Ultrasonic cleaning is largely used in large scale and mass production facilities for removal of grease, oil, scale, rust, polish residues, loose layers of soot and other contaminants from the surfaces of small parts of complex configuration prior to coating. As a rule, the objects chosen to be subjected to ultrasonic cleaning feature deaf and threaded holes, deep depressions, grooves, hard to reach areas, etc, in other words,
Ultrasonic cleaning of parts from oil and grease contamination is oftentimes carried out in an aqueous alkaline solution. The choice of formulation depends on the nature and properties of the contaminants and the material from which the manufactured parts.
These compositions in some given amount include caustic soda, soda ash, sodium silicate, trisodium phosphate, potassium potassium bichromate, surfactants and etc. In order to reduce the viscosity of contamination and better action of the solution, the bath temperature should be warmed up to 55-60°C. The solution is partially or completely heated through the absorption of the ultrasound energy. Bath can also have its own heating and cooling systems.
Purified items washed in hot water are blown with compressed air until complete drying. Steel parts, if required, are passivated in sodium nitrite. Ultrasonic cleaning is carried out by corrosion in acid solutions and in water. The compositions of acid solutions as diverse use them depending on the material of the workpiece. These solutions include various combinations and amounts of sulfuric, hydrochloric, nitric and hydrofluoric acids, sodium chloride, calcium fluoride, potassium fluoride, and other substances. Prior to ultrasonic cleaning, to soften the scale and oxides and for better penetration into the pores of the cavitation bubbles can be subjected to etching.
Paint, enamel and resin surfaces of the parts are removed in ultrasonic baths with organic solvents: fuel (gasoline, acetone, benzene) and nonflammable-tetrachloride, pentachloride and trichloride ethylene materials.Depending on the composition and properties of impurities ultrasonic cleaning lasts from several tens of seconds to several minutes.
Installations for ultrasonic cleaning consist of vibration sources, power supplies and bath or unit. The source of the vibrations are usually electromechanical, piezoelectric and magnetostrictive transducers. Power supplies converters are alternators of ultrasonic frequency. Some companies take advantage of innovative, patented technologies: thus, Hilsonic, one of the largest ultrasonic cleaner manufacturers, is known for its advanced protection mechanisms, installed in mid and high-end class equipment, which guarantees long years of trouble-free functioning and naturally a prolonged warranty.
Ultrasonic cleaning baths are typically made of stainless steel, with acid and alkali-resistant rubber coating. Ultrasound machines, in which all the operations are mechanized, processing the materials with cleaning products (washing, cleaning, passivation, secondary lavage) can also be used.
Ultrasonic method provides a high quality surface finish, its use reduces the consumption of chemical materials and the use of expensive organic solvents. The main disadvantages are: the need for large electrical capacity, operational complexity and high cost of electrical equipment and appliances; plus problems may occur when cleaning truly bulky items.