four major factors affecting the pressure inside the tank First, the difference in the filling amount of the contents makes the volume of the head gap smaller, which affects the pressure inside the tank. Second, the non-condensable gas in the contents tissue escapes during heating and affects the pressure inside the tank. Third, the mixed gas contained in the contents of the tissue escapes during heating and affects the pressure inside the tank. Fourth, due to the different coefficients of thermal expansion, the contents will have different volume increments as the temperature increases. Under the condition that the volume of the empty tank is constant, the shrinkage of the headspace volume varies widely, resulting in different pressure changes in the tank.
Method for judging the degree of vacuum The product is judged by a small crowbar before packing, and the degree of vacuum of the can is judged according to the clear and turbid sound emitted by the bar striking. This is a vacuum detecting method commonly used by enterprises.