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Liquid silicone injection molding:

1 shrinkage rate

Although LSR does not shrink in the mold, they often shrink by 2.5%-3% after demolding and cooling. As for the amount of shrinkage, it depends to some extent on the formulation of the compound. However, from a mold perspective, shrinkage may be affected by several factors, including the temperature of the mold, the temperature at which the compound is demolded, and the pressure within the mold cavity and the subsequent compression of the compound.

The location of the injection point is also worth considering because the shrinkage of the flow direction of the compound is generally greater than the shrinkage of the vertical flow direction of the compound. The outer dimensions of the product also have an effect on the shrinkage rate, and the shrinkage of the thicker product is generally smaller. If secondary vulcanization is required, it may shrink by an additional 0.5% to 0.7%.

2 parting line

Determining the location of the parting line is one of the first few steps in designing a silicone rubber injection mold. Exhaust is mainly achieved by grooves located on the parting line, such grooves must pass through the area where the injection molding material finally arrives. This helps to avoid internal bubble generation and reduce the strength loss at the bond.

Due to the low viscosity of the LSR, the parting line must be precise to avoid spillage. Even so, the parting line is often seen on the shaped product. Demolding is affected by the geometry of the article and the location of the parting surface. Designing the article to be slightly chamfered helps to ensure that the article has a consistent affinity for the other half of the cavity required.