Application of Ceramic Production Iron Remover

As we all know, the grade of the product lies in its appearance and internal quality. One of the important factors affecting the appearance and quality of ceramic products is the level of iron contained in ceramic materials. Therefore, in the ceramic products, especially the production of white or light-colored building sanitary ceramic products, iron removal should be regarded as an important production process.

1 The working principle and main types of iron remover

1.1 Characteristics and Classification of Ferromagnetic Materials

Ferromagnetic substances, such as Fe, Co, Ni, etc., can only become magnetic when exposed to an external magnetic field. This phenomenon is called magnetization and has the following main characteristics:

(1) When the ferromagnetic material is magnetized, it has the hysteresis loop characteristic, that is, under the action of the external magnetic field (H), the material is magnetized and magnetically significant, and the magnetic induction intensity (B) and B value change with the H value, Both synchronous and lagging.

Curve features:

(a) At the beginning of magnetization, B and H rise synchronously;

(b) After the saturation point, B does not rise with H;

(c) After the external magnetic field H disappears (point 0), B does not decrease back to 0 with H, but only returns to the Br point, which is called residual magnetic induction.

The Br content of a ferromagnetic material is the maximum value of the magnetic induction obtained when the material is magnetized. It is a key parameter in the manufacture of artificial permanent magnets, which is the B value of the magnetic core in the ferrite core rod used by us. It is used to indicate the strength of the magnetic field generated by magnetic induction after the material is magnetized: B=mμoH. Where mμo is the material's magnetic permeability, μ is a variable number, and μL is not the same for different materials; the Br value and its holding time are also not the same: a good material (such as: aluminum nickel alloy and high The number of NdFeB, etc.) Br value up to 10000 Gauss (Gs) or more. Theoretically, external factors do not change, can be permanently maintained at room temperature, and can be maintained for 8-10 years in actual use; poor materials (such as ferrites, etc.) have a Br value of only 2000-3000 Gs, and demagnetization is very fast during use. Can only stay for 1-2 years or even shorter.

(2) Magnetic field attractive to ferromagnetic materials, referred to as magnetic force.

The magnetic force acting on the unit mass particles is F

F=kH(dH/dh)

In the formula:

K——specific susceptibility (cm3/g)

H——Magnetic field strength (A/m)

dH/dh - gradient of magnetic field distribution (A/m2)

The susceptibility of a unit mass material, called the specific susceptibility (k), also called the susceptibility, indicates the magnitude of the force that the magnetic field can exert on the material;

The amount of magnetic field strength is called magnetic field strength (H).

In the field, H is proportional to the current;

The magnetic field intensity (dH/dh) is the rate at which the magnetic field strength at one point in the magnetic field decays with the change in the distance h from the point to the field source.

From the analysis of the formula, we can see that for the same ferromagnetic substance (with the same k-value), there are two measures to increase the magnetic field: first, increase the threshold, which will lead to increase the cost of production and use; second, increase the value of the ladder , It can be achieved through the production process, changing the shape of the core and the arrangement method. Such measures are not very costly and can achieve good results.

(3) Ferromagnetic substances As the ambient temperature increases, the susceptibility decreases.

After the ferromagnetic substance is magnetized, if the temperature rises, the magnetic induction B will decrease; when the temperature rises to reach the critical temperature (such as iron Tc=357°C), the magnetic flux will drop rapidly and lose magnetism; different materials, Different treatment methods can affect the temperature change curve, that is, there are different use temperatures. The current use of magnetic rods to extend the use of time, should work at 60-82 °C below, better materials can only be used below 100 °C.

(4) According to the magnetic susceptibility of iron-containing materials, they can be divided into the following categories:

Strong magnetic, k> 3000 × 10-6cm3 / g, such as magnetite (Fe3O4), 80000 × 10-6;

Magnetic, k (300-3000) × l0-6, such as black ilmenite (FeTi03), 399 × 10-6

Weak magnetism, k (25 ~ 300) × l0-6, such as limonite (2Fe2O3, · 3H20) 80 × 10-6;

Non-magnetic, k<25×10-6, such as pyrite (FeS2) 7.5×10-6

1.2 The basic principle of iron remover

The use of magnetic fields for the attraction of ferromagnetic materials, the equipment that separates iron minerals from raw materials is called a separator, also called a magnetic separator. The basic condition for the purpose of sorting is that the attractive force (F) of the magnetic field to the ferromagnetic material is greater than the resultant force (Fc) that prevents the magnetic particles from being separated out. Fc is also called a competitive force. It includes the gravity, centrifugal force and inertia of the ferromagnetic particles. Force and fluid resistance.

When the material is iron-removed, the inertia force and fluid resistance are the major parts of the competitiveness. At this time, the fluid resistance:

Fc=πηdυ

In the formula:

η - mud viscosity

d - diameter of mineral particles

v - mud flow rate

It can be seen that the viscosity of the slurry, the size of the iron mineral particles, and the flow velocity of the mud all directly affect the size of the competitiveness, that is, the effect of removing iron. Therefore, in the use of iron remover, we must carefully grasp the slurry's "four degrees" (concentration, viscosity, speed and particle size): Particle size should be determined by the choice of mesh size of the screen mesh; speed and flow are directly related; viscosity and slurry , concentration properties and additives; concentration and water ratio.

A practical iron remover should have the following three conditions:

(1) Strong enough magnetic field source (F>Fc);

(2) Adequate contact area to ensure the opportunity and place for prey;

(3) Clean (separate) ferromagnetic impurities that have been absorbed in a timely and effective manner. Cleaning is the key to effective iron removal.

1.3 Common Types of Iron Remover in Ceramic Industry

(1) According to the principle of minerals, there are dry powder and wet (slurry) separators;

(2) There are permanent magnets and electromagnets in the form of magnetic fields;

(3) According to the external structure: slurry tank closure type, slurry tank settlement type, cylindrical tank type; dry powder is suspended, belt type and bucket vibration cabinet (box) type;

(4) According to cleaning methods: manual cleaning, semi-automatic and automatic;

(5) According to work status: intermittent and continuous.

2 Application Status and Development Requirements of Iron Remover in Ceramic Industry

Building sanitary ceramics manufacturers are paying more and more attention to the issue of iron removal. The use of iron remover has been expanding: from the original glaze to iron to the billet but also to iron removal; more and more iron removal products are needed, in addition to iron The requirements are also getting higher and higher. A production line has been installed with a deironing device and it has been developed to install 3-4 multi-stage series separators; an iron-removing magnetic bar with iron slots has also been developed from the original dozen to two or three hundred. Branches, magnetic rods and iron investment are getting bigger and bigger.

Due to the excessive consumption of mine resources, many companies have been unable to find nearby and can not afford to buy low-quality iron-containing raw materials. They have to use poor raw materials, use a large number of iron removers, and use up to a dozen operations in an online iron removal process. Workers, with the increasing cost of iron.

Cleaning depends on manual operation and quality is difficult to guarantee. When the iron content of the raw material is high, there often occurs a thick layer of iron mud paste around the magnet bar, which occupies an effective magnetic path of the field source, and the iron removal effect is significantly reduced to disappear. Coupled with many human factors, the quality is difficult to control.

The permanent magnetic bars sold in the market are of unstable quality, resulting in a continuous decrease in the average life span of the magnetic bars. Normal conditions should be guaranteed for more than two years, and some of them should not absorb iron. Secondly, the "nominal" value of magnetic bar B on the market. The general virtual height is mostly 50% to 100% higher than the measured value.

The dry powder iron removal uses the hopper vibration box (frame) type permanent magnetic iron remover and the belt drive iron remover, which is mainly used to remove rust impurities that fall from the powder during long-distance transportation. The use of dry powder to remove iron is increasing.

Electromagnetic iron separator development trials earlier, the general response is good, especially high-power and strong magnetic field, the weak magnetic materials present in the sorting ore is more appropriate. However, the investment is too large, the power consumption is high, and the magnetically permeable material is easily oxidized, thus affecting its popularization and application.

At present, China's ceramic production enterprises also very much hope that the manufacturers of iron removal equipment will produce new iron-removing products with strong magnetic separation capability, long service life, high degree of automation, and more economical and applicable. Specific requirements:

(1) The permanent magnetic iron removal magnet bar B value should be more than 6000Gs, the use of temperature above 70-80 °C; service life should be guaranteed more than two years, B value is not less than 50%;

(2) Electromagnetic separators have high magnetic induction, but the manufacturing and procurement costs must be reduced, and the electromagnetic energy conversion efficiency should be high. Secondly, the airtight materials should be sealed to avoid oxidation and shorten the service life; multiple flow rates should also be produced. Different power separators to meet the needs of economical use in multi-stage series connection;

(3) The degree of automation of the deferrifier cleaning is higher, and the loss of the slurry (powder) material and water is reduced at the same time, especially the iron removal from the glaze;

(4) In the spray drying tower, the effective flow rate of the iron remover is required to be large, and it can be adapted to a pulp throughput of 20t/h or more;

(5) The structure should be simple, easy to maintain, the volume is as small as possible, safe and reliable to use;

(6) In the transmission route of the slurry (powder) material, high-quality stainless steel shall be used to prevent secondary rust and other impurity contamination.

3 Suggestions

Iron removal process should pay attention:

(1) According to the characteristics of ferromagnetic materials on ceramic products, analyze the source and severity of ferromagnetic impurities in the products, and then take appropriate treatment measures to block the source of impurities.

(2) When arranging the position of the iron remover, the following principles should be followed:

a) Removal of iron should be carried out in the screened raw material to prevent large particles and other impurities from entering the nearby iron trough (box) and impeding the normal functioning of the iron remover;

b) Removal of iron should be as low as possible in order to extend the service life of the magnet;

c) According to the category of ferromagnetic material, choose the appropriate magnetic separator; use weak magnetic field (such as 0.2-0.3T) in addition to strong magnetic impurities to reduce the cost of purchase and use; in addition to weak magnetic impurities must use strong Magnetic field (such as 0.5-2T), when it is expensive to purchase and use. In the same production line, strong magnetic impurities should be removed before removing weak magnetic impurities. Based on this, some people put the old rods with more demagnetization on the downstream part of the iron removal process.

(3) The height of the slurry section of the permanent magnetic slurry interceptor and the iron separator should be appropriate, and the ferromagnetic impurities in the uppermost level should be basically guaranteed to be within the effective magnetic range.

(4) The cleaning magnetic bar is the key to guarantee the iron removal effect, especially the high gradient magnetic field, its radial attenuation is faster, and the effective magnetic path is shorter; only when the working surface of the iron magnetic bar (block) is cleaned in time can it be normal. Play the role of magnetic fields and gradients. The interval between cleanings should be based 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 bars, magnetic bars should be selected according to the use temperature, in order to achieve the purpose of economical use.

(6) The oxidation (rust) of the magnetic rod (core) will cause the magnetic field to weaken, so be sure to clean the magnetic source carrier when the iron remover is deactivated; be sure to check both ends of the seal when purchasing the iron magnetic stick. Whether it is intact, there can be no leaks, to prevent the magnetic core from contacting the slurry to oxidize or corrode and demagnetize.

(7) Strikes and vibrations will change the direction of part of the magnetic moment of the magnetic source material, thereby weakening the magnetic field. The operator must be very careful.

(8) Several measures for the economic use of iron removal equipment:

a) Permanent magnet electromagnetic mixing can be used on the same production line; b) When selecting the diameter of the permanent magnet iron removal rod, it should not be selected too large. c) The old magnetic bar is magnetized and refurbished. As long as the magnet bar is not bad, the magnetic core is not oxidized and deteriorated, and the renovation can reach the original level, and the investment can save about 50%.

In order to solve the current demand of the ceramic industry for iron removal equipment, Foshan Jingyan Electromechanical Co., Ltd. has introduced high-magnetism, high-gradient, high-quality, permanent-magnet, full-automatic, high-efficiency iron remover. Through practical application of several companies of the Group, the effect is satisfactory and the design is achieved. Indicators; There are many iron remover manufacturers are also in combination with the company's need for research on iron removal technology, gradually introduced automatic permanent magnet electromagnetic iron remover, high-field high-temperature iron removal magnetic bar and other new products to meet the production of ceramic enterprises Needs.