Mold sticking during demolding of liquid silicone rubber products is a high-frequency issue on the production floor. When products partially or entirely adhere to the mold cavity, it at minimum affects production efficiency and at worst causes product tearing and scrapping. The causes of mold sticking involve multiple aspects including mold surface condition, degree of vulcanization, and mold design.

Mold Surface Treatment: Surface Finish and Coatings

The surface condition of the mold cavity is the primary factor determining ease of demolding. If the surface is rough or has defects, LSR tends to mechanically interlock with the mold after curing. Industry practice shows that highly polishing the mold cavity to a mirror finish and applying a durable hard coating can significantly improve demolding performance.

The use of mold release agents must be restrained. Technical documentation cautions against increasing the dosage and frequency of mold release agents simply for demolding convenience. Excessive mold release agent easily causes mold surface contamination, which at minimum affects product appearance and at worst impairs subsequent screen printing and spray coating adhesion.

Degree of Vulcanization: The Dilemma of Under-Cure and Over-Cure

In an under-cured state, the product is too soft, prone to tearing and remaining in the mold during demolding; in an over-cured state, the product becomes brittle and may slightly adhere to the mold steel. Precisely controlling vulcanization temperature and time to find the optimal vulcanization window is the process foundation for resolving mold sticking issues.

Uneven mold temperature also leads to localized differences in vulcanization degree, which in turn causes localized mold sticking. Using a mold temperature controller for multi-point temperature control to ensure temperature consistency across all cavity regions helps reduce such problems.

Mold Design: Draft Angle and Ejection System

Insufficient draft angle or the presence of undercut structures directly leads to demolding difficulties. Technical documentation recommends ensuring adequate draft angle, typically 1° or more, and optimizing the ejection system by using more ejector pins, air ejection, or push blocks to apply force evenly.

For injection molds, sticking often occurs on the cooler half of the mold. If the upper mold temperature is 175°C and the lower mold temperature is 165°C, the product will generally stick to the lower mold upon opening. The solution is to first polish and clean the mold interior with polishing paste, then evenly spray a layer of mold release agent.

Recommended Handling Procedure

When mold sticking occurs, it is recommended to troubleshoot sequentially in the order of "check vulcanization parameters → confirm mold temperature uniformity → check mold surface condition → evaluate mold release agent usage → check mold design." For precision molds, soaking in dish soap solution (at a 1:5 ratio) under vacuum treatment allows the cleaning solution to penetrate precision clearances, followed by drying before reuse.

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