Is parts drying hot air or something else? Part II

Abstract

~ nterior and exterior sections can hold fluid droplets in corners, blind holes, threads, depressions, cavities, etc. Inside sections of tubing can be very difficult to dry. I f hot a i r can d i rec t ly con tac t the l iquid, i t can evapora te the liquid and t ha t area. But i f hot air can ' t access corners , b l ind holes, etc., t hen hot a i r mus t h e a t the pa r t to a t e m p e r a t u r e where evaporat ion occurs. H e a t i n g the p a r t t akes t ime and adds cost, as well as ra i s ing concern about pa r t damage. I f there is a continuous downward pa th where centrifugal force can pull liquid from interior sections, the centrifugal dryer will likely be an excellent choice. For example, interior threads tha t are hor izonta l ly p r e sen t ed usua l ly can be dried while interior threads tha t are vertically presented cannot. Compressed air blowoff can only pa r t s if all surfaces can be impacted by the highvelocity air s t ream. How is dry? This factor is easier to evaluate. Don' t parts any more than you need to based on what will be done next with the parts. The reason is that drying investment and costs are a lmost exponential ly dependent on the degree of dryness needed. I f you aren' t sure how your parts have to be, assume dry to the touch is adequate. To the touch means remaining is in the range of about i to 5%. Parts drying choices include: • I f you are going to paint your par ts af ter cleaning, match the carr ier in the pa in t to the carr ier in the cleaning agent (water or solvent). • I f plating is the next step after cleaning, use an aqueous cleaning agent, rinse well, and don't worry about adding water to the plating bath. • I f the par ts are to be stored after drying, consider lett ing t hem air in s t o r a g e i f deposi t ion of airborne particles can be avoided. I f a very high level of dryness is needed ( -<25 ppm), the drying should be done in two steps: from wet down to ~1% moisture and from ~1% down to 2 5 ppm. The reason is the costs of polishing d ry ing are dependent on the amount ofmoisture being removed. I f your par ts are larger than a desk, you have a difficult p roblem--espec ia l ly if you cannot tolerate surface imperfections such as watermarks. A useful solution can be to use aqueous cleaning agents in a spray cabinet with the last spray rinse being with DI water. For large par t s tha t can tolerate surface imperfections, hot air is p robably the best recommendat ion . I f the na ture of the soil requires solvent cleaning, hot air drying can be used. However, there will be a VOC emission unless the solvent is VOC exempt. Cent r i fuga l d ryers are an excellent choice if your par ts are small enough to fit into a dryer. This technology has been in use for m a n y decades, but its use is relatively new to the cleaning industry. Par t s are loaded into a cylindrical mesh or plast ic basket . There may be discrete sections for holding indi-