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Analysis on the filter material of compressed air filter
The air from nature, after being compressed by air compressor, becomes compressed air with kinetic energy and is widely used as power energy. In the process of air compression and compressed air transmission, various size of dust, impurities, oil mist, water mist, microorganisms and other pollutants are inevitably mixed, which will affect the quality of compressed air. If not handled well, it will cause harm to the gas equipment, production process, product quality and even human body at the gas end. These injuries not only include equipment damage, product scrap, and even threaten human life. The filter of compressed air is responsible for handling the particulate impurities contained in the compressed air. Then, what kind of filter material can be used to filter out these impurities? This paper will make a brief analysis.
With the development of material science and people's in-depth research on filters, there are many materials that can be used as compressed air filters, which are mainly divided into the following categories:
1. Fiber filter materials: such as cotton, wool, silk, etc. in natural fibers, glass fibers, chemical synthetic fibers (polyester, polypropylene, etc.) in man-made fibers.
In pneumatic technology, there are three main types of fibers that can be used as filter materials, namely natural fibers, chemical fibers and man-made fibers.
Natural fibers are fibers in natural form, commonly including wool, cotton and bislin.
The properties of natural fibers vary greatly according to varieties, planting and storage conditions. For example, cotton fiber will be brittle, broken and blocked after being used for a long time, which will reduce the filtration efficiency and increase the filtration resistance; Degreasing fiber will reduce the filtering effect due to moisture absorption.
There are many kinds of chemical fibers. Because the properties of raw materials are changed by chemical methods in the fiber production process, its properties are completely different from the chemical properties of raw materials. Chemical fiber has many incomparable advantages, and is convenient for large-scale industrial production. Its quality and cost are easy to control. Therefore, it is the preferred material to replace natural fiber. Chemical fiber has high strength, good corrosion resistance, temperature resistance and abrasion resistance superior to natural fiber, such as nylon, polyester and other chemical fibers have been widely used in various industries.
The man-made fiber separates the fiber form from the raw materials by physical methods, or forms the raw materials into fibers. The chemical properties of the fibers do not change after they are made, and glass fiber is one of them. The filter material made of glass fiber has high efficiency, high dust capacity, low resistance, resistance to biological erosion, thermal stability and non combustibility.
2. Filter paper
Filter paper generally includes cellulose filter paper, glass fiber filter paper and synthetic fiber filter paper.
Cellulose filter paper is generally made of vegetable elements, such as short cotton wool. Its efficiency belongs to the range of medium efficiency to sub efficiency, and increases with the increase of filtration rate; The filtering efficiency has great difference to the type of dust to be filtered. Its surface concentration ratio is slightly higher than that of glass fiber, reaching 60-70%.
The glass fiber filter paper is made of alkali free glass with good quality, and the fiber with very fine diameter (1~1.3 μ m) The paper making technology is used to make 0.25~1mm thick fiber filter paper. Its density is 0.38/mm3, and the mesh gap is 10~15 times smaller than that of cotton, so it has a good filtering efficiency. When the air flow rate is 20cm/s, 0.3 μ The filtration efficiency of m DOP particles is 99.995%, and the pressure loss is only 3mm water column.
Synthetic cellulose filter paper is a filter paper made of synthetic chemical materials. Because of the high resistivity of synthetic materials, they can carry more static charges, and are ideal materials for making electrostatic filter materials. Polypropylene fiber filter paper is one of the better performance, and its dust accumulation, hydrophobicity, temperature characteristics, strength characteristics, oil absorption characteristics are all good for compressed air filters. Because the thickness of the filter paper can be very thin, it can be made into a folded filter element, so that within its limited shell volume, the filter area can be dozens of times larger than the windward area, thus greatly reducing the resistance.
3. Powder metallurgy materials: mainly sintered bronze, sintered stainless steel and monel alloy. After the spherical particle powder of these materials is pressurized and formed during manufacturing, the powder surface is fused and bonded at a temperature lower than the melting point, and the gap between particles is maintained to form a microporous channel that can filter the air. The pore size of the filter material depends on the particle size of the original metal powder. This type of filter material has high strength, long service life, renewable, high temperature resistance, high humidity resistance, no pretreatment requirements for the filtered air, and is better for medium efficiency filtration. For example, some centrifugal compressor oil system uses 40 μ M stainless steel powder metallurgy filter material can effectively prevent the intrusion of solid particles, and the service life of centrifuge bearings can be increased to 10-20 years.
4. Filter ceramics: mainly quartz, aluminum oxide and diatomite, which belong to inorganic non-metallic solid materials. It has high hardness, high temperature resistance (300 ℃~ 900 ℃), good oxidation resistance and corrosion resistance, but its texture is fragile, and it can not withstand the impact of knocks, collisions and instantaneous high-pressure gas, so it has poor quenching and heating performance. Quartz filter can be used to filter solid particles and moisture in compressed air; Aluminum oxide filter ceramics are used to filter oil mist particles in compressed air; Diatomaceous earth filter can be used to remove fine dust and bacteria from compressed air
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