Principle And Introduction of Ultrasonic Metal Atomization

Ultrasonic atomization technology is an efficient and low-cost method for producing fine metal powders. The powders produced using this method have good sphericity, controllable particle size, and a narrow size distribution, making it a promising technology in the metal powder industry. Ultrasonic metal atomization is one of the applications of ultrasonic atomization technology, and its principles are similar to those of ultrasonic atomization.

Ultrasonic metal atomization involves the process of converting molten metal (liquid) into fine mist droplets in a gas phase. High-frequency ultrasound vibrations are applied to the surface of the molten metal, causing the droplets to separate and break up from the surface due to the peaks of the ultrasonic waves. As the frequency of the ultrasound gradually increases, the atomized droplets become finer. With continuous action of the ultrasonic vibrations, extremely fine droplets can be obtained.

Forms of Ultrasonic Metal Atomization

Ultrasonic metal atomization is the process of using high-frequency ultrasound vibrations to generate fine mist droplets from molten metal in a gas phase, which then solidify into metal powder after cooling.

The first form involves direct or indirect contact between the molten metal and the ultrasonic atomization head. The high-frequency electromagnetic waves generated by the generator are converted and amplified by the ultrasonic transducer and amplitude modulator, ultimately transferring the high-frequency vibrations to the molten metal flow. The molten metal is atomized under the high-frequency vibrations of the ultrasound.

The second form involves concentrating the energy generated by the high-frequency ultrasound vibrations in a small space and directly using the ultrasound to atomize the molten metal.

The third form combines ultrasound atomization with traditional atomization techniques to create a new hybrid atomization technology.

Ultrasonic Atomization Mechanism

There are two explanations for the mechanism of ultrasonic atomization: the surface tension wave theory and the microshock wave theory. A compromise viewpoint suggests that both theories play a role in ultrasonic atomization.

Surface Tension Wave Theory

Under the action of surface tension waves, when the amplitude of the vibrating liquid reaches a certain value, droplets fly out from the wave peak and form a mist. Surface tension waves generate droplets at the wave peaks, and the size of the droplets is proportional to the wavelength of the surface tension waves. Under the influence of surface tension waves, the liquid metal is atomized from the surface by the ultrasonic frequency and the vibrating surface of the droplets. In ultrasonic gas atomization, the molten metal flow is impacted and fragmented by multiple high-speed gas pulses.

Microshock Wave Theory

The microshock wave theory suggests that ultrasound atomization is related to cavitation, which refers to the generation of a large number of bubbles when high-frequency ultrasound vibrations act on molten metal. These bubbles continuously grow and collapse. During the closure of the bubbles, the vibration acting on the liquid transforms into work done on the bubbles. When the bubbles collapse, some of their energy is converted into heat and light radiation, and the remaining energy produces microshock wave radiation. This theory suggests that the cavitation caused by high-frequency ultrasound vibrations below the liquid surface ultimately leads to the formation of droplets.

Equipment Introduction

Ultrasound Generator

The ultrasound generator converts 220V AC into high-frequency electrical oscillations to provide sufficient electrical energy for the entire atomization equipment.

Ultrasound Transducer

The most common type is a sandwich-type piezoelectric ceramic transducer. Its function is to convert high-frequency electrical oscillation signals into mechanical vibrations, converting electrical energy into high-frequency vibrations.

Amplitude Modulator

The ultrasound amplitude modulator, also known as the ultrasound concentrator, amplifies the displacement and velocity of the mechanical vibration, concentrating the ultrasound energy in a smaller area.

Atomization Head

The ultrasound atomization head is the component that directly contacts the material and is generally made of an alloy. The melting point of the atomized metal is limited by the material of the atomization head, making this method more suitable for the preparation of medium- to low-melting-point metals and alloys. The transducer and amplitude modulator transmit high-frequency vibrations to the atomization head, which acts on the molten metal, transforming the molten metal into fine particles or powder.

Atomization Process

Ultrasound metal atomization is the process of using high-speed ultrasonic vibrations to impact and atomize molten metal or alloy flows, ultimately producing fine metal powder. Metal ultrasonic atomization involves the generator converting AC into high-frequency electromagnetic waves, which are then converted into high-frequency vibrations by the ultrasound transducer. The amplified vibrations are finally transmitted to the tool head (atomization head) using the amplitude modulator. When the ultrasound atomization head acts on the molten metal, the molten metal spreads into a liquid film under the high-frequency vibrations. When the ultrasonic amplitude reaches a certain level, the molten metal is shattered, and the fragmented droplets fly out from the vibrating surface, forming a mist.

The ultrasound metal atomization process can be roughly divided into two stages: fragmentation and condensation. The first stage involves breaking down the heated and melted metal or alloy, resulting in the production of metal droplets and affecting the size of the final metal powder. The second stage of condensation determines the formation of the final metal particles, directly influencing the shape of the metal powder, and mainly involves heat conduction.