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Food packaging material permeability test

Hits:   source:未知 Time:2016-09-09

(a) determination of the gas transmission rate
In a fixed volume, the total pressure of a mixture of gases is the pressure of a variety of gases, and the pressure of a particular component is the same as that of a particular component.
The velocity of a particular gas through a non porous material is a function of the pressure difference between the material and the material, rather than a function of the total pressure difference between the two sides of the material.
There are three main methods to measure the transmittance of a material: the pressure boosting method, the volume increase method and the concentration change method. Here are the three methods of measuring the working principle.
(1) this method is generally to determine the total pressure difference of the gas through the isolated material, as well as the pressure difference of the gas on each side of the sample. Because the pressure difference between the two sides of the gas is equal to the total pressure difference, therefore, the gas flow from the high pressure side of the isolated material toward the side of the low pressure side.
Pressure difference can be increased from one side of the pressure, or in the side of a vacuum, or to take two kinds of comprehensive methods to achieve. The volume of the side of the low pressure chamber remains constant, and the velocity of the gas pressure can be measured. Using this principle, several different instruments can be designed. The instrument structure of the British standard method is illustrated in Figure 10.8. At the bottom of the test chamber, a pipe type glass pressure gauge is arranged, and one end of the tube is sealed with an epoxy resin. A glass dish of a cavity is fixed on the base surface, forming a flat surface, and then the sample covered in glass plates, heavy to thickness up to about 7---8mm. The sample is covered with a soft rubber pad. Clamp the top of the test chamber to ensure complete sealing.
The instrument is pumped into a vacuum, and the gas is introduced into the upper chamber. At this time the pressure gauge can be stabilized in an appropriate value (6.6661-13.3322Pa) will be tilted to the instrument, so that the mercury from the mercury tank into the capillary tube and U tube, and then the instrument vertical v. At this time, the pressure of the gas through the sample increased, from the capillary pressure drop in the level of mercury. Figure 10.9 is the relationship between the decrease of the mercury column and the time when the oxygen transmission rate is measured. The gas permeation rate can be calculated.