The atomization method is a powder preparation method in which a fast-moving fluid (atomization medium) impacts or otherwise breaks the metal or alloy liquid into fine droplets, and then condenses into a solid powder. The atomized powder particles not only have the same uniform chemical composition as the established molten alloy, but also due to the rapid solidification to refine the crystal structure and eliminate the macrosegregation of the second phase. The commonly used atomization medium is water or gas, and the corresponding ones are called water atomization and gas atomization. The fine metal powder prepared by water atomization has a high yield and economic efficiency, and has a fast-cooling rate, but the powder has a high oxygen content and irregular morphology, usually in flake shape. The powder prepared by gas atomization technology has fine particle size, high sphericity and low oxygen content, and has become the main method for producing high-performance spherical metal and alloy powders.
Vacuum smelting high-pressure gas atomization powder technology combines high-vacuum technology, high-temperature smelting technology, gas high-pressure and high-speed technology, is produced to meet the needs of the latest development of powder metallurgy, especially suitable for the production of high-quality active elements Alloy powder. The gas atomization pulverizing technology is a new rapid solidification technology. Due to the high cooling rate, the powder has the characteristics of refined grain, uniform composition and high solid solubility.
In addition to the above-mentioned advantages, the metal powder produced by vacuum melting and high-pressure gas atomization has the following three characteristics: ①pure powder, low oxygen content; ②high fine powder yield; ③high appearance sphericity. Structural materials or functional materials made of this kind of powder have many advantages in physical and chemical properties that conventional materials do not have.
The vacuum atomization powder making method is a new type of technology developed in the metal powder manufacturing industry in recent years. It has the advantages of not easily oxidizing materials, rapid quenching of metal powder, and high degree of automation. The specific process is that after the alloy (metal) is melted and refined in an induction furnace, the molten metal liquid is poured into the heat preservation pipe and into the draft tube and nozzle. At this time, the melt stream is atomized by the high-pressure gas stream. The atomized metal powder is solidified and settled in the atomization tower, and then falls into the powder collecting tank.
Atomization equipment, atomization gas and metal liquid flow are the three basic aspects of the gas atomization process. In the atomization equipment, the atomized gas injected is accelerated and interacts with the molten metal stream to form a flow field. In this flow field, the molten metal stream is broken and cooled and solidified, thereby obtaining a powder with certain characteristics. The parameters of atomization equipment include nozzle structure, catheter structure, catheter position, etc. Atomizing gas and its process parameters include gas properties, inlet pressure, air flow velocity, etc., while metal flow and its process parameters include metal flow Nature, superheat, liquid flow diameter, etc. Aerosolization achieves the purpose of adjusting the particle size, particle size distribution and microstructure of the powder by adjusting various parameters and the combination of various parameters.
The structure of gas atomized powder making device is composed of the following parts: intermediate frequency induction melting furnace, holding furnace, atomization system, atomization tank, dust collection system, air supply system, water cooling system, control system, etc.
At present, various researches on aerosolization mainly focus on two aspects. On the one hand, the structure parameters of the nozzle and the characteristics of the jet flow are studied. Its purpose is to obtain the relationship between the air flow field and the nozzle structure, so that the air flow reaches the maximum velocity at the nozzle outlet and the gas flow is the minimum, which provides a theoretical basis for the design and processing of the nozzle. On the other hand, the relationship between atomization process parameters and powder properties is studied. It aims to study the influence of atomization process parameters on powder characteristics and atomization efficiency on the basis of specific nozzles to optimize and guide powder production. In short, improving the productivity of fine powders and reducing gas consumption are leading the development direction of gas atomization technology.