RU2783096C1 - Method for production of metal and ceramic powders with given shape and particle size, using technology of plasma-arc spraying with water screen, and device for its implementation - Google Patents

Abstract

FIELD: powder metallurgy.

SUBSTANCE: invention relates to powder metallurgy, in particular to the production of metal or ceramic powders by plasma-arc spraying. Heating and spraying of material in the form of one or several bars are carried out in a chamber with a controlled atmosphere by a plasma-arc flow generated by a direct-acting plasma torch. Cooling with slowing down of sprayed particles are carried out by means of a cylindrical water screen formed by a waterflow continuously circulating and evenly flowing along walls of the spraying chamber. A device for spraying contains a spraying chamber with a branch pipe for separation of waste working gas and cooling water, a direct-acting plasma torch for formation of a plasma-arc flow, at least one device for supply of bar material to the plasma-arc torch, and a pump for provision of continuous circulation of the waterflow to form the cylindrical water screen.

EFFECT: obtainment of powders of a given chemical composition with a homogenous granulometric composition.

2 cl, 2 dwg

Description

The invention relates to a method and apparatus for producing powders of metals, alloys and their chemical compounds using plasma-arc spraying.

Known plasma-arc reactor [Patent RU 2708200 C1, IPC B22F 9/02, B22F 9/12, B22F 9/14, H05H 1/24, H05H 1/48 publ. 12/05/2019] to obtain a powder of metals, alloys and metal compounds from a wire, containing a housing, a first electrode and a second electrode placed at a distance from it with the possibility of forming a plasma arc between them, the first electrode being made with a channel, the outlet of which goes into space between the first and second electrodes, a means for introducing plasma-forming gas into the space between the first and second electrodes, a means for forming a plasma arc in the space between the first and second electrodes, and a means for feeding the wire through said channel outlet into the space between the first and second electrodes. The disadvantage of this invention is that there is no stabilization of the arc discharge for stable production of powders with a given shape and size of particles, and the device does not provide a cooling system for the resulting powder particles.

A device for producing metal powders by plasma spraying is known, operating according to the method described in the application for the invention [Patent 92011252, IPC B22F 9/06, B01J 2/00, publ. 04/20/1995]. The device contains a plasma torch for creating a plasma flow, which is used to heat and spray the material supplied to the plasma flow. The disadvantage of this invention is that the heating and spraying of the material is carried out in an open atmosphere, which leads to a change in the chemical composition of the sprayed material. In addition, for the absence of sintering and deformation of powder particles, a long span of powder particles (up to 10 meters or more) is required. Powder particles have a wide range of sizes and shapes.

A device for producing metal and ceramic powders is known, containing a water-cooled chamber with a controlled atmosphere, which houses a device for feeding bar material, one or more plasma torches located at an angle to the axis of supply of bar material, a powder collector installed in the lower part of the working chamber [ US patent 5707419, IPC B22F 9/22, 01/13/1998]. The disadvantage is that for the absence of adhesion and deformation of the particles, a large length of their span (up to 6 meters or more) is required, which leads to significant dimensions of the device and the required production volumes.

A known method for producing metal and ceramic powders, according to which the heating and spraying of the material in the form of one or more rods is carried out by a plasma-arc flow generated by a direct plasma torch, and the spraying is performed in a chamber with a controlled atmosphere [Patent US 6398125 B1, IPC B05B 1/24 , B05B 17/04, A62C 5/02, publ. 06/04/2002], which includes the following steps: (a) the process of heating the rod material in the device of the first stage and spraying it to supply a stream of superheated drops of liquid metal of fine fraction to the spray chamber of the second stage, which contains the supply of spray gas, consisting of at least measure, from a reactive and inert gas in a given proportion; (b) actuating the second stage atomization device by directing the atomizing gas into a chamber for supplying superheated metal liquid droplets into the stream, in order to further crush the metal liquid droplets into ultrafine particles and allow the reactive gas to pass through to react with the reactive alloying element to form a protective layer on the surface of the particles; and (c) cooling the particles to form ultrafine solid powders.

The disadvantage of this method is that in the known method, the cooling and deceleration of the sprayed particles occurs with the help of the oncoming movement of the powder particles of the gas flow, which does not allow them to be effectively cooled, and it is also difficult to control the distribution of gas flow parameters, which leads to uneven cooling and deceleration of the powder particles. , their chaotic movement, which complicates the production of powders with specified parameters.

Also known is a device for producing metal powder [Patent RU 2532215, IPC B22F 9/14, publ. 27.10.2014] according to which heating and spraying of the material in the form of one or more rods is carried out by a plasma flow generated by a plasma torch, and spraying is performed in a cooled chamber with a controlled atmosphere, characterized in that a circulating gas flow is created in the cooled chamber towards the movement of particles. A device for producing metal and ceramic powders, containing a working water-cooled chamber, in the upper part of which a plasma torch is installed for forming a plasma flow, one or more devices for feeding bar material into the plasma flow, a powder collector, characterized in that a parallel to the working chamber is installed connected to it using the upper and lower nozzles, a parallel branch, a fan is located in the lower nozzle to create a circulating gas flow towards the movement of particles, the upper bypass pipe is located below the point of intersection of the plasma flow with the bar material, and an additional collection of particles is located at the bottom of the parallel branch.

The disadvantage of this invention is that it does not provide a high cooling rate of the powder to obtain the required microstructure of the powder. In addition, powder particles have a large scatter in size and a low yield of powder of the required fraction for additive technologies, for example, from SV-08 wire, the scatter is in the range of 160-1600 μm, 45% of the main fraction with a size of 700 μm, and from 10Kh18N9T wire, the scatter is in the range 50-400 microns, the main fraction is represented by a powder with a particle size of 400 - 630 microns and is about 20% [Strukov N.N. Development of technology for plasma spraying of bar materials in a counterflow chamber: Cand. cand. tech. Sciences: 05.02.10: - defended 15.06.12 / Strukov Nikolai Nikolaevich. - Perm., 2012 - 126 p. - Bibliography: p. 93-99].

The technical problem to be solved of the proposed method for obtaining metal and ceramic powders with a given shape and size of particles, using the technology of plasma-arc spraying with a water screen and a device for its implementation, is to provide the possibility of obtaining metal and ceramic powders with a given shape and particle size of various chemical composition in the absence of particles sticking together, reduction of gas consumption, dimensions and weight of equipment used to obtain powders.

Under the given shape and size of particles, one should understand the provision of the necessary characteristics of metal and ceramic powder, for example, for additive technologies. The general requirement for metal and ceramic powders for additive technologies is the spherical shape of the particles and high uniformity of particle size distribution, particle sizes are usually in the range from 20 to 100 microns.

The technical problem to be solved in the method for producing metal and ceramic powders was solved due to the fact that the heating and spraying of the material in the form of one or more rods is carried out by a plasma-arc flow generated by a direct-acting plasma torch, and the spraying is performed in a chamber with a controlled atmosphere, characterized in that that the sprayed particles are cooled by means of a water screen located not only in the lower part of the spray chamber, but also flowing evenly from the walls, which provides more efficient cooling of all molten particles, forming the necessary microstructure of the powder.

The technical problem to be solved in the device for obtaining metal and ceramic powders was solved due to the fact that in a known device for obtaining metal powder, containing a spray chamber, in the upper part of which a direct-acting plasma torch is installed to form a plasma-arc flow, where as one of the electrodes bar material protrudes, one or more devices for feeding bar material into the plasma-arc flow, characterized in that a water screen is created in the spray chamber, which is not only in the lower part of the spray chamber, but also flows evenly from the walls forming a continuous cylindrical flow of water.

List of drawings

Figure 1 shows a functional diagram of a device for obtaining metal and ceramic powders with a given shape and particle size, using the technology of plasma-arc spraying with a water screen.

Figure 2 shows the appearance of the powder of steel 08G2S.

A device for obtaining metal and ceramic powders with a given shape and size of particles, using the technology of plasma-arc spraying with a water screen (figure 1) contains a spray chamber 1, in which a direct-acting plasma torch 2 is installed in its upper part to form a plasma-arc flow, device 3 (one or more) for supplying material in the form of a rod 4 in the direction transverse to the axis of the plasma-arc flow. Inside the spray chamber 1, a water screen 5 is created, with the help of running water flowing down evenly along the walls of the spray chamber 1. Water circulates with the help of a pump 6 through the nozzle 7, where the water heated during the spraying process and the exhaust gases are separated, which are removed using a fan 8. Purification and recovery of exhaust gases takes place in the regenerator 9. To compensate for gas losses, a cylinder 10 with gas is used. The water is cooled in the heat exchanger 11 with running water or in a chiller. A collector of powder particles 12 is installed in the lower part of the spray chamber 1. The movement of the obtained particles in the spray chamber 1 is shown by dashed lines 13.

A distinctive feature of this device is the use of cooling of molten particles obtained by the interaction of a plasma-arc flow of a direct-acting plasma torch 2 on a rod 4, which is one of the electrodes, a water screen 5, while the water screen 5 is located not only in the lower part of the spray chamber 1, but also flows evenly from the walls, forming a cylindrical water screen 5, the lower part of the spray chamber is narrowed to collect the powder in the collector of powder particles 12, also in the spray chamber 1 there is a branch pipe 7 for separating the exhaust working gas and cooling water circulating in a closed circuit.

The presence of a cylindrical water screen 5 in the spray chamber 1 increases the cooling efficiency of all sprayed particles, ensures their deceleration and prevents their deformation upon impact with the walls of the spray chamber 1. Increasing the cooling rate of the particles and their deceleration by the cylindrical water screen 5 makes it possible to reduce the dimensions (length) of the chamber , reduce the required production volume, reduce the cost of equipment.

Consider the proposed method for obtaining metal and ceramic powders with a given shape and size of particles, using the technology of plasma-arc spraying with a water screen and a device for its implementation shown in Fig. 1 in work.

Air is removed from the working spray chamber 1 by blowing with plasma-forming gas through the switched off direct-acting plasma torch 2, which is supplied from the cylinder 10, the fan 8 is turned on to start the gas circulation. The pump 6 is turned on, the water begins to circulate, creating a water screen 5 for effective cooling of the sprayed particles and obtaining the necessary fine-grained structure. The direct action plasma torch 2 is switched on, generating a plasma arc, the device 3 (one or more) is switched on for supplying material in the form of a rod 4, the rod material is melted by the plasma-arc flow and sprayed in the form of spherical particles of a given size. The atomized powder particles move along the working spray chamber 1 (the direction of movement is shown by dashed lines 13). Water screen 5 slows down and cools the sprayed powder particles. The cooled powder particles are collected in the powder particle collector 12. There is no deformation and sintering of the powder particles.

An example of a specific implementation.

According to the proposed scheme, an installation with a working chamber with a diameter of 200 mm and a length of 1000 mm was made. The camera is installed vertically. The plasma torch installed in the spraying chamber ensures operation in the arc current range of 20-150 A. The gap between the nozzle exit and the wire is 2-5 mm.

The installation received powders of spherical shape (figure 2) from steel 08G2S. The main granulometric composition (more than 50%) of metal and ceramic powder is 20-100 microns. The spread of particles is in the range of 5-200 µm. Productivity of installation: 1-5 kg/hour.

Thus, the claimed invention provides for the production of metal and ceramic powders with a given shape and particle size of a given chemical composition in the absence of particle sticking while reducing the size and weight of the equipment used to obtain them.

Claims (2)

1. A method for producing metal and ceramic powders with a given shape and particle size by plasma-arc spraying with a water screen, including heating and spraying the material in the form of at least one rod with a plasma-arc flow generated by a direct-acting plasma torch in a chamber with a controlled atmosphere and cooling, characterized in that cooling with braking of the atomized particles is carried out by means of a cylindrical water screen formed by a water flow continuously circulating and evenly flowing down the walls of the atomization chamber. 2. A device for obtaining metal and ceramic powders with a given shape and particle size by the method according to claim 1, containing a spray chamber, in the upper part of which a direct-acting plasma torch is installed to form a plasma-arc flow, and at least one device for feeding bar material, acting as an electrode into the plasma-arc flow, characterized in that it contains a pump to ensure continuous circulation of the water flow with the formation of a cylindrical water screen, and a branch pipe is made in the spray chamber to separate the exhaust working gas and cooling water.

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