Parting line
Determining the position of parting line is one of the first steps in the design of silicone rubber injection mold. The exhaust is mainly realized by the groove on the parting line, which must be in the last area of the injection molding compound. This will help to avoid internal bubbles and reduce the strength loss of the adhesive joint.

Due to the low viscosity of LSR, the parting line must be accurate to avoid overflow. Even so, parting lines are often seen on the finished products. Demoulding is affected by the geometrical dimension of the product and the position of parting surface. The product is designed to have a slight chamfer, which helps to ensure that the product has the same affinity to the required other half of the cavity.

exhaust
With the injection of LSR, the air trapped in the mold cavity is compressed when the mold is closed, and then discharged through the vent groove as the mold is filled. If the air can not be completely discharged, it will stay in the rubber (this will often cause part of the product exposed white edge). Generally, the width of the ventilation groove is lmm-3mm, and the depth is 0.004mm-0.005mm.

Vacuuming in the mould can create the best exhaust effect. This is achieved by designing a gasket on the parting line and rapidly vacuuming all the cavities with a vacuum pump. Once the vacuum reaches the rated level, the mold is completely closed and the injection begins.

Some injection molding equipment allows operation under variable closing force, which allows the processor to close the mold under low pressure until 90% - 95% of the cavity is filled with LSR (making it easier for the air to be discharged), and then switch to a higher closing force to avoid rubber overflow due to expansion of silicone rubber.