JPS58177403A - Method and device for manufacturing ceramic-free high purity metal powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for producing ceramic-free high-purity metal powders in which molten metal flowing freely from a melting vessel is atomized by a gas stream and subsequently solidified.

The method based on the above concept is also referred to as the 5-metal spray method.

In this case, many of the devices atomize the molten metal from induction furnaces with ceramic lining.

Providing ceramic tantalizers belongs to the state of the art. Both the ceramic lining of the induction furnace and the ceramic lining cause contamination of the forming powder with ceramic particles, thus significantly reducing the quality of the metal powder.

Therefore, to date centrifugal projection methods have been used to split molten metal in order to produce ceramic-free metal powders. In this case, the material used is an ingot whose ceramic content has been removed by remelting in a vacuum furnace, an electron beam furnace, or an electroslag remelter. Each ingot was newly melted and the dripping or flowing molten metal was guided onto a so-called centrifuge, on which the molten metal was divided into fine droplets under the action of centrifugal force (German Published Patent Application No. 25 28 999).

Although high-purity metal powder can be produced by such a method, the drawbacks are that the particle size spectrum is coarser and the processing capacity of the equipment is smaller than in the gas atomization method.

It is also already known to use an ingot as a consumable electrode and to generate an arc between this electrode and a rotating water-cooled P ram, which melts the ingot. In this method as well, the particle size spectrum is broad and the throughput of the equipment is significantly low.

The combination of electron beam melting and metal atomization is of no use since it is practically impossible to obtain a sufficiently high vacuum due to economical costs, since the atomizing gas is continuously supplied during metal atomization. The use of an electron beam requires a vacuum as good as possible.

It has become clear that the combination of metal atomization and plasma melting methods is not usable due to low efficiency and energy balance, requiring equipment with an uneconomically high plasma melting capacity. The object of the invention is to provide a method of the above concept which makes it possible to produce a powder free of ceramic particles, despite the atomization process and the high feed rate of molten metal required for it per unit time.

The purpose of this invention is to produce and hold molten metal in a melting vessel using an arc electrode using a known method, and to create a solidified metal j- in the melting vessel by controlling the heat balance of the melting vessel.
The solution is to allow the molten metal to flow out of the overflow of the melting vessel and atomize the area below the overflow.

Unlike electron beam melting, arc electrode melting can also be carried out at atmospheric pressure, and the melting process is not hindered by the supply of significant amounts of atomizing gas. By creating a solidified metal layer on the inner wall of the melting vessel, interaction between the molten metal and the melting vessel is effectively prevented. The solidified metal layer is often also referred to as the skull. Although this type of melting method is known in principle, until now it has only been used for the production of precision casting parts in vacuum.The thickness of the solidified metal layer is determined by the heat balance of the melting vessel, i.e. by the arc method It is related to the amount of heat and the amount of heat extracted by the cooling medium. It is therefore possible to control the thickness of the solidified metal layer by controlling the amount of heat supplied and extracted.

In this case, it is very important that the molten metal flows out of the overflow opening, ie from the highest point of the molten metal bath, without first coming into contact with the material of the melting vessel and is atomized below the overflow opening. Since the amount of heat supplied, which also determines the rate of dissolution, can be varied within a wide range, the dissolution capacity required for high throughput can be easily achieved by the method of the invention. Metal atomization is also a method that achieves high atomization rates. In this case, a large range of variations in the particle size spectrum is possible. The particle size spectrum becomes narrower or wider depending on the method and the ξ parameter, and the maximum of the Saraji particle size spectrum can be moved. Furthermore, favorable cooling properties are obtained with metal atomization resulting in significantly faster solidification of the molten metal.

Simply put, the present invention is a combination of the Surle melting method and the metal atomization method! be.

Furthermore, according to the invention, it is particularly advantageous to heat the overflow opening of the melting vessel for capacity adjustment by means of a plasma torch in such a way that the flow of molten metal is kept approximately constant. By this means two properties of the molten metal are controlled: viscosity and surface tension. Retention or enhanced flow of molten metal can be achieved by weak or strong heating.

This of course requires that a sufficient amount of molten metal be replenished;
In other words, it is assumed that the process is controlled by adjusting the arc heating. However, regardless of this, the amount of molten metal in the melting container becomes a buffer amount to some extent. This is because a kind of meniscus is formed above the highest point of the overflow opening, and its size is 1, which is related to the surface tension. If the overflow opening is heated strongly, this equilibrium is immediately influenced in the direction in which a large amount of molten metal flows out per unit time. Furthermore, there is no semi-solidified molten metal at the overflow port.

The invention further relates to a device for carrying out the method of the invention. The device consists of a melting and atomization chamber containing a melting vessel, a heating device, an atomization nozzle, a cooling section and a powder collection vessel.

To solve the same object, it is further provided according to the invention that the melting vessel is formed as a liquid-cooled melting vessel with an overflow opening, the heating device having an arc electrode placed above the melting vessel, and a gas overflowing atomizing nozzle. A device placed under the mouth is suggested.

As arc electrodes, permanent electrodes (graphite electrodes, water-cooled metal electrodes) or, especially in this method, so-called consumable electrodes made of the same metal as the metal powder to be produced are used! Such a device is furthermore advantageous due to the features of the invention, in which the melting and atomization chamber has a transverse projection in one part, which extends as a continuation in the direction of the overflow opening and which has a cooling section. and a powder collection container is disposed at the end of the protrusion.

A so-called closed arc furnace in which the melting process is carried out in an inert gas is generally a furnace having a structure in which the main axis runs vertically. The invention therefore consists in adding to such a furnace, which extends primarily in the vertical direction, a laterally or horizontally extending projection. This horizontal projection also has a cooling section for the metal powder, which solidifies relatively quickly due to the high gas pressure.

The metal powder spreads out in this cooling zone f almost horizontally, but in the form of a parabola with a very strong transverse component. The transverse component is important to the functioning of the device of the present invention. This construction feature eliminates the need to increase the construction height of the entire device. In this case, the known metal atomization method, in which the gas flowing out at high speed from a ring-slit nozzle injects metal particles almost downward, requires a so-called drop shaft, which significantly increases the structural height of such a device. You must be careful.

Next, embodiments of the apparatus of the present invention will be described with reference to the drawings.

The device consists of a dissolution and atomization chamber 1, which has an approximately cylindrical shaft 2 in its upper and middle parts. The chamber consists of a chamber upper part 3 and a chamber upper part 4, the two parts being connected to each other by a removable flange connection 5 for charging. The upper part of the chamber and the upper part of the chamber are formed with double walls as shown in the figure, and have a coolant inlet pipe 6 or 7 and a coolant outlet pipe 8.
or 9. The upper part of the chamber is fixed to a pivoting column (not shown), by means of which it can be pivoted laterally.

A t-pole rod passes through a slide seal 10 in the upper part of the chamber, and this rod is connected to a power supply device via a conductive wire 12.

A supporting device 13 is fastened to the lower end of the electrode rod 11, into which an electrode strip 14 is inserted in a positive and releasable manner. The electrode strip 14 is an electrode 1 designed as a consumable electrode.
5 by welding.

Below the electrode 15 there is a melting vessel 16 which is connected via a conductor 17 to the counter electrode of the power supply. The melting vessel is constructed as a double-walled liquid-cooled vessel and is provided on one side with an overflow opening 18 in the form of a so-called pouring nose. During the melting process, an arc is struck between the electrode 15 and the molten metal in the melting vessel 16, which keeps the molten metal in liquid form and continuously melts new material in the electrode 15. By controlling the heat balance of the melting vessel 16 as described above, a layer of solidified material called a skull is formed between the molten metal and any of the inner walls of the melting vessel. This layer (not shown) prevents contact between the molten metal and the melting vessel.

The pot flowing downward from the irrigation opening reaches an atomizing nozzle 19 which is connected via a conduit 20 to a compressed gas source, not shown.

In the absence of gas flow, the metal exiting from the overflow opening 18 flows away in front of the atomization nozzle 19. However, atomization nozzle 1
A suitable compressed gas from 9 atomizes the metal stream into very fine droplets, which are injected approximately horizontally to the right (in the drawing).

For this purpose, a transverse projection 21 is added in the lower region of the chamber upper part 4, the double wall of which is connected to the cooling system, and this projection 21
A cooling section 22 is formed. It is clear from the figure that the projection 21 follows approximately in the direction of the overflow opening 1B and in the flow direction of the gas exiting the atomization nozzle 19. The lower partition wall at the tip of the protrusion 21 is formed in the form of a horn 23 to which a powder collection container 25 is connected via a powder gate 24 to the lower outlet of the horn.

A plasma torch 26 is arranged on the chamber wall at the transition between the chamber upper part 4 and the lateral projection 21 and is directed toward the overflow opening 18, which is heated by a plasma flame 27. Things can happen.

[Brief explanation of the drawing]

The drawing is a longitudinal sectional view of the device of the invention.

Claims (1)

[Claims] 1. A method for producing ceramic-free high-purity metal powder in which molten metal freely flowing out of a melting vessel is atomized by a gas flow and then solidified, the molten metal being introduced into the melting vessel by an arc electrode. It is characterized by manufacturing and holding, creating a solidified metal layer in the melting container by controlling the heat balance of the melting container, causing the molten metal to flow out from the overflow port of the melting container, and atomizing it below the overflow port. A method for producing high-purity metal powder that does not contain ceramics. 2. The method according to claim 1, wherein the overflow port is heated with a plasma torch so as to maintain a constant flow of 111F metal to control the capacity. 3. In an apparatus for producing ceramic-free high-purity metal powder, which consists of a melting and atomization chamber including a melting vessel, a heating device, an atomization nozzle, a cooling section and a powder collection device, the melting vessel (16) is overflowing. It is configured as a liquid-cooled melting vessel with a flow opening (18) and a heating device is connected to the melting vessel (16).
To manufacture a high-purity metal that does not contain ceramics, characterized in that there is an arc electrode (15) 1 disposed above and an atomization nozzle (19) is disposed on the F side of the overflow port (18). Device. 4. The melting and atomization chamber (1) has a lateral protrusion (
21), which protrusion extends as a continuation in the direction of the overflow opening (18) and has a cooling section (22), at the end of which a powder collection container (25) is arranged. 3. The device according to claim 3. 5. Device according to claim 3, characterized in that a plasma torch (26) directed towards the overflow (18) is arranged in the melting and atomization chamber (1).