1 Particle Size: The screening efficiency is significantly reduced when the particle granularity is close to screen size. The total screening efficiency obviously decreases with the increasing proportion of the particles whose sizes are close to the screen size. This kind of particles has various influences. These particles tend to limit or block screen aperture, which leads to the reducing of effective sieving area. This is a frequently appeared process in closed-circuit crushing. In closed-circuit flowsheet, screening efficiency decreases gradually with the increasement of materials in screen aperture.

     2 Feeding Speed: The analysis principle of screening degree is that it can reach almost complete separation with lower feed speed and longer sieving time. In the practice of screening, considering the economic cost, it is required to adopt a higher feed speed and reduce the staying time of materials on screen surface. With a higher feeding speed, a thick bed is formed on the sieve surface. Fine particles must get through the thick layer then they have a chance to pass the sieve surface. The final result is that the screening efficiency is reduced. High yield and high efficiency are often two conflicting requirements for any separation operation. In order to get best results, we must comprehensively consider the two indicators. 

     3 Sieve Obliquity: If particles approach screen aperture with a small angle, the screen will look like effective aperture of the end and particles whose sizes are close to screen aperture will hardly get through. The dip angle of screen surface influences the angle of particles into screen aperture. Some sieves are used this effect to separate materials which are finer than screen aperture. The angle of sieve also affects the velocity of particles along the screen surface, the staying time of particles on the sieve surface and the probability of particles passing sieve surface. 

    4 Particle Shape: Most particles processed on sieves are non-spherical. When spherical particles have equal probability to get through in all directions, irregular particles (whose sizes are close to screen aperture) must get through the screen aperture by certain direction. Slender particles and platy particles have smaller cross sectional area in a certain direction and larger cross-sectional area in the other directions. Therefore, the screening efficiency is reduced for those quite irregular particles.

    5 Effective Sieving Area: The probability of passing sieves is proportional to the percentage of effective screening area. Effective screening area refers to the ratio between the clear area of screen and the total area of screen surface. The smaller the screen material, the greater the probability of particles into sieve is. Effective screening area decreases with the decreasing of screen size. Therefore, in order to increase the effective area of screen aperture, we must use thin and crisp screen wire. But this screen is easy to wear and has lower processing capacity, which is the reason why we use grader to separate fine materials instead of fine screen. 

    6 Vibration: In order to make materials leave the sieve, the sieve should be vibrational. Materials fall back to the sieve again and move along the direction of screen surface by this vibration. Appropriate vibration can cause material lamination which makes fine particel get through the bed of material and down to the screen surface, and then big particles rise to the top. This lamination increases the passing rate of the middle part. 

   7 Moisture: The surface moisture content of ore significantly affects screening efficiency, which is similar to clay and other viscous materials. Wet feeding is difficult to screen. Do not screen damp materials in case of clogging pores. These measures also includes using heat coverings to break the surface tension of water between screen and materials, using spherical plate under the screen surface to generate nearby vibration or use non-clogging sieve cloth weaving. Wet screening can effectively screen 250um or even more fine-grained materials. The adhesive slurry can be rushed down from big mineral particles, therefore, screen can be washed clean by pulp flow and wash water.