I am wondering what the best way would be to minimize process/cleaner dragout on a continuous conveyor (no indexing allowed) that is used to clean parts that are, in some cases, longer than the stage itself. I know about silhouettes, drain boards, angling nozzles and curtains, as well as increased temperature, wetting agents, counterflowing and decreased concentration. How do other manufacturers handle the issue of stage cross-contamination when faced with shorter-than-desired washer footprints coupled with long or unusual part geometries? It is not unusual for a part to be washing and rinsing at the same time.J.S.
From what you have said in your question, you clearly realize that this is a less than desirable washer design. For the readers who may not know everything you are referring to, all the design parameters listed above are important to good washer design in order to keep the solutions contained in their respective stages and operating at peak efficiency. When designing a washer, all stages should be large enough so that the largest part being processed is contained within one stage and does not deflect spray into other stages. This can be further minimized by allowing adequate space between stages, allowing solution dripping off the workpiece to flow back to the previous stage as it exits and making sure nozzles are properly positioned so they are not spraying into other stages.
Regarding the current situation, one suggestion would be the addition of an airknife between stages that would, hopefully, minimize the amount of dragout from the cleaner into the rinse. The racking may also be able to help to a limited extent, depending on the final use of these parts. Final rinse quality may be important if these are being painted, for instance. In the case of the part that is simultaneously washed and rinsed, it would be helpful to have the part in the rinse slightly higher than the part in the wash. Water will flow into your cleaner (where you will need a certain amount of make-up water anyway) and minimize contamination of your rinse tank. It sounds like you have thought through most other options and, short of adding additional length onto the washer stages, I cannot make any further suggestions.
Most parts that are very large and require cleaning are often done with some form of manual pressure washer in a booth (think of your local coin-operated, manual car wash). There are equipment manufacturers that specialize in nothing more than this type of equipment for industrial use. A list of some of these manufacturers can be found at the Suppliers page on www.pfonline.com or on page 404 of the 2001 Products Finishing Directory under Cleaning Equipment, high-pressure wand. The moral of this story for the readers is to size any new washer according to not only what your current needs are but also to what you think you may have to clean over the life of the equipment.