Maintenance & Reliability · SOP

CNC Coolant Concentration Brix And pH Testing

Standard procedure for measuring coolant concentration (Brix) and pH level on CNC machining centres and lathes. Proper coolant chemistry extends tool life, prevents corrosion, and reduces downtime.

Estimated Time

15 min

Difficulty

Basic

Regulation

CSA Z432 / ISO 14110

Version

1.0

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Purpose

Maintain consistent coolant concentration (measured as % Brix) and pH within manufacturer specifications to optimize cutting performance, prevent microbial growth, and avoid corrosion or skin irritation. Routine testing ensures coolant remains effective and machine components are protected.

Scope

Applies to all CNC machines using water-miscible metalworking fluids (emulsions, semi-synthetics, synthetics) where concentration and pH must be verified regularly. Frequency: weekly for normal operation; daily if heavy bacterial load or tramp oil contamination is suspected.

Safety Precautions

LOTOLockout/Tagout the machine before reaching into sump or accessing coolant lines. De-energize spindle and coolant pump.
PPEWear nitrile gloves, safety glasses, and fluid-resistant apron. Coolant may contain bacteria or irritants.
CHEMNo food or drink near testing area. Wash hands thoroughly after handling coolant. Dispose of used test strips and rinsate per local environmental regulations.

Required Tools & Materials

Clean sample cup or beaker
Handheld refractometer with ATC (0–32% Brix scale)
pH meter (with calibration buffers) or pH test strips (range 6.0–9.5)
Distilled water in wash bottle
Lint-free wipes
Coolant concentrate and pH adjuster (if correction needed)
Pen and PM log sheet or digital log

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Procedure: Step-by-Step

1 Wash hands and put on nitrile gloves. Ensure machine is in safe mode (LOTO applied, spindle off, no movement).

2 Collect a representative coolant sample from the machine sump using a clean cup. Avoid surface foam and bottom sludge – sample from mid-depth in the return stream.

3 If using a refractometer with automatic temperature compensation (ATC), proceed. Otherwise, measure coolant temperature and adjust reading per manufacturer chart.

4 Place 2–3 drops of coolant on the refractometer prism, close the cover, and look through the eyepiece. Read the Brix % at the boundary line between blue and white fields. Record value.

5 Compare Brix reading to machine manufacturer specification (typically 5–12% for most emulsions). If outside range, adjust by adding coolant concentrate or distilled water.

6 Rinse refractometer prism with distilled water and dry with lint-free wipe.

7 Calibrate pH meter with buffer solutions if required. For pH strips, dip strip into coolant sample for 2 seconds, shake off excess, and compare colour to chart after 15 seconds.

8 Record pH reading. Acceptable range is typically 8.0–9.2 for most metalworking fluids. Below 8.0 indicates bacterial growth; above 9.2 may cause skin irritation.

9 If Brix or pH is out of spec, adjust coolant concentration by adding coolant concentrate or distilled water. Add biocide or pH adjuster as needed per fluid manufacturer instructions. Re-circulate for 10 minutes before retesting.

10 Repeat steps 4–8 after adjustment. Document all readings and corrective actions in the PM log. Dispose of sample, rinse water, and test strips according to local environmental regulations.

CNC Coolant Concentration Brix And pH Testing

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