In mold design, there are generally the following forms:
1) Hot runner
More wasteful materials, simple design, low cost, mostly used for large products.
2) Cold runner with needle valve
Can realize automation and short cycle.
3) Cold runner without needle valve

Because the LSR has a high expansion coefficient, it expands when heated, but shrinks slightly when cooled, so the part cannot maintain accurate side margins in the mold. Therefore, cold runner processing can be used. The LSR should maintain a lower temperature and fluidity. The cold runner adopts a closed system. During the injection cycle, the closed system uses a "sealing needle" or "needle valve" in each runner. "To control the accurate metering of LSR materials. Silicone rubber has significant thermal expansion characteristics, with a shrinkage of 2% to 4% (vulcanization temperature is 150 ° C). At the same time, silicone rubber has the characteristics of compression deformation.