RU2623608C1 - Method of milling the powder from plastic material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: to grind the powder, the original iron-containing material is treated in the mill. The mill is loaded with ground raw iron-containing material and working bodies. The working bodies are made in the form of steel balls. Preliminarily, the initial powder and steel balls with a diameter of 6-22 mm in a ratio of 10:1, respectively. Fill with liquid nitrogen with the addition of ethyl alcohol. Place the vibrating mill in the chamber. Seal and create a vacuum of 1 kgf/cm². Fill the chamber with argon gas and grind for 1-4 hours, followed by analysis of the particle size.

EFFECT: invention simplifies the process and increases the grinding effect.

2 cl, 8 dwg

Description

The invention relates to the field of powder metallurgy, and in particular to a method for grinding iron-containing powder from a plastic material.

It is known that upon receipt of highly porous materials a mixture is prepared from metal powders, as well as from stainless steel powders [Antsiferov V.N., Beklemeshov A.M., Gilev V.G., Porozova S.E., Shveikin G.P. Problems of powder materials science. Part II Highly porous powder materials. Yekaterinburg: Ural Branch of the Russian Academy of Sciences, 2002. S. 3-56]. Moreover, in powder metallurgy, vibration mills are widely used for energy grinding of powder materials. However, the grinding of the powder obtained from a plastic material in order to reduce the particle size presents certain difficulties associated with the aggregation of particles in the grinding process. The problem of grinding plastic materials was solved using the phenomenon of mechanodynamic diffusion under the influence of gaseous helium at its excess pressure.

Due to the small size of the atom, helium gas is able to easily penetrate from the surface through dislocations and microcracks into the depth of the dispersible material and embrittle the particles. The additional effect of ultrasound on dispersible particles outside the vibratory mill allowed to reduce the size of the barite particles from 4.5 to 3 ÷ 0.5 microns [Method of grinding crystalline powder material: US Pat. No. 2423182 (RU): IPC В02С 17/00, В02С 19/18, decl. 11/24/2009; publ. 07/10/2011. Bull. No. 19. - 8 p.]. A disadvantage of the analogue is the difficulty of grinding the powder obtained from a plastic material in order to reduce particle size.

The closest in technical essence and the achieved result to the proposed solution is a method for producing a magnetically hard composite material with a nanocrystalline structure (US Pat. RF No. 2203515, IPC B22F 1/00, H01F 1/11, publ. 04/27/03). This method includes processing the source of iron-containing material in a high-energy mill, which is loaded with crushed source material and working bodies made in the form of steel balls, obtaining an intermediate iron-containing material and its heat treatment in furnaces. As the starting material, natural powder material of the following composition is used, wt.%: Fe ₂ O ₃ 93.0-99.3, FeO 0.20-2.00, SiO ₂ 0.20-3.00, the rest is related impurities. A magnetically hard composite material with a nanocrystalline structure is obtained having high magnetic properties. This method is taken as a prototype.

The disadvantages of the prototype method are the complexity of the process and significant energy costs.

The objective of the invention is to eliminate the disadvantages of the prototype and expand the grinding capabilities of the iron-containing powder from a plastic material.

The problem is solved using the characteristics specified in the 1st claim that are common with the prototype, such as a method of grinding powder of plastic material, including processing the source of iron-containing material in a mill, into which the crushed source of iron-containing material and working fluids made in in the form of steel balls, and distinctive essential features, such as pre-loading the source powder and steel balls with a diameter of 6-22 mm in a ratio of 10: 1, respectively, pour t with liquid nitrogen with the addition of ethyl alcohol, placed in a chamber of a vibration mill, sealed, created a vacuum of 1 kgf / cm ² , filled the chamber with gaseous argon and milled for 1-4 hours, followed by analysis of particle size by known methods.

According to paragraph 2 of the claims, austenitic chromium steel PR0X18H10 is used as the starting iron-containing material.

The above set of essential features allows you to get the following technical result - simplification of the process and increase the grinding effect, as well as expanding the possibilities of grinding iron-containing powder from plastic material.

The proposed method is illustrated by the following example and graphs.

Example

Powder steel was prepared for testing by melting stainless steel scrap in vacuum (~ 0.1 MPa) and spraying the melt at a temperature of 1620 ° C with argon of purity 99.998. The elemental composition of the powder was determined on an EDX-800H energy dispersive X-ray fluorescence spectrometer from Shimadzu (wt.%): 68.61 - Fe, 18.53 - Cr, 10.24 - Ni, 1.28 - Mn (other elements in the amount of 1.34 wt.% not specified). The resulting composition is close to the grade of powder steel PR0X18H10 (GOST 14086-68).

Next, the steel powder was dispersed in a vibratory mill grade MB - 0.005. As grinding media there were ball-bearing balls with sizes from 6 to 22 mm and a total weight of 5 kg. The mass of the initial powder was 0.5 kg, thus, the mass ratio of the grinding media and the powder was 10: 1. Balls and powder were loaded into a separate container; slowly, in a thin stream, liquid nitrogen was poured from a Dewar vessel in an amount covering the level of the loaded materials and 100 ml of ethanol. Then the contents were transferred to the mill chamber, while part of the nitrogen escaped. The mill cover was hermetically sealed and air was evacuated, creating a vacuum of ~ -1 kgf / cm ² , then gaseous argon was launched into the mill. Vacuum was measured with an ECV-1U brand vacuum gauge, argon pressure with a manometer. The grinding time ranged from 1 to 4 hours, in some cases 14 hours. After each time interval, the lid was opened, a batch of powder was taken to measure the powder characteristics on an Analysette 22 NanoTec laser particle analyzer (with a liquid dispersion unit, which allows measuring particle sizes in the range from 0.01 to 1000 μm), carefully fill in a new batch of nitrogen, close the lid, and after pumping air with a plunger pump fed argon.

From the part of the particles selected for analysis, the size was measured and the obtained histogram of the particle distribution was evaluated at a measurement range of 0.1 to 300 μm, pre-installed on the sensor of the device. Part of the powder was analyzed with a measurement range in the range from 0.1 to 100 μm.

Micrographs of the powders were taken on an Axiovert 40MAT inverted reflective light microscope slide from Carl Zeiss. Germany The nitrogen content was determined on a Vario El cube elemental analyzer.

In FIG. 1 shows an integral curve and a histogram of the distribution of particles of the original stainless steel powder. On the integral curve, related to the left axis of the graph and designated as Q3 (x), each point of the curve shows which% of the particles have a size smaller than or equal to this one. This value is obtained by extrapolating the vertical lines of the histogram to the integral curve. The right axis of the histogram graph, designated as q3 (x), represents the percentage of particles with a given size. Particle sizes (in microns) in a logarithmic scale are located on the lower axis of the abscissa.

FIG. 1. Integral curve and histogram of particle size distribution of powder of steel PR0X18H10.

The amount of 97% of the particles corresponds to a size of 154.49 microns, and the average d is 70.28 microns. Symbol d [Pimenova N.V. Modern methods for studying the particle size distribution of powders. - Perm: Publishing house Perm. state tech. Univ., 2010. 51 pp.] for calculating the average value of particles means that the numerator takes the sum of the "diameters" of the particles in the fourth, and in the denominator - the sum of the "diameters" in the third degree. The obtained values most accurately reflect the volumetric (mass) average values of the particles, which differ greatly both in mass and in size. Fractional sizes are not of practical interest; they are displayed by computer programs of the device, by automatic calculations and are recorded on a printed sheet of measurement results.

Similar measurements were carried out after grinding in liquid nitrogen for 1 ÷ 4 hours. In FIG. 2 shows the curves taken on a laser analyzer after 4 hours of grinding with nitrogen.

FIG. 2. The histogram and the integral curve of the particle size distribution of steel after grinding for 4 hours in a liquid nitrogen environment.

The maximum 97% number of particles has a size of 99.22 microns, and the average value is 53.71 microns.

In FIG. Figure 3 shows the time dependences of the effect of liquid nitrogen during grinding on the size of the resulting stainless steel particles.

FIG. 3. The effect of grinding time on the particle size of stainless steel in a liquid nitrogen and argon environment. It can be seen that the curve when fixing the sizes of the maximum fraction differs from the curve of averaged sizes calculated by the mathematical formulas of the laser analyzer computer programs d. The maximum number of particles decreases in size by 1.5 times, and the average size value changes by 1.27 times.

In FIG. Figure 4 presents snapshots of PR0X18H10 steel powder before grinding.

FIG. 4. Micrographs of powders of steel PR0X18H10. It can be seen that the shape of the particles is mainly globular and varies both in size and in shape. There are elongated particles in the form of dumbbells, and at the edges of the globular particles are surrounded by small satellite balls.

After grinding the starting powders in a vibratory mill for 14 hours, micrographs are shown in FIG. 5.

FIG. 5. Steel powder PR0X18H10 after grinding in a vibration mill with the addition of ethyl alcohol for 14 hours. It is seen that the particles after grinding from the globules turned out to be flattened with high reflectivity of light from the granules. Their size even slightly increased across. Therefore, the grinding time in liquid nitrogen was reduced to 4 hours.

In FIG. Figure 6 shows micrographs of particles after grinding in liquid nitrogen with the addition of alcohol. FIG. 6. Microphotographs of the powder after grinding for 4 hours in liquid nitrogen. It can be seen that the particle size decreased significantly compared to the 14 hour grinding process without treating the contents of the mill with liquid nitrogen. Smooth, shiny surfaces are characteristic of both large and small particles. As the fraction of small particles increased, a histogram was taken with a reduced measurement range from 0.1 to 100 μm. The integral curve and the histogram are shown in FIG. 7.

FIG. 7. Integral curve and histogram of the fine fraction of particles after grinding for 6 hours with nitrogen. It can be seen that in the fraction of small particles three separate peaks are fixed, which together give an average size of 23.49 microns, and the maximum amount of 97% have a size of 65.24 microns. If we analyze the peaks of the histogram separately, then the maximum of the smallest peak corresponds to a size of ~ 11, and the maximum of the average peak corresponds to ~ 28 μm. The maximum particle sizes of the third peak are close to 65 μm. The number of particles smaller than 11 microns, ~ 36%, medium about 28%, and the largest about 36%.

The change in the size of particles measured in the range 0.1–100 μm, depending on the grinding time in nitrogen, is shown in FIG. 8.

FIG. 8. The effect of grinding time in a nitrogen medium on the particle size recorded in the measurement range of 0.1 ÷ 100 microns. It can be seen that in this graph, the effect of nitrogen on the decrease in the size of the initial powder appears after one hour of grinding, and then it changes little with increasing grinding time.

In the process of grinding in nitrogen, an assumption arose about the possible formation of nitride. Therefore, an elemental analysis for nitrogen content was carried out on a Vario El cube analyzer, showing a result of 0.01%.

Thus, grinding in a vibration mill in the presence of alcohol leads to flattening of the particles and an increase in their diameter. When grinding in the presence of liquid nitrogen, the number of smaller particles increases with a clear identification of three groups in the histogram by the size of small ones with maxima up to 11, medium 28 and large 65 microns. The effect of grinding is observed after the first hour of grinding and changes little over time. This is due to the release of heat during friction of grinding media and powder, which reduce the effect of cold brittleness. The positive point of using liquid nitrogen and ethyl alcohol is the absence of adhesion and agglomeration of plastic particles, leading to their enlargement.

Claims (2)

1. A method of grinding powder from a plastic material, including processing the source of iron-containing material in a mill, into which the crushed source of iron-containing material and working bodies made in the form of steel balls are loaded, characterized in that the source powder and steel balls with a diameter of 6- are pre-loaded into the vessel 22 mm in a ratio of 10: 1, respectively, is poured with liquid nitrogen with the addition of ethyl alcohol, placed in a chamber of a vibration mill, sealed, a vacuum of 1 kgf / cm ^{2 is created} , the chamber is filled with gas argon and carry out grinding for 1-4 hours, followed by analysis of particle size by known methods. 2. The method according to claim 1, characterized in that as the starting iron-containing material using austenitic chrome steel grade PR0X18H10.

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