Q: We are using Detonox detergent in our ultrasonic baths and are loving it. We use a visual inspection method (cloudiness of solution) to determine when to change the bath and are moving to conductivity and pH. It appears pH stays constant regardless of concentration?
A: As a broad statement, detergent concentration does very little to affect pH due to buffers, as well as salts, micelles and other constituents. A pH meter wouldn’t be used to control for concentration on anything but very gross scales. What you’re seeing is expected.
The short answer for when to dump the tank is when the parts are no longer getting clean. It is important to note that if the product/part is not as clean as you require, it doesn’t matter what the pH, concentration, or any other parameter indicates. Parts meeting expectation is the first control parameter of any bath monitoring.
Depending on the criticality of your cleanliness needs, many will dump baths on a set time (i.e. once a day, once a shift) or per batch of parts to ensure no cross contamination. Adding an instrument-based monitoring of the bath can serve as another control parameter to ensure within these time frames, the bath is behaving as expected.
There is no set number where Detonox detergent transitions from effective, to not effective. As the pH dips into the pH 9 range (normally approx. pH 10.5), it is clear fouling has begun. If it is a full pH point from original unused dilution pH, it has been used.
Moving to conductivity for measuring would allow for more precise control. A conductivity change of 5% indicates the bath should be changed.
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