PAG for Metalworking Fluids: Foam, Lubricity and Cloud Point
Why Traditional Surfactants Fail in CNC Machining
High-pressure coolant delivery supports heat and chip removal but can increase foam under some fluid, water-quality and contamination conditions. Compare wetting and dynamic foam in the complete metalworking fluid at the intended pressure, temperature and shear.
One candidate family is PAG (Polyalkylene Glycol). Because of its unique inverse solubility, PAG should be compared for lubricity and foam control across the intended temperature range.
1. The “Cloud Point” Effect: Automatic Foam Control
Unlike traditional surfactants that remain dissolved and stabilize foam across all temperatures, PAG (Polyalkylene Glycol) features a unique Cloud Point property:
- 🔹 High-Shear Agitation: As mechanical energy increases the fluid temperature, the PAG reaches its cloud point and becomes insoluble.
- 🔹 Result: The insoluble PAG droplets act as highly efficient mechanical foam breakers, so measure dynamic foam height, break time and air release under recirculation.
- 🔹 Recovery: Once the fluid cools in the reservoir, the PAG re-dissolves, maintaining a clear, stable solution without leaving oil spots or “fish-eyes” on the metal surface.
2. Lubricity, Water Washability and Residue Testing
Based on Kemaix laboratory data, our PAG series offers significantly higher film strength than standard alcohol ethoxylates:
- Extreme Pressure (EP) Support: PAG molecules align on the metal surface to minimize friction, extending tool life by 15-20% in high-speed CNC operations.
- No Silicon Interference: Unlike silicone-based defoamers, our PAG for Metalworking Fluids is a candidate for water-washability testing—critical for parts requiring subsequent painting, plating, or welding.
3. Technical Benchmarks for MWF Selection
| Metric | Performance (Kemaix PAG) | Why it matters to you |
|---|---|---|
| Dynamic Defoaming | ★★★★★ | Prevents sump overflow during 24/7 high-pressure operations. |
| Thermal Stability | ★★★★★ | The product won’t degrade or turn yellow under high-heat cutting. |
| Wetting Property | ★★★★☆ | Ensures the coolant reaches the very tip of the cutting tool. |
| Hard Water Tolerance | ★★★★★ | Maintains stability even in regions with high calcium/magnesium content. |
4. Troubleshooting: Making the Switch to PAG
Problem: Recurrent Foaming in Fresh Batches.
Solution: Replace 20% of your primary surfactant with a low-foaming PAG block copolymer to stabilize the surface tension.
Problem: Sticky Residue on Machined Parts.
Solution: Increase the PAG ratio to improve water-washability while maintaining superior film lubricity.
Optimizing Your Tool’s Life Starts Here
Explore our full technical specs in the PAG Selection Guide or contact our technical team for custom EO/PO adjustments.
Frequently Asked Questions (FAQ)
Q1: How does PAG compare to traditional silicone defoamers in MWF?
A: While silicone defoamers are cheaper, they often cause “fish-eyes” and coating defects in downstream processes like painting or plating. PAG (Polyalkylene Glycol) provides a “clean” defoaming action. Since it re-dissolves when the fluid cools, chemistry alone does not establish a residue-free metal surface, so validate surface cleanliness, exposure controls and downstream-process compatibility.
Q2: Will PAG surfactants affect the biological stability of my coolant?
A: On the contrary, PAGs are chemically stable and less prone to bacterial degradation compared to natural fatty acid esters. This helps maintain the pH of the sump and extends the service life of the metalworking fluid, reducing the frequency of costly tank clean-outs.
Q3: Can I use PAG in both synthetic and semi-synthetic fluids?
Yes, you can use PAG for Metalworking Fluids in both synthetic and semi-synthetic formulations to boost extreme pressure (EP) performance.
Q4: At what temperature does the PAG defoaming effect kick in?
A: This depends on the specific Cloud Point of the PAG grade you choose. Typically, for metalworking, we recommend grades with a cloud point between 30°C and 50°C. When the friction of machining pushes the fluid temperature above this range, the defoaming properties are immediately activated.
Q5: Is PAG compatible with yellow metals like copper and brass?
A: Most Kemaix PAG grades are non-corrosive and safe for use with a wide variety of metals, including aluminum and yellow metals. However, we always recommend verifying the specific pH-buffer system of your final formulation to ensure total compatibility.
Quick answer: use PAG to control the foam mechanism, not only the visible foam height
PAGs can support low-foam lubrication and fluid stability in synthetic or semisynthetic metalworking fluids, but performance depends on EO/PO structure, molecular weight, water solubility, temperature, shear and the rest of the additive package. Compare PAG candidates at equal active matter under actual pump shear, contamination and water hardness; verify lubricity, corrosion protection, filtration and mist behavior alongside foam.
| MWF symptom | Variable to isolate first | Confirmation before scale-up |
|---|---|---|
| High initial foam | Air entrainment under pump/nozzle shear | Dynamic circulation test, not shake foam alone |
| Slow foam decay | Surfactant film persistence and contamination | Foam decay with tramp oil and fines |
| Low foam but poor lubrication | PAG structure or insufficient boundary-lubricity support | Machining or tribology test at use dilution |
| Clouding at operating temperature | EO/PO balance and electrolyte load | Temperature-solubility map using plant water |
| Stable lab sample, unstable sump | Microbial load, tramp oil, metals and concentration drift | Used-fluid simulation and fluid-management controls |
Safety boundary: low foam does not establish low aerosol exposure or occupational safety. NIOSH recommends controlling metalworking-fluid aerosols and implementing a comprehensive safety and health program; review the complete fluid, process and exposure controls.
Technical review: Grace Dou, metalworking-fluid applications team. Reviewed 14 August 2026.
Primary references
- NIOSH: occupational exposure to metalworking fluids
- US EPA Safer Choice criteria for defoamers
- ISO 696: modified Ross-Miles foaming method
Compare PAG structures in the PAG selection guide and connect the result to the broader cutting-fluid surfactant framework.
