RU2705748C1 - Method of producing powder from metal chips - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy, particularly, to production of powder metal materials from metal chips. First, the initial raw material is cleaned from the cutting fluid, for which purpose the chips are poured with white spirit, the white spirit is stirred and drained. Chip chips are filled in centrifugation device for removal of white spirit, treatment is performed for 3–10 minutes, after that remaining amount of coolant is burnt out in chamber furnace at temperature from 100 °C to 200 °C. Crushing of chips is carried out in ball mill of attritor type, grinding bodies with size of 5–15 mm, at ratio of weight of material to grinding bodies in range of 1:10–1:30. Chamber of attritor is blown with inert gas for 5–10 minutes and milled for 1–4 hours. Obtained powder is cooled to ambient temperature, screened from grinding bodies on sieve with cell diameter of 3 mm and screened obtained powder into fractions with separation of fraction not larger than 150 mcm. Thereafter, plasma powder is spheroidized and washed in an ultrasonic bath containing, for example, deionised water.

EFFECT: stabilization of granulometric properties of powder, reduced morphological diversity of particles, increased bulk density and fluidity, as well as reduced sensitivity to friction.

1 cl, 6 dwg

Description

The invention relates to the field of powder metallurgy, in particular, to methods for producing powder metal materials from secondary raw materials, including metal chips (mainly heat-resistant steel).

Powder metallurgy is a field of science and technology that encompasses a set of methods for the manufacture of powders of metals, alloys and metal-like compounds, semi-finished products and products from them or their mixtures with non-metallic powders without melting the main component.

Of the various methods of metal processing that are available, powder metallurgy occupies a special place, since it allows one to obtain not only products of various shapes and purposes, but also to create fundamentally new materials that are either very difficult or impossible to obtain in a different way.

The technological process of manufacturing products by powder metallurgy begins with the production of metal powders. A large number of methods for their preparation are known.

The variety of methods used is explained by the fact that the qualitative characteristics of powders and products are largely determined by the method of manufacturing powders. Powder of the same metal, depending on the production method, dramatically changes some of the properties that determine its applicability for a particular purpose.

In practice, metal powders are characterized by their physical, chemical and technological properties.

The physical properties of powders usually include the predominant particle shape and particle size distribution of the powder. The shape of the particles mainly depends on the method of preparation and can be spherical, spongy, fragmentation, dendritic, dish-shaped and scaly. The shape of the particles affects the density, strength and uniformity of the product. The particle size distribution of the powder is the relative content of fractions of particles of various sizes. In combination with other properties, it decisively affects the achievement of specified mechanical properties of sintered products.

The chemical properties of powders include primarily the content of the base metal, impurities and impurities.

The technological properties of powders are understood as the bulk density of the powder, fluidity and compressibility.

The bulk density of the powder is the mass of a unit of its volume with free filling. It is determined by the density of the powder material, the size and shape of its particles, the density of the particles and the state of their surface. For example, spherical powders with a smooth surface provide higher bulk density.

Powder fluidity is the ability to move by gravity. It is estimated by the time of expiration of a certain sample through a calibrated hole. The fluidity depends on the density of the material, particle size distribution, shape and state of the surface of the particles and affects the performance of automatic presses during pressing, as it determines the time it takes to fill the mold with powder. The fluidity deteriorates when the powder is wetted, its specific surface area and the fraction of the fine fraction increase.

Compressibility of a powder is the ability of a powder to acquire and hold a specific shape and size under the influence of an external force.

Powders of the same chemical composition, but with different physical characteristics, may have different technological properties, which affects the conditions for the further transformation of powders into finished products.

Therefore, the physical, chemical and technological properties of the powders are directly dependent on the method of obtaining the powder.

All methods for producing powders that are found in modern practice can be divided into two groups: mechanical methods and physicochemical methods.

Mechanical processes for producing powders are considered such technological processes in which the source material is crushed as a result of external forces without changing the chemical composition.

Physicochemical methods include such technological processes in which powder production is associated with a change in the chemical composition of the feedstock as a result of deep physicochemical transformations.

Mechanical grinding or grinding is carried out in various devices, namely: in ball, planetary, vibration, vortex, gyroscopic, jet mills, attritors.

Attritor devices are one of the varieties of ball mills. The grinding bodies are located in a vertically located stationary drum, inside of which a vertical paddle mixer rotates at a speed of more than 100 rpm. Circulation of grinding bodies and abrasion of the crushed material is ensured by strokes inclined on the mixer blades. Attritor mills are structurally simple, easy to operate and allow the grinding process to be carried out continuously. As a result of grinding, powders are obtained with a fairly uniform distribution of particle sizes, while the required dispersion is achieved several times faster than in conventional ball mills.

As a prototype of the selected method of producing fine powder from metal chips in a drum grinder [RU2090313]. When implementing this method, the grinding of metal shavings in a drum grinder is carried out under the influence of vibration and rotational movement of the drum around its own axis, which increases the intensity of the grinding process.

The disadvantage of this method is the low quality of the obtained powder, since the method does not provide for preliminary cleaning of the chips from various kinds of pollutants, including cutting fluid, which leads to the appearance of impurities in the powder that impair the quality of the final products. The powder obtained after grinding consists of particles of irregular shape with a loose structure, which makes it non-technological and limits the scope. It has unstable granulometric properties, low bulk density and fluidity, which reduce the performance of the pressing process, due to the increase in the time it takes to fill the mold with powder.

Thus, the technical problem to which the invention is directed is the development of a method for producing powder from chips that improves the quality of the final product.

The solution to this technical problem is achieved due to the fact that when using the method of producing powder from high-alloy heat-resistant steel shavings, including grinding the feedstock mechanically, the coolant is preliminarily cleaned from the feedstock, for which the shavings are poured with white spirit and mixed, then white spirit drained; pour the chips into the centrifugation device to remove the white spirit, while the treatment is carried out from 3 to 10 minutes depending on the weight of the material, after which the remaining coolant is burned in the chamber furnace at a temperature of from 100 ° C to 200 ° C; shavings are crushed in an attritor type ball mill, using grinding bodies from 5 to 15 mm in size, and the ratio of the material loading mass to the grinding bodies is selected in the range 1: 10-1: 30; purge the attritor chamber with inert gas for 5-10 minutes, then produce a grinding process for 1-4 hours; after grinding is completed, the resulting powder is cooled to ambient temperature and the resulting product is unloaded by screening it from grinding bodies on a sieve with a mesh diameter of 3 mm, then the resulting powder is sieved into fractions, and particles not larger than 150 microns are used in the next step; at the last stage, plasma spheroidization of the powder is performed, for which the plasma spheroidization plant is purged with an inert gas (argon, helium) and the process parameters are set, namely: hydrogen flow rate from 3 to 4 standard liters per minute, chamber pressure from 0.88 to 1 atmosphere, the carrier gas flow rate from 2 to 5 standard liters per minute, the powder flow rate from 1 to 3 kg / h, the powder entry point into the plasma (zero point) ± 15 mm, and the process of low-temperature plasma spheroidization is started, after which the spheres ized powder is washed in an ultrasonic bath containing, for example, deionized water, in a weight ratio of 1: 1.

When implementing the proposed method, which consists in a three-stage processing of metal chips, the quality of the finished powder is improved, expressed in the stabilization of its particle size distribution, a decrease in the morphological diversity of particles, an increase in bulk density and fluidity, as well as a decrease in sensitivity to friction.

On the drawings attached to the description is given:

- Three stages of the implementation of the method for producing powder (Fig. 1);

- The first stage is the purification of raw materials (Fig. 2);

- The scheme of the device attritor mill (Fig. 3);

- The second stage is grinding chips (Fig. 4);

- The third stage is the spheroidization of the powder in a low-temperature plasma (Fig. 5);

- A fragment of the installation for plasma spheroidization (Fig. 6).

The method of obtaining powder from recycled materials (chips) consists of three stages (Fig. 1).

At the first (Fig. 2), the feedstock is cleaned of the cutting fluid (coolant). Coolant removal is carried out as follows.

First, pour the chips with white spirit and mix. Then the white spirit is drained.

Pour the chips into the centrifugation device to remove the white spirit. Processing is carried out from 3 to 10 minutes, depending on the weight of the material.

The remaining amount of coolant is burned out in a chamber furnace at a temperature of from 100 ° C to 200 ° C.

At the second stage, chips are crushed in an attritor type ball mill (Fig. 3).

The mill consists of a vertically located stationary drum 1 containing an outer 2 and an inner 3 wall, between which there is a cavity 4. Water or other cooling liquid can be supplied into this cavity. The inner wall of the drum forms a grinding vessel 5. Inside the drum there is a mixer shaft 6 with blades 7 located on it, grinding bodies 8 and crushed material 9.

The vertical paddle mixer rotates inside the drum at a speed of more than 100 rpm. Circulation of grinding bodies and abrasion of the crushed material is ensured by strokes inclined on the mixer blades.

Before grinding weigh the crushed material (Fig. 4). The attritor tank is filled with chips and grinding bodies, while the size of the grinding bodies is from 5 to 15 mm, and the ratio of the mass of the material loading to the grinding bodies is in the range of 1: 10-1: 30.

The attritor chamber is flushed with inert gas for 5-10 minutes, then the grinding process is carried out for 1-4 hours. After grinding is completed, the resulting powder is cooled and the resulting product is unloaded by screening it from the grinding bodies on a sieve with a mesh diameter of 3 mm.

Measure the mass of the obtained powder, then sieving it into fractions:

- less than 45 microns;

- from 45 to 71 microns;

- from 71 to 90 microns;

- from 90 to 125 microns;

- from 125 to 150 microns.

The powder mass is measured and the yield of the product fraction is calculated. Powder larger than 150 microns is not suitable for further use, it is sent for secondary grinding.

At the third stage (Fig. 5), plasma spheroidization of the powder is performed.

To do this, the installation for plasma spheroidization (Fig. 6 shows a fragment of the installation 10, including the nozzle 11) connect the gases used (hydrogen, argon, helium) and blow it with an inert gas.

The values of the technological parameters of the plasma spheroidization process are set:

- The mass of powder loaded into the plasma spheroidization apparatus is from 0.1 to 10 kg;

- The consumption of hydrogen from 3 to 4 standard liters per minute (0.18 - 0.24 m ³ / hour);

- The pressure in the chamber from 0.88 to 1 atmosphere;

- Consumption (speed) of carrier gas from 2 to 5 standard liters per minute;

- Powder feed rate from 1 to 3 kg / h;

- The point of entry of the powder into the plasma "zero point" ± 15 mm (Fig. 6, zero point 11).

From the specified range of parameters, with a decrease in the fraction of the powder used, a greater consumption of products is selected.

Start the process of low-temperature plasma spheroidization. In this case, the fine powder fractions evaporate and precipitate in the form of nanosized powder particles on the surface of the large powder fractions. After the passage of all the powder, the installation is flushed with an inert gas. At the end of the process, the powder is removed from the installation.

The spheroidized powder is washed in an ultrasonic bath containing deionized water or ethyl alcohol or hexane in a weight ratio of 1: 1.

Claims (1)

A method of producing powder from high-alloy heat-resistant steel shavings, including mechanical grinding of the feedstock, characterized in that the coolant is first cleaned of the feedstock by pouring white spirit into the chips and mixing, then pouring the white spirit into the centrifugation device and filling removal of white spirit, while processing is carried out from 3 to 10 minutes depending on the weight of the material, after which the remaining coolant in the chamber furnace is burned out at a temperature of 100 ° С up to 200 ° С, shavings are crushed in an attritor type ball mill, grinding bodies from 5 to 15 mm in size are used, and the ratio of the material loading mass to grinding bodies is selected in the range 1: 10-1: 30, the attritor chamber is blown with inert gas within 5-10 minutes, then the grinding process is carried out for 1-4 hours, after grinding is completed, the resulting powder is cooled to ambient temperature and the resulting product is unloaded by screening it from grinding bodies on a sieve with a mesh diameter of 3 m m, then the obtained powder is sieved into fractions, particles no larger than 150 microns are used at the next stage, plasma spheroidization of the powder is carried out at the last stage, for which the plasma spheroidization plant is purged with an inert gas in the form of argon, helium and the process parameters are set including flow rate hydrogen from 3 to 4 standard liters per minute, the pressure in the chamber from 0.88 to 1 atmosphere, the flow rate of carrier gas from 2 to 5 standard liters per minute, the flow rate of powder from 1 to 3 kg / h, the point of entry of powder into the plasma in the form the zero point is ± 15 mm, and the process of low-temperature plasma spheroidization is started, after which the spheroidized powder is washed in an ultrasonic bath containing, for example, deionized water, in a weight ratio of 1: 1.

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