Parting line
Determining the location of the parting line is one of the first steps in designing a silicone rubber injection mold. Exhaust is mainly achieved through the grooves located on the parting line. Such grooves must be in the area where the injection molding compound finally reaches. This helps avoid internal bubbles and reduces strength loss in the glued joint.
Due to the low viscosity of LSR, the parting line must be precise to avoid glue overflow. Even so, parting lines can often be seen on shaped products. Demolding is affected by the geometric dimensions of the product and the position of the parting surface. Designing the part with a slight chamfer helps ensure that the part has consistent affinity to the desired other half of the mold cavity.

Exhaust
With the injection of LSR, the air trapped in the mold cavity is compressed when the mold is closed, and then is discharged through the ventilation grooves during the mold filling process. If the air cannot be completely discharged, it will remain in the rubber compound (this will often cause white edges to appear on parts of the product). Ventilation grooves generally have a width of lmm-3mm and a depth of 0.004mm-0.005mm.
Applying a vacuum inside the mold creates the best possible degassing effect. This is accomplished by designing a gasket on the parting line and using a vacuum pump to quickly evacuate all mold cavities. Once the vacuum reaches the rated level, the mold is completely closed and injection begins.
Some injection molding equipment allows operation with variable closing force, which allows the processor to close the mold at low pressure until 90%-95% of the mold cavity is filled with LSR (allowing air to escape more easily) and then switch to higher pressure. The closing force is to prevent the silicone rubber from expanding and causing glue overflow.