SU908533A1 - Method of obtaining spherical metallic powder - Google Patents

Description

(B) METHOD FOR OBTAINING SPHERICAL AND IETALLIC

POWDER

The invention relates to "hard and super hard non-alloys and alloys" and will find application in the metallurgical industry for the preparation of a semi-finished product from spherical molten particles, which is used for the fabrication of shaped parts by powder metallurgy. There is a known method for producing spherical particles, according to which the molten metal continuously falls on the fixed plate, which is not wetted by the melt and decayed obliquely, which ensures droplets from it and their ingress into the cooling medium {1J. The disadvantage of the method is that it takes place in an oxidizing environment and leads to the formation of large particles. There is a method according to which the melt is crushed to a drip state, and then the formed granules are cooled in the presence of an inert liquid, which leads to the formation of a film of this liquid 2 around droplets. The disadvantages of this method are that it is unsuitable for obtaining spherical particles of refractory metals, as well as the fact that a solid film is formed on the particles from the inert liquid composition. Also known is the melting of core material with its further fragmentation. The end is heated by an electron beam in a vacuum chamber into which the inert gas is introduced. Separation of the droplets is carried out by ultrasonic melt oscillations. The division of these drops occurs when they fall on the aerated tip, then the drops get into the refrigerator-silicone oil 31. The disadvantages of this method are the complexity of the equipment, the need to use an inert gas, the formation of large particles. The closest to the prepositional is the method, according to which the end of the rod electrode in an inert medium is applied to the arc discharge and participates in orbital rotation. Due to the centrifugal forces, the separation of the particles takes place and when they are struck on the cooler, they cool down and at the same time their spherical or close to non-shape remains. The apparatus for carrying out this method is a chamber with a hole for the shaft. A hole is drilled inside the shaft at an angle to the longitudinal axis of the shaft through which the consumable rod electrode is supplied. The power sources ensure the rotation of the shaft about its axis, the rotation of the consumable electrode through the shaft into the chamber, the maintenance of the arc discharge between the electrodes Ts}. The disadvantages of this method are that the consumable electrode must rotate at high speed, the presence of a gas inert atmosphere. These drawbacks significantly affect the design of the device, its performance, product quality, and cost. When the end of the core is melted, a force proportional to the area of contact of the melt with the surface must be applied to separate the melt from the electrode surface. To detach the droplets with a diameter of 10 cm, it is necessary to rotate the melt in an orbit with a diameter of 10 cm with an angular velocity of 2000–2500 revolutions per minute. Such speeds are difficult to achieve given that it is necessary to ensure the supply of electricity to the rotating electrode, as a result of which an arc will be formed at the contact site, which will interfere with the normal process flow. Another obstacle is the movement of the electrode itself, as a result of which the arc is unstable, and in order to increase stability, the arc power must be increased in this case, which is prevented by the occurrence of switching effects. Therefore, reduce the diameter of the electrode, but this leads to low productivity and the formation of large drops. Small drops with a diameter of less than 10 cm on an industrial scale cannot be obtained by this method. On the other hand, if it is necessary to create a non-oxidizing medium, the structure is placed in an inert gas, which increases the cost of the process and it is inapplicable if it is necessary to obtain drops of fast-acid metals, since even in well-cleaned gases there are impurities of nitrogen and oxygen. The disadvantages of the method entail an increase in the complexity of the installation design, the presence of several rotating parts under stress, and the presence of several heat sources. The purpose of the invention is to obtain a fine powder and increase its quality. To achieve this goal, in the method of obtaining a spherical metal powder, the electrode is made in the form of a bundle of wires with a diameter of 10 -10 cm, and the melting is carried out at a medium pressure of 5 10 - torus arc discharge, burning in the mode of increasing portion of the current-voltage characteristic, drops are passed through the discharge area. In the proposed method, the area of contact between the melt and the electrode surface, which is determined by the cross-sectional area of the wire, is significantly reduced. For other constant forces, the force required to detach a drop from the electrode surface is proportional to the area of contact between the melt and the surface. Therefore, reducing the diameter of the wire, at the same time reducing the force required to detach a drop from the electrode. With the passage of a drop of the discharge area (arc column), it experiences an additional thermal effect, leading to a rapid boiling of the drop material, as a result of which its further division occurs. At the same time, an additional dewaxing of the drop occurs and this will occur more intensively, the longer the droplets are in the area of the arc column. Prolonged degassing drops during the passage of the arc column improves product quality, increasing the uniformity of the material, destroying cavities. The choice of the arc burning mode on the ascending portion of the current-voltage characteristic gives a clearly pronounced spot on the anode, moving at a speed of 0.5–2 cm / s, which

The rate of wire beam erosion and, thus, eliminating the possibility of uncontrolled arc transfer, which significantly increases the reliability of the device and the process.

The drawing shows a diagram of a variant of the device for implementing the method.

The device contains a beam 1 wire, an insulator sleeve 2, a potential-free tube 3, a firing electrode, an annular cathode 5, a load resistance 6, a constant current source 7, a resistance 8 in the ignition electrode circuit, a cooler S The method is as follows.

A bundle of wire 1 is inserted into the vacuum chamber and passed through the insulator sleeve 2 so that the wire bundle protrudes a mm below the end of the potential-free tube 3- Then the chamber is hermetically sealed and the system of vacuum pumps pumps out air to the residual pressure below the SW tor, after which they set fire to the electrode k, excite a stably burning arc between the cathode 5 and the anode-butt of beam 1 of the wire. By adjusting the load resistance 6 and the voltage on the DC source 7, the arc burning mode is set corresponding to the increasing portion of the current-voltage characteristic. Resistance 8 is much greater than resistance 6. In this case, the ends of the wires are melted to form spherical droplets on their surface. When the discharge is burned, an arc column will be formed, one end evenly distributed over the cathode surface, thanks to the inputs symmetrically connected to it, and the other end resting against the melting ends of the wires. After the wire is melted, a drop is formed at the end of the wire, which, with a certain mass, is detached and, due to the geometry of the device, is directed along the arc column and passes through the cathode ring 5. In the arc column, the droplet is subjected to intensive bombardment.

particles and explosively divided. The division of the drops occurs during their flight, after leaving the arc column. The main mass of the droplets is divided by a distance of 20 cm from the arc gap, therefore, the refrigerator 9 should be installed at a distance of 20-50 cm from the arc. As the refrigerator 9, a cooled bath filled with silicone oil can be used.

The arc discharge ignites in a vacuum chamber at a medium pressure of 6-10 torr. The cathode is a molybdenum ring, and the anode is a bundle of too wires with a diameter of 70. Idling voltage of a direct current source 110 V, arc current a. When the arc is burning, the wires are melted with droplet ejection. The average size of the formed droplets is 1.5-2.5 times the diameter of the wire, and the purity of the powder increases as its porosity decreases.

Claims (3)

1. US patent number 38889S6, cl. 2b4-5, pub. 1975. 2. For Japan No., class 13/7, published. 1975. 3.Patent UK M-, cl. C 7 X, pub. 1967i / US Patent number, class. publish 1971.