Critical Issues During Demolding in Composite Insulator Production

The manufacturing process of composite insulators has evolved significantly, from dry-sleeve assembly to integral injection molding. Simultaneously, core rods have advanced from standard types to high-temperature, acid-resistant, and high-impact-strength versions to meet the demands of modern production techniques.

Currently, the integral injection molding combined with crimped end-fittings is the most recommended structure for suspension insulators. However, a technical contradiction exists: according to polymer characteristics, core rods with higher heat resistance often exhibit lower impact strength. Solving this requires collaboration between core rod and insulator manufacturers to ensure the rod can withstand injection temperatures while maintaining the high impact strength necessary for secure crimping.

The Problem: Many breakages occur not during injection itself, but during demolding due to “hard prying,” which causes core rod fractures or silicone rubber tearing.

Section I: Causes of Mold Sticking (Adhesion)

Adhesion between the insulator and the mold is a primary cause of demolding failures. Key factors include:

• Mold Quality: Poor material quality, low surface finish, or failure to apply release agents in a timely manner.
• Silicone Rubber Formula: Inappropriate rubber hardness or formula ratios that are not adjusted for seasonal temperature changes.
• Process Parameters: Excessive mold temperature, over-vulcanization, or incorrect holding time and pressure.
• Core Rod Thermal Resistance: Standard mold temperatures reach approximately 155°C at the center and 170°C on the surface. If the core rod lacks sufficient heat resistance, its structural integrity is compromised during the cycle.

Section II: Preventative Measures to Avoid Breakage

1. Optimize Mold and Release Agents: Use high-quality metal for molds with a high-precision surface finish. Ensure the consistent use of premium release agents.
2. Stabilize Raw Materials: Maintain a stable silicone rubber formula. Operators must clearly understand the relationship between material ratios, temperature, pressure, and time, including the impact of ambient environment changes.
3. Post-Injection Cooling: After the mold opens, do not pry the insulator out immediately if it sticks. Allow it to rest for 3 to 5 minutes or use fans/cool air to lower the temperature of the core section. Core rod strength increases significantly as it cools, drastically reducing the risk of fracture.
4. Control the Demolding Angle: Experience shows that for 110kV composite insulators, the angle between the core rod and the mold during prying should not exceed 30 degrees. If it exceeds this angle without releasing, alternative measures must be taken. In a well-optimized process, the insulator should ideally drop out under its own weight or with a light touch.
5. Balance Quotas with Quality: When setting production quotas or piece-rate wages, manufacturers must consider equipment limitations, personnel skills, and material characteristics. The goal should be the unification of quality, quantity, and economic efficiency.

Conclusion

Success in composite insulator manufacturing depends on standardized operations and continuous experience summary. By focusing on mold quality, cooling times, and proper demolding angles, manufacturers can eliminate core rod breakage and ensure high-yield production of reliable insulating products.