A. Current Practice: Chlorinated solvents like TCE, PCE etc. are the choice solvent used through the industries in their cleaning process. They are very popular due to their good solvency, lower heat of evaporation, high or absence of flash point, non-corrosive nature, relative stability & compatibility with metals & glass. However all chlorinated solvents are hazardous to human health & environment. Some chlorinated solvents are suspected to cause cancer (Carcinogenic) over prolong exposure. Being hazardous to health their usage has come under intense investigation from pollution control & health authorities & has already been banned by developed countries. This has lead to shift to alternative cleaning technology based on aqueous solvents.
Another factor driving the shift to aqueous cleaning is the environmental hazard caused by chlorinated solvents due to their Ozone depleting property. Due to this they have been targets of strong Government regulations throughout the world. It may be not long before similar legislation is introduced in India to phase out their usage.
B. AQUEOUS CLEANING TECHNOLOGY: THE ALTERNATIVE.
Aqueous 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.)
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 c