Getting to know the atomization process

Getting to know the atomization process

Atomizing is one of the physical methods of powder production, which we will discuss below

In this method, the melt is converted into particles smaller than 150 microns. Metal powder such as iron, copper and its alloys, aluminum and its alloys, cobalt alloys, tin, stainless steel and tools and superalloys can be produced in this way.

Atomizing has different methods, which are:

   1- Atomizing with fluid (water or gas): In this method, water or gas hits a stream of molten metal through special pressurized nozzles. As a result, the melt freezes while breaking into small particles and metal powder is created.

Aqueous atomization method is suitable for mass production of powder with lower cost. The reason for that is the high cooling speed of the water. In this method, the shape of the powder is irregular and the amount of surface oxygen is high. But the dosage of the gas atomizing method and the cooling speed are low, so the cost of powder production is higher. In this method, the shape of the powder is almost round, and if neutral gas is used, the amount of surface oxygen is very low.

   2- Atomizing with centrifugal force: In these methods, centrifugal force is used to accelerate the melt flow and overcome its surface tension force. The amount of powder production in these methods is much less and more limited than the liquid atomization method. In this method, the cost of powder production is very high. The most important of these methods are:

       (1) Rotating electrode method: In this process, the end of a rotating rod is melted around its longitudinal axis, the molten droplets are centrifugally thrown around and solidified in a spherical shape. Melting may be done by means of an electric arc through a non-consumable tungsten electrode. The advantages of this method are the good surface quality of the particles, the spherical shape of the particles, the size distribution of the particles in a certain range and the possibility of producing powder of active metals.

       (2) Rotating disk method: In this method, a thin stream of melt is poured directly into the rotating plate, which is rotating at a high speed, and due to the rotation, it accelerates and is thrown into the surrounding environment in the form of molten droplets and freezes. be made Blowing a cooling gas or using water accelerates the solidification of the particles. In this method, the shape of the grains is spherical and their size depends on the disk speed.

      (3) Method of rotating disk in melt: In this method, the environment of a disk that has a toothed state (like a gear) is placed in contact with the surface of a molten metal. The molten metal sticks between the teeth, turns into a paste and the disk starts to move. Then, due to the rotational movement of the disk, it is separated from it and after traveling a distance, it freezes. In this method, the shape of the powder particles is irregular. Also, fine powder particles cannot be produced with this method.

       (4) Rotating cup method: In this method, the melt is poured into a cup-shaped container. This cup rotates at a high speed, the molten particles are mechanically thrown out from its edge, and are frozen by the cooling gas along the way.

- Atomizing in vacuum: in this method, the energy released due to the release of dissolved gas from solubility is used to disintegrate the melt. First, the melt is pressurized by a suitable gas. In this case, the gas (usually hydrogen) dissolves into the supersaturated state in the melt. Then the melt is transferred to the vacuum chamber by the refractory tube. By reducing the pressure of the gas, it is removed from the solubility and is removed from the melt in molecular form. In this case, the gas occupies a larger volume. In this way, the melt is disintegrated in a vacuum and turns into small particles. In this method, the powder particles are spherical. Also, due to the use of vacuum, the amount of surface oxygen is low.