5 Most Common Defects in Epoxy Resin Casting and How to Solve Them

In the production of instrument transformers and insulators using Automatic Pressure Gelation (APG), achieving a 100% yield rate is a constant challenge. Small mistakes in the resin mix, mold design, or temperature control can lead to costly rejects. At Bibo, we believe that a great machine is only half the battle—the other half is the Process Package. Here are the 5 most common defects we see in the field and how to fix them.

1. Cracks and Internal Stress

Symptom: Fine cracks appearing after demolding or during cooling.

Cause: Improper heating/cooling curves or high shrinkage of the resin.

Solution: Optimize the segmented heating zones of your APG machine. Ensure the resin-to-filler ratio is precise. Our Process Package includes a pre-calculated curing curve tailored to your specific product geometry.

2. Surface Bubbles and Voids

Symptom: Small pits or bubbles on the surface of the finished part.

Cause: Moisture in the filler or insufficient vacuum during the mixing stage.

Solution: Use a high-efficiency vacuum stirring system. Preheat the filler to remove moisture before mixing. Our stirring equipment ensures a degassing level of < 1mbar for a smooth, marble-like finish.

3. Incomplete Filling

Symptom: The top or corners of the part are not fully formed.

Cause: Resin gelation is too fast or the injection pressure is too low.

Solution: Adjust the catalyst ratio to slow down gelation or increase the holding pressure of the APG clamping machine. Proper mold venting (venting grooves) is also critical.

4. Partial Discharge (PD) Failure

Symptom: Electrical test failure despite a perfect visual appearance.

Cause: Micro-voids or impurities inside the casting.

Solution: This is the "silent killer." It requires a combination of ultra-clean raw materials and precise pressure control during the gelation phase to collapse any microscopic internal voids.

5. Mold Sticking

Symptom: Difficulty removing the part, leading to surface damage.

Cause: Poor quality release agent or worn mold surface.

Solution: Use high-grade silicone release agents and ensure your molds are polished to a mirror finish. Our molds are treated with a specialized coating for easier release and longer lifespan.

Struggling with high reject rates in your APG production? A machine alone won't solve it—you need a system. Download our "APG Process Audit Checklist" or contact our technical team for a free consultation on optimizing your resin casting workflow.