Application of iron separator in the production of

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Application of iron separator in ceramic production

at present, China's output of building ceramics has accounted for 50% of the world's total. With the improvement of product grade, especially after China's entry into the WTO, the export of building ceramics has increased significantly, reaching more than 10% of the world's total export, second only to Italy and Spain, the world's oldest ceramic countries. Unfortunately, most of China's products are medium and low-grade products. In order to occupy more shares in the international market, the only way is to produce more high-grade and high-quality ceramic products to meet the needs of the international market and strive to create international famous brands

as we all know, the key to the grade of a product lies in its appearance and internal quality, and one of the important factors affecting the appearance and internal quality of ceramic products is the current iron content of ceramic raw materials. Therefore, in ceramic products, especially in the production of white or light colored building and sanitary ceramic products, iron removal should be regarded as an important production process. 1. Working principle and main types of iron remover 1.1 characteristics and classification of ferromagnetic substances. Ferromagnetic substances, such as Fe, Co, Ni, etc., show magnetism externally only under the action of external magnetic field. This phenomenon is called magnetization, and has the following main characteristics: (1) when ferromagnetic substances are magnetized, they have the characteristics of hysteresis loop, that is, under the action of external magnetic field (H), the substances are magnetized and show magnetism, resulting in the variation law of magnetic induction intensity (b) b value with H value, Both synchronous and lagging. Curve characteristics: (a) at the beginning of magnetization, B and H rise synchronously; (b) After the saturation point, B does not rise with the increase of H; (c) After the external magnetic field H disappears (point 0), B does not return to 0 with the decrease of H, but can only return to br point, which is called residual magnetic induction intensity. Br value of ferromagnetic material is the maximum magnetic induction value that can be obtained after the material is magnetized. It is a key parameter in the manufacture of artificial permanent magnets, that is, the b value of the magnetic core in the ferromagnetic bar we use. It is used to express the strength of the magnetic field generated by magnetic induction after the material is magnetized: b=m oh. Where Mo is the magnetic conductivity of the material, and the value is a variable number, and the L value of different materials is different; Br value and its holding time are also different: better materials (such as aluminum nickel diamond alloy and high serial number neodymium iron boron, etc.) Br value can reach 10000 Gauss (GS) or higher. Theoretically, the external factors do not change, which can be maintained permanently at room temperature and for years in actual use; The br value of poor materials (such as ferrite) is only GS, and the demagnetization speed is very fast in use, which can only be maintained for years, or even shorter time. (2) Magnetic field attracts ferromagnetic materials, which is called magnetic force for short. The magnetic force acting on the particle per unit mass is f f=kh (dh/dh). In the formula: K specific magnetization coefficient (cm3/g) H magnetic field intensity (A/M) DH magnetic field distribution gradient (A/m2) the magnetization coefficient of the material per unit mass is called specific magnetization coefficient (k), also called magnetization, which indicates the coefficient of the force that the magnetic field can produce on the material; The quantity indicating the strength of the magnetic field is called the magnetic field strength (H). When the magnetic field is generated by the current, h is directly proportional to the current; It refers to the rate at which the magnetic field strength of a certain point in the magnetic field decreases with the distance h between the point and the field source, which is called the magnetic field gradient (dh/dh). From the analysis of the formula, we can see that for the same ferromagnetic material (the same K value), there are two measures to improve the magnetic field: first, increase the gate value, which will increase the cost of production and use; The second is to increase the ladder value, which can be achieved by means of manufacturing technology, changing the shape and arrangement of magnetic cores, etc. this measure has little investment and can achieve good results. (3) The susceptibility of ferromagnetic materials decreases with the increase of ambient temperature. After the ferromagnetic material is magnetized, if the temperature increases, the magnetic induction intensity B will decrease accordingly; When the temperature rise reaches the critical temperature (such as tc=357 ℃ of iron), the magnetic susceptibility will decline rapidly, and even lose magnetism; Different materials and different treatment methods can affect the temperature change curve, that is, there are different service temperatures. In order to prolong the service time of the magnetic rod currently used, it should work below 6082 ℃, and better materials can only be used below 100 ℃. (4) According to the magnetic susceptibility of iron containing substances, they can be divided into the following categories: strong magnetism, K 3000 cm3/g, such as magnetite (Fe3O4), 80000; Medium magnetic, K (300 3000) l, such as black ilmenite (feti03), 399 weak magnetic, K (25 ~ 300) l, such as limonite (2fe2o3, 3h20) 80; Non magnetic, K 25, such as pyrite (FeS2) 7.5 2. The basic principle of iron separator is to use the attraction of magnetic field to ferromagnetic substances. The equipment that separates iron minerals from raw materials is called iron separator, also known as magnetic separator. The basic condition for achieving the purpose of sorting is that the attraction (f) of the magnetic field to ferromagnetic substances is greater than the resultant force (FC) that prevents the separation of magnetic particles. FC is also called competitiveness, which includes the gravity, centrifugal force, inertia force and fluid resistance of ferromagnetic particles. When removing iron from the material, inertia force and fluid resistance are the main parts of competitiveness. At this time, fluid resistance: fc= D, where: mud viscosity D mineral particle diameter V mud flow rate. From this, it can be seen that the viscosity of the slurry, the size of iron mineral particles and the flow rate of the mud all directly affect the size of competitiveness, that is, affect the effect of iron removal. Therefore, when using the iron separator, we should carefully grasp the four degrees of slurry (concentration, viscosity, speed and particle size): the particle size should be determined by the selection of the aperture of the vibrating screen; Speed is directly related to flow; Viscosity is related to the properties of size, concentration and additives; The concentration is related to the moisture ratio. A practical iron separator should have the following three conditions: (1) a sufficiently strong magnetic field source (f FC); (2) Sufficient contact area to ensure the opportunity and place to absorb prey; (3) Timely and effectively clean (separate) the absorbed ferromagnetic impurities. Cleaning is the key to effective iron removal. 1.3 types of iron removers commonly used in the ceramic industry (1) according to the characteristics of mineral principle, there are dry powder and wet (slurry) iron removers; (2) According to the way of magnetic field generation, there are permanent magnets and electromagnets; (3) According to the appearance structure, it can be divided into: slurry tank interception type, slurry tank settlement type, cylindrical tank type; The dry powder includes suspension type, belt type and bucket vibrating cabinet (frame) type; (4) According to the cleaning methods: manual cleaning, semi-automatic and full-automatic; (5) According to the working state: intermittent and continuous. 2. The current situation and development of iron remover in the ceramic industry requires that building and sanitary ceramic manufacturers pay more and more attention to iron removal, and the application of iron remover continues to expand: from the original iron removal of glaze to that of blank; There are more and more products that need iron removal, and the requirements for iron removal are also higher and higher. A production line has developed from installing an iron remover to installing a multistage series iron remover; The iron absorbing magnetic rods of an iron removal tank have also developed from a dozen to twoorthree, and the investment in iron removal of magnetic rods is increasing. Due to the rapid consumption of mine resources, many enterprises have been unable to find and purchase high-quality raw materials with low iron content nearby, so they have to use poor raw materials and use a large number of iron removers. As many as a dozen operating workers are used in an online iron removal process, the cost of iron removal is getting higher and higher. Cleaning depends on manual operation, and the quality is difficult to guarantee. When the iron content of the raw material is high, there is often a thick layer of iron mud impurities pasted around the magnetic rod, which occupy the effective magnetic path of the field source, and the iron removal effect decreases significantly and disappears. Coupled with many human factors, the quality is difficult to control. The quality of permanent magnetic rods sold on the market is unstable, resulting in the continuous decline of the average life of magnetic rods. Under normal circumstances, it should be guaranteed to use for more than two years, and some do not absorb iron for half a year; Secondly, the nominal b value of magnetic rods in the market is generally falsely high, mostly 50% - 100% higher than the measured value. Most of the dry powder iron removal uses the suction vibrating cabinet (frame) permanent magnet iron remover and belt drive iron remover, which are mainly used to remove the rust impurities that fall into people during the long-distance transportation of powder. The use of dry powder to remove iron is increasing. The electromagnetic iron separator has been developed and tried out for a long time, and generally has a good response, especially the high-power and strong magnetic field, which is more suitable for the separation of weak magnetic materials in raw ore. However, the energy used in the investment accounts for about 12% of the total energy consumption of the national economy. It consumes a lot of electricity, and the magnetic conducting material is easy to oxidize, which affects its popularization and application. At present, China's ceramic manufacturers also hope that the manufacturers of iron removal equipment can produce new iron removal products with strong magnetic separation ability, long service life, high degree of automation and more economical and applicable. Specific requirements: (1) the b value of permanent magnet ferromagnetic bar should be above 6000gs, and the service temperature should be above 7080 ℃; The service life shall be more than two years, and the b value shall not be less than 50%; (2) the technical and economic indicators are advanced. The magnetic induction intensity of the electromagnetic iron separator is high, but the manufacturing and purchase costs should be reduced, and the electromagnetic energy conversion efficiency should be high; The second is to do a good job in the sealing technology of magnetic conductive materials to avoid oxidation and shorten the service life; In addition, a variety of iron separators with the same flow and different power should be made to meet the needs of economic use in multi-stage series connection; (3) The cleaning automation of iron remover should be high, and the loss of slurry (powder) and water should be reduced at the same time, especially the iron removal of glaze slurry; (4) In the spray drying tower, the effective flow rate of the iron separator is required to be large, which can adapt to the slurry treatment capacity of more than 20t/h; (5) The structure should be simple and easy to repair and maintain, mainly based on gb/t 15970.7 ⑴ 995 corrosion of metals and alloys. The volume of stress corrosion test should be as small as possible, and the use should be safe and reliable; (6) High quality stainless steel shall be used in the slurry (powder) transmission path to prevent secondary rust and other impurity pollution. 3. Several suggestions for iron removal process should be noted: (1) according to the influence characteristics of ferromagnetic substances on ceramic products, analyze the source and severity of ferromagnetic impurities in products, and then take appropriate treatment measures to block the source of impurities. (2) When arranging the location of the iron separator, the following principles should be followed: a) iron removal should be carried out in the screened raw materials to avoid large particles and other impurities entering the nearby iron tank (frame), which will hinder the normal performance of the iron separator; b) The iron removal should be at a lower temperature as far as possible to prolong the service life of the magnetic rod; c) According to the category of ferromagnetic materials, choose the iron separator with appropriate magnetic field strength; Use weak magnetic field (such as 0..3t) to reduce the purchase and use cost when removing strong magnetic impurities; In addition to weak magnetic impurities, strong magnetic fields (such as 0.t) must be used. At this time, its purchase and use costs are high. In the same production line, strong magnetic impurities should be removed first, and then weak magnetic impurities. According to this, some people put the old rod with more demagnetization in the last part of the downstream of the iron removal process, which has little effect. (3) The height of the slurry section of the permanent magnet slurry tank intercepting iron remover should be appropriate, and it should basically ensure that the ferromagnetic impurities at the top layer can be within the effective magnetic range. (4) Cleaning the magnetic rod is the key to ensure the effect of iron removal, especially the high gradient magnetic field, which has faster radial attenuation and shorter effective magnetic path; Only when the working surface of the ferromagnetic rod (block) is cleaned in time can the magnetic field and gradient function normally. The cleaning interval should depend on the amount of iron in the slurry (powder) combined with empirical data. (5) Due to the different prices of high and low temperature magnetic rods, magnetic rods should be selected reasonably according to the use temperature, so as to achieve the purpose of economic use. (6) The oxidation (rust) of the magnetic rod (core) will lead to the weakening of the magnetic field, so when the iron separator is out of service, the magnetic source carrier must be cleaned up; When choosing a ferromagnetic bar, be sure to check whether the seals at both ends are intact without leakage, so as to prevent the magnetic core from contacting the slurry to oxidize or corrode and demagnetize. (7) Both knocking and vibration will change the direction of some magnetic moments of the magnetic source material, thereby weakening the magnetic field. Required operation

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