screen type of sieves gives more fine powder than wire woven sieves why
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Answer:
Sieves and filters remove foreign and extraneous matter on the basis of size, and are equally applicable to both wet and dry systems, to the full spectrum of food materials, and all levels of manufacturing output. They range from simple mobile hand-operated systems to integrated dedicated in-line installations. The simplest sieves are static grids, with meshes of any size, depending on the separation required. Other systems include perforated plates with square or round holes, which can be made from materials such as woven steel, copper or bronze wire. More complex systems can be built up, consisting of a series of meshes arranged vertically, horizontally or inclined. The sieving efficiency can be assisted by any combination of brushes, hammers, bouncing balls, aeration, or vibratory or rotary movement.
Sieves should normally be employed early in the process when used as a primary cleaner, because they are capable of removing a wide range of contaminants. However, they can be used at any stage throughout a process, depending on where foreign bodies are likely to occur. They cannot, of course, remove particles of similar size to the material being cleaned. Sieves are susceptible to mechanical damage, and also to blinding or blocking. Wet sieving can give rise to bacteriological and/or corrosion problems, whilst dry sieving can present a fire and explosion hazard.
The aggregate should be oven-dried at high temperature before sieving to prevent lump formation of the fine particles due to moisture content, which might clog the fine sieve holes.