RU2381870C2 - Compression method of beads from powders of refractory metal and press mould for its compression - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy, particularly to receiving of beads principally from powders of tungsten, molybdenum. It can be used for manufacturing of rods, wire and bands for illumination engineering, electronic industry and instrument engineering. During compression of beads simultaneously with vertical clamping powder is cogged in horizontal direction with reduction in thickness, equal to reduction in thickness in vertical direction and with specific stress, equal to specific stress in vertical direction. Powder is filled into cavity of press mould, width of which is equal to (1.5-2)B₁, where B₁ - width of finished bead. Press mould contains horizontal punch, contacting by working surface to face surface of vertical punch, installed in casing of press mould with ability of horizontal displacement. Bottom plate of press mould contacts by face surface with working surface of sidewall, mounted in casing with ability of vertical displacement. Punches are spring-loaded relative to casing.

EFFECT: obtained beads allow uniform stress distribution and density by height and width.

2 cl, 3 dwg, 1 tbl

Description

The invention relates to powder metallurgy, in particular to the production of long billets (piles) of square and rectangular sections, mainly from tungsten and molybdenum powders, intended for the manufacture of rods, wire and ribbons for the lighting, electronics and instrumentation industries.

A known method of pressing from tungsten powders stubs [1], including filling the powder into the mold and its vertical compression.

The disadvantages of the method include the difficulty of filling the powder into a narrow blade of the mold, in which the length is 63-100 times the width of the cavity. This leads to the loss of expensive powder and the formation of air jams when filling it, which leads to the rejection of staffs and the inability to obtain high quality products with specified mechanical and physical properties during subsequent heat and plastic treatments, especially if tungsten powders have alloying additives.

A known mold for obtaining the previously described method [2]. The mold consists of a punch and a die. The matrix contains two cheeks, in one of which a cavity is made for filling the powder. The cheeks are connected by pins.

The disadvantages of this mold include the difficulty of extracting the finished staff from the mold. As a result of pressing under high pressure, after removing the pressing force in the head, an “elastic consequence” occurs, i.e. the size of the staff is increasing, and to the greatest extent along its length. But the increase in the length of the staff is prevented by the fixed end parts of the cavity of the mold cheek. Thus, the staple is jammed in the cheek cavity, micro- and even macrodefects appear in it, leading in many cases to its destruction in the extraction operation. The rejection of staffs for extraction operations exceeds 50% of suitable staffs.

The closest in technical essence and the achieved effect to the proposed method is a method of pressing powders from tungsten and molybdenum powders [3]. From molybdenum powders pressed square racks in sizes from 14 × 14 × 600 to 60 × 60 × 650 mm and rectangular racks in sizes 40 × 70 × 600 mm. This method allows you to expand the range of powders used refractory metals, as well as the size range of the manufactured beads. The method includes pressing the powder in a mold with a split die by vertical compression. This method in comparison with the above analogue facilitates the removal of the staff after pressing from the mold.

The main disadvantage of this method is the low quality of the obtained staffs. Very high compression ratios of the powders in the mold cavity, exceeding 300% and changing the powder volume 3-4 times in the same vertical direction, in the presence of large values of the reactive forces of friction of the powder on the cavity walls lead to heterogeneous stress distribution and uneven density of the stacks along the height , width and length. So, the upper layers of the staffs, which have a stress diagram close to full compression, are always denser than the lower layers, which have a stress-strain diagram less favorable for compaction. After the operation of heat treatment of sintering, such piles receive different shrinkage in height, width and length, as well as anisotropy of density, hardness and microhardness over sections and lengths. It is impossible to obtain products (rods, wire and tape) of high quality and long-term performance from such sintered pads by subsequent heat treatment (welding) and plastic deformation, especially from molybdenum and tungsten powders with additives.

The closest in technical essence and the achieved effect to the proposed one is a mold for pressing tungsten and molybdenum powders [4]. The mold contains a die and a punch. The matrix is made collapsible and contains two sidewalls (cheeks), the bottom plate, the end plates are connected by pins. The length of the sidewalls is 5-6 times their height and 25-30 times their width. The cross section of the punch corresponds to the cross section of the working cavity of the matrix, and the height of the punch is 3-4 times higher than the height of the finished staff.

After pressing, the mold matrix is disassembled into separate parts and the bead is released from contact with the sidewalls, end plates, as a result of which the beadwork is excluded from the operation of removing it from the cavity of the mold.

The disadvantage of this mold is the low quality of the obtained staff. The mold has only one vertical punch, which when moving in the cavity of the matrix, the width equal to the width of the punch, changes the volume of the powder 3-4 times. With such a very large deformation of the powder, the stack after pressing has an inhomogeneous stress state and uneven density both in cross section and in length. Further heat and plastic processing of such beads leads to the amisotropy of the mechanical and physical properties of the finished products. One of the reasons for the heterogeneity of stresses and uneven density of the beads is the large movement of the powder and punch in the cavity of the mold during pressing, it is 2-3 times higher than the height of the beads and leads to the appearance of large values of the reactive friction forces on the surfaces of the contact of the powder with the walls of the cavity, which and contribute to reducing stress heterogeneity and density unevenness.

The objective of the proposed solutions is to improve the quality of the obtained beads by applying an additional compressive force in the horizontal direction to the powder of refractory metals.

The problem is solved in the proposed method of pressing beads made of refractory metal powders, including vertical compression of the powder in the mold, according to the invention simultaneously with vertical compression, the powder is pressed in the horizontal direction with absolute compression equal to the absolute compression in the vertical direction, and with a specific force equal to specific force in the vertical direction, while the powder is poured into the cavity of the mold, the width of which is (1.5-2.0) B ₁ , where B ₁ is the width of the finished staff.

Horizontal compression leads to a stress state pattern close to the all-round compression pattern, which increases the uniformity of stress and density distribution over the height and width of the staff. In this case, the absolute reduction in height of the powder decreases by 1.5-2 times. All this improves the quality of the received staff.

To obtain a uniform density in height and width, the absolute compressions and the specific forces of pressing the powder in the vertical and horizontal directions should be equal.

The increase in the width of the mold cavity is more than 2B, where B is the width of the finished bead, as well as the decrease in this value less than 1.5V, due to the given dimensions and density of the bead.

The problem is solved in a mold for pressing pads made of refractory metal powders, which contains a vertical punch, sidewall and bottom plate, according to the invention it further comprises a horizontal punch in contact with the end surface of the vertical punch installed in the mold body with the possibility of horizontal movement, while the bottom plate is in contact with its end surface with the working surface of the sidewall, which is mounted in the housing with possibility of vertical movement, the punches are biased relative to the housing.

The fact that the inventive mold is additionally equipped with a horizontal punch will allow compressing the powder of refractory metals both in height and in width, which will create a favorable stress-strain state diagram, increase the density of the beads and its uniformity over its cross section. This helps to improve the quality of staffs. The possibility of horizontal compression in this mold will reduce the height of the mold, facilitate the filling of powder in it with a wider cavity, and reduce its loss.

The proposed method for pressing the beads and a mold for pressing them is illustrated in FIGS. 1-3, where FIG. 1 shows a cross section of a mold to obtain a square bead, FIG. 2 is the same at the end of pressing, in FIG. 3 shows a plan view of the mold.

The mold contains a vertical punch 1, a horizontal punch 2 in contact with the end surface of the vertical punch 1. The working cavity 3 of the mold is formed by vertical and horizontal punches 1, 2, sidewall 4, lower plate 5. The lower plate 5 is in horizontal contact with the end surface punch 2. Sidewall 4 is installed in the housing 6 with the possibility of vertical movement. The punch 1 through the sidewall 4 is spring loaded relative to the housing 6 by an elastic element 7 (for example, polyurethane buffer). The horizontal punch 2 is also spring-loaded by the elastic element 7 relative to the housing 6.

The mold works as follows.

Refractory metal powder is poured into the working cavity 3 of the mold. Turn on the drive (not shown). The vertical and horizontal punches 1, 2 begin to move, forming a stick of powder. When moving the vertical punch 1, it moves down the sidewall 4, compressing the elastic element 7.

When moving, the horizontal punch 2 shifts the horizontal punch 1 in the horizontal direction, compressing the elastic element 7. Shaping of the head takes place with the punches 1, 2, the lower plate 5 and the sidewall 4.

After the process of forming elastic elements 7, the punches 1, 2, sidewall 4 are returned to their original position and the head is freely removed from the mold.

According to the proposed method were made of tungsten racks of grade VA with a size of H ₁ × B ₁ × L ₁ = 15 × 15 × 600 mm. The powder was poured into the cavity of the mold, exceeding 1.5-2 times the width of the staff. The height of the mold cavity was 22.5-30 mm. For comparison, similar staffs were made by a known method [3].

Test data are summarized in table.

Table No. p / p Absolute compression, mm Specific pressing force, kg / mm ² Mold Width, mm Quality indicators Density, g / cm ³ Layout,% one. 15 = H ₁ = B ₁ twenty 30 = 2V ₁ fourteen No 2. 15 = H ₁ = B ₁ twenty 26.25 = 1.75V ₁ 13 No 3. 15 = H ₁ = B ₁ twenty 22.5 = 1.5V ₁ 12 No four. 15 = H ₁ = B ₁ twenty 18 = 1.2V ₁ 9 No 5. 15 = H ₁ = B ₁ twenty 33 = 2.2V ₁ 16 10% bundle Existing technology pressing [3] 6. 45 twenty fifteen 12 13% of the separation

As tests have shown, the density of the piles increased by 10-20%, the spacing decreased by 10% with a specific pressing pressure of 20 kg / mm ² .

This method and mold will find application in the electrical, electronic and other industries of new technology.

Information sources

1. Slitells C.J. Tungsten. M .: Metallurgizdat, 1958, p. 125-130.

2. Slitells C.J. Tungsten. M.: Metallurgizdat, 1958, p. 126 Fig. 30.

3. Zelikman A.N. Molybdenum. M.: Metallurgy, 1970, p. 315-318.

4. G.I.Abashin, G.M. Poghosyan. Technology for producing tungsten and molybdenum. M.: Metallurgizdat, 1960, p. 124.

Claims (2)

1. The method of pressing piles of powders of refractory metals, including vertical compression of the powder in the mold, characterized in that simultaneously with vertical compression, the powder is pressed in the horizontal direction with absolute compression equal to the absolute compression in the vertical direction and with a specific force equal to the specific force in the vertical direction, while the powder is poured into the cavity of the mold, the width of which is (1.5 ÷ 2) B ₁ , where B ₁ is the width of the finished staff. 2. A mold for pressing pads made of refractory metal powders containing a vertical punch, sidewall and bottom plate, characterized in that it further comprises a horizontal punch contacting the work surface with the end surface of the vertical punch installed in the mold body with the possibility of horizontal moving, while the bottom plate is in contact with its end surface with the working surface of the sidewall, which is mounted in the housing with the possibility of vertical movement I, and the punches are spring-loaded relative to the housing.

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