Electrolytic polishing surface treatment technology report —— The ultimate solution for stainless steel super clean surface
I. Functions and Core Values
Core functions
- Extreme cleanliness: surface roughness Ra ≤ 0.1μm (mirror grade), reducing microbial adhesion by 90%+
- Improve corrosion resistance: the passivation film is thickened by 3 times, and the salt spray test is more than 1000 hours (5-8 times higher than the original substrate)
- Debearding and uniformity: selective dissolution of microscopic protrusions to achieve full surface smoothness of complex cavities
- Medical grade safety: eliminate embedded iron particles on the surface and prevent metal ion precipitation pollution
Key problem solving
| Industry pain points | Electrolytic polishing solutions |
| Bacterial growth in pharmaceutical pipeline | Ra0.08μm super slippery surface inhibits biofilm |
| Metal pollution in semiconductor equipment | Remove the surface 5-20μm defect layer |
| The mechanical polishing texture is uneven | the whole surface is electrochemically leveled |
II. Working Principle
Dual mechanism of anodic dissolution and passivation film reconstruction
Microscopic leveling process:
① The precipitated ions are preferentially dissolved → ② the viscous layer of the electrolyte is formed → ③ the depression is protected by the passivation film → ④ the surface tends to be atomic level flat
Figure: Microscopic pimple selective dissolution and passivation film formation mechanism (SEM observation)
III. Process operation process
Precision control steps
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Pre-treatment
- Alkaline degreasing (60℃× 10min) → ultrasonic cleaning → pure water rinsing
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Electrolytic polishing
- Electrolyte: 65% phosphoric acid + 15% sulfuric acid + 20% glycerol (60-80℃)
- Parameters: voltage 12-18V, current density 20-50A/dm², time 5-15min
- Tooling: The titanium basket cathode is 100-150mm away from the workpiece
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Post-treatment
- Triple backflow rinse → pure water ultrasonication → nitrogen drying
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Quality control standards
- Roughness: Ra ≤ 0.1μm detected by white light interferometer
- Corrosion resistance: Copper salt accelerated acetic acid salt spray test (CASS) ≥48h without discoloration
IV. Compare with other processes
| Characteristic | Electrolytic polishing | Mechanical polishing | Chemical polishing |
| Surface roughness | Ra 0.02-0.1μm (mirror finish) | Ra 0.1-0.4μm (texture) | Ra 0.2-0.5μm (orange peel) |
| Improved corrosion resistance | ★★★★★(Passivation film thickening) | ★★☆☆☆(Infiltration contamination) | ★★★☆☆(Uniform corrosion) |
| Complex structure processing | Full coverage of inner cavity/microholes | Access is only possible on the outer surface | The depth of the hole is unstable |
| Spillage of material | 5-20μm precision removal | 10-100μm abrasive wear | Anisotropic dissolution of 20-50μm |
| Environmental protection | The recovery rate of waste acid is>85% | Dust pollution | Nitrogen oxide emissions |
| Prime cost | ¥150-300/㎡ | ¥80-150/㎡ | ¥50-100/㎡ |
Medical industry empirical evidence:
Electrolytic polishing of surgical instruments:
- Residue of bacteria: <5 CFU/cm² (mechanical polishing> 200 CFU/cm²)
- The cleaning and disinfection time is shortened by 40%
V. Application Scenario Guide
• Irreplaceable areas:
- ✅ Biopharmaceutical equipment (fermentation tank/freeze dryer pipeline)
- ✅ Ultra high purity fluid system (semiconductor process cavity/gas pipeline)
- ✅ Implantable medical devices (orthopedic screws/cardiovascular stents)
• Economic alternatives:
- ❌ Ordinary decorative parts (recommended mechanical polishing)
- ❌ Large structural parts (high cost)
Conclusion: Electrolytic polishing achieves dual breakthroughs in functionality and safety for stainless steel through atomic-level surface leveling combined with passivation film reconstruction. Mingli Metal's Class 1000 cleanroom can process micro-porous components with diameters Φ3mm, achieving surface oxygen content <0.5% (XPS analysis) that meets ASME BPE and FDA cGMP standards, providing ultra-clean surface solutions for high-end industries.
Appendix: Comparison of electrolytic polishing effect
Figure: Comparison of micro surface and corrosion resistance between mechanical polishing (left) and electrolytic polishing (right)
• Technical appendix
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Membrane composition analysis (XPS detection):
- Cr₂O₃ content: 75-85% (mechanical polishing only 40-60%)
- Fe/Cr ratio: ≤0.1 (medical grade requirement ≤0.3)
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Limit parameters:
- Maximum processing accuracy: Ra 0.008μm (monocrystalline silicon grade)
- Minimum aperture processing: Φ 0.5mm deep hole (length-to-diameter ratio 10:1)
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Innovative process:
- Pulse electrolytic polishing: reduce material loss by 30%
- Low temperature plasma assistance: energy consumption reduced by 40%