Precision Cleaning, Passivation,
& Finishing Systems
Desiccants are used to absorb the water found in humid conditions to reduce or eliminate condensation. It can also be added directly to liquids to absorb the water content from the fluid. We are used to seeing the small white bags of desiccant found in packaging for everything from shoes to electronic equipment. Most of this desiccant is silica – typically in gel form. Other common substances used as desiccants are activated charcoal and calcium chloride.
The desiccant used in vapor degreasers is 3 Angstrom Molecular Sieve, small pellets of zeolite clay. Like all desiccants, the zeolite clay adsorbs water from the solvent, and may be reused by baking it dry. Desiccants are most often used in a vapor degreaser if the solvent contains an alcohol. This is often the case with solvents used for defluxing processes on soldered boards and leads. Water found in the separator extracts the alcohol from the solvent and in turn the water and alcohol is absorbed by the zeolite clay. If a degreaser is operated in a very humid environment a desiccant may be need to effectively remove the water from the solvent.
If you’ve ever been wearing glasses as you walked into an air-conditioned building on a hot summer day, you already have a good understanding of part of the Vapor Degreaser process works. (For those in colder northern climates, walking outside while wearing glasses on a cold winter day is an even better example)
A vapor degreaser has two tanks (sumps) of solvent inside. One boils the solvent (boil sump) which creates a vapor or mist of the solvent. The second sump (ultrasonic sump) is heated but not to the boiling point and is used as the second cleaning stage. The vapor degreaser also has bands of cooling coils inside just above the level of the sumps. These coils cause the vapor to return to a liquid state and fall back into the sump. The effect is like small “clouds” of the solvent are formed between the top of the sumps and the cooling tubes.
As parts at room temperature are lowered through the cooling area into the vapor, the vapor from the boil sump condenses on the parts just like moisture in the air does on your glasses in the examples above. This condensation contains the solvent that dissolves the oils on your parts, and the beading action creates droplets which run across the surfaces of the parts and fall back into the boil sump. The parts are then moved to the ultrasonic sump which contains heated but non-boiling solvent. This allows the parts to be lowered into the sump so that any blind holes or internal features are also thoroughly exposed to the solvent.
Finally parts are raised into the cooling coil area to allow the solvent to quickly dry and and then raised through a second layer of freeboard coils near the very top of the vapor degreaser that insure complete drying and the recapture of the solvent from the parts.