Pretreatment

Q. I am setting up a new Batch operation and wanted to know which pretreatment to go with. A 3 stage dipping system, or is a 3 stage hot pressure cleaning solution wash, Clear Rinse and sealant? Will the Iron railings benefit from a 3 minute dipping more than a power wash manually? Thanks A.S.

A. Immersion or spray? Seems like a simple question where you could almost flip a coin to get to your answer. For such a seemingly simple question, there are several options to consider. First, what is the configuration of the parts? Do they lend themselves to a spray cleaning? In other words, will all surfaces be impinged by the line-of-sight that a spray washer requires? From your description (iron railings), it sounds like they will be able to be cleaned and coated by either method, spray or immersion.

Second, what type of contaminants are you trying to remove in the cleaning stage and how consistent are they? In other words, if they are light mill oils are shop dirt, either cleaning method will do a good job. However, if you have heavy soiled parts, or if they enter the pretreatment line under a variety of conditions, it may be better to have an immersion line. The immersion tank will typically run hotter than the spray wash, so you will stand a better chance of removing some soils. Also, if the parts sometimes require more work because of variability of the incoming cleanliness, the immersion tank will allow you to tailor your cleaning cycle to fit the cleaning you need at the time. With a spray wash system, the remainder of your process is typically linked in series by conveyor. Unless you have a power-and-free system, you may not be able to really customize your cleaning without effecting all the processes on the conveyor. For instance, if you needed additional time to get your parts clean, the rinse, seal, dry, and coating operations would all be slowed down (assuming their all tied into the same conveyor).
Another consideration is floorspace. If you have consistent, similar, higher volume parts, with no hard to clean recesses, you should probably be leaning towards spray washing which will minimize labor. Now you will need to consider floorspace. The size of the pretreatment operation will generally hinge on their size and required process parameters. You should first do some homework up front to determine what your required process will be. Longer process times and higher conveyor speeds will directly translate into a larger size and footprint for the overall system. The larger the system, typically, also the higher the capital cost. The immersion system could get by on a smaller floorspace, but will generally have more labor associated with it. Automated immersion systems are available, but generally will equal the cost of the conveyorized spray system and usually require loading and unloading, separate from the rest of the line.

A possible alternative to these would be a cabinet style spray washer. It would require the same loading and unloading of an immersion system, but would likely have the smallest footprint for your shop. I know of systems that can be made to do at least two different steps, like wash and rinse. If your rinse solution can go to the drain (check with you local municipality), you would be able to use the two sumps of the washer for your wash and seal, respectively. This could be used to customize your cleaning parameters such as time and temperature, without effecting other processes downstream of pretreatment.