How to demold smoothly is a very common and crucial issue in the production of molded silicone foam. Poor demolding can lead to low production efficiency, product tearing, deformation and even scrapping. To solve this problem, it is necessary to start from a systems engineering perspective and consider the three core elements: molds, mold release agents, and formula processes.
Optimize the use of mold release agents
1.Select the appropriate type of mold release agent
Solvent-based mold release agents: The most commonly used, they have good film-forming properties, but attention should be paid to ventilation and safety.
Water-based mold release agent: More environmentally friendly and safe, but it takes time to dry and may affect production efficiency.
Solvent-free mold release agents (paste or wax form) : Suitable for complex molds, with good durability, but may affect the surface gloss of the product. For silicone foaming, it is essential to choose a mold release agent specifically designed for silicone and suitable for foamed products. Incorrect release agents may lead to incompatibility, inhibit vulcanization or transfer to the product surface, affecting subsequent processing (such as bonding, spraying).
2.The correct coating method is of vital importance
Cleaning is the first prerequisite: Before spraying the new mold release agent, the mold cavity must be thoroughly cleaned with a soft cloth or cotton swab to remove any residual silicone and mold release agent dirt.
The principle of "eating small meals frequently" : It is better to spray a thin and even layer each time and do it multiple times than to spray too thickly at one time. A too thick layer of mold release agent will flow into the vent plug and contaminate the mold. More importantly, it will cause defects such as orange peel and pinholes on the product surface and affect the dimensional accuracy.
Uniform coverage: Use a spray gun to maintain a certain distance and ensure that every corner of the mold is covered with an extremely thin film through cross-atomization. For hard-to-reach areas such as deep holes and narrow crevices, cotton swabs can be used to assist in application. Regular consolidation: After each few molds are produced, carry out rapid re-spraying while the mold is still warm to maintain the demolding effect.
Fundamental Solution: Mold Design and Maintenance,
1.Surface finish of the mold
The surface polishing of the mold cavity must reach a high grade (such as mirror polishing #A1). The smoother the surface, the smaller the friction force and the smoother the demolding. For new molds or worn molds, surface treatment can be considered, such as chromium plating: It has high hardness, a smooth surface, and is corrosion-resistant, making it a commonly used and effective choice.
Teflon (PTFE) coating: It has excellent non-stick properties and can significantly improve demolding, but the durability of the coating needs attention and may require regular recoating.
2.Reasonable Draft Angle:
The draft Angle must be taken into account when designing the mold. For soft and easily deformable materials like silicone foam, the draft Angle should be appropriately increased, usually recommended to be no less than 3 degrees. The greater the slope, the smaller the demolding resistance
3.Perfect mold structure:
Avoid upside-down: In the design, it is absolutely necessary to avoid an upside-down structure; otherwise, the product will be directly jammed.
Optimization of the ejection system: Ensure that ejection devices such as ejector pins and push plates are placed at the most reasonable force-bearing parts of the product (such as rib positions and thick wall areas), and that the ejection is smooth and synchronous. The ejector pin itself also needs to have sufficient smoothness and an appropriate draft Angle.
Fine adjustment of processes and formulas
The vulcanization process and the rubber compound formula themselves also profoundly influence the demolding behavior.
1.Optimize vulcanization conditions:
Avoid overvulcanization: Overvulcanization can make the silicone rubber brittle, increase its adhesion to the mold, and lead to difficulties in demolding or even tearing. Precisely control the vulcanization time and temperature to find the optimal vulcanization point.
Utilize mold temperature: Operate at the optimal demolding temperature of the mold. Usually, whether the mold is too hot or too cold will affect demolding. A stable demolding temperature range can be specified in the process regulations.
2.Check the rubber compound formula
Internal mold release agent: Communicate with your silicone supplier and add an appropriate amount of internal mold release agent to the rubber compound. It can migrate from the inside to the interface, playing an auxiliary demolding role, and has a better synergistic effect with external demolding agents.
Vulcanization system: Different vulcanizing agents (such as platinum vulcanization vs. peroxide vulcanization) and additives may affect the adhesion of the rubber compound to the mold. Discuss the possibility of fine-tuning with the formula engineer.