Which type of silicone rubber should you use, RTV Silicone or LSR?

Which type of silicone rubber should you use, HCR or LSR?

There are 4 main types of silicone rubber:

LSR: Liquid Silicone Rubber; RTV: Room Temperature vulcanization; HTV: High Temperature Vulcanization; HCR: High Consistency Rubber.

For Liquid Silicone Rubber and Room Temperature vulcanization Silicone, they are both in liquid state. For Liquid Silicone, which belongs to High temperature vulcanization and can cures at high temperture. But for RTV Silicone, which is a type of room-temperature-vulcanizing silicone that can cures at room temperature.

Please check the table of silicone materials for reference:

Different Properties between RTV and LSR:

Room Temperature vulcanization Silicone belongs to soft-medium hardness material, the hardness normally is from 15 to 40 Shore A. It is usually in a liquid state, and it begins to solidify after contact with air, and the entire curing process can be carried out at room temperature without additional high temperature and without the use of a mold.

Liqud Silicone Rubber has wider hardness range: from 5 to 90 Shore A.

RTV Silicone not only has two-part material but also has one-part material. For 2-part grade RTV, the cure time is very fast and the curing reaction occurs at room temperature. And for 1-part grade RTV silicone, which also cure at room temperature but with slower cure rate compared to 2-part RTV.

LSR are two-part grade silicone, use platinum as the catalyst, and the curing reaction occurs at high temperatures or when the two parts come in contact.

Different forming method for RTV Silicone and Liquid Silicone

RTV Silicone:

Injection Molding, Gravity Casting and Vacuum Casting

Liquid Silicone:

Liquid Injection Molding (LIM), Compression Molding, and Transfer Molding

Compression molding is the most economical and simplest molding compared to Liquid Injection Molding and Transfer Molding, which is designed to place solid silicone rubber materials in mold cavities to molded by heat and pressure. Compression Molded process just like make cake mold. Transfer molding is a combination of liquid silicone injection molding and compression. There is a pot on the top plate and a ram above the pot.

Note: Please check our analysis the difference between compression molding and transfer molding.

Tips: There are many parameters that will affect the choice of  molding method. Need to balance the material, the product design, quality and requirements.

Conclusion:

From the forming methods for these two materials, you can tell that RTV Silicone cures at room temperature and is a good choice for prototype, 3D print, sculpture with low volume and simple structure design. Such as: small and thin-wall parts, scale models, dental plates, cases, housings. And industrial applications: aviation, aerospace, consumer electronics, and microelectronics.

Liquid Silicone Rubber is a good choice for complicate designs, very close dimensional tolerances and higher quality requirement parts with high volume. As liquid injection molding can achieve automated process with short cycle time, and with low material waste.Such as: Gaskets, seals, O-rings, cushion pads, automotive parts, Medical products and babycare parts.