1 introduction
Screening is a very common operation in the mineral processing industry, almost every concentrator or processing plant can see the screening work.There are two definitions of sieving. One is the method of separating particle swarm according to powder properties such as particle size, specific gravity, electrification and magnetism.The other refers to the use of perforated screen size of mixed materials into different particle size levels of the operation is called screening.The mineral processing industry often refers to the latter - particle size grading operations.The non - metallic industry is more stringent screening operations, in each non - metallic mineral processing, screening operations is an essential procedure.
Screening and screening equipment
The screening operation has different functions and purposes in different sections.According to the purpose of screening, screening operations can be divided into the following types: 1.(2) pre-screening, often used for mineral processing operations before crushing qualified products pre-screening;(3) check screening, from the crushing equipment products, the particle size of unqualified products screening, to ensure that the finished product does not exceed the required particle size;(4) prepared for screening, often used for the follow-up work to provide different grades of selected minerals;(5) select screening, screening the product according to weight, density or taste, etc.6 dehydration screening, for the removal of excess water in the product;7) screening, commonly used to remove products containing because of mineral processing operations and into the medium.In addition, when the cement content of the material is high, it is also used to screen for desliming.In the non-metallic mineral processing, all kinds of screening operations may be used, independent screening, pre-screening, screening inspection and preparation screening in the non-metallic mineral processing operations is the most frequently used operation, almost every non-metallic mineral processing plants or processing plants can have the existence of these kinds of screening operations.
There are many factors affecting the screening operation efficiency, mainly has the effect of material properties, including moisture content, silt content, particle size characteristics and density characteristics, etc.(2) the impact of the performance of the sieve, including the form of screen movement, screen device parameters and screen surface structure parameters;(3) the influence of operating conditions.In different working sections, different screening materials are selected by different screening operations and screening equipment.
The selection of screening equipment is often very important in the screening operation, if the selection of screening equipment is not appropriate, then the screening operation will not be able to carry out normally.Common screening equipment includes:
Vibrating screen, fixed screen, cylinder screen arc screen and fine screen.Commonly used vibrating screen has inertia vibrating screen, self - centered vibrating screen;The latter is widely used, domestic large and medium-sized concentrator in the screening of medium and fine materials more use of this kind of screening equipment.There are two forms of fixed screen: grillage screen and strip screen.Bar screen for coarse and medium crushing pre - screening, tilt installation.In small and medium-sized enterprises are generally used in the linear vibrating screen, or round vibrating screen.Compared with large screening equipment, linear vibrating screen and circular vibrating screen price moderate, screening effect can also be accepted by the majority of enterprises, so linear vibrating screen is widely used in small and medium-sized enterprises.At the same time, linear vibrating screen can be installed with some electrical control equipment, easy to use.While some other equipment such as rotary vibrating screen, ultrasonic vibration screen is mainly used in the production requirements are not very high but the screening requirements of the industry;Relaxation screen can be used to screen fine materials with high moisture content.
In the non-metallic mining industry, the screening operation is playing an increasingly important role, and some new screening equipment is emerging one after another. However, the principle is that there is a relative movement between the material and the screen surface, and the purpose is to grade the material to meet the requirements of the product.Ultrafine screening will be a great development trend in non - metallic mining industry.
3 screening method
There are many screening methods in non - metallic ore dressing.According to the different movement modes of materials under the action of screening and the different driving forces of screening, the screening operations can be divided into the following types:
(1) sliding screening method: the materials slide down by their own weight on the inclined fixed screen surface;This is the early use of the screening method, its screening efficiency is low, small processing capacity.This method is rarely used in non-metallic mineral processing, only in the special fragile, can not use the driving force to screen minerals can use the weight of the mineral itself for natural screening.
(2) push screen method: as the screen bar of the screen surface rotates, the materials are pushed by the relay of the moving component of the screen surface, moving forward along the screen face, such as the roller screen.In non - metallic ore dressing, push - type screening is often used to screen dry materials.
(3) rolling screening method: the screen surface is a tilted cylinder, which rotates at a constant speed when working. Materials roll in the tilted cylinder.
(4) shaking type screening method: the screen surface can be placed horizontally, but also can be tilted, the screen surface in the plane to do reciprocating movement.In order to make the relative movement between the material and the screen surface, if the screen surface is placed horizontally, the screen surface should do differential movement;When the screen surface is tilted, the screen surface vibrates in the plane, and the materials move forward step by step using the right and wrong of the screen.
(5) projectile screening method: screen surface in the vertical vertical plane to do wipe vibration or quasi-wipe vibration.Screen surface movement trajectory is straight, can also be round or oval.Material is ejected in a vertical plane, such as a vibrating screen.At present in the non - metallic mineral processing is the most used in the projectile screening method of vibrating screen.
From the above various screening methods, although the material and the screen surface relative movement mode is different, its purpose is to make the material in a certain loose state, so that each particle can obtain the energy and space necessary for mutual displacement, and ensure the fine particles through the screen.
In addition, according to the number of screening equipment and the number of layers of the screen can be divided into the following screening methods:
(I) overlapping screening method: in the coarse to fine screening, the screen surface of the straight screen overlaps, the upper screen hole is large, the following layers gradually reduce, because there are gaps on both sides of the straight screen frame, will cause the reduction of screening accuracy, this screening method is suitable for the processing of large volume of material;
(2) stratified sequence screening method: generally speaking, the screening of multi-layer equipment is from coarse to fine, the top is the thickest screen, decreasing down, the equipment maintenance is convenient, easy to observe the work of each layer of equipment screen surface;In the screening from fine to coarse, the order of the screen surface is the opposite, uniaxial equipment, rotary vibrating screen each screen can be discharged along the length of the entire screen surface, its screening effect is very obvious, each layer does not affect each other;
(3) combined screening method, also known as mixed screening method: in the combined process, one part of the screen surface is arranged from coarse to fine, and the other part is arranged from fine to coarse;In practical production, circular vibrating screen is usually used by coarse to fine or combined screen shunt process;Circular vibrating screen is made according to the special requirements of screening materials, screening accuracy and trajectory are very ideal, in the non-metallic mineral processing is most suitable for screening coarse particle materials.
According to the actual situation of mineral processing operations can be divided into dry screening or wet screening, in different non-metallic mineral processing, dry screening and wet screening have their own advantages, the selection of screening equipment is also different.At present at home and abroad dry screening of the most fine classification can reach about 100 mesh, wet screening operation of the most fine particle size can reach about 325 mesh.
Suggestions on the development of screening operations in nonmetallic ore dressing
(1) in non-metallic mineral processing, some minerals need to be screened by wet method, and some minerals need to be screened by dry method.For wet screening, due to its short screening time, the width of the screen is more important than the length, the wider screen can be efficient screening;For dry screening, should be used in high frequency, low amplitude screening, and the length of the screen than the width is important, so it should be as much as possible to increase the length of the screen.
(2) because of the non-metallic mineral industry is more complex, mineral is a lot of more phyletic, and physical and chemical properties of various kinds of mineral is large, is also the purpose of the product is not the same, so the screening homework also have very big difference, especially as some clay minerals such as kaolin, etc.), fibrous minerals (such as asbestos, etc.) in the grain of hydrous minerals, etc., screening and low work efficiency, poor screening effect, we can be targeted to adopt different methods of screening.For example, clay minerals and fine minerals with water content can be screened by wet method, which can greatly improve the screening efficiency, while for fibrous minerals, screening equipment with rectangular mesh can be selected for screening.
(3) for non-metallic minerals that are easy to agglomerate, it is easy to block the screen and difficult to screen materials due to agglomeration in the screening process. Therefore, the problem of blocking the screen of the materials that are easy to agglomerate can be solved by adjusting the screen or the characteristics of the screen, such as the appearance of "sandwich" screen.In the aspect of blocking, there are many ways to improve the screening equipment, such as adding bouncing balls to the screen, adding cleaning device to the screen surface or making the screen surface Angle bigger.
(4) the screen screen of screening equipment has a prominent impact on the screening effect, and the degree of wear is also a serious problem in the screening process. Therefore, the degree of wear resistance of screening equipment is also very important. The screen screen should be made of wear-resistant materials as far as possible to reduce the cost of enterprises.At present, the most widely used screen materials at home and abroad are metal steel wire, low carbon, high carbon steel wire, polyurethane screen.In addition, the opening of the sieve mesh also has a great impact on the screening efficiency. For the screening equipment of the projectile screening method, the sieve holes can be improved.The original square screen hole is made into a rectangular screen hole, and the self-deformation ability of the screen can be used to solve the problem of blocking the screen.
(5) in non-metallic mineral dressing, after some dressing products may be corrosive or higher temperature, then the sieving equipment will improve the corrosion resistance and high temperature resistance, for this problem, the screening equipment can be anti-corrosion paint, high temperature processing or use of corrosion resistant materials, high temperature resistant materials screening equipment.
(6) due to the appearance of "lean, low and fine" in non-metallic mineral processing, the screening equipment is increasingly required, especially in the screening of fine-grained materials, which will be a problem worthy of further investigation.
In addition to the above aspects, in the improvement of screening equipment can also be in the feeding mode, the choice of exciter, screening equipment installation mode (tilt size, etc.) as well as the replacement of the screen screen and screening equipment price, etc.
5 concludes
It is necessary to screen in nonmetallic ore dressing. Therefore, how to select the screening equipment and how to screen the equipment to better serve nonmetallic ore dressing will be a question worth pondering.At present, the domestic and foreign screening equipment development is very rapid, and has been the original metal mineral processing and coal mineral processing in the gradual transformation to non-metallic mineral processing, which will produce earth-shaking changes in the non-metallic mineral industry.
In non - metallic ore dressing, high efficiency, super - refinement, specialization and specialization of screening equipment will be the final development result of non - metallic ore screening equipment.For non - metallic mineral processing complex, screening equipment will become colorful.Independent screening, pre-screening, inspection screening and preparation screening and other screening operations in non-metallic mineral processing will be more and more attention, screening equipment, anti-blocking, anti-corrosion, anti-high temperature and wear resistance will be the key direction of screening equipment development.As screening plays an irreplaceable role in mineral processing of non-metallic ores, the development of screening of non-metallic ores will be paid more and more attention with the development of non-metallic ores.
