How do you determine when it is time to change out chemical tanks. Dissolved soils or just the cost because it is taking so much more product to titrate? M.C.
There is no defined time or method to determine when it is time to dump your cleaning tank for so many reasons. Each cleaner is different, each manufacturer’s definition of clean varies, production schedules change over time and the list goes on. One possibility is to come up with a standard test method for evaluating cleanliness (direct or indirect) and then use that to track the bath over time.
One simple and direct method is the water break test. A part will exit a cleaning process and sheet water from it if it is free of organic residue. As the bath builds contaminants over time, it will remove less contamination and eventually the parts come out with a surface that tends to bead water more than it sheds it.
An example of an indirect method would be paint performance (or something else that makes sense for your parts). After cleaning, paint the part and do typical performance tests for paint (adhesion, flexibility, salt spray). Doing this with a clean tank and one that just doesn’t appear to be giving you your desired results may provide you with an indication of when to dump.
You can also track the amount of chemical added to the bath between charge and dump along with one of the methods suggested above. This could allow you to better anticipate when a tank will be ready for dump before it gives out completely. Complementary to this is the method of measuring free and total alkalinity of a cleaning bath. The free alkalinity titration is the standard method you use to check for cleaner concentration which will vary between the limits you have set for your tank. The total alkalinity method will titrate to a lower pH indicator. This value should generally increase over the life of the bath as more and more cleaner is added. You can use this relationship (sometimes done in the form of a ratio of total:free alkalinity) also to estimate when it may be time to dump your cleaning tank. Again, it will be important that you qualitatively judge when your tank is ready to be dumped, then start to apply these methods of tracking it so you can anticipate future tank dumps.