Liquid Silicone Rubber (LSR) Molding Guide

LSR Molding Overview

Liquid Silicone Rubber (LSR) injection molding is a specialized process for producing flexible, heat-resistant, and biocompatible rubber parts. Chinese LSR molding capabilities have grown significantly, with factories concentrated in Shenzhen, Dongguan, and Shanghai.

LSR vs Thermoplastic Molding

Key differences: (1) LSR uses a two-component mixing system instead of a plasticating screw. (2) LSR cures (vulcanizes) in the hot mold (150-200C) rather than cooling. (3) LSR has lower viscosity, enabling thin-wall and intricate designs. (4) LSR requires cold runner systems (no hot runners) to prevent premature curing. (5) LSR molds are typically built with tight venting and degassing provisions.

Applications

Common LSR parts made in China: medical devices (respiratory masks, seals, valves, catheters), baby products (feeding bottle nipples, soothers), automotive (connector seals, gaskets), consumer goods (watch bands, kitchen tools), and industrial seals and gaskets. LSR is increasingly used for multi-component (2K) molding with thermoplastics.

Buyer's Tip: LSR molding looks simple but is technically demanding. Key quality issues: (1) Incomplete curing from insufficient temperature or cycle time, (2) Flash (LSR flash is very thin and hard to detect), (3) Contamination (LSR attracts dust electrostatically), (4) Mold fouling (cured LSR buildup). Chinese LSR specialists should have dedicated LSR equipment, not converted thermoplastic machines. Ask about their cold runner supplier (Arburg, Ducoe, Engel).

What This Means for Your Project: LSR from China offers significant cost savings (40-60%) vs European suppliers. Medical-grade LSR (platinum-cured, FDA-approved) is available from Wacker, Momentive, and Shin-Etsu. Ensure your supplier has experience with your specific LSR material grade. LSR tooling costs are similar to thermoplastic tooling, but per-part cost is typically lower due to faster cycles with cold runner systems.

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