RU2547368C2 - Metal chip briquetting process - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metal forming and can used for fabrication of pellets for further processing by, for example, forging or ESR process. Chips are ground, compacted and subjected to sputter-ion sintering along with compressive pressure. Note here that that pressure is varied from 0.06 to 0.15 of breaking point of initial process material while the number of pulses is varied from 2 to 8. Duration of one pulse varies from 0.5 to 2.0 s while that between two individual pulses varies from 0.2 to 1.0 s, total duration of pulses making 1-16 s. Specific power supplied at sputter-ion sintering is defined by the formula E_sp= k · T_fus · C, where k is factor selected to make 0.6-0.95; T_fus is metal fusion point, K; C is specific heat capacity, kJ/(kg·K).

EFFECT: lower electric power input and higher strength.

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Description

The invention relates to the field of briquetting metal chips and can be used in the manufacture of briquettes for further processing, for example, by forging or electroslag (ESR) remelting.

Known methods for briquetting metal chips using electric current passing through a briquetted material.

For example, in the method [1], exposure to pulsed current with a density of up to 2000 kA / cm ² and a duration of 2 to 20 μs is used. The disadvantages of this method include significant local overheating of the material due to the high current density, leading to the formation of microdefects in the form of through holes, which impairs the mechanical characteristics of the resulting briquette.

The method [2] uses a superposition of direct current with a density of 0.4 kA / cm ² and alternating current with a density of 0.1 kA / cm ² and a frequency of 2 kHz for 60 s. The disadvantage of this method is the high residual porosity (up to 15-20)%, caused by insufficient intensity of energy supply.

As a prototype, a briquetting method was adopted, including shredding, pressing, furnace and electric discharge sintering (EDS) by passing a constant electric current with a density of 2-3 kA / cm ² through the briquette material for 20 to 30 s with a compressive pressure of 200- 300 MPa [3].

The disadvantages of the prototype include: high energy consumption of 1500-2000 kJ / kg and 7500-8000 kJ / kg for briquettes made of steel and titanium chips, respectively, and a low value of strength characteristics.

The technical result of the invention is the development of a method for briquetting metal chips, which reduces energy costs and increases the strength characteristics of the material.

The technical result is achieved due to the fact that in the method of briquetting metal chips, including grinding chips, pressing and electric sintering with simultaneous exposure to compressive pressure, according to the invention, the compressive pressure during pressing varies from 0.06 to 0.15 tensile strength of the starting briquetted material, the number of pulses varies from 2 to 8, the duration of one pulse from 0.5 to 2 s, the duration of the interval between two separate pulses from 0.2 to 1 duration and pulse, while the total duration of the pulses is from 1 to 16 s, and the specific energy supplied during electric discharge sintering is determined by the formula

E _yd = k · T _square · C,

where k is the coefficient selected in the range from 0.6 to 0.95;

T _PL - the melting temperature of the metal, K;

C is the specific heat, kJ / (kg · K).

In particular, the total energy for iron and titanium alloys varies between 430-690 kJ / kg and 590-940 kJ / kg, respectively.

The basis of the invention is the use of uneven temperature distribution over the volume of the porous material when a pulsed electric current is passed through it. The highest current density and, correspondingly, the amount of released energy falls on the pore boundaries. In particular, for pores of spherical shape, the specific energy release, according to theoretical calculations, is 4 times higher than the average volume of the briquette. Heating helps to increase the compactibility of the briquette by reducing the strength characteristics of the material and increasing the plastic characteristics.

The presence of compressive pressure leads to intense deformation of the material along the pore boundaries, to an increase in the contact area between the particles, to an increase in the strength and density of the briquette material, which is very important during its further melting.

The authors of the proposed technical solution established the optimal range of compressive pressure. The use of pressure below 0.06 of the ultimate strength does not lead to a noticeable deformation of the material. The use of pressure in excess of 0.15 of the ultimate strength leads to uneven deformation, the appearance of cracks and a decrease in strength characteristics.

The impact of a pulsed electric current reduces the total energy consumed by the remelting of the briquette.

The use of a pulse lasting more than 2 seconds leads to the redistribution of heat throughout the volume of the material and makes heating of the pore boundaries less effective.

Using a pulse of less than 0.5 seconds is not enough to heat the pore boundaries to the temperature of plastic deformation.

An energy supply of less than 0.6T _pl · C leads to insufficient heating of the boundary regions of fragments of particle metal waste (SMO).

An energy supply in excess of 0.95T _pl · C causes the appearance of layered cracks due to uneven deformation of the metal and leads to a decrease in strength characteristics and to energy overruns.

The number of pulses less than 2 is inefficient and insufficient to increase the strength characteristics of the material.

The use of more than 8 pulses leads to an excessive consumption of energy and to a decrease in strength characteristics due to the formation of microcracks.

The interval between pulses is less than 0.2 pulse duration causes the sample to overheat and energy overrun.

The interval between pulses, exceeding the duration of one pulse, does not provide heating of the boundaries between fragments of particles to the temperature of plastic deformation due to the dispersion of energy into the surrounding space.

The following are examples of the implementation of the proposed method of briquetting metal chips.

Samples of 55 × 10 × 10 mm in size, 5.5 cm in volume from SMO fragments crushed to a size of less than 3 mm were examined of three compositions of St3 GOST 380, copper M2 GOST 855 and titanium VT1-2 GOST 1987.

The crushed SMO fragments were pressed at a pressure of 600 MPa, 300 MPa, and 500 MPa, respectively, and sintered at a temperature of 1000 ° C in dissociated ammonia (steel and copper) and in a vacuum of 0.133 Pa (titanium).

The main characteristics of the briquette material are determined: density according to GOST 18898, strength according to GOST 1497, electrical resistivity (in accordance with the certified MVI technique No. 26107.17.038 / 2009).

The voltage required to supply the appropriate amount of energy was calculated by the formula:

, где: $$U=\sqrt{\frac{E_{\mathrm{at}d}\cdot \rho \cdot \frac{\iota }{s}\cdot d\cdot v}{n\cdot \tau }}$$

where:

U is the voltage, V,

E _beats - specific energy, kJ / kg,

ρ - resistivity, Ohm-m,

ι is the length of the sample, m,

s is the cross-sectional area of the sample, m ² ,

d is the density of the sample, kg / m ³ ,

v is the volume of the sample, m,

n is the number of pulses, pcs,

τ is the duration of one pulse, s.

The initial data for calculation by the formula are given in table 1.

Table 1 The results of examples of implementation of the invention are shown in tables No. 2,3,4. No. Material Source components Briquette p / p heat capacity, kJ / (kg · K) melting point, K strength, MPa density, kg / m ³ resistivity, μOhm · m one CT3 GOST 380 0.473 1808 360 6400 0.36 2 GOST 859 copper M2 0.389 1356 160 7300 0.056 3 Titanium VT1-2 GOST 19807 0.595 1933 340 3700 1,66

table 2 An example implementation of the invention (St 3 GOST 380) The characteristic features of the method and the results obtained The proposed method Comparison with prototype lower value average value upper value The characteristic features of the method Specific energy kJ / kg 513 662 812 2400 Specific energy variation coefficient - 0.6 0.78 0.95 - Voltage applied AT 1.89 0.88 0.59 0.82 Compressive pressure MPa 22 38 55 250 Number of pulses PC. 2 5 8 one Pulse duration from 0.5 1,2 2 25 Interval between pulses from 0.1 1,0 2 - Total pulse duration from one 6 16 25 Results obtained Material density kg / m ³ 7100 7300 7500 6800 Tensile strength MPa 280 340 330 180

Table 3 An example implementation of the invention (Copper M 2 GOST 859) The characteristic features of the method and the results obtained The proposed method Comparison with prototype lower value average value upper value The characteristic features of the method Specific energy kJ / kg 316 435 554 1880 Specific energy variation coefficient - 0.6 0.78 0.95 - Voltage applied AT 0.61 0.29 0.20 0.29 Compressive pressure MPa 96 60 24 200 Number of pulses PC 2 5 8 one Pulse duration from 0.5 one 2 5 Interval between pulses from 0.1 one 2 - Total pulse duration from I 6 16 25 Results obtained Material density kg / m ³ 8200 8400 8500 7600 Tensile strength MPa 128 147 144 86

Table 4 An example implementation of the invention (Titanium VT 1-2 GOST 19807) The characteristic features of the method and the results obtained The proposed method Comparison with prototype lower value average value upper value The characteristic features of the method Specific energy kJ / kg 690 851 1092 9280 Specific energy variation coefficient - 0.6 0.78 0.95 - Voltage applied AT 3,58 1,66 1.12 2,39 Compression pressure MPa twenty 34 51 300 Number of pulses PC. 2 5 8 one Pulse duration from 0.5 one 2 thirty Interval between pulses from 0.1 0.5 2 - Total
duration
momentum from one 5 16 thirty Results obtained Material density kg / m ³ 4000 4200 4300 3800 Tensile strength MPa 260 323 306 166

As follows from the data given in tables No. 2,3,4, the use of the parameters of the EMF claimed in the invention leads to improved properties of materials while reducing energy consumption, compared with the prototype, 3-3.5 times for STZ and 8 , 5-12.5 times for the alloy based on titanium VT1-2 and 3.4-5.4 for copper M2.

An increase in the parameters above the declared limits leads to an excessive consumption of energy and to obtain lower characteristics of the material of the briquettes.

A decrease in the parameters below the declared limits also leads to a decrease in the characteristics of the briquette material, a tendency to shedding and breakage, which is unacceptable for use with precision smelting methods.

The technical and economic effect is characterized by a reduction in energy consumption in the manufacture of briquettes.

Information sources

1. Yu.I. Golovin, V.M. Finkel, A.A. Sletkov. In the journal "Physics and Chemistry of Material Processing", No. 3, 1977, pp. 17-22.

2. A.I. Raichenko, M.Z. Kolchinskaya, D.A. Levin. In Sat “Powder Metallurgy”, Riga, Lat. Inti, 1975, p. 124-126.

3. V.P. Kurochkina, M.V. Romanovsky, V.P. Pupynin. In the book. "Basic construction materials." Proceedings of the All-Union Seminar on Sintered Structural Materials, pp. 45-50. Kiev, April 2005 - prototype.

Claims (1)

The method of briquetting metal chips, including grinding chips, pressing and electric sintering with simultaneous exposure to compressive pressure, characterized in that the compressive pressure during pressing varies from 0.06 to 0.15 tensile strength of the initial briquetted material, the number of pulses varies from 2 to 8, while the duration of one pulse is set from 0.5 to 2.0 s, the duration of the interval between two separate pulses is from 0.2 to 1.0 of the pulse duration, at m total duration of the pulse is set from 1 to 16 s, and the specific energy of the discharge sintering decal is determined by the formula E _sp = k · _Tm · C
where k is a coefficient selected in the range from 0.6 to 0.95,
T _PL - the melting point of the metal, K,
C is the specific heat, kJ / (kg · K).