Differential Pressure Moisture Analyzer

The commonly used methods for measuring trace moisture in plastic particles include differential pressure method, electrolytic method, Karl Fischer method, etc. Among them, the differential pressure method for moisture determination has been widely used for its advantages of rapidity, accuracy, easy operation, and low use cost. Applied in the intermediate process of the chemical fiber plastics industry, especially the determination of the content of trace moisture that directly affects the spinning quality after the drying treatment of polyester chips, nylon 6, nylon 66 and other particles before melt spinning . It is also suitable for the general trace moisture measurement of nylon 6 and nylon 66 particles and plastic resins. At present, there is no supply of complete sets of equipment in the country, and it is quite troublesome for customers to customize and produce according to their needs. This device refers to the national standard and the international standard method (see appendix) and the habits of many domestic manufacturers, assembling complete sets, providing users with considerable convenience and testing guarantee.

The differential pressure method moisture measuring device is suitable for measuring a very small amount of moisture combined with the internal molecular structure of the raw material, but is not suitable for measuring the equilibrium moisture between the raw material and the environment. If the material contains water, the temperature will increase and melt, which will cause the material to degrade and reduce the intrinsic viscosity, which will directly affect the product quality. In general, before spinning, the moisture content is less than 0.03%. Therefore, after the raw material is dried and before spinning, its internal extremely low moisture content must be measured by the differential pressure method. Vacuum-packed plastic moisture content can also be used differential pressure method.

The maximum water content measured by this device is 1.5 mg.

When the sample contains many volatile mixed substances other than water, it should pay attention to the reliability of its test results.

The test device is an airtight system consisting of glass tubes and test tubes, glass bulbs A and B. In the U-shaped pipe L, there is a certain amount of silicone oil. When the gas valve G is open, the system is brought to a high vacuum. If the entire system is airtight, then the gas valve G is closed. The gas pressures at the liquid surfaces D and E on the left and right sides of the silicone oil should be the same. The two liquid levels are on the same level. If, for some reason, the pressure on the right side rises, the pressure on the right fluid surface D rises, the fluid level of the silicone oil changes up and down, the right fluid surface drops, and the left fluid surface rises. If in a test tube, some kind of water-containing material is preliminarily placed, and the water can only be released under certain conditions (such as heating), the liquid surface pressures of D and E are equal if the water release conditions are not reached. After the water release conditions are reached, the pressure in the pipe on the right side of the system is increased due to the action of water vapor, the pressure on the D liquid surface rises, the liquid level drops, the E liquid level rises, and the pressure difference between the D and E liquid levels and the right side The vapor pressure balances. The more water vapor, the greater the pressure generated and the greater the liquid level rise and fall. When the moisture content reaches a certain value and the water vapor pressure reaches the critical point of saturated steam, part of the water vapor recondenses into water (in the form of fog or water droplets) and the pressure no longer rises. Corresponds to the moisture content of this saturated steam critical point, which is the highest water content that the device can measure.

The differential pressure method uses the contrast method for determining the moisture content. Experiment with different known moisture content to find out the different D and E liquid level rises and falls corresponding to different moisture content. Then, when the material with unknown moisture content is tested, it will rise and fall according to different levels of D and E fluids. , also know the moisture content.

This method is commonly used by domestic manufacturers to determine the moisture content of polyester chips and nylon after drying. The general test temperature is:

Polyester chips 220±5°C

Polyamide 6,66,69,610,612195±5°C

Polyamide 11,12170±5°C

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