According to the structure and operation characteristics, the sieves commonly used in the mineral processing industry can be divided into the following types:
(1) Fixed sieve. Includes fixed grid screens, fixed strip screens and cantilevered divisions. Because of its simple structure and no power, it is widely used in the beneficiation process for the screening of large ores.
(2) A cylindrical sieve. Including cylindrical sieve, conical sieve and pyramid sieve. It is mainly used for screening and cleaning crushed sand in the construction industry. It is also used in the beneficiation process for washing and de-slipping.
(3) Vibrating screen. Including mechanical vibrating screen and electric vibrating screen. Among the former are inertial vibrating screens, self-centering vibrating screens, linear vibrating screens and resonant screens; the latter have electric vibrating screens. The following is a review of the research progress of screening equipment .
1 vibrating screen
A conventional vibrating screen
The common problems of various types of vibrating screens currently used are: after the equipment is enlarged, the structural strength is not easy to guarantee, resulting in more problems such as tearing of the side plates and breakage of the vibrating beam; second, the screening efficiency is not high, especially Screening of wet fine-grained minerals can easily cause plugging and pasting, and the screening efficiency is reduced. At present, screening equipment research has been improved from the following aspects.
(1) Structural improvements and the use of new materials extend the service life. YKR/ZRK type vibrating screen adopts screen box reinforced structure design to effectively extend the service life of the screen machine. At present, the structural design of the screen support device of the commonly used vibrating screen is not reasonable enough, and the screen mesh is easily damaged. By snap-on cards are opened flat iron fine rubber, shape and size of the slot are matched with flat iron, and the flat iron is uniformly fixed to the beam, the rubber strip can be prevented from slipping off, effectively prevent abrasion screen [1] . By improving the screen and improving the wear of the screen, Li Suozhu et al. developed a curved screen mesh. The curved inner surface formed by the multiple screen strips of the curved structure is the working screen surface, and the wear condition Improved [2] . The recently developed elastic rotary screen plate solves the problem of wear of the elastic rod screen and the mounting hole [3] . Chengpei Jun invented a composite integral rubber vibration sieve sieve, sieve and the metal outer surface of the skeleton oblong through hole inner walls are wrapped in a rubber layer, using a high elasticity, high toughness and wear resistance characteristics of the rubber, to improve the Service life and screening efficiency [4] .
(2) Optimize the screen surface structure, increase the screen surface amplitude, and increase the sieving rate. In view of the problem that the conventional screen surface has no secondary vibration and the material is easy to get stuck, which affects the screening efficiency, a spring is installed between the screen surface and the support beam, and the spring for mounting the floating support beam may be a rubber shear spring, a composite spring or a coil spring [ 5] . A non-metallic elastic material strip is arranged between the side guard plate and the sieve plate and between the sieve plate and the sieve plate to realize secondary vibration of the sieve surface, and the screening operation of the sieve hole can be cleaned [6] . The researchers also developed a tensionable linear sieve plate with high opening ratio, good elasticity, high permeable rate, no plugging, tensioning, replacement and maintenance convenience [7] . Peng Youhe has developed a comb-toothed step vibrating screen. Through the combination of comb and step structure, the screening of wet and viscous materials below 6mm is easily completed, and the minimum screening size is 2mm [8] . There is also an amplitude-increasing elliptical banana sieve, the elliptical motion trajectory on each section of the sieve surface, and the amplitude of the discharge end of the sieve surface is small, and the amplitude of the material end of the sieve surface is small, so that the material is at the discharge end. The sieve section does not accumulate, does not block holes, has a high permeability and a large throughput [9] . By increasing the throwing strength of the screen surface, the ability of the material to penetrate the screen surface can also be improved. Xu Wenbin and others have developed a large-strength-strength vibrating screen. The material has strong penetrating ability to the screen surface and high projectile strength. In addition, the screen surface can be generated under the action of the load-bearing beam while vibrating with the vibrator. The "breathing" state of motion has a self-cleaning function [10] .
(3) The trajectory of the screen surface is complicated, the vibration frequency is diversified, and the screening efficiency is improved. Different screening methods are adopted for materials with different particle sizes or materials with different viscosity and humidity, in order to maximize the screening efficiency and achieve the best screening effect. In recent years, with the improvement of manufacturing level, the application of computer-aided design, the development of vibrating screen movement trajectory is complicated, Li Suzhen and others have developed a spiral track vibrating screen [11] , through two sets of excitation sources The reasonable combination can also achieve the spherical trajectory vibration of the screen surface, so that the screen box produces a spherical motion trajectory [12] . Yang Yongzhu and others have developed a composite trajectory composite vibrating mesh screen to effectively improve the processing capacity and screening efficiency of the vibrating screen [13] . By diversifying the vibration frequency, the screening efficiency of the vibrating screen can be improved. Huang Tao et al. developed a variable frequency vibrating screen, which has the characteristics of convenient frequency conversion and low cost [14] . Hou Yongjun and others developed a dual-frequency vibrating screen to improve the screening efficiency [15] .
(4) The size of the equipment. Yang Yongzhu et al. developed a self-synchronizing circle or elliptical vibrating screen with forced synchronization, which can realize the large-scale vibrating screen without the need for large-scale vibrators [16] . Wang Haisheng developed an elliptical vibrator that can be disassembled as a whole, which improves the screening efficiency and productivity of the vibrating screen [17] .
B high frequency vibrating screen
For the screening of fine ore, the high frequency and low amplitude screening method is very effective, and the screening frequency is 1200-3600 r/min. Guo Jinsheng developed a multi-line hitting high-frequency vibrating mesh screen, which uses multiple lines and multiple points for vibration [18,19] . The high-frequency vibrating mesh screen developed by Wang Qiwei et al. uses a two-way vibrating arm to improve the vibration frequency and screening efficiency of the vibrating screen [20] . Shaker gradually large-scale development, Peng Friends of developed large high frequency vibration sieve screen box in the middle of a plate is designed such that the sieve box into a double-channel, can be manufactured in large widths up to 2400mm high frequency vibrating screen [ 21] .
C Several new vibrating screens
The parasitic energy-saving vibrating screen is provided with a base for carrying the crusher , the base is supported by an elastic support mechanism, the vibrating car body is arranged under the base, and the crusher outlet of the crusher is adapted to the inlet of the vibrating car body, and the crusher is used. The side effects caused by the eccentric shaft excitation force during the crushing movement complete the screening operation [22] .
The sub-resonant double-mass energy-saving vibrating screen comprises an upper body and a lower body. The upper and lower bodies are connected by a group of excitation springs and a plate spring group, and a vibration motor is arranged on the upper body, and the vibration motor is generated. The exciting force drives the upper body vibration, and the upper mass body drives the lower body vibration through the excitation spring group to form a sensitive sub-resonance system [23] .
2 swing screen
    The oscillating screen is effective in improving the screening efficiency and processing capacity compared to the linear vibrating screen [24] .
The intelligent vibrating screen is an intelligent anti-blocking vibrating screen. The vibrating motor is arranged at the feeding end and the discharging end of the vibrating screen box. When the stacking or plugging occurs on the screen surface, the vibrating motor can automatically start to realize the screen. Surface cleaning operations [25] . The screening system is operated at maximum throughput without damaging the screening equipment [26] .
3 other types of screening equipment
Large-scale relaxation sieve: The relaxation sieve can dry-screen the difficult-to-screen materials with high viscosity, and can greatly improve the stability and overall life of the vibrating screen [27] . Centrifugal sieve: The centrifugal material is obtained by rapidly rotating a cylindrical or conical sieve surface to classify the particulate material [28] . Wash sieve with a screen section: circular profile and a cylindrical washing machine Sieve minerals to meet part of the metal (such as manganese ore) classification and washing of claim [29]. Roller sieving machine: the height difference between adjacent rollers, the height of a certain roller is changed by selecting the thickness specification and quantity of the gasket, and then the gap between the rollers is adjusted [30]
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[2] Li Suozhu, He Desheng, Fu Hongliang, etc. selected from the sieve bend screen for coal: China, CN202621457U [P / OL] 2012-12-26 .
[3] Xu Wenbin, Li Suzhen. Elastic Rod Screen: China, CN201815476U[P/0L].2011-05-04.
[4] Cheng Peijun, a composite rubber-plastic vibrating screen for coal separator: China, CN103331259A[P/OL].2013-07-03.
[5] Xu Wenbin. Floating sieve vibrating screen: China, CN202199499U[P/OL].2012-04-25.
[6]Xu Wenbin. Large-scale vibrating screen for secondary vibration of screen surface: China, CN201768687U[P/OL].2011-03-23.
[7] Xu Wenbin. Tensionable linear sieve plate: China, CN102284422A[P/0L].2011-12-21.
[8] Peng Youhe. A comb-toothed step vibrating screen: China, CN203030501U[P/0L].2012-07-03.
[9] Xu Wenbin. Amplitude plus-type elliptical banana sieve: China, Z1200820138456.4[P/OL].2008-09-02.
[10] Xu Wenbin. Large-projection intensity vibrating screen: China, 2013102398038A[P/0L].2013-06-18.
[11] Li Suozhen, Xu Wenbin. A spiral track vibrating screen: China, CN101690930A[P/0L], 2010-04-07.
[12] Xu Wenbin. A spherical trajectory vibrating screen: China, CN201500643U[P/OL].2010-06-09.
[13] Yang Yongzhu. Variable motion trajectory composite vibrating screen: China, CN201565417U[P/0L].2010-09-01.
[14 Huang Tao, Yang Yongzhu. Variable frequency vibrating screen: China, CN201940360U[P/0L].2011-08-24.
[15] Hou Yongjun, Fang Pan. A dual-frequency vibrating screen: China, CN202316288U[P/OL].2012-07-11.
[16] Yang Yongzhu. Self-synchronizing circle or elliptical vibrating screen with forced synchronization: China, CN102284416A[P/0L].2011-12-21.
[17] Wang Haisheng. Large-scale multi-layer elliptical trajectory equal-thickness vibrating screen: China, CN201692933U[P/OL].2011-01-05.
[18] Guo Jinsheng. Multi-line hitting high frequency vibrating screen: China, CN2010202252752U[P/OL].2010-06-11.
[19] Xu Wenbin. High-frequency translational fine screening: China, ZL200820134346.9[P/OL].2009-11-04.
[20] Wang Qiwei, Sun Haijun. High-frequency vibration mesh screen: China, ZL200820007462.6[P/OL].2008-12-03.
[21] Peng Youhe. Extra large high frequency vibrating screen: China, CN202860825U[P/0L].2013-04-10.
[22] Zhu Xingliang. A parasitic energy-saving vibrating screen: China, CN202845308U[P/OL].2013-04-03.
[23] Zhang Enlin, Li Guangming, Zheng Yongcheng, et al. Sub-resonant dual-mass energy-saving vibrating screen: China, CN102744203A[P/0L].2012-10-24.
[24]XiaoJ, Tong X.Characteristics and efficiency of a new vibrating screen with a swing trace[J]. Particuology.2013,11(5)601-606.
[25] Huang Tao, Yu Yunbo, Yang Jiwei. Intelligent anti-blocking vibrating screen: China, CN102225392A[P/OL].2011-10-26.
[26] Antila K, Heman H, Peltonen M. Method for controlling a screening machine and a screening machinet [J/OL]. Google Patents, 2011.
[27] Wang Haisheng. Large-scale relaxation sieve: China, CN201728190U[P/OL].2011-02-02.
[28] Walton O. Dreyer C, Riedel E. Centrifugal Size-Separation Sieve for Granular Materials, 2012.
[29] Deng Yongzhen, Chen Yanghui, sieve washing cylinder and cylinder screen washing machine with sieve section: China, CN202343432U[P/0L].2012-07-25.
[30] Gao Hongtie, Shi Rong, Song Yu. Roller Screening Machine with Adjustable Clearance: China, CN2011204151746[P/0L].2011-02-07.
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