Liquid silicone molds are molds used for casting products using liquid silicone. Liquid silicone exhibits excellent properties such as transparency, tear strength, resilience, anti-yellowing, thermal stability, water resistance, good breathability, heat aging resistance, and weather resistance. It has moderate viscosity, making it easy to handle. Liquid silicone molds produce high-quality products with high transparency, allowing for the detection of defects such as air bubbles. The linear shrinkage rate is ≤0.1%, ensuring precise replication of product dimensions.
Liquid silicone molds have wide application in various industries, including medical, baby products, electronic industrial parts, diving supplies, kitchen utensils, and daily necessities. They are particularly suitable for products with food-grade and medical-grade requirements.
The design of liquid silicone molds can be understood from two aspects:
1. Classification based on glue feeding methods:
- Solid to liquid (manual): Low precision, low efficiency, low cost, and minimal waste. Suitable for simple mold structures without runners.
- Solid to liquid (automatic): High precision but can result in significant waste. High efficiency. Suitable for molds with relatively complex structures that require runners.
- Hot runner: Also known as a runnerless mold, it uses heating devices to keep the runner molten. It has a simple design and low production cost. Waste generation is higher compared to other methods and requires trimming.
- Needle valve cold runner: The gate is small and cooled by water circulation. It requires a runner plate and has higher production costs compared to hot runners. It reduces waste generation, saves raw materials, and has the distinctive feature of a needle valve for injection and ejection.
2. Classification based on molding methods:
- Compression molding: Used with ordinary compression machines.
- Vertical liquid silicone injection molding machine: Suitable for large products and secondary molding. It can be a single or double sliding plate type, with the double sliding plate type improving production efficiency. Commonly used for overmolding products, iron piece molds (with inserts made of metal, silicone, or high-temperature resistant materials like ABS, PS, PC, PA, PPSU), and secondary molding in industries such as electronics, medical, maternal and child care, and kitchen and bathroom.
- Horizontal liquid silicone molding machine: Enables fully automated production with automatic product drop-off, fast mold adjustment, and precise position control. Used for products like liquid silicone pacifiers, straws, teats, pacifiers, and teething toys.
Some considerations when manufacturing liquid silicone molds include:
- Shrinkage: Although liquid silicone does not shrink in the mold, it typically experiences a shrinkage of 2.5% to 3% during demolding and cooling. The exact shrinkage depends on the compound formulation. Factors such as mold temperature, demolding temperature, pressure within the cavity, and subsequent compression can influence shrinkage. The location of the injection point is also important since shrinkage is typically greater in the direction of compound flow than perpendicular to it. Thicker products generally experience less shrinkage.
- Parting line: The first step in designing a liquid silicone injection mold is determining the parting line’s position. Venting is achieved through grooves on the parting surface that must be located in areas where the injected rubber will ultimately reach to avoid bubble formation and minimize strength loss at bonding joints. Due to the low viscosity of liquid silicone, accurate parting lines are necessary to prevent overflow. However, visible parting lines are often present on the final product. The design of a slightly chamfered product helps ensure consistent mating with the desired counterpart cavity influenced by the product’s geometric dimensions and parting surface location.
Silicone Pro Co., Ltd. is committed to producing LSR parts, liquid silicone rubber products for all customers.
You are welcome to contact us anytime with your drawings or design. Professional technical assistance can be provided for you.
