WO2016178603A1

WO2016178603A1 - Fine grinding mill

Info

Publication number: WO2016178603A1
Application number: PCT/RU2016/000270
Authority: WO
Inventors: Михаил Николаевич РОЖКОВ; Андрей Валерьевич КОНДРАТЬЕВ; Валерий Иванович ВАРЛАМОВ; Сергей Константинович Гордеев
Original assignee: Общество С Ограниченной Ответственностью "Доминант"
Priority date: 2015-05-06
Filing date: 2016-05-04
Publication date: 2016-11-10
Also published as: RU2603038C1

Abstract

The invention relates to devices for fine grinding very hard, brittle materials and can be used in metallurgy, construction, and the chemical industry. A mill comprises a closed housing with connection pipes for the ingress and egress of a product; a cylindrical working chamber, situated inside the housing and having an external water jacket and an internal lining; and a vertical rotor, axially mounted inside the chamber. The vertical rotor is connected to a rotary drive and is configured in the form of a shaft having connected thereto horizontal supporting discs, to which grinding elements are fastened via pivot axes. The centre of gravity of the grinding elements is offset from the pivot axis, and the grinding elements, consisting of a metal body with a grinding insert fastened thereto, are made of a ceramic composite material, containing diamond - 20-75 vol%, silicon carbide - 20-75 vol%, and silicon - 3-40 vol%. The mill is characterized by an extended operating life as a result of low wear on the grinding elements and the lining when particularly hard materials are ground to produce micropowders.

Description

Fine grinding mill

Technical field

The invention relates to metallurgy, construction and the chemical industry, and in particular to devices for fine grinding of brittle high-solid materials in dry form or in a liquid medium and can be used to obtain micropowders of ceramic materials, pigments, additives in fuel and other materials.

State of the art

A large number of devices are known for grinding powders of brittle materials by combining crushing and shear forces on crushed particles (for example, cone-inertial crushers, roller-ring mills). The experience of the use of such devices in practice has proved that the impact of shear forces on the material being ground allows a significant increase in the grinding efficiency of brittle materials. This is due to the mechanical properties of brittle materials: high compressive strength combined with relatively low tensile and shear strength. Therefore, the development of grinding devices with a significant contribution of the effects of shear loads on the milled material is of great interest.

A centrifugal mill is known, consisting of a vertical housing with a working chamber, in which a rotor with supporting disks is mounted on which grinding elements in the form of segments are fixed [RF patent JY_> 2004328, cl. B02C 13/14, 1991]. The grinding elements are installed with a gap relative to the wall of the working chamber, which provides the necessary dispersion of the resulting product.

A disadvantage of the known device is the inability to use it to obtain fine powders, for example, less than 10 microns in size, since for this it is necessary to install a rotor and grinding elements with the same size (10 microns) of the gap between the grinding elements and the surface of the working chamber, which impossible with the practical use of the mill.

The closest analogue of the proposed technical solution, according to the authors, is an inertial mill described in RF patent JN ° 2033857 [class B02C 15/00]. The mill has a vertical casing with an inner lining and production inlet and outlet pipes, and a rotor installed in the casing in the form of a drive shaft and movable grinding elements mounted on rotation axes displaced relative to their center of gravity, mounted between supporting disks connected to the drive shaft. The grinding elements in a horizontal section are segmented in shape, and their axis of rotation is offset from its center of gravity by at least 0.5 of its length.

During operation of the known mill, the rotation of the rotor provides (due to the centrifugal force acting on the grinding element, and the possibility of turning the grinding element around the axis of rotation) pressing each of the grinding elements to the surface of the lining. Particles of the starting material cast by the rotor onto the surface of the lining are crushed due to the combined effect of compressive (crushing) and shear forces on them. Compressive forces are provided by the centrifugal force of pressing the grinding element to the lining, and shear forces by the movement of the surface of the grinding element relative to the surface of the lining. The absence of a gap between the surface of the grinding element and the lining simplifies the installation of the rotor relative to the lining, and also allows you to obtain highly dispersed powders of materials, for example, with a size of less than 10 microns.

A disadvantage of the known device is its small resource when grinding high hard materials. This is due to the large wear of the used ceramic-metal grinding elements and the lining due to the abrasive action of the particles of highly hard ground material. In addition, the mill is difficult to maintain: replacing grinding elements requires disassembling the mill rotor.

Disclosure of invention

The technical task of the proposed invention is to increase the life of the mill, simplifying repair services and expanding the areas of its use.

The problem is solved in the proposed invention so that a mill for fine grinding of materials, having a closed housing with nozzles for input and output of products in which there is a cylindrical working chamber with an external water jacket and an inner lining, and installed in the chamber along its axis, connected to the drive vertical rotor in the form of a shaft and horizontal supporting disks connected to it, on which grinding elements are fixed on the axis of rotation, whose center of gravity offset relative to the axis of rotation, the grinding elements consist of a metal housing and a grinding insert fixed to it, which, when the element rotates, is in contact with the surface of the lining. At the same time, the grinding inserts and the lining of the working chamber are made of ceramic composite material containing diamond - 20-75% vol., Silicon carbide - 20-75% vol., Silicon - 3-40% vol.

The use of lining and grinding inserts made of composite material with a diamond content of less than 20% vol. and with a silicon content of more than 40% vol. impractical since materials have low wear resistance, not providing an effective resource of the mill. The manufacture of lining and grinding inserts from a material with a diamond content of more than 75% vol. and a silicon content of less than 3% vol. impractical since obtaining such materials is technologically very difficult.

Brief Description of the Drawings

The technical solution is illustrated by the following figures:

Figure 1 A cross section of a mill, which shows:

1 - pipe to enter the crushed material (products),

2 - pipe for output of crushed material (products),

3 - working chamber,

4 - water jacket of the working chamber,

5 - lining of the working chamber,

6 - shaft

7 - shaft drive,

8 - reference disk

9 - axis of rotation of the grinding elements, 10 - grinding elements.

Figure 2 The appearance of the grinding element:

11 - case,

12 - grinding insert,

13 - hole for installation on the axis of rotation.

SUMMARY OF THE INVENTION

The invention consists in the following.

The mill for fine grinding of materials has a vertical closed housing with nozzles for input and output of products. The branch pipe of the input of the product (the initial ground powders) is located on the upper part of the housing, for example, on its upper cover. The outlet pipe of output (crushed material) is located in the lower part of the body - on the lower cover. In the middle of the case is a cylindrical working chamber. The working chamber has a cooling water jacket, necessary to maintain the temperature in the working chamber and to remove excess heat generated during the grinding of materials. The inner surface of the working chamber has a lining made of a ceramic composite material diamond - silicon carbide - silicon.

In various designs of the mill, it is possible to use the lining as an inner casing of the working chamber, cooled by water, providing structural strength. The lining can be made of a single hollow cylinder, the inner diameter of which corresponds to the inner diameter of the working chamber, or of individual elements assembled together using gluing or soldering methods, and also other methods. A rotor having a shaft is installed in the mill body. The rotor shaft is installed along the axis of the working chamber, passes through the top cover of the housing and is connected to a drive that provides rotation of the shaft during operation of the mill. In the area of the working chamber on the shaft, perpendicular to it, supporting disks are installed, the diameter of which is smaller than the inner diameter of the lining. Several support discs can be installed on the shaft, but at least two. The distance between the discs can be the same or different, depending on the design of the mill. In the outer zone of the supporting disks, perpendicular to them, the rotation axis of the grinding elements are installed. These axes can be made, for example, as cylindrical shafts mounted between two adjacent support disks and fixed in them. The number of axles installed between the two discs depends on the design of the mill, but they cannot be less than two. In this case, it is advisable to symmetrically set the axes in a circle, because this provides the best balance of rotor rotation during mill operation.

Grinding elements are installed on the axes of rotation. On one axis of rotation, in height, several grinding elements can be installed. The grinding elements have a housing made of metal, in which a grinding insert of a ceramic composite material diamond - silicon carbide - silicon is fixed. The grinding elements are mounted on the axes of rotation so that the center of gravity of the element does not coincide with the axis of rotation, and when the rotor rotates, the grinding element is rotated on the axis of rotation and the grinding insert is pressed against the surface of the lining. The use of a grinding element with a metal casing and a grinding insert increases the reliability of the mill design compared to the installation completely ceramic grinding elements directly on the axis of rotation. Ceramic composites diamond - silicon carbide - silicon have a significantly lower strength (compared with metal) at tensile stresses arising in the grinding element during mill operation, as well as greater brittleness, which can lead to destruction of ceramic elements during operation. A grinding insert made of a ceramic composite and fixed in the housing of the grinding element provides the necessary wear resistance of the element as a whole. In addition, such an insert can be easily replaced by a new one during maintenance of the mill without removing the grinding elements from the axis of rotation.

The mill operates as follows. The mill drive provides rotor rotation. In this case, the grinding elements in which the center of gravity is displaced relative to the axis of their rotation, due to the centrifugal force acting on them, are rotated on the rotation axes, thereby moving the grinding insert to the surface of the lining. Grinding inserts are pressed to the surface of the lining and slide on it with the angular velocity of rotation of the rotor.

Starting materials — powdered materials to be ground, are fed through an inlet pipe located above the working chamber. Sinking down due to its own weight into the working chamber, the powder particles are discarded by the rotor on the surface of the lining and are subjected to abrasion by the grinding inserts moving along the surface of the lining, thereby causing the destruction of particles and grinding of the material. The increase in peripheral speed, the rotation of the rotor increases both the linear speed of the grinding insert on the surface of the lining, and the pressing force of the grinding insert to lining surfaces. Thereby, the degree of grinding of the starting materials is controlled. If several grinding elements are installed along the height of the mill, on the axis of rotation, in the zone of the working chamber, then the crushed material after exposure to the upper grinding elements under its own weight falls into the zone of influence of the next highest elements on it. Thereby, an increase in the degree of grinding of powdered materials is achieved, which then, under their own weight, are removed from the mill through an outlet pipe located below the working chamber.

The use of lining and grinding inserts made of ceramic composite material diamond - silicon carbide - silicon in the mill design significantly increases the life of the mill and expands its field of application. Due to the presence of diamond in the structure of the material, its hardness is increased. As experiments have shown, such a composite has high wear resistance when working in a friction pair "by itself", including in the environment of powders of solid materials, in combination with strength and resistance to shock. This made it possible to efficiently use the composite in the mill design. The proposed mill can be used for grinding extra hard materials, for example, alumina, silicon carbide, boron carbide, while the known mills of this design cannot be used in these cases. The high hardness of the composite and the linings and grinding inserts made from it determines the very low wear of these elements of the mill, which not only ensures the efficient use of the mill without replacing the corresponding elements, but also allows you to get clean powdered powders that are not contaminated with “grinding” parts of grinding devices.

The proposed mill can be used for grinding powdered materials in liquid media. In this case, the material to be ground is fed into the mill in the form of a suspension, for example, in water. When grinding in liquid media, it is preferable to feed the suspension into the working chamber from below, and the output of the finished product from above. The principles of the mill are similar to grinding dry powders on it.

An example embodiment of the invention

The proposed technical solution is illustrated by an example of the application of the proposed mill for the production of boron carbide micropowders.

Obtaining micropowders of boron carbide is as follows. The initial powders of boron carbide with a particle size of 80 to 63 μm are fed using a feeder into a rotary abrasive mill with a working chamber diameter of 105 mm, the engine power for rotor rotation is 2 kW. The surface of the working chamber is made of six rings of ceramic composite material installed on top of one another, having the composition: diamond - 42% vol., Silicon carbide - 50% vol., Silicon - 8% vol. The mill has 24 grinding elements with a metal casing fixed in a non-grinding insert made of a ceramic composite of the same composition. Grinding elements are installed in 6 vertical rows of 4 elements around the circumference, and are fixed on vertical axes with the possibility of rotation about the axis, which ensures their friction on the surface of the lining when rotating the rotor of the mill. The mass flow rate of powders supplied for grinding is 1 kg / h. Grinding is carried out at a rotor speed of 400 rpm. The average particle size of the obtained micropowder is 2.4 microns. The iron content in the obtained micropowder is less than 0.05%. The resource of the mill is more than 1000 hours.

Industrial applicability

The proposed mill is applicable for obtaining micropowders of various materials, including materials of high hardness. The mill has an increased service life due to the low wear of the grinding elements and the lining, provides an expansion of its application areas, including grinding of extra hard materials, as well as high efficiency, both by increasing the overhaul life for replacing worn elements of the mill, and the ease of replacing grinding inserts during technical maintenance, while maintaining the reliability of the mechanical properties of grinding elements, the housing of which is made of metal.

Claims

Claim

A mill for fine grinding of materials, including a closed housing with nozzles for input and output of products in which a cylindrical working chamber with an external water jacket and an inner lining is located, and a vertical rotor in the form of a shaft and connected to a rotation drive is installed in the chamber along its axis with it horizontal supporting disks on which grinding elements are fixed on the axis of rotation, the center of gravity of which is offset from the axis of rotation, characterized in that the grinding elements consist of metallic case and the grinding insert fixed on it, which during rotation of the element is in contact with the surface of the lining, and the grinding inserts and the lining of the working chamber are made of ceramic composite material containing diamond - 20-75% vol., silicon carbide - 20-75% vol. silicon - 3-40% vol.

SUBSTITUTE SHEET (RULE 26)