Parting line
Determining the location of the parting line is one of the first steps in designing a silicone rubber injection mold. Ventilation is mainly achieved through grooves located on the parting line. Such grooves must be located in the area finally reached by the injection molding compound. This helps avoid air bubbles inside and reduces strength loss at the joint.
Due to the low viscosity of the LSR, the parting line must be accurate to avoid causing glue overflow. Even so, parting lines can often be seen on shaped products. Demolding is affected by the geometry of the article and the location of the parting surface. Designing the product to be slightly chamfered helps to ensure that the product has a consistent affinity for the other half of the mold cavity required.


Exhaust
With the injection of LSR, the air trapped in the cavity is compressed when the mold is closed, and then discharged through the ventilation grooves during the filling process. If the air cannot be completely exhausted, it will be trapped in the rubber (this will often cause the product to show a white edge). Ventilation grooves generally have a width of lmm-3mm and a depth of 0.004mm-0.005mm.
Evacuation in the mold creates the best venting effect. This is achieved by designing a gasket on the parting line and quickly vacuuming all the mold cavities with a vacuum pump. Once the vacuum reaches the rated level, the mold is completely closed and injection pressure is started.
Some injection molding equipment allows operation under a 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 air easier to vent) and then switched to a higher Closing force, so as to avoid silicone rubber expansion and overflow.