Pretreatment chemical and system suppliers will recommend maintenance, monitoring, recording, and chemical schedules. They may even provide the service as well. These recommendations are critical because wash systems need continual monitoring since they constantly change. The changes affecting wash systems include: the product being cleaned; the concentration, total dissolved solids (TDS), and pH levels; the age of the bath; and to clean the surface of the substrate, each substrate requires more or less impingement than the previous substrate. A powder-coating user needs sufficient pressure to properly clean the soil from the part. Cleaning a large heavyweight object requires the part to be run more slowly through the wash system to enable the temperature and impingement action to work. A user must be able to decrease or throttle the pressure applied to smaller lightweight parts, or parts will be lost into the tank. Too much pressure and the lighter-weight parts may be forced from the holding rack and damaged as they are thrown into the tank. A user needs to be concerned as the TDS climb. TDS levels need to be controlled at appropriate intervals. In addition, the concentration level changes due to the part’s geometric configuration and the washer itself. To ensure a pretreatment system is performing satisfactorily, testing must be performed on the substrate. If a user believes the washer system is functioning properly, a valid technique is to check for water-break-free surface cleanliness at the end of the washer outlet or vestibule. Inorganic surface cleanliness can be checked at the end of the dry-off oven.
By Gary Conner
By George N Bullen FSME