Aqueous ultrasonic cleaners are environmentally benign, technically feasible alternative to solvent cleaning. The medium used for cleaning is predominantly water compounded with Alkali, Surfactants, Water conditioners, Corrosion inhibitors, Foam stabilizers etc.

Aqueous systems in many cases have replaced solvents without sacrificing cleaning performance. However due to the nature of solvent used, successful implementation of aqueous systems require a careful design effort necessitated due to the multistage operations involved like 1) Cleaning with Aqueous solution. 2) Removal of contaminated solution with water rinse. 3) Removal of water.

While solvent based cleaning primarily rely on chemical properties of the solvent, whereas aqueous cleaning systems rely on the mechanical properties like high-pressure spray, Ultrasonic agitation, dunking, etc. apart from the chemical properties of the aqueous medium. Therefore it is always recommended to have higher ultrasonic power per liter of volume. (Normally 16 to 20 watts per liter.)

Cleaning solution :
As good cleaning depends on the cleaning solution the right choice of cleaning solution cannot be over emphasized. Cleaning solution has to be compatible with the parts being cleaned, provide appropriate surfactants to enhance removal of specific contaminate, prevent foaming, prevent corrosion of parts etc.

Alkaline cleaners are the most viable substitutes for halogenated solvents for degreasing metals. Alkaline cleaners contain Alkyl Benzene sulphonates & other anionic surfactants as active ingredients in addition to inhibitors added to minimize the effect of alkaline cleaners on the metal surface. These cleaners react with contaminates such as oil, grease, to effect good cleaning. Though many alkaline cleaners are commercially available they need to be tested to ensure that they are effective for specific application.

TRANSONIC
Further as the aqueous solvents are water based, there may be an additional stage involved to wash the components of the aqueous solvents. In this case special care has to be taken in deigning the machine to ensure the surface liquid to be free from floating oil/grease.

Process steps involved in aqueous cleaning :
Wetting or pre-rinsing: Wetting or pre-rinsing is normally done at a higher temperature for loosening the contamination over the parts. This tank is coupled with an auxiliary tank for continuous skimming of floating particles.

Aqueous solvent dip with mechanical agitation : Though there are number of methods like, Air agitation, Dunking, Centrifuge circulation, Ultrasonic Vibrations etc. Out of all these Ultrasonic is suppose to be the best method as it penetrates the metal from all the angles uniformly, which are otherwise not physically accessible. Dunking mechanism by disturbing the solvent in the immediate vicinity of the component helps in exposing the component to the fresh solvent. The obstinacy of the contaminate may warranty repetition of the first or the second step.

Water rinse : Unlike solvent based cleaning where drying directly follows cleaning, aqueous cleaning requires a rinse step to remove residual chemicals and avoid re-deposition of contaminates. This is done either by spraying water or immersing the components in the water bath. Ultrasonic can also be used in water bath to effect better results. Rinsing is normally done in two stages. Soft water rinse followed by rinse with Demineralised water.

As soft water contains dissolved salts, only soft water followed by drying may leave behind these salts on the components leading to staining. This is unacceptable when the surface finish of the component is a critical factor as in the case of Brass components before lacquering. This is taken care by washing the components with Demineralised water after the soft water wash.

Drying : In solvent based cleaning application, a volatile cleaner evaporates very rapidly. Whereas water with its higher boiling point can take hours to evaporate at ambient temperature.& pressure. Inadequate removal of water can lead to a number of problems like corrosion, pitting of metal parts etc. Hence it is essential that water from the earlier washing process be removed thoroughly and expeditiously. Drying may take the form of hot air blowing, Centrifugal drying, Vacuum drying etc. The method of drying practiced will depend on the nature of the components, time available, cost of drying etc.

Drying is not an important factor in case of electroplating, Furatic Lacquering, & other wet process.

Recycling the aqueous solution can be done by deemulsication by using on line oil & grease separator. Demineralised water can be recycled by using Ion exchangers or can be used in soft water rinsing.

Features included in all compact systems :

• Ultrasonic to Stage 1 with filtration and solution heating
• Hydroflow undersurface jets to all wet stages
• Weir overflow to all wet stages
• PLC control panel with function display and process timers

Optional features :

• Pre-cleaning module: repeat of Stage 1 specification and/or Hydroflow with oil separator
• Vertical agitation to all wet stages
• Closed loop high purity demonized water treatment to Stage 3
• Double basket capacity hot air dryer
• Autocrats RKT Automation