Coolant pH value and bacterial concentration
The chemical balance of the cutting fluid is one of its most important properties. In particular, monitoring pH levels and bacterial concentration is essential to keep the emulsion stable, protect machines and tools, and maintain a pleasant and odor-free work environment.
The Importance of pH Levels
Monitoring the system’s pH level is a key part of cutting fluid maintenance. The pH indicates how acidic or alkaline the fluid is, which directly affects its ability to prevent corrosion, lubricate, and inhibit microbial growth.
If the pH drops, it often signals that the concentration is too low or that microbial growth has started in the fluid. The metabolic byproducts of bacteria and fungi acidify the fluid, which quickly weakens its protective properties.
Most cutting fluids should have a pH of at least 9.0. In a new and properly mixed emulsion, the pH is typically between 9.0 and 9.6, but the exact value depends on the specific product.
The pH should be measured at least once a week, and the results should be recorded in a maintenance log along with concentration measurements. If the pH drops below the recommended value, the emulsion should be analyzed and corrected as needed—either by adding concentrate, raising the pH with a booster, or replacing the fluid entirely.
How to Measure pH
pH can be measured with a pH meter or a pH test strip.
- A pH test strip is a quick and easy option. Simply dip the strip into a clean sample, then compare its color to the chart provided with the packaging.
- A pH meter provides a precise numerical value and is especially suitable if measurements are taken regularly or if the system contains several different emulsions.
It’s important to ensure the sample is taken from clean emulsion—not from the surface of the tank, where there may be leaking oils or other contaminants that can skew the results.
Measuring Bacterial Concentration
Bacteria are one of the leading causes of cutting fluid spoilage. They lower the pH, reduce corrosion protection, produce unpleasant odors, and can form slippery biofilms that clog pipes and filters.
Bacteria multiply quickly if there are “dead spots” in the system, stagnant fluid, or organic debris for them to attach to. That’s why bacterial concentration should be measured regularly—at least once a week.
The most common method is a contact dip slide test, where a special strip is dipped into an emulsion sample and incubated at room temperature. After two days, the number of colonies that appear on the strip shows the activity level of bacteria present.
If bacterial concentrations are high, the fluid’s properties deteriorate rapidly. In such cases, a biocide treatment, increasing the pH, or, if needed, a complete system cleaning and fluid replacement may be required.
Summary
Controlling pH levels and bacterial concentration is crucial in cutting fluid maintenance.
- pH ≥ 9.0 ensures corrosion protection and emulsion stability.
- Regular bacterial monitoring prevents acidification and odors in the fluid.
By performing these measurements regularly and quickly reacting to deviations, the service life of the cutting fluid is extended and machining process quality is maintained—while also reducing unnecessary downtime and maintenance costs.
