Breakthrough in epoxy resin casting process: secret to 40% increase in breakdown field strength of insulation components

2025-09-27 14:08:24

A certain high-voltage switch manufacturer was once plagued by excessive production of finished insulation rods, with a long-term scrap rate of up to 15%. After introducing the new processes of "molecular level defoaming" and "gradient solidification", not only did the scrap rate decrease to below 3%, but the breakdown field strength of the insulation rod also jumped from 22 kV/mm to 31 kV/mm, an increase of over 40%, which reduced the size of the new generation of switchgear by 20%.

1、 Bottleneck analysis: Why is it difficult to improve the breakdown field strength?

The breakdown of epoxy resin castings begins with microscopic defects inside the material. These defects are like the shortcomings of a wooden barrel, determining the upper limit of insulation strength. The main problems with traditional craftsmanship are as follows:

1. Microscopic bubbles (main culprit): Invisible bubbles (10-100 μ m) that are entrained during the mixing and pouring process, have a much lower dielectric constant than epoxy resin under an electric field, withstand higher field strength, cause partial discharge, and gradually corrode the insulation.

2. Internal stress cracks: During the resin curing process, internal stress caused by uneven heat dissipation and shrinkage can lead to microcracks. These cracks become electric field distortion points.

3. Interface defects: The bonding between epoxy resin and metal inserts or fillers is not tight, resulting in air gaps or weak interface layers.

4. Impurities and molecular defects: Impurities, low molecular weight substances, and incomplete cross-linked networks after curing in raw materials are weak links in insulation.

2、 Technological Breakthrough: Four Key Technological Paths

To achieve a breakthrough in breakdown field strength, a set of interlocking "combination punches" is needed. Its core lies in the precise and defect free control of the entire process from material pretreatment to curing, and its systematic process flow is shown in the following figure:

Key one: Molecular level vacuum degassing - from "coarse degassing" to "fine degassing"

Traditional process: Pull to -0.095MPa at once and maintain for 10-20 minutes.

Breakthrough technology:

Step by step vacuuming: First, evacuate to -0.08MPa and hold for 5 minutes to allow large bubbles to escape smoothly; Slowly draw to -0.1MPa.

2. Dynamic adjustment: At -0.1MPa, through program control, briefly release pressure and then vacuum (such as 3-5 cycles), using pressure changes to "tear" the surface tension of the liquid, forcing tiny bubbles to coalesce and escape.

3. Temperature synergy: Accurately control the resin temperature at 40-45 ℃ (near its lowest viscosity point), greatly reducing the resistance to bubble escape.

Effect: The bubble content in the mixture can be reduced to below 0.05%, basically achieving a "bubble free" state.

Key 2: Low temperature and low-speed stirring - inhibits bubble regeneration and molecular chain damage

Traditional process: High speed stirring (>300 rpm) is used to improve efficiency, but it may involve a large amount of air and cause resin pre polymerization due to shear heating.

Breakthrough technology:

Speed control: Low speed stirring at<100 rpm is adopted, and anchor or spiral stirring blades are used to achieve gentle and uniform mixing.

Temperature control: The mixing kettle is equipped with a precise cooling system to ensure that the entire process temperature is below 40 ℃.

Effect: Avoid the generation of new bubbles, protect the molecular chains of epoxy resin from mechanical shear damage, and ensure the intrinsic properties of the material.

Key three: Precise temperature control pouring - ensuring a "smooth landing"

Traditional craftsmanship: Ignoring mold temperature or uneven preheating temperature.

Breakthrough technology:

1. Mold preheating: Preheat the mold to 50-60 ℃ (slightly higher than the initial temperature of the resin).

2. Bottom slow injection: The pouring port is set at the bottom of the mold, using a slender conduit to inject at a stable and slow flow rate. This can minimize splashing and air entrapment to the greatest extent possible.

Effect: The resin has the best fluidity, can fully infiltrate fillers and inserts, and smoothly fill the cavity, avoiding surface defects caused by cold molding.

Key four: Gradient pressure solidification - the core of eliminating internal stress

This is the most critical and complex step, which aims to "gently" complete the transition of epoxy resin from liquid to solid state.

3、 Effect verification: Data speaks for itself

Through the above technological breakthroughs, the following substantial improvements can be achieved:

1. Breakdown field strength: increased from the traditional 20-25 kV/mm to 28-35 kV/mm, achieving a significant increase of 40%.

2. Local discharge capacity: ＜ 5 pC (even below the apparent discharge detection threshold under power frequency withstand voltage).

3. Internal defect rate: Ultrasound scanning (C-Scan) shows that the area of internal defects (bubbles, delamination) accounts for less than 0.1%.

4. Mechanical strength: The bending strength is increased by about 20%, and the internal stress is reduced by more than 50%.

4、 Summary: From "Skill" to "Science"

The breakthrough in epoxy resin casting technology is essentially the transformation of the "skill" that relies on the experience of experienced masters into a quantifiable, replicable, and material science based "science".

The core secret lies in precise control over every aspect:

Defoaming: It is no longer a simple vacuum pumping process, but a dynamic and collaborative physical process management.

Curing: It is no longer a simple heating and insulation process, but a chemical crosslinking reaction kinetics management coupled with temperature pressure time.

For high-voltage electrical equipment manufacturers pursuing high reliability and miniaturization, investing resources in the aforementioned process innovations will bring decisive improvements in product performance and market competitiveness. This is not only about cost, but also about the future market discourse power.