Tiêu chuẩn và hướng dẫn sử dụng nước trong dầu cắt gọt hòa tan , Độ cứng, pH và chất lượng nước chuẩn kỹ thuật

TECHNICAL REQUIREMENTS FOR WATER IN SOLVENT CUTTING OIL

1. Role of Water in Metalworking Fluid Systems

Water accounts for 90–95% of water-soluble cutting fluids.
The quality of water directly affects:

Emulsion formation and stability
Lubrication, cooling, and rust prevention performance
Fluid life and microbial growth rate

If non-standard water (too hard or too soft) is used, the emulsion will become unstable, separate, form white deposits, or cause metal corrosion.

2. Water Hardness – The Most Critical Parameter

Water hardness indicates the concentration of calcium (Ca²⁺) and magnesium (Mg²⁺) ions in water,
measured in mg/L (ppm) as CaCO₃ equivalent.

Water Type	Hardness (mg/L as CaCO₃)	Technical Characteristics
Very Soft Water	< 30 mg/L	Poor emulsion stability, phase separation, corrosion risk, unstable pH.
Standard Water for Metalworking Fluids	50 – 150 mg/L	Excellent emulsion stability, balanced pH, minimal corrosion and residue.
Moderately Hard Water	150 – 250 mg/L	Usable, but monitor for residue and clean periodically.
Very Hard Water	> 250 mg/L	Causes white scum deposits, nozzle clogging, emulsion breakdown, cloudy appearance.

Recommended Value:
Ideal water hardness for soluble cutting fluids: 100 ± 50 mg/L as CaCO₃.

3. Why Groundwater Should Not Be Used

In Vietnam, groundwater often contains:

Iron (Fe²⁺/Fe³⁺) and manganese (Mn²⁺) → cause oxidation and discoloration of the fluid.
Chloride (Cl⁻) and sulfate (SO₄²⁻) ions → accelerate corrosion of copper and aluminum.
Organic matter and microorganisms → produce foul odors and promote bacterial contamination.

Therefore, groundwater is not suitable for preparing metalworking fluids.

4. Recommended Water Sources

Water Type	Technical Characteristics	Usage Recommendation
Tap Water	Moderate hardness (50–150 mg/L), pH 7–8	Best suited for most water-soluble metalworking fluids.
RO Water (Reverse Osmosis)	Very low hardness (5–30 mg/L), slightly acidic pH	Should be blended with tap water to achieve 50–100 mg/L hardness.
DI Water (Deionized)	Nearly all ions removed → very “soft”	Do not use directly — add trace minerals (Ca/Mg) to stabilize emulsion.
Groundwater	High Fe, Cl⁻, and other metal ions	Not recommended.

5. Consequences of Using Improper Water

Problem	Water-Related Cause	Practical Effect
Emulsion separation, oil floating	Water too soft (lacking Ca, Mg)	Poor cooling, rust on workpieces
White deposits, cloudy fluid	Water too hard	Nozzle clogging, dirty sump, shortened fluid life
Rapid fluid degradation, pH drop	Water contaminated with bacteria or heavy metals	Odor, microbial growth
Staining or corrosion on Cu/Al parts	Water high in Cl⁻ or SO₄²⁻	Discoloration, reduced surface finish

6. Practical Operation Recommendations

Test water hardness monthly using a CaCO₃ test kit or TDS meter.
If water is too hard (>200 mg/L): use a water softener or dilute with RO water.
If water is too soft (<50 mg/L): blend with tap water or add trace Ca/Mg minerals to stabilize the emulsion.
Always record the water source and hardness value in the coolant maintenance log.