What's the Difference Between LSR and Thermoplastic Injection Molds

Using different ejecot pins is the main difference to tell thermoplastic injection mold and LSR mold.

For plastic molds, usually use straight-wall ejector pins. The straight pins can cross over the parting line of the plastic parts, so that half the ejector pin is on the part and another half is on the parting line shutoff.

For LSR molds, must use the ejector pins with a tapered shutoff and can’t invade the parting line shutoff area.

Liquid silicone rubber molding processing has a special requirement that is cacuum.

LSR molding also needs a chemical curing process. Liquid silicone rubber comes in two tubes. One tybe has a catalyst and the other one has the crosslinker. And because these two parts mix a chemical reaction takes place that can creat some gas. It is important to remove any air from the cavity before injection to ensure that the mold can properly vent the gases evolved during curing.

During the thermoplastic mold process, plastic material will create outgassing, the mold will have enough gaps in the fit and release areas to release these gases along with the air contained in the cavity area.

LSR and thermoplastic injection molds another difference: Temperature control

LSR Mold:  mold must be heated to 320-420F to cure the material, most commonly with electrical cartridfe heaters.

Plastic Injection Mold: temperature is commonly less than 170F. Becuase themoplastic molding requires cooling the material in the mold, temperature control is typically achieved with circulating oil or water.