The Working Principle And Advantages Of Ultrasonic Spraying Equipment

Spraying has always been in our lives and has been used for a long time for a variety of purposes, including spraying decorative and protective coatings. Therefore, it is another tool available to materials scientists for thin film preparation. In spraying, nozzle size, spray shape, nozzle-to-substrate distance, spray speed, and heating of the substrate during spraying are parameters that can be controlled to achieve the best results.

Using ultrasonic nozzles, the spray solution can be homogenized, droplet size can be effectively controlled (nozzle frequency affects droplet size), and the amount of micro-mist can be dispensed, ensuring uniformity of composition and structure and precision of the resulting films and patterns. Material waste is kept to a minimum and there is less risk to the equipment operator.

01 How it works

The working principle of ultrasonic nozzles is to use ultrasonic transducers to convert high-frequency sound waves into mechanical energy, which is then converted into liquid, thereby generating standing waves. As the liquid leaves the atomizing surface of the nozzle, it breaks up into a fine mist of uniform micron-sized droplets. Unlike traditional nozzles that rely on pressure and high-speed motion to break up liquids into small particles. The ultrasonic nozzle uses liquid ultrasonic atomization, and the ultrasonic vibration energy is low. Liquid can be delivered to the spray head by gravity or low pressure liquid pumps for continuous or intermittent atomization.

02 Disadvantages of traditional spraying

Pressure nozzles were originally used for spraying. Pressure nozzles have poor durability when spraying, are prone to clogging, require slightly more complex systems (for generating pressure), a lot of material waste and environmental pollution, which are especially dangerous for those who spray.

Air atomization spraying has low conversion rate and high waste; the spraying time is a bit long due to low pressure; when the air circulation is not smooth, overspray or paint mist is prone to occur; because the final appearance is very smooth, the dust and air requirements on the surface are very high Strict; paint viscosity needs to be reduced by adding solvent or heat to achieve good appearance.

03The advantages of ultrasonic spraying

Unlike pressure nozzles, ultrasonic nozzles do not use high pressure to force liquid through small holes to create a spray. The liquid is fed through the center of the nozzle with a larger orifice without pressure and atomized due to ultrasonic vibrations in the nozzle. The nozzles of the liquid supply channels and orifices are relatively large, enabling a clog-free spray.

Spray stable

The ultrasonic spraying system can work with automated integrated equipment, and the spraying quality is stable, and the particle size is between 25μm and 50μm.

Higher uniformity

Compared with the traditional spraying technology, the spraying uniformity and controllability of the ultrasonic spraying system are greatly improved. The common defects on the surface of medical device coatings are eliminated, and technical support is provided for the preparation of excellent performance of the surface coatings of interventional medical devices.

Can be equipped with heated platform

Ultrasonic sprayers can be equipped with a heating platform for the substrate, such as a heating plate. Multiple independently controlled syringes (coating solution containers) can be used to process different materials, which is essential for multi-layer fabrication or forming different films on different parts of the substrate - if necessary, one of the syringes can contain a clean liquid, such as distilled water, to avoid contamination. Ultrasonic sprayers can be used in combination with dip coaters, in which case the dip coating module remains stationary while it can be moved.

Precise control of droplet distribution

Each ultrasonic nozzle operates at a specific resonance frequency, which determines the median size of the droplets. The droplet size is almost unchanged and can fall within the strict predicted droplet distribution mathematically. The size of the atomized particles is basically a function of the operating frequency, the higher the frequency, the smaller the atomized particles.

Anti-pollution

The nozzles are made from extremely high strength titanium alloys and other proprietary metals, making them particularly chemical resistant and have excellent acoustic properties. The electroactive element is contained within a sealed housing that protects the nozzle assembly from external contamination. The supply tube runs the entire length of the nozzle. The design of the nozzle ensures that the liquid only comes into contact with the titanium inside the nozzle.

04

Nozzle Performance Factors

liquid properties

Nearly all drop size data provided by nozzle manufacturers is based on water spray at 70°F (21°C) under laboratory conditions. The effect of liquid properties should be understood and considered when selecting nozzles for processes that are sensitive to droplet size.

Temperature

Liquid temperature changes do not directly affect nozzle performance, but can affect viscosity, surface tension and specific gravity, which in turn affect nozzle performance.

Proportion

Specific gravity is the ratio of the mass of a given volume of liquid to the mass of the same volume of water. In spraying, the main influence of the specific gravity of the liquid other than water is the capacity of the nozzle. All supplier-supplied nozzle performance data is based on water spray.

Viscosity

Dynamic viscosity is defined as the property of a liquid to resist changes in the shape or arrangement of its elements during flow. Liquid viscosity mainly affects spray pattern formation and droplet size. Compared to pure water, liquids with higher viscosities require a higher minimum pressure to start forming a spray pattern and produce a narrower spray angle.

Surface Tension

The surface tension of a liquid tends to assume the smallest possible dimension, acting as a membrane under tension. Any part of the surface of a liquid exerts tension on adjacent parts or other objects in contact with it. The force is in the plane of the surface and the force per unit length is the surface tension. The main effect of surface tension is on factors such as minimum working pressure, spray direction angle, and droplet size.

Nozzle wear

Nozzle wear is indicated by an increase in nozzle capacity and a change in spray pattern, where distribution (uniformity of spray pattern) worsens and increases droplet size. Selecting wear resistant materials of construction can extend nozzle life. Because many individual fluid nozzles are used to meter flow, worn nozzles can result in excessive fluid usage.