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Filter Media Commonly Used in Filters and Their Main Properties

Filter Media Commonly Used in Filters and Their Main Properties

1. The filter cloth of the cylindrical strainer


It is a filter medium with many varieties and wide applications in industry. Filter cloth is divided into textile filter cloth and non-textile filter cloth.


Its component materials are all natural fibers (cotton, wool, silk, hemp) or synthetic fibers. The filtering performance of the filter cloth is determined by the material, fiber weaving and post-processing.


(1) Textile filter cloth.


The textile filter cloth of the cylindrical strainer is woven from three different types of yarns: monofilament (single strand yarn), multifilament (fixed-length fiber yarn) and staple fiber (multiple strand yarn).


Monofilament is generally a single filament with a diameter of 0.16-0.32 (or even 1 in some occasions) drawn from synthetic fibers. The filter cloth made from it has a smooth surface, small voids, small specific resistance, uneasy plugging, excellent slag discharge performance and are easy cleaning and other advantages. But the filter cloth of the cylindrical strainer can only trap particles with a larger diameter, which is not suitable for precision filtration.


When separating the suspension liquid with a wide particle size distribution range, the separation effect will be affected.


Multifilament yarn is twisted and spun from two or more strands of raw silk. The filter cloth woven by it has good tensile strength, better interception performance of particles than monofilament, but slightly poorer slag discharge performance.


Staple fiber is made by twisting multiple strands of natural cotton, wool fiber or synthetic short fiber. Because of its fluffy fiber, it has good interception performance of particles and excellent sealing performance. However, its disadvantage is that it has poor performance of cleaning and slag discharging because the pores are easily blocked by particles.


(2) Non-textile filter cloth


The fibrous structure of the filter cloth of this cylindrical strainer is not regular but messy and densely arranged, so its strength is worse than that of textile filter cloth, but is stronger than filter paper, and its porosity is coarser than filter paper, so its specific resistance is smaller than filter paper.


Non-textile filter cloth has already been used in filter presses and horizontal disc filters, mainly for clarification and filtration, and purification of solid particles in low-concentration suspensions.


Such as the filtration of beverages, milk slurries, varnishes, lubricants and vegetable gums etc. The filtration mechanism of non-woven filter cloth is roughly staging filtration, that is, the surface layer of this filter cloth intercepts large particles (greater than 100), while the inner layer intercepts highly dispersed small particles.


2. The filter screen of the cylindrical strainer


The filter screen is also a kind of woven filter medium, and its material is mainly metal. Any metal and alloy that can be brushed, such as stainless steel, brass, monel, nickel, silver, etc., can be used as the material of the wire mesh.


Recently, there are also filters made of plastic raw silk.


Just because the material is metal, the surface of the cylindrical strainer is smooth, wear-resistant, corrosion-resistant and high-temperature resistant. It basically does not shrink or stretch. It is not easy to be blocked by particles and is easy to clean and regenerate. It has a longer service life than the fiber filter cloth.


The one-time investment is more expensive, but the operating cost is lower than filter cloth.


3. The filter felt of the cylindrical strainer


Synthetic fibers (such as polyacrylonitrile fiber, nylon, polypropylene, etc.) or wool fibers are compacted into felts with different thicknesses with or without resin bonding agent (such as thermal bonding) in an irregular dense arrangement.


It can be installed on filter press or rotary drum vacuum filter. When the pleated metal mesh is set, it can be used as a cylindrical strainer element. The filtration mechanism of filter felt belongs to deep filtration.


Synthetic fiber filter felt has the advantages of anti-corrosion, mildew resistance, good particle retention performance, etc., and is more widely used than felt.


4. The filter pad of the cylindrical strainer


The filter pad is a modeling filter medium made from asbestos and cellulose, with a thickness of 2~5mm, a fiber diameter of 200~250 angstroms, and a cellulose fiber with a diameter of 20~30 as the support. The asbestos fiber forms a gap in it and can be used on the filter press.


If it is filled with diatomaceous earth particles, the porosity of the pat can be increased. Because the void ratio of the filter pad of the cylindrical strainer is very tiny, it is mainly used for precision filtration to process suspension liquid with low solid content and fine particles.

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