The selection of mold opening form and mold line is extremely important. Firstly, it facilitates mold removal. Secondly, the mold line should be positioned so as not to affect the overall effect of the product. Thirdly, it must not compromise product quality — for example, if the mold line of water feature series products is too high, more material is required when sealing the mold line, making the product prone to cracking. Fourthly, it reduces process operations, such as opening a half-mold.
To prevent silicone from flowing arbitrarily, fix the mold master in a regular range using wooden blocks or planks. When opening a split mold, separate the first part to be opened with planks and oil clay, ensuring no gaps between the oil clay and the mold master, and that the oil clay surface is smooth and flat. After completing the above preparations, apply petroleum jelly or spray mold release agent on the plaster mold or mold master. For smooth products, dip a clean pure cotton cloth in petroleum jelly and apply it evenly on the mold master, then let it stand for 30 minutes to allow the mold master to fully absorb the petroleum jelly before wiping the surface clean with another clean pure cotton cloth until it is shiny. For textured products, simply apply petroleum jelly evenly. Prepare the silicone according to the formula, stirring in irregular directions to fully mix the curing agent with the silicone while minimizing air entrapment. For smooth products, it is best to vacuum the first layer of silicone once, maintaining a vacuum degree of -0.1MPa for 7-8 seconds.
After preparing the silicone, start mold making promptly. Pour the silicone liquid onto the highest part of the mold master in a trickling manner, allowing it to flow naturally. Use an oil painting brush to spread the silicone evenly in areas that are not fully covered. For split molds, the silicone should not only fill the entire product but also be applied evenly on the oil clay. Each product requires at least three layers of silicone, each with a thickness of 1mm. During the application process, wait for each layer to cure completely before applying the next. When applying the third layer, add a layer of gauze on top of the second layer to enhance the silicone’s strength. The total thickness of the silicone part of the mold should be controlled between 3-4mm depending on the product size, and the width should not exceed the product width by 60mm. The silicone starts to set in 20 minutes.
- Clean and dry the master mold, then perform a smoothing treatment (apply a layer of mold release wax or a coat of mold release agent).
- Pour 500-1000 grams of mold silicone rubber (also known as mold silicone, mold gum, or silicone rubber) into a plastic basin for later use.
- Weigh the hardener according to the weight ratio (generally 1.5-2.5%), add it to the container, and mix thoroughly until uniform.
- Add an appropriate amount of silicone thinner if necessary (especially for the first layer) and mix until homogeneous, usually taking 3-5 minutes.
- After mixing the mold silicone rubber with the hardener, the reaction occurs at room temperature and releases low-molecular-weight alcohols. To remove the alcohol molecules from the colloid, degas under negative pressure for 1-3 minutes. Equipment may not be required depending on the mold maker’s operational experience.
- For multi-layer split mold application, it is advisable to ensure simultaneous curing of the inner, middle, and outer layers. When the amount of hardener is relatively small, the reaction time is prolonged, the reaction is more complete, and the colloid quality is better. Therefore, it is recommended to use less hardener for the inner layer and more for the outer layers. Wait for the first (inner) layer to dry before applying the second layer. The operating time is 30-50 minutes, the mold demolding time is 10-15 hours, and the curing time is 24 hours. Note that adding mold cloth after applying the first and second layers can greatly extend the mold’s service life (do not use glass fiber cloth, as it may cause delamination and render the entire mold useless).
- For three-dimensional casting molds, a curing time of 10-15 hours is generally optimal.
