The effects of vibration parameters on particle screening efficiency were studied by using dried silicon powder, molybdenum powder and zinc powder as typical materials, which is helpful to solve the problem of screen hole block and improve the screening efficiency of vibratory separator. 1.Effect of vibration frequency on screening efficiency. Vibration frequency is an important parameter of shaker, which determines the pulsation frequency of particles on the screen surface and the number of contact and collision of the screen surface. When the vibration frequency is low, the particles on the screen surface can not be thrown up, easy to block the screen hole, resulting in low screening efficiency. However when the frequency is high, the movements of particles on the screen surface is active. Collisions between particles and the mesh are intensified, causing particles not to fall smoothly, it may cause low screening efficiency. In order to get the relationship between screening efficiency and frequency more accurately, the influence of vibration frequency on screening efficiency is demonstrated experimentally in this paper, so as to obtain the screening efficiency under the optimal frequency. There are many factors affecting the screening efficiency, so the control variable method is adopted, that is other parameters remain unchanged, only change the vibration frequency of the shaker. According to the parameters selected in the simulation study, the vibration frequency is set as 25, 30, 35, 40, 45 and 50Hz. Initial experimental conditions, the amplitude was 3mm, the included angle of the eccentric block was 45 degree, the material was silicon powder and the thickness of the material was 8mm. Use the stopwatch to make sure the test time is the same for each group. In order to reduce the influence of other factors on the screening efficiency, electronic scale is used to weight the particle quality, so as to ensure that the ratio of the material with particle size greater than the aperture of the sieve and the material with force less than the aperture of the sieve is certain. It can been seen from the experiment that when the frequency is 25Hz, the material particles blocked obviously. With the frequency increasing to 50Hz, the phenomenon of hole plugging was significantly improved. According to the vibration strength formula, the vibration strength is directly proportionally to the quadratic square of the vibration frequency. At first, due to the vibration frequency is small, the vibration intensity of particles is small, the particles are difficult to loose, not easy to stratify, so the screening efficiency is low. With the increase of vibration frequency and the increase of particle looseness, the contact area between the particles and the screen surfaces increases and the size particles are easier to be layered, thus the performance of screening is improved. Screen efficiency calculation formula can be used to obtain the screening efficiency of vibratory screen at each vibration frequency.
2.Effect of angle of eccentric block on screening efficiency. According to the working principle of the vibratory separator, because of the center of mass of the up and down eccentric block on the vibrating screen motor does not coincide with the center of mass of the part of the reference vibration, a rotating main fault and main moment are acted on the screen surface, causing the screen surface to produce rotational motion. The included angle of eccentricity block is the space phase angle of eccentricity block. By adjusting the angle of space, different excitation forces are generated to change the direction of material particles. Therefore, the include angle of eccentric block is an important parameter that affects the screening efficiency of vibratory separator. In order to obtain the best screening efficiency under the eccentricity quick inclined angle, the relationship between the inclined angle of eccentricity block and the screening efficiency of vibratory separator was studied. According to the inclined angle of eccentric block commonly used in the vibrating screen, set the degree of 15, 30, 45, 60, 75 and 90. Initial conditions: amplitude 3mm, vibration frequency 50Hz, material silicon powder, material thickness, 8mm. It is concluded that when the included angle of the eccentric block is small, the material flows from the center to the circumference along a straight line and can only be roughed screened. When the included angle of the eccentric block is large, the objective moves from all sides to the center. They all concentrate in the center of the sieve in uneven distribution, which can also affect the screening efficiency. Therefore the included angle of the optimal eccentric block is 45 degree.