RU2096131C1 - Method for hot pressing of conducting powders - Google Patents

Abstract

FIELD: powder metallurgy. SUBSTANCE: prior to be caked, powder is compacted under pressure up to 25 MPa with zero current, whereupon, after pressure is reduced to 5-10 MPa, pulse alternate sinusoidal current with frequency 45-65 Hz is passed first with density 3.2-6.8 A/sq.mm for 10-60 s and then with density 10.6-15.4 A/sq.mm for 5-110 s. Hot pressing is carried out in apparatus wherein punchers also function as current contacts, casing is reinforced by steel bandage, and there is a separating layer between punchers and powder being caked. EFFECT: reduced electrical and mechanical power of equipment.

Description

 The invention relates to the field of powder metallurgy, in particular to the production of products from powder materials by their simultaneous compaction and sintering by passing an electric current.

A known method of pressing metal powders with simultaneous exposure to pulsed current of various densities at the preliminary and final stages of pressing (1). The current density is 100 1000 A / mm ² , the pulse duration is from 10 ^-2 to 10 ^-5 s, and the pulse frequency is 20 25 Hz; pressure reaches 580 600 MPa.

 However, the resulting semi-finished product requires sintering with a protective atmosphere for 2 hours.

 The closest in technical essence and the achieved result to the proposed one is a method of manufacturing sintered products, which includes simultaneous compaction and sintering by a pulsed single-half current with a force of 7000 8000 A, a frequency of 50 60 Hz and a voltage of 0.5 2.0 V (2).

 The present invention allows to solve the problem of reducing the electrical and mechanical power of the equipment, which allows the use of less powerful installations, or with the same power of the equipment to increase the size of the powder products without compromising the quality of sintering. In the process of testing the proposed method, the density of the products was 96 100% of the density of the compact material.

The solution to this problem is ensured by the fact that, in contrast to the prototype, before sintering, the powder is compacted with a pressure of up to 25 MPa without current, and then, reducing the pressure to 5 10 MPa, an alternating sinusoidal current with a frequency of 45 65 Hz of various densities is passed: first with a density of 3.2 6, 8 A / mm ² for 10 80 s, then with a density of 10.6 15.4 A / mm ² for 5 110 s.

In the described invention, the degree of pre-compaction is only 15 to 20%, which differs significantly from the values known from the prior art. Compared with the prototype method, the process of simultaneous compaction and sintering is carried out in two stages with different current density on each of them, while in the case of obtaining powder products with a cross-sectional area of 150 mm ² , for example, the current strength decreases by 3 4 times, and pressure is 7 to 20 times relatively known.

EXAMPLE 1 A layer of powder containing graphite and alumina, which acts as a separating spacer, is poured onto a lower punch made of bronze BRAJ 9 4 located in a case made of beryllium oxide. Copper powder is poured on top in the amount necessary to obtain the product, and again separating the powder. The upper punch is installed and pressed at a pressure of 20 MPa using petrolatum with molybdenum disulfide as a lubricant. Then the outer ends of the punch are fixed in the clamps of the welding machine MCP-50 with a capacity of 50 kW. At a pressure of 5 MPa, a current of 45 Hz with a density of 3.2 A / mm ^{2 is} passed for 40 s and then for 5 with a density of 15.4 A / mm ² . The result is a cylindrical product with a density of 8.5 g / cm ³ , i.e. 96% density of compact material.

Example 2. The lateral surfaces of the housing and punches lubricated with technical petroleum jelly with molybdenum disulfide. A powder interlayer consisting of graphite and alumina is poured onto a lower punch made of BrA5 alloy, located in a housing made of zirconium oxide. Then carefully mixed powders of copper (79.8 wt.) And green silicon carbide (20.2 wt.) Are poured into the body. Again the powder layer is poured, the upper punch is installed and pressed at a pressure of 25 MPa. The outer ends of the punches are clamped in an MCP-50 machine and a current with a density of 4.1 A / mm ^{2 is} passed for 80 s at a pressure of 8 MPa, and then for 10 s with a density of 12.1 A / mm ² , the current frequency is 65 Hz. As a result, the sintered material has a 100% degree of compaction.

Example 3. After lubricating the inner surface of the casing and the outer surface of the punches with petroleum jelly with the addition of molybdenum disulfide, insert the lower punch of copper into the casing of beryllium oxide. Then a powder layer is poured onto the lower punch. BrA9ZH3R4 bronze powder and a layer are again loaded on top. Having installed the upper punch, it is pressed at a pressure of 25 MPa and the assembly is transferred to the MCP-50 welding machine, where at a pressure of 10 MPa a current of 53 Hz is transmitted with a density of 6.8 A / mm ² 10 s and a density of 10.6 A / mm ² 110 s . As a result, the density of the sintered product is 98% of the density of the compact material.

 Using the selected parameters of simultaneous compaction and sintering provides high-quality products with a significant decrease in current density and pressure in comparison with the known ones.

Claims (1)

A method of hot pressing electrically conductive powders, including sintering by directly passing a pulse current through the powder while applying pressure to it, characterized in that before sintering, the powder is compacted with pressure up to 25 MPa without passing current, then the pressure is reduced to 5 10 MPa and sintering while applying pressure 5 10 MPa is carried out by an alternating sinusoidal current with a frequency of 45 65 Hz in two stages: first, with a current density of 3.2 6.8 A / mm ² for 10 80 s, then with a density of 10.6 15.4 A / mm ² for 5 110 .