Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 108 of 707

in/out of holes. Parts in many instances are cleaned in baskets (see Figs. 5 and 6). But unlike spray or turbulation systems, parts in baskets do not mask themselves, allow- ing full baskets of components to be effectively cleaned due to the agitation movement. The mechanical action of agitation removes oils and greases, while loosening and removing metallic fines and chips. One hundred percent immer- sion of baskets in and out of solution is much more effective than partial immersion. Adding rotation to the agitation further enhances this capability by allowing all holes, recesses, and cavities to fill and drain effectively with the aqueous chemistries. With the vertical agitation concept, the amount of agitation can be adjusted for each tank in a process. With the advent of programmable controllers, systems can be programmed to agitate and rotate baskets under solution while occa- sionally raising the baskets out of solution to drain, then totally immersing the baskets in solution again. Baskets can effectively rotate out of solution for complete draining prior to transfer to subsequent tanks. This drain cycle great- ly reduces chemistry drag over and prolongs rinse tank clarity. Vertical agitation systems are also very effective for chip removal, as turbulation can also be added to vertical agitation systems. The turbulation in vertical agitation systems serves a second purpose. The turbulation keeps chips and fines in suspension in the solu- tion until they can be evacuated by high-volume pumps and filters. The vertical agitation movement also makes this concept readily adaptable for use with ultrasonics. The agitation can be programmed to move slowly up and down while moving through a focused ultrasonic field. This slow up-and-down movement exposes the entire workload to the full power of the ultrasonic scrub- bing action, allowing full cavitation, generated both by ultrasonics and agitation, to effectively engage components. In agitation systems, ultrasonics are side- wall, bulkhead mounted. This will guarantee that the parts will pass through the high-concentration ultrasonic field. Slow rotation through the ultrasonic field also ensures 100% exposure, allowing blind holes to be effectively filled with solu- tion and engaged with the ultrasonic energy. Drying Good dryer design employs louvers that will direct the air flow directly against the components and baskets, if they are employed. The dryer design should contain an internal duct system that directs the air flow from multiple directions against the parts or baskets. This design will ensure uniform exposure of all sur- faces, edges, and recesses of components to this air flow. As with interaction of chemistry with components, time is a variable in the dry- ing process and end users should be aware that shortening dryer time to save space can be detrimental and compromise the effectiveness of dryer design. On belt- or monorail-type systems, air knives can be used prior to drying to remove puddled water from recesses and cavities. Air knives are important when parts cannot rotate, either prior to or in the drying process. Air knives on belt or monorail systems can also be used between wash and rinse stages to minimize cross-tank contamination. This will effectively remove chem- istry residues from the belt as well as parts. Newer style air knives can employ either low pressure and volume shop or self-generated air-style delivery systems. 107

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