Cleaning everyone touches, seems to be extremely common and ordinary work, but for some special cleaning object is not an easy thing. Ultrasonic cavitation in the liquid due to its role in obtaining outstanding cleaning effect, in some of the cleaning difficulty and high quality requirements of the occasion has a unique position.
The transducer will ultrasonic frequency electrical energy into mechanical vibration and through the cleaning tank wall to the cleaning fluid contained in the tank radiation ultrasonic waves. Existing in the liquid micro-bubbles (known as cavitation nuclei) in the role of sound waves vibration, when the sound pressure or sound intensity reaches a certain value, the rapid growth of bubbles, and then suddenly closed. In the bubble closure, shock waves, around the bubble to produce 1012 ~ 1013Pa pressure and local high temperature, this physical phenomenon is called ultrasonic cavitation. The huge pressure generated by cavitation can destroy the insoluble dirt and make them dispersed in the solution. Steam-type cavitation on the dirt layer of direct repeated impact, on the one hand, to destroy the dirt and cleaning parts of the surface of the adsorption, on the other hand, will also cause fatigue damage to the dirt layer and detachment. Gas-type bubble vibration on the solid surface scrubbing, dirt layer once there are cracks to drill, bubbles can also be "drilled" into the cracks for vibration, so that the dirt layer off. Due to cavitation, the two liquids at the interface quickly dispersed and emulsified, when the solid particles are wrapped in oil and adhering to the surface of the cleaning parts, the oil is emulsified, the solid particles fall off by themselves. Ultrasonic propagation in the cleaning fluid will produce positive and negative alternating acoustic pressure, impact cleaning parts, and at the same time due to the nonlinear effect will produce acoustic flow and micro-acoustic flow, and ultrasonic cavitation in the solid and liquid interfaces will produce high-speed micro-jet, all of which can damage the dirt to remove or weaken the boundary layer of dirt to increase the mixing, diffusion, accelerate the dissolution of soluble dirt, strengthen the cleaning effect of the chemical cleaning agent. Visible from the citation, wherever the liquid can be dipped into, the presence of sound field are cleaning effect, and cleaning speed, high quality, especially for cleaning parts of the surface shape of complex, such as cavities, slits and other detailed cleaning, easy to realize the cleaning automation. On some occasions, you can use water instead of organic solvents for cleaning, or reduce the concentration of acid and alkali, for some damage to human health cleaning, such as cleaning radioactive dirt can be realized by remote control or automated cleaning. Ultrasonic cleaning also has its limitations, such as sound reflection of strong materials such as metal, ceramics and glass cleaning effect is good, while the sound absorption of large materials such as fabric, rubber and viscosity of the dirt cleaning effect is poor.
Ultrasonic cleaning began in the early 1950s of this century, with the advancement of technology applications are expanding. Currently has been widely used in the electronics industry, cleaning semiconductor devices, tube parts, printed circuits, relays, switches and filters, etc.; machinery industry for cleaning gears, bearings, oil pumps and oil nozzles coupling, fuel filters, valves and other mechanical parts, such as the engine and missile parts, such as watch parts; in the optics and medical equipment used to clean a variety of lenses, eyeglasses and frames, medical In the optical and medical equipment used to clean a variety of lenses, glasses and frames, medical glassware, syringes and surgical instruments, etc.; used in the textile industry to clean the spinneret, food bottles, caps, molds and carving crafts and so on.
The above examples of ultrasonic cleaning, generally with 20 ~ 40kHz low-frequency ultrasound, in recent years the United States developed a technology called Megasonic cleaning, that is, 1MHz high-frequency ultrasound to clean large-scale integrated circuits, can remove less than 1μm of dirt, the cleaning mechanism is not ultrasonic cavitation, but mainly particle velocity and acoustic flow. In the 90's the United States Crest claimed that they invented the 68kHz ultrasonic cleaning floppy disk drive, the efficiency is twice as high as using 40kHz.
China's ultrasonic cleaning in the following aspects of the more effective application:
1) mechanical parts before and after plating cleaning or spraying before cleaning, dismantling parts cleaning. Require a high degree of cleanliness such as oil pump oil nozzle coupling, bearing cleaning.
2)Printed circuit boards, silicon wafers, signal control relays for railroad systems, components, picture tubes and electro-vacuum devices and other cleaning.
3) microscopes, telescopes and other optical systems and sampling glass pieces of cleaning.
4)Medical instruments such as oral and surgical instruments cleaning, medicine bottles and some food bottles, dispensing room, biochemistry laboratory used in the cleaning of bottles and jars.
5)Cleaning of spinnerets, eyeglass frames, molds, engraved handicrafts, etc.
Recently developed ultrasonic cleaning of automobile chassis frame, with a special cleaning solution, will remove rust, oxide film and phosphating a cleaning process is completed, drying can be sprayed paint, to overcome the past artificial rubbing of rust, strong acid cleaning process features, both to improve labor conditions and reduce environmental pollution.
Ultrasonic cleaning equipment has two major categories: one is an aqueous solution as a cleaning agent equipment, such equipment, including ultrasonic frequency power source, ultrasonic transducer and the corresponding ultrasonic containers and electric heaters; one is a single-slot type, the other is a multi-tank (multi-station) continuous cleaning equipment, often with timing and automatic conveyor. Another type is to volatile organic solutions, such as trichloroethylene, trichloroethane and freon as a cleaning agent, this type of equipment in addition to the above components, but also need to have a condensation cycle, oil and water separation and filtration to recover the organic solution of additional equipment. At present, the main domestic and foreign production and development of a variety of specialized cleaning equipment, online production of complete sets of equipment. Also produces desktop, compact cleaning equipment, such as medical cleaner and small jewelry glasses home cleaner.
Ultrasonic frequency is generally 20 ~ 50kHz, small equipment, the electric power of only a few days, large-scale complete sets of equipment up to dozens of kilowatts to hundreds of kilowatts. Ultrasound transducer 50 ~ 60 years most of the magnetostrictive transducer, most of the current use of high-efficiency piezoelectric transducer; ultrasound frequency electric power source in the past with tube devices, has been eliminated and the use of solid-state devices, with the device produced by high efficiency and small size, the use of the combined structure, the power can be made very large for the expansion of high-power ultrasound applications to create a good condition.
The United States production of ultrasonic cleaning equipment, there are about 40 companies, the more famous about 10, Western European countries to produce cleaning equipment is mainly Britain, France, Germany and Switzerland and other countries. China's ultrasonic cleaning equipment, the main manufacturers of about 10, small-scale individual companies countless.
Foreign manufacturers pay much attention to the supply of chemical cleaning agents and cleaning process consulting services, which is the majority of domestic manufacturers are most lacking, the domestic manufacturers mainly consider the production of ultrasonic cleaning equipment, few specialized departments engaged in the development of cleaning agents to adapt to the needs of different cleaning objects. If the ultrasonic cleaning equipment and chemical cleaning agents will be a good combination of better results, because the main physical mechanism of ultrasonic cleaning is ultrasonic cavitation phenomenon, and cavitation strength in addition to ultrasonic power density, frequency and other related to the viscous coefficient of the cleaning fluid, surface tension, vapor pressure and temperature and other parameters. At present, from the perspective of environmental protection requirements to water-based cleaning agent instead of organic solvents for ultrasonic cleaning, and many domestic manufacturers have not yet been able to adapt to this challenge, but also the need for a variety of cooperative development.