In today’s smart hardware market, particularly in the high-end smartphone sector, waterproof performance has become a standard requirement. The core component for achieving this performance is often the tiny, high-precision Liquid Silicone Rubber (LSR) waterproof ring.
Unlike traditional thermoplastic processing, LSR is favored for its eco-friendliness, durability, and superior physical properties. However, its processing difficulty is significantly higher. To find the perfect balance between mold materials, shrinkage control, and cold runner systems, MINHUI suggests that manufacturers must master the following three critical aspects of precision injection molding.
Ensuring thorough mixing of liquid silicone components
LSR typically consists of two components, Part A and Part B. To ensure the vulcanization effect and physical properties of the final product, the mixing process is the first hurdle.
- Precise Mixing Ratio: LSR must be mixed strictly at a 1:1 ratio. If producing colored liquid silicone products, the pigment ratio must also be controlled with milligram-level precision to ensure color consistency across batches.
- Efficiency of the Static Mixer: The static mixer is a vital component in the injection system. Only after the A and B components are thoroughly and uniformly mixed by the static mixer can the silicone injected into the mold be fully vulcanized. As a leading solution provider, MINHUI designs its equipment’s mixing systems to ensure materials reach an ideal state of uniformity before entering the injection chamber.
Component sealing and temperature control of the injection molding machine
Due to its low viscosity, LSR demands near-stringent precision from the processing equipment.
1. Structural sealing to prevent backflow
LSR has much higher fluidity than traditional plastics, making it prone to backflow and leakage during injection. This requires the screw of the injection molding machine to have extremely high sealing performance. When designing micro-injection molding solutions, MINHUI utilizes specialized sealing components optimized for low-viscosity materials to eliminate flash and leakage at the source.
2. The utility of water-cooled nozzles
The characteristic of LSR is that it “cures upon heating,” while the mold is typically kept at a high temperature. To prevent the material from curing prematurely and clogging the nozzle before it enters the mold, using a water-cooled nozzle structure is essential. This ensures the nozzle temperature remains low enough to maintain continuous production.
Precision control of the finished product during injection
Smartphone waterproof rings are often overmolded onto metal or plastic parts, meaning they are tiny and require an extremely high degree of fit.
- Vacuuming and Parting Lines: When designing the mold, the position and accuracy of the parting line must be pre-considered to avoid air entrapment and welding lines, which prevents burrs. Using a vacuum pump to evacuate all cavities before injection is an effective way to avoid defects.
- Compensating for Shrinkage: Although LSR has virtually no shrinkage during the actual injection, it typically experiences 2% to 3% shrinkage after demolding and cooling due to its high coefficient of thermal expansion. MINHUI engineers fully account for this variable during the mold design phase, combining it with precise gate placement for compensation.
- Temperature Uniformity: The temperature distribution within the mold must be uniform, with the temperature difference controlled within ±10°C. Uneven temperature can lead to inconsistent vulcanization, affecting the seal reliability of the waterproof ring.
Conclusion
Liquid silicone injection molding is an art of speed and extreme precision. From the accurate mixing of A/B components to the cooling control of the nozzle and the creation of a vacuum environment in the mold, every step determines the final quality of the waterproof ring.
If you are looking for more efficient and precise liquid silicone processing solutions, MINHUI is dedicated to helping you overcome the challenges of precision LSR manufacturing through innovative molding technologies.
