Liquid vs. Solid Silicone: How to Tell Them Apart and Choose a Machine

Customers often ask whether they need a liquid silicone (LSR) injection machine or solid silicone equipment. Here is how to tell the two apart.

Appearance

LSR parts are highly transparent and odorless, with a visible injection gate and no obvious parting-line flash. Solid silicone parts are less transparent, may smell of curing agent, have no injection gate, and show a parting line where the upper and lower molds meet.

Applications

• LSR: baby products, kitchenware and medical products — items that come into direct contact with food and the body.
• Solid silicone: daily-use goods, industrial parts, waterproof seals for electronics and automotive components.

Material safety

LSR is a highly transparent, high-safety material; no curing agent or other additives are added during molding. Solid silicone requires a curing agent to speed up vulcanization, demolding and feeding.

Molding process

LSR is vulcanized in an injection molding machine. The process is simple, accurate and productive, and saves labor, power and material. Solid silicone is mixed, cut to size and placed into the mold, then formed in a compression press at a set temperature, with mold cleaning required after demolding.

Tooling

Solid silicone molds are relatively simple and inexpensive — a cavity machined to the part's dimensions. LSR molds are more complex: gate location, cold runner system, venting and mold temperature monitoring must all be designed in, so tooling costs more.