How to Improve Cased Nanocrystalline Core Performance: The Game-Changing Impact of Varnish Curing Before Casing

As a professional OEM/ODM manufacturer and global exporter of nanocrystalline and amorphous magnetic cores, we’ve faced — and solved — one of the most frustrating problems in magnetic component manufacturing: performance degradation of cased nanocrystalline cores after copper winding.

Despite our best efforts with process control and material optimization, the issue remained. Until we discovered one simple yet powerful step that changed everything: varnish curing of the core before casing.

In this article, we’ll walk you through the core problem, why conventional fixes don’t work, and how pre-casing varnish curing is a proven solution to improve cased nanocrystalline core performance in real-world production.

The Problem: Performance Degradation After Winding in Cased Cores

What Happens in Production

Cased nanocrystalline cores — usually toroidal or rectangular cores sealed with plastic, epoxy, or metal shells — are widely used in:

• High-frequency transformers

• Common mode chokes

• EMI filters

• Inverters and power supplies

Before being integrated into magnetic components, these cores are typically cased for mechanical strength, electrical insulation, and ease of handling. However, once copper winding is applied to these cased cores, we consistently observed a decline in performance, including:

• Lower initial permeability

• Higher core loss

• Reduced stability under temperature variation

• Poorer high-frequency behavior

These issues directly affect the quality and efficiency of the final device.

Why Traditional Solutions Don’t Work

1. Process Optimization

We tried:

• Adjusting winding tension

• Controlling ambient humidity and temperature

• Improving casing procedures

• Post-winding annealing

None of these consistently prevented the performance drop in cased cores after winding.

2. Material Substitution

We experimented with:

• Different casing materials

• Various adhesives and bonding resins

• Modified insulation layers

Again, results were unstable. The degradation continued.

Root Cause: Internal Stress and Magnetic Structure Disruption

Nanocrystalline ribbon is highly sensitive to mechanical stress and surface tension. During the winding process, pressure from the copper wire and friction from the casing interface can disturb the internal magnetic domains of the ribbon.

In cased products, this stress is harder to relieve because the core is confined within a rigid structure. Once distorted, the magnetic domains no longer function optimally — permeability drops, core loss increases, and overall stability suffers.

The Real Solution: Varnish Curing Before Casing

After multiple tests, we found a breakthrough: spraying insulating varnish on the bare nanocrystalline core and curing it before applying the casing and winding.

This varnish — specifically, a solvent-free polymer-based varnish such as V852-3 — forms a thin, flexible, nanograde insulating layer on the surface of the core. Once cured, it acts as a buffer between the magnetic material and mechanical stress.

How Varnish Curing Works

Step-by-Step Process

1. Core Surface Cleaning: Dust, oil, and oxidation are removed.

2. Varnish Spraying: The varnish is evenly sprayed over the entire surface.

3. Curing: The core is baked at 80–120°C for 30–60 minutes, depending on size.

4. Casing: The cured core is then inserted into the casing.

5. Winding: Copper coils are applied as usual.

How It Improves Magnetic Performance

• Reduces Stress Sensitivity: The cured layer absorbs winding pressure and mechanical stress from the casing.

• Preserves Magnetic Domains: Magnetic alignment remains stable under force and heat.

• Improves Thermal Cycling Stability: Coating remains intact even after repeated temperature changes.

• Enhances Surface Uniformity: Coating smooths minor imperfections, improving magnetic consistency.

Real-World Results from Our Factory

After adopting varnish curing in our production line, we observed the following:

We also received positive feedback from export customers in Europe, South Korea, and the US, especially those working in automotive power supplies, photovoltaic inverters, and EV charging systems.

Why Varnish Curing Beats Other Solutions

Application Fields That Benefit Most

• High-frequency transformers (20kHz–100MHz)

• Common-mode chokes for EV charging

• EMI suppression for power electronics

• Photovoltaic inverters and wind converters

• UPS systems and power storage devices

• DC-DC converters in automotive and rail

We Are a Leading Manufacturer and Exporter

With over 10 years of experience in nanocrystalline and amorphous magnetic core production, we provide:

• Customized OEM/ODM services

• Cased and uncased cores in toroidal, cut, and block shapes

• High-frequency, high-efficiency materials

• Mass production with stable quality control

• Global export logistics and multilingual support

We do not manufacture varnish, but we successfully integrate varnish curing into our own core production lines to deliver the best performance for our customers.

✅ Improve Your Magnetic Core Reliability Today

If you're tired of post-winding performance issues in cased cores, consider switching to a better solution.

Let us help you:

• 🧪 Request free samples

• 🛠 Get custom nanocrystalline core / amorphous core solutions

• 📦 Start stable OEM/ODM partnerships

• 🌍 Deliver globally with technical support

📞 Contact Us

• 🌐 Website: www.amorphousoem.com

• 📱 WhatsApp: +86 13686646827

• 📩 Email: julia@amorphousoem.com

• 🕘 Working Hours: Mon–Sat, 8:00–18:00 (China Time)

💬 Let’s Build a Better Core — From the Inside Out.