RU2597443C1 - Method of producing steel powders electroerosion dispersion of wastes of ball bearing steel in water - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy. Method of producing steel powder of ball bearing steel comprises spark erosion dispersion in distilled water with voltage of 90-110 V, capacity of discharge capacitors of 60-75 mqF and pulse repetition frequency of 95-105 Hz.

EFFECT: production of spherical steel powder.

1 cl, 5 dwg, 2 ex

Description

The invention relates to powder metallurgy, in particular to the production of metal nanoscale powders. In industry, physical and physicochemical methods are used to obtain metal powders.

A known method of producing powder from grinding wastes containing water and oil of implementation [RU Patent for the invention No. 20144960, B22F9 / 04, B22F1 / 00.1994], which consists in the fact that the grinding wastes of steel SHX-15 are pre-washed with water, 1% - sulfuric acid solution and water; washing is carried out in a dense, pre-packed waste layer in a barrel with a perforated bottom when filtering the liquid through the waste layer under the influence of gravity. Dehydration of waste is carried out to a moisture content of 20 - 25% by weight. Waste is discharged onto a vibrating screen with 4 mm cells, dispersed during sifting, loaded onto mesh pallets 50 mm high and placed in a vacuum filter with a fan and an electric air heater for heating the air. Depending on the initial oil content in the waste, the concentration of sulfuric acid in the aqueous solution is changed.

The disadvantages of this method are the length of the sludge process, the need for significant areas under the sludge of waste in water, and the drying of the material with a residual moisture content of about 4%.

A known method of producing steel powder (Author's certificate No. 1510982, B22F9 / 04, 1989) from non-abrasive sludge, in which wet sludge with a content of cutting fluid in the amount of 20-30% is dried in closed boxes with openings in the feed-through conveyor furnace in the atmosphere of the products of decomposition of the coolant to achieve a residual moisture content of 0.1-0.2%. In the heat treatment process, an overpressure of non-oxidizing gas occurs inside the box, which contributes to the creation of a protective atmosphere during the drying of sludge. The efficiency of the process is increased due to the exclusion of special measures to create a reducing environment for sludge, refusal from the grinding operation and other simplification of the process.

The disadvantages of this method is the length of the drying process, drying sludge with a high liquid content (20-30%) requires high energy consumption.

The invention is aimed at solving the problem of obtaining steel powders from waste with low cost, low energy costs and environmental cleanliness of the process.

The problem is achieved by the method of electroerosive dispersion (EED).

The figure 1 presents the stages of obtaining steel powder.

The figure 2 presents a diagram of the EED process.

The figure 3 presents the results of x-ray microanalysis of steel powder.

The figure 4 presents the size distribution of microparticles of a sample of steel powder (working fluid water): 1 - integral curve; 2 - a histogram.

The figure 5 presents a micrograph of particles of steel powder.

The EED process is the destruction of conductive material as a result of local exposure to short-term electrical discharges between the electrodes [3]. In the discharge zone, under the influence of high temperatures, heating, melting and partial evaporation of the metal occur.

To obtain high temperature in a limited area of small volume, a large concentration of energy is required. Achieving this goal is carried out using pulsed voltage, and EED is carried out in a liquid medium that fills the gap between the electrodes, called the interelectrode gap or interelectrode gap.

Due to the fact that any smooth surface has its own macro- or microrelief, there will always be two points between two electrodes, the distance between which will be less than between other points of the electrode surfaces. When a current source (in this case, a pulsed one) is connected to the electrodes, a current flows between the electrodes and an electric field arises, the intensity of which between the nearby points of the electrodes will reach its maximum value. Under the influence of an electric field in the zone of the highest voltage, ionization of the working medium occurs with the formation of a channel with increased cross-country ability, i.e. disturbed electrical strength of the working environment. And between these two nearby points there is a breakdown of the interelectrode gap. Between the points at which the breakdown of the working medium occurred, a channel with high electrical conductivity is formed.

The cross section of the discharge channel is small, and its expansion is impeded by a magnetic field that compresses the channel. The working environment surrounding the discharge channel plays the same role. The length of the discharge channel and its diameter are very small and therefore the energy density in it reaches large values, and the temperature in this local volume is tens of thousands of degrees. At points where the discharge channel is supported by electrodes, the material is melted and vaporized from the surface of the electrodes. The working medium surrounding the discharge channel decomposes and evaporates under the influence of high temperatures. All these processes occur in very small periods of time and with the release of large energies, so they are dynamic explosive in nature.

Under the action of forces developing in the discharge channel, liquid material and vaporous material are ejected from the discharge zone into the working medium surrounding it and freeze in it with the formation of individual particles. Wells appear on the surface of the electrodes at the site of the current pulse, which are formed due to the removal of material by a pulsed discharge. Thus, electrical erosion of ball bearing steel waste is carried out, shown by the example of the action of a single pulse, with the formation of one erosion hole. After the termination of the pulse discharge, the voltage at the electrodes drops. The process of deionization of the working environment begins, i.e. neutralization of charged particles, and the electric strength of the working medium is restored. The interelectrode gap is prepared for the passage of the next discharge. If a pulse voltage is periodically supplied to the electrodes from the generator, the process will be repeated. In this case, each new pulse discharge will occur in the place where the distance between the electrodes is minimal. If the pause between pulsed discharges is sufficient to deionize the working medium, then the process will be repeated with the formation of new erosion holes on the surface, and this is the reason for the EED process.

Obtaining steel powder was carried out according to the scheme shown in figure 1, in three stages:

- 1 stage - preparation for the process of electroerosive dispersion;

- 2 stage - the process of electroerosive dispersion;

- Stage 3 - powder unloading from the reactor and its drying.

At the first stage, ball bearing steel wastes were sorted, washed, dried, degreased, and weighed. The reactor was filled with a working medium - distilled water, the waste was loaded into the reactor. Mounted electrodes. Mounted electrodes were connected to a generator. The necessary process parameters were set: pulse repetition rate, voltage at the electrodes, capacitor capacitance.

At the second stage - the stage of electroerosive dispersion included installation. The EED process is presented in figure 2. The pulse voltage of the generator 1 is applied to the electrodes 2 and 3 and then to the waste of ball-bearing steel 6 (waste ball-bearing steel also serves as the electrodes). When a voltage of a certain value is reached, an electrical breakdown of the working medium 5 takes place, located in the interelectrode space, with the formation of a discharge channel 7. Due to the high concentration of thermal energy, the material at the discharge point 8 melts and evaporates, the working medium evaporates and surrounds the discharge channel with gaseous decomposition products 9 ( gas bubble). As a result of the significant dynamic forces developing in the discharge channel and the gas bubble, droplets of molten material 4 are ejected outside the discharge zone into the working medium surrounding the electrodes and freeze in it, forming droplet-like particles of copper powder.

At the third stage, the powder is unloaded from the reactor, dried, weighed and then analyzed.

Powder materials obtained by ball bearing steel waste EDF can be effectively used in the manufacture and restoration of machine parts in various ways.

Example 1

In an experimental setup for the production of nanodispersed powders from conductive materials in distilled water, a ball-bearing steel waste was dispersed with a load mass of 3000 g. The following electrical parameters of the installation were used:

- pulse repetition rate 75 ... 85 Hz;

- voltage at the electrodes from 60 ... 80 V;

- the capacitance of the capacitors is 40 ... 55 uF.

These electrical parameters of the installation did not contribute to the process of powder formation of the dispersible material due to insufficient pulse energy. Therefore, at the next stage, the parameters were increased.

Example 2

In an experimental setup for the production of nanodispersed powders from conductive materials in distilled water, a ball bearing steel waste was dispersed with a load mass of 3070 g. The following electrical parameters of the installation were used:

- pulse repetition rate 95 ... 105 Hz;

- voltage at the electrodes from 90 ... 110 V;

- capacitance of capacitors 60 ... 75 microfarads.

The resulting steel powder was investigated by various methods. The phase composition of the electroerosive steel powder was studied using an EDAX energy dispersive X-ray analyzer built into a Nova NanoSEM 450 scanning electron microscope. As a result of studying the elemental and mineralogical composition of the sample, the results shown in Figure 3 were obtained. The main material in the samples is iron - 72 , 42%, oxygen - 12.96% and carbon - 9.02%.

Then, the resulting steel powder was analyzed using a Analysette 22 NanoTec laser particle size analyzer to determine the size distribution of the obtained powder particles (Figure 4). It was found that the average particle size is 26.25 μm, the arithmetic value is 26.245 μm, and the specific surface area is 23545.95 cm ² / cm ³ . The elongation coefficient (elongation) of 7.433 micron steel particles is 1.39, which indicates the spherical shape of the steel powder particles.

To study the shape and morphology of the obtained steel powders, photographs were taken on a Nova NanoSEM 450 scanning electron microscope. Based on Figure 5, the powder obtained by the EED method from ball bearing steel waste mainly consists of particles of regular spherical shape (or elliptical), with inclusions of particles of irregular shape (conglomerates) and fragmentation shape.

Information sources

1. Board N.Yu. New technology for processing solid and heavy alloy waste // Instrument. - 1996. No. 6 - S. 47-49.

2. Zalikman A.N. Obtaining hard alloys from regenerated WC-Co mixtures obtained from lumpy wastes by the zinc method // Non-ferrous metals. - 1993. No. 1 - S. 10.

3. Nemilov EF Electroerosive processing of materials. - L .: Engineering, Leningrad. Otdel, 1983. - 160 p.

Claims (1)

A method of producing steel powder from ball-bearing steel waste, characterized in that electroerosive dispersion of ball-bearing steel waste in distilled water is carried out at a voltage of 90-110 V at the electrodes, 60-75 μF capacitance of discharge capacitors and a pulse repetition rate of 95-105 Hz.

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