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Silicone molds are specialized mold-making materials used in crafting and industrial applications. They are known for their high heat resistance, corrosion resistance, strong tear strength, and excellent flexibility. These properties make them ideal for creating detailed and durable molds for a wide range of products.
Here is a simplified overview of the silicone mold production process. The first step involves choosing the right mold opening style and selecting an appropriate mold line. This decision should consider ease of mold removal, the overall appearance of the product, and the impact on product quality. For example, if the mold line is too high on a water series product, it may lead to excess material and cracking. It’s also important to minimize the number of steps in the process, such as using half-mold techniques.
To prevent silica gel from flowing out, the mold is often fixed with wood or other supports. When the mold is opened, the wooden parts separate cleanly, ensuring no gaps between the mold and the sludge. The surface of the sludge should be smooth and even. Before applying the silicone, the mold is coated with Vaseline or a release agent. For smooth surfaces, a clean cloth is used to apply Vaseline evenly, allowing it to absorb fully before wiping off any excess. For textured surfaces, Vaseline is applied uniformly, and the silica gel is adjusted accordingly.
When mixing the silica gel, it's essential to stir in an irregular direction to ensure thorough mixing of the curing agent and the gel, while minimizing air bubbles. For the first layer, vacuuming is recommended at -0.1 Mpa for 7-8 seconds to remove trapped air. Once mixed, the silica gel should be poured into the highest part of the mold and allowed to flow naturally. A brush can be used to guide the gel into place.
If making a single-layer mold, the entire surface should be evenly coated. Each layer should be cured before applying the next. At least three layers are typically applied, with each layer about 1mm thick. When applying the third layer, a reinforcing mesh is added to the second layer to increase strength. The total thickness of the silicone mold should be around 3-4mm, with a width not exceeding 60mm. The initial setting time is approximately 20 minutes.
The process starts by washing and drying the master mold, optionally applying a mold release wax or agent. Then, 500-1000 grams of silicone rubber (also known as mold glue or silicone) is placed into a container. The hardener is weighed according to a ratio (usually 1.5-2.5%) and mixed thoroughly. Depending on the situation, especially for the first layer, a small amount of silica gel thinner may be added to achieve a uniform mix, typically taking 3-5 minutes.
Once mixed, the silicone rubber reacts at room temperature, releasing low molecular alcohol. To remove these molecules, negative pressure is applied for 1-3 minutes. Alternatively, this can be done manually based on experience. For multi-layer molds, all layers should be cured simultaneously. If the amount of hardener is low, the reaction time increases, resulting in better curing. It’s best to use less hardener than necessary. After the first and second layers are applied, adding a mold cloth improves the mold's durability. However, glass fiber cloth should be avoided to prevent delamination.
For three-dimensional molds, curing usually takes 10-15 hours. After the soft mold is completed, a plaster or FRP jacket is added for support. Mold line selection is crucial—choose a position that doesn’t affect the product’s appearance, is easy to process after pouring, and allows for easy disassembly without deforming the product.
Common issues when using mold silicone include:
1. **Why does the mold silicone produce fewer casts?**
Excessive silicone oil can weaken the molecular structure, reducing the mold’s lifespan. High-hardness silicone may become brittle, while low-hardness silicone may lack strength, leading to deformation.
2. **Why does the mold silicone burn?**
Adding peroxide-based curing agents to unsaturated resins can cause excessive heat, leading to burning if the mold isn't removed quickly enough.
3. **Molding methods and types of molds:**
Slicing or sheet molds are made by brushing or pouring vacuum-treated silica gel. For stencils, a release agent is applied first, followed by the silicone. Reinforcing fabric is added for strength.
4. **Why does the silica gel appear dry?**
Condensation-type silica gel requires moisture to cure. If there's insufficient moisture, it may seem dry, but adding 0.05% water can resolve this.
5. **Why does the mold have poor pull strength?**
Adding too much silicone oil reduces the gel’s tear strength, leading to a weaker, shorter-lasting mold.
6. **Why does the mold look oily?**
Using mineral oil instead of silicone oil during the process can cause an oily residue.
7. **Why is the mold not resistant to acid, alkali, or aging?**
Excessive silicone oil can damage the molecular structure, reducing chemical resistance and longevity.
8. **Why do the mold surfaces have marks or streaks?**
Poorly polished models or uneven application of release agents can result in an unattractive finish.
9. **What are the common uses of mold silicone?**
It’s widely used in toy, gift, and craft industries, as well as in resin, candle, and furniture manufacturing. It’s also used for reproducing characters, statues, and architectural elements.
Each application may require different parameters, so it’s important to adjust the process accordingly. Whether for small details or large-scale production, silicone molds offer versatility and reliability.