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Mechanical sieving is the major feed mill using screening techniques, screening equipment, main component is the screen surface, a widely used is the steel plate punching and weaving sieve screen. Feed processing technology in the screening focused on two aspects, one of the raw materials to clean the impurities, and second, the raw materials or products according to size grading, including impurities cleaning, grinding materials, grading, impurities cleaning powder before granulation, granulation product classification. In the screening process is good or bad effect on feed quality and production have a considerable influence. A screening efficiency and its influencing factors Screening efficiency, including two areas: material is expected to be retained sieve sieve sieve retention ratio of compounds and should be expected through the sieve screen surface material under the sieve retention ratio of compounds. These two indicators of impact in the clean-up operation, the removal of impurities and the net effect of the loss of raw materials, the grading operation affect product size and yield, in testing the impact of the reliability of grading. The former is called the net rate of screening, which is called wrong screen ratio, with the formula expressed as: 1 = The formula, 1? Sieve net rate,%; 2? Wrong screen ratio,%; W1? Expected to screen on the screen on the left the stock of material, kg / h; W2? Sieve material is expected to total kg / h; W3? expected to screen the screen on the left under the property stock, kg / h; W4? expected to screen materials under the total, kg / h. The above two indicators used to evaluate the efficiency of clean-up screen when the screen on the matter as impurities, 1 rate equivalent to impurity, 2 equivalent to a net loss of raw materials. 1.2 The screening effect of the factors affecting Materials through the sieve of the largest particle diameter estimated by the following formula: d = D cos -e sin The formula, d? Through the sieve of largest diameter, mm; D? Sieve diameter, mm; e? Screen mesh wire diameter, mm; ? Screen surface inclination. Can be seen from the type 3, sieve diameter, mesh wire diameter, angle of sieve surface are affected through the sieve of the largest particle size. However, type 3 only of the critical particle size, less than the critical size of a particle through the sieve can also depend on other conditions. 1.2.1 The shape of particles and sieve Type 3 calculation with spherical particles and circular sieve, based on actual production in the feed industry, the screening of raw materials are mostly graded cylindrical pellets or irregular particles, sieve both round again rectangular sieve material particle contact state when the particles can be passed on the great influence, such as a? 4 × 10mm vertical particle can pass through the sieve of a 5mm diameter, horizontal, you can not. Therefore, the particle has some chance through or not, can only be studied through statistical means. Particles generally cylindrical, rectangular mesh by better performance; but not very different for each direction of irregular size particles through the holes of better performance. 1.2.2 screen surface open porosity Screen surface openings rate increased by the better the performance. Ensure that the case of screen surface strength, woven screen can get higher than the sieve hole punching rate, which is superior to the latter by the former. 1.2.3 Material thickness Use the flat screen, if the material through the screen surface layer is too thick, solid layer of small particles through the mesh upper difficulties, will rise in the rate of the wrong screen, the clean-up in raw materials will increase the net loss of raw materials, the particles sub- will reduce the output level of the upper layer of screen material is too thick, the lower impact product quality screen material layer too thick. Thin layer over the screening material production is too low, nor desirable. The appropriate material thickness should be determined by experiments, screen inclination angle is small, the amplitude is large sieve material layer thicker. In theory, the material thickness of the production decision, but the actual use, because of uneven screen surface feeding, material may be concentrated in the side of the screen surface, causing local material layer is too thick to affect the screening results. Cylinder screen and the cone screen similar problems, when the instantaneous material flow excessive, the screening effect also affected. 1.2.4 sieve state of motion Screening process is a necessary condition for selection of materials and the screen surface relative motion between the appropriate, resulting in relative movement of the ways this is the level of screen surface for the rectilinear motion of rotation, vibration or vertical reciprocating linear motion combination of both. Only horizontal reciprocating sieve or vertical reciprocating motion, screening effect is not ideal. The latter because the lack of materials and the level of the relative motion screen surface, likely to cause material layer of uneven thickness. Practice shows that the two kinds of movement of the rotary shaker combination is better. 1.2.5 Material Characteristics Material particle size, moisture, friction properties, mobility and so on and screening processes. Material differences in particle size is the premise of separation of materials screening components, and this difference the greater the screening process more easily. The higher the moisture content of materials, internal and external friction angle greater liquidity worse, the performance of its particles through the sieve the worse. Therefore, the actual use, to get a good screening effect, should be based on the specific materials to choose different parameters. 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