The performance capability and longevity of a cleaning bath are essentially dependent on four factors:
The first two factors can be highly variable, depending on factors such as prior process chemistry, part size, part geometry and production rate. These factors, in turn, determine the third. A number of test procedures to determine cleanliness, including the widely used “water break test” in which the surface of the metal is examined. The test is based on the ability of a supposedly clean metal surface to sustain an unbroken film of water. However, the best and most commonly used method for determining cleaner life is to operate until problems arise, dump the cleaner, then devise a dump schedule in advance of projected problems.
Knowledge and control of soil type and drag-out rate, to the degree possible, will extend the solution service cycle and permit more efficient maintenance schedules. Unit cost for a cleaner can be determined by careful collection and analysis of daily operating data such as throughput, amount and type of chemical additions, type and frequency of waste treatment costs and dump frequency.
Pollution prevention techniques that are effective in reducing process solution drag-out tend to increase the concentration of contaminants. Alkaline cleaners, unlike plating baths, are designed to remove contaminants from the workpiece and retain them in the cleaning bath. Recovery of process solution or a reduction in drag-out may actually increase the need for removal of contaminants through more frequent maintenance by decantation, filtration or other purification process. It is generally more desirable, however, to contain contaminants in the cleaning bath than allow them to be carried to process solutions further down the line. Each application should be carefully examined.