SU1636124A1 - Method of producing articles from powders - Google Patents

Abstract

The invention relates to powder metallurgy and can be used for the manufacture of products from powders mainly on iron or copper base. The goal is to increase the density while ensuring uniform porosity distribution. To do this, mix the mixture of metal powders with the addition of 0.5 wt.% Zinc stearate, compress the briquettes in the first mold with a pressure of 450-550 MPa, extrude the briquette and place it in the second mold with a gap, subjected to plastic deformation by pressure 950- 1050 MPa, sintering and final heat treatment are carried out. The gap between the compact and the walls of the die is determined from the ratio 6 D {1-exp - (0.03-0.04)}, where D is the outer size of the compact. 1 tab. w fe

Description

The invention relates to powder metallurgy, can be used for the manufacture of products from powders mainly on iron or copper base and is especially effective in the manufacture of products with a developed lateral surface.

The aim of the invention is to increase the density while providing products with a uniform distribution of porosity.

Example. Mix the mixture of iron powders ПЖ2М: ПХ13М2 stainless steel, pencil graphite and 0.5 May.% Zinc stearate, with a pressure of 500 MPa, a gear wheel with a module of 1.25, an outer diameter of 19.8 mm and an internal diameter of 10.3 mm are pressed into blanks of the part. in the first mold, the gear blank after extrusion is placed in the second mold, where it is pressed with a pressure of 1000 MPa, then sintered in an atmosphere of ammonia at a temperature of 1250 ° C for 3 hours, carried out

cementation, quenching and tempering in standard mode.

Table 1 shows data on the technological modes of the proposed method and prototype.

These data show that high values of final density (97.7-98.3) with its uniform distribution are obtained with a gap size of 0.6 ... 0.8 mm and pressing pressures Pi 450 ... 550 MPa and P2 950 .. .1050 MPa (examples 1,2,3,6,7,10 and 11).

When the gap between the briquette and the walls of the second mold is changed to more than 0.6 mm (example 4) or less than 0.8 (example 5), low densities of the gear cores and surface layers are obtained.

A decrease in the pressing pressure in the second mold below 950 MPa (Example 12) leads to a decrease in the density of the blanks and to an increase in

ON CO O

to

uneven distribution of residual porosity.

An increase in the pressing pressure in the second mold above 1050 MPa (Example 13) does not affect the density of the products or the distribution of the residual porosity.

Thus, the optimal technological mode, which allows to obtain a product density of 98.3% with a uniform distribution of residual porosity, the relative energy consumption is 0.62, is the mode given in example 3, the gap size is 0.7 mm, the pressing pressure in the second press form 1000 MPa.

Compared with the prototype, in which the core density is 90.4%, the surface layer is 89.5%, the powder parts obtained by the proposed method have a relative density of 8% more and are characterized by a more uniform distribution of porosity.

The gap between the pressing and the walls of the second mold must be chosen such that when the degree of deformation is 4.5 ... 5.0%, the pressing touches the walls of the mold with its side surface. The gap between the pressing and the wall in the second mold must be calculated by the equation

5 0 {1-ehrko, 03-0,04)}, (1)

where D is the outer size of the compact.

If the gap between the briquette and the walls of the second mold is chosen greater than the value calculated by equation (1), then due to the destruction of the briquette in the process of its free draft and decompaction, the final density of the products decreases,

this increases the inhomogeneity of the distribution of residual porosity.

If the gap between the side surface of the briquette and the walls of the mold is chosen to be less than the value calculated by equation (1), then the contact between the briquette and the walls of the mold takes place when the degree of deformation of the briquette is less than Epr. As a result, the wedging of particles does not occur to the full extent due to their insufficient rotation during plastic deformation along the planes of maximum stresses, which ultimately leads to the achievement of reduced density values and preservation of uneven distribution of residual porosity, which is concentrated mainly in the surface layers .

Claims (1)

Claims method of obtaining products from powders mainly on iron or copper base, including two-stage pressing of a powder with intermediate extraction of a compact from one matrix and placing it into another with a gap and subsequent sintering, characterized in that in order to increase the density while ensuring uniform distribution of porosity , the first stage of pressing is carried out at a pressure of 450-550 MPa, the pressing in the second stage is carried out at a pressure of 950-1050 MPa, and the gap 6 between the pressing and the wall of the die is at w swarm stage of compression set ratios 5 D {1-exp - {0.03-0.04)}, where D is the outer diameter of the compact.