How Does Insulation Spraying On Magnetic Cores Affect Performance?

In the development of energy-storage converters, vehicle-mounted power supplies and server power supplies, amorphous and nanocrystalline magnetic cores often undergo insulation-spraying treatment. Many engineers focus on the magnetic permeability and loss parameters of magnetic cores themselves, yet tend to overlook the cascading effects brought by insulation coatings.

 

Prototypes may pass all tests smoothly, but problems such as poor voltage resistance, inductance offset after winding, abnormal temperature rise and batch-to-batch performance fluctuations may occur after mass production. Quite a few of these issues root in the insulation-spraying process of magnetic cores. This article discusses the positive effects of insulation spraying on magnetic-core components, as well as hidden engineering pitfalls.

 

I. Practical Benefits of Magnetic-Core Insulation Spraying

Amorphous and nanocrystalline materials are metallic soft-magnetic materials with favorable magnetic conductivity, while featuring relatively low resistivity. Micro-burrs or sharp tips may exist on their surfaces. If windings are applied directly, enameled wires will come into direct contact with the magnetic-core substrate. Under high-voltage and high-frequency operating conditions, breakdown or short-circuit faults are highly likely to happen, and potential safety hazards will be aggravated. Insulation spraying forms a dense, uniform protective coating with sufficient voltage-withstanding strength on the magnetic-core surface, ensuring safe clearance between windings and the magnetic core.

 

🔹 First, realize electrical isolation to meet safety voltage-withstanding requirements.

The coating separates the metallic magnetic core from windings to satisfy safety-standard withstand-voltage tests. It can replace traditional plastic housings, fit the miniaturization and compact-design trends of equipment, and cut down volume occupation caused by housings.

 

🔹 Second, protect magnetic-core bodies and improve environmental adaptability.

Amorphous and nanocrystalline strips are susceptible to oxidation and moisture. Qualified spray coatings can isolate moisture and salt spray. For vehicle-mounted and energy-storage applications with drastic temperature-humidity variations, the coating slows magnetic-core aging and extends component service life.

 

🔹 Third, optimize winding-processing performance.

The coating buffers friction and collision during winding, lowering the risk of enameled wires being cut by sharp edges of metallic magnetic cores, and improving production yield.

 

For many high-voltage power-application scenarios, insulation spraying has become a mainstream and critical process for magnetic cores. However, thicker coating does not mean better performance. Poor process control will instead impair overall equipment performance.

 

 

II. Adverse Performance Impacts Caused by Improper Spraying-Process Control

Many hidden problems encountered in projects stem not from defects of magnetic-core base materials, but cascading effects triggered by out-of-control insulation-coating processes.

 

Induced internal stress leading to magnetic-performance deviation

Amorphous and nanocrystalline magnetic cores are highly stress-sensitive. High-temperature curing and shrinkage during coating curing in spraying introduce extra stress to magnetic cores, resulting in decreased inductance and increased loss. For identical base materials, mismatched curing temperature and baking duration against soft-magnetic-material characteristics will lead to obvious inductance deviation before and after spraying for magnetic cores of the same specification, and cause poor batch consistency.

 

Coating thickness affects winding-window utilization

The coating occupies space of inner- and outer-diameter windows of magnetic rings. Thicker coating leaves less space for windings. With compressed window space, wire arrangement becomes more difficult under the same number of turns. It may even require upsizing magnetic-core dimensions, which contradicts the original intention of boosting power density.

 

Coating defects bring voltage-withstanding and reliability risks

Pinholes, thin coating spots and missing coating on corners are major concerns for spraying. The surface may appear intact, yet intermittent voltage-breakdown occurs during high-voltage tests. Under long-term high-temperature-high-humidity operation, moisture invades through weak coating areas, gradually oxidizes magnetic cores and causes late-stage equipment-performance drift.

 

Heat-conduction changes trigger temperature-rise variations

Insulation coatings feature limited thermal conductivity. Excessively thick coatings hinder heat dissipation from magnetic cores. Under long-term full-load operation of high-power equipment inside enclosed cabinets, heat accumulation will be aggravated.

 

III. SUNBOW Amorphous Spraying Process: Balancing Insulation and Magnetic-Core Performance

To address the industry pain point of stress sensitivity for amorphous and nanocrystalline magnetic cores, SUNBOW supports in-house spraying procedures for amorphous products. Coating-material selection and full spraying workflows are adapted to soft-magnetic-material properties to minimize negative interference brought by spraying to magnetic cores.

 

- Strictly control curing temperature and baking duration, avoid temperature ranges that trigger drastic coating shrinkage or abrupt thermal-stress changes. Reduce internal stress caused by coating shrinkage, constrain inductance and loss fluctuation before and after spraying, and maintain stable base-material performance after coating.

 

- Customizable coating thickness according to customer voltage-withstanding requirements. On the premise of meeting safety-standard voltage-withstanding indexes, keep coating thickness within a reasonable range to reduce winding-window occupation. Balance insulation performance and winding manufacturability, and avoid coating accumulation on corners.

 

- Control spraying uniformity in production, reduce defects such as pinholes and missing coating, improve coating adhesion. The finished cores resist paint peeling under winding and assembly impact, and can withstand common complex environments of energy-storage and vehicle-mounted applications including high-low temperature, humidity and salt spray (subject to corresponding specification conditions).

 

- Besides appearance inspection for each batch of sprayed magnetic cores, sampling tests are conducted on post-spraying magnetic performance and voltage-withstanding performance. Products are delivered with finished-state parameters, so as to reduce batch discrepancies for end-users and lower uncertain risks during prototype-to-mass-production transition.

IV. Conclusion

Insulation spraying is essentially a double-edged sword. It addresses practical demands for magnetic-core voltage resistance, corrosion protection and processing protection. Nevertheless, careless process control may trigger stress-related issues, inductance drift, window-space loss and reliability risks.

 

Many engineers only focus on base-material parameters during magnetic-core selection and regard spraying as a simple secondary process, ignoring its cascading impacts on complete equipment. Prototypes may work well, yet various tricky problems emerge in mass-production phases.

 

By understanding the influences of insulation spraying on magnetic cores and incorporating coating-process evaluation in early-stage design, rework in later debugging can be reduced and stable mass-production operation of products can be guaranteed.

 

✨SUNBOW, Your Best Partner of Magnetic Materials