Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.8 Electronic industry 917
Figure 14.8.17. Closed-loop batch vapor degreasing process.
ards. Equipment designs and operating processes have been totally re-engineered to reduce
solvent losses to near zero.
Referring to Figure 14.8.17, a modern vapor defluxing process can be described as follows.
The cleaning equipment contains a cylindrical process chamber within which the
complete cleaning, rinsing and drying process takes place. The process chamber may include
spray manifolds and/or ultrasonic transducers (frequency of 40kHz) to provide the
mechanical energy necessary for advanced precision cleaning. Following the final vapor
rinse, remaining vapors are passed through a heat exchanger to condense the vapors to liquid,
which is returned to the solvent recovering device. The vacuum then extracts any remaining
solvent molecules, which are either exhausted from the machines directly or
passed through carbon absorption system in order to limit solvent emissions to extremely
low levels. The use of vacuum distillation for solvent recovery and vacuum drying assures
minimal solvent consumption. Distillable solvents with a flash point above 55°C like
Zestron � VD by Dr.O.K. Wack Chemie are suitable for such a process.
Many benefits provided by solvent cleaning are evident. Among these are:
• no process chemistry to mix or maintain,
• solvent is reclaimed automatically in the cleaning equipment,
• only few process variables to be managed,
• very easy and cost-effective to operate, and
• typically small footprint of the cleaning equipment.
14.8.5 CRITERIA FOR ASSESSMENT AND EVALUATION OF CLEANING
RESULTS
There are a number of different processes that can be customized to monitor the cleaning
process and cleaning results. Depending upon the existing requirements, simple “qualitative
tests” can be applied to produce a “Good” or “Poor” rating, or more elaborate quantita-