RU2603043C1 - Method of producing micropowders of solid materials - Google Patents

Abstract

FIELD: food industry.

SUBSTANCE: invention relates to methods of producing micro powders of solid materials, for example, micro powders of ceramic materials, pigments. Method comprises milling particles of solid materials in rotary grinding mill, wherein grinding inserts and lining of working chamber are made of ceramic composite material containing diamond - 20-75 vol%, silicon carbide - 20-75 vol%, silicon - 3-40% vol%.

EFFECT: method enables to obtain chemically pure micropowders of solid materials.

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Description

The invention relates to a technology for grinding materials, namely, to methods for producing micropowders of materials by grinding larger grains and can be used to obtain micropowders of ceramic materials, pigments and other materials.

One of the most common methods for obtaining micropowders of materials is the grinding of larger grains of such materials. Grinding is carried out in mills of various types (ball, planetary, jet, etc.). Such methods for producing micropowders of materials with relatively low hardness are quite effective due to the simplicity of the technology and the simple design of the devices used.

Upon receipt of micropowders of high hardness materials, such as, for example, silicon carbide and boron carbide, the efficiency of the grinding methods described above is significantly reduced. This is primarily due to the contamination of the resulting micropowders with the material of grinding elements. Pollution occurs due to the abrasive wear that occurs when exposed to grinding powders on the details of grinding devices. Therefore, to obtain pure micropowders, their subsequent chemical purification is required, usually in acid solutions, which is laborious and reduces the effectiveness of such methods for producing micropowders of solid materials.

As the closest analogue, the authors chose a method for producing micropowders of solid materials, described in the article "Some features of the process of grinding and pressing of boron carbide" / L.I. Struk, V.B. Fedorus, G.N. Makarenko, E.V. Prilutsky. - Powder Metallurgy, 1985, No. 6 p. 29-33. The method consists in grinding powder of boron carbide in a magnetic vortex apparatus. The method provides the production of powders of solid material (boron carbide) with a size of less than 2 microns.

The disadvantage of this method is the significant pollution of the resulting micropowders with iron, which does not allow the use of such powders to obtain ceramics. Their chemical cleaning is required. In addition, due to active abrasive wear, the life of the grinding equipment is significantly reduced.

The technical task of the invention is to increase the efficiency of obtaining micropowders of solid materials, namely: increasing the chemical purity of micropowders and increasing the life of the equipment.

The problem is solved in the present invention in that the grinding of particles of solid material is carried out in a rotary abrasive mill, in which grinding inserts and 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 a lining and grinding inserts of composite material with a diamond content of less than 20 vol.% And with a silicon content of more than 40 vol.% Is impractical because 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.% Is impractical because obtaining such materials is technologically very difficult.

The invention consists in the following.

The grinding of particles of solid material, for example, such as silicon carbide, boron carbide, etc., is carried out on a rotary abrasive mill. The design of the mill provides grinding powders of solid materials by combining the simultaneous impact of crushing and shear forces on the crushed particles. The impact on the particles of the material of shear forces can significantly increase the grinding efficiency of solid materials. This is due to the mechanical properties of solid materials: high compressive strength combined with relatively low tensile and shear strength.

The mill used to implement the method has a vertically 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.

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 not less than 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 discs, 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 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 grinding insert made of a ceramic composite diamond - silicon carbide - silicon and fixed in the housing of the grinding element, provides the necessary wear resistance of the element.

The proposed method of manufacturing micropowders of solid materials is as follows. Turn on a rotary abrasive mill. In this case, the mill drive provides the rotation of the rotor. Grinding elements in which the center of gravity is offset relative to the axis of their rotation, due to the centrifugal force acting on them, rotate on the axis of rotation, 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.

The use in the design of the mill used to implement the method, lining and grinding inserts of ceramic composite material diamond - silicon carbide - silicon significantly increases the life of the grinding equipment, which increases the efficiency of the method. The increase in the service life of the equipment is due to the fact that the ceramic composite used in the mill construction has a high hardness (up to 55 GPa) which is higher than the hardness of the crushed material, for example, aluminum oxide, silicon carbide, boron carbide (20, 23, 40 GPa, respectively ) 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 grinding equipment without replacing the corresponding elements, but also allows us to obtain pure powdered powders of solid materials that are not contaminated with “grinding” parts of grinding devices .

The crushed powders of solid materials are fed through an inlet pipe located above the working chamber. Sinking down due to their own weight into the working chamber, the powder particles are rotor discarded on the surface of the lining made of ceramic composite material diamond - silicon carbide - silicon and are subjected to abrasion by the grinding inserts moving along the surface of the lining, also made of ceramic composite material diamond - silicon carbide - silicon. The compression and shear forces applied to the particle (abrasion) cause the destruction of the particles and the 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 the surface of the lining. 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. Due to this, an increase in the degree of grinding of powder materials is achieved, which then, under their own weight, are removed from the mill through an outlet pipe located below the working chamber.

The proposed technical solution is illustrated by example.

Example. The preparation of silicon carbide micropowders is as follows. The initial powders of boron carbide with a particle size of 63 to 50 μm are fed using a feeder to 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 a ceramic composite material having the composition: diamond - 42 vol.%, Silicon carbide - 50 vol.%, Silicon - 8 vol.%. The mill has 36 grinding elements with inserts from a composite of the same composition. The mass flow rate of the supplied powders is 1 kg / h. Grinding is carried out at a rotor speed of 500 rpm. The average particle size of the obtained micropowder is 1.2 microns. The iron content in the micropowder is less than 0.1%. The resource of the mill is more than 500 hours.

Thus, the proposed method provides for the production of chemically pure micropowders of solid materials, while the grinding equipment has a long service life.

Claims (1)

A method of manufacturing micropowders of solid materials, which consists in grinding particles of solid materials, characterized in that the grinding is carried out in a rotary abrasive mill, in which the grinding inserts and the lining of the working chamber are made of ceramic composite material containing diamond - 20-75 vol.%, Carbide silicon - 20-75 vol.%, silicon - 3-40 vol.%.