How to choose the right coating for magnetic cores—electrical insulation, environmental protection, and winding compatibility
Introduction
Magnetic cores are sharp, brittle, and often conductive. Bare cores don’t last long: wire cuts on edges, iron cores rust, dust contaminates. Every magnetic core is coated before winding—but not all coatings are equal.
Shaanxi SiRui Technology Co., Ltd. supplies coated magnetic cores with various coating options for different applications.
1. Coating Types Comparison
Epoxy Coating (Most Common)
- Thickness: 50–200 μm, dielectric: 10–20 kV/mm
- Temperature: -40°C to +155°C
- Pros: lowest cost, good all-around performance
- Best for: general-purpose inductors and transformers
Parylene Coating (Premium)
- Thickness: 5–50 μm (ultra-thin!), dielectric: 20–30 kV/mm
- Temperature: -65°C to +200°C
- Pros: perfectly conformal, pinhole-free, best high-voltage isolation
- Cons: highest cost, slower process
- Best for: high-voltage isolation, medical, harsh environments
Silicone Varnish (Flexible)
- Thickness: 30–100 μm, flexible, not brittle
- Temperature: -60°C to +200°C
- Best for: amorphous and nanocrystalline cores, thermal cycling
Heat-Shrink Tubing (Easy Apply)
- Thickness: 0.5–2 mm (thick!), easy to apply
- Temperature: -40°C to +125°C
- Best for: prototyping, low-volume production
2. Coating Comparison Summary
| Coating | Thickness | Temp Range | Cost |
|---|---|---|---|
| Epoxy | 50–200 μm | -40°C to +155°C | Lowest |
| Parylene | 5–50 μm | -65°C to +200°C | Highest |
| Silicone | 30–100 μm | -60°C to +200°C | Medium |
| Heat-Shrink | 0.5–2 mm | -40°C to +125°C | Low |
3. How to Choose
- Determine your voltage requirement (low/medium/high voltage)
- Consider temperature range (standard vs high temp)
- Evaluate environment (indoor/outdoor/chemical)
- Check winding window constraints (thick coating = fewer turns)
- Balance cost vs performance
4. Common Mistakes
- Using cheapest coating for everything (don’t compromise safety!)
- Underestimating coating thickness (winding window!)
- Ignoring temperature effects on coating properties
- Not testing hi-pot after coating
5. Custom Coated Cores from SiRui-Tech
At Shaanxi SiRui Technology Co., Ltd., we supply standard epoxy-coated cores, parylene-coated high-voltage isolation cores, silicone varnish-coated amorphous/nanocrystalline cores, and heat-shrink tubing for prototyping.
Conclusion
Magnetic core coating is often an afterthought—but it’s critical for reliability and performance. As power electronics push toward higher voltage and higher temperature, coating requirements are getting stricter.