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The 11 materials used in this study included PE+Acrylic A, PE+Acrylic B, PE+PTFE A, PE+PTFE B, PTFE, PE, PP, PPS, PA, PE+X and woven cloth, and the 6 types of fine particles included flour, corn starch, vitamin B3, SiO2, urea and CaO.
This study can be divided into two parts. First, the physical and chemical properties of filtering materials and fine particles are examined. Testing items for filtering materials consist of bibulous, speed of descend, water segregation, resistance to alkalis and acids, tensile strength, extension, splitting resistance, stiffness, dust sliding angle and pH, etc.
The second part of this study focuses on the filtering resistance test, and the influence of the filtering velocity and dust concentration on the pressure drop.
Major results of this study can be summarized as follows:
1. The characteristics of water absorption and segregation are mainly determined by the type of materials of filter bags. Coating treatment is also an important factor. If the filter cloth has been coated, it tends to have a good water segregation property. However, this may not be true for water absorption. For instance, PTFE neither has good water segregation, nor has good bibulous property.
2. The vibration characteristics of filter bags can be seen easily from the stiffness testing. The better the stiffness is, the worse the vibration characteristics is, and vice versa. Experiment results have shown that PE+PTFE A, PE and PA have better stiffness and the PTFE is the worst.
3. Resistances to alkalis and acids are closely related to the raw material. For instances, PTFE, PP, PPS and PTFE show good resistance to acids, and PTFE shows good resistance to alkalis. The remainder will harden after the treatment of alkalis and acids. And the tensile strength and extension become poor after the treatment of acid or alkali. Polyster+PTFE A and PE+Acrylic A have the worse performance.
4. Tensile strength and extension tests are performed for warp wise fabrics and filling wise fabrics. Generally speaking, the tensile strength strongly depends on the material and its weaved pattern. In general, the materials coated by PTFE membrane have bigger extension.
5. In the filtering resistance testing, filtering materials with higher initial air resistance, e.g., PE+ PTFE A, may not have higher pressure drops under a high filtering velocity and high dust concentration. On the other hand, the materials with less initial air resistance may not have a smaller pressure drop under a high filtering velocity and a high concentration of dust. When the concentration of dust is low, the pressure drops or the changes in filtering velocity are relatively stable. But if under a high pressure-drop and a high dust concentration, the filtering velocities, for example, for PE and PA, have declined rapidly.
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