Xiamen Better Silicone Rubber Co., Ltd
Liquid Silicone Rubber Molding / LSR Mold Design Guide

Liquid Silicone Rubber Mold with Cold Runner (Needle Valve)

Liquid Silicone Rubber Mold, also called LSR Mould or Silicone Injection Mold, which have some types according to liquid silicone rubber materials feeding systems, silicone materials state, mould runner systems and silicone molded machines types etc.
Actually, for mass production and precision liquid silicone molded parts or products, silicone mold manufacturers or customers mainly choose liquid silicone rubber injection molding with shut-off & needle valves, which can save lsr materials, have long mold lifetime, more precision and easy to automatic production etc.

LSR Silicone Injection Mold:
Following mainly talking about liquid silicone rubber injection mold with needle valves & silicone injection mold designs

LSR Injection Molding Design Guide
Silicone Injection Molding with Cold Rubber Systems Design Guide

Liquid Silicone Injection Molding for Medical Grade Resusicator Oxygen Face Mask
Two different types of LSR injection machines and liquid silicon injection molded designs
1. Vertical LSR Injection Machines and Mold Designs:
This kinds of LSR injection mold & machines mainly designed for 2-shot & liquid silicone rubber overmolding, like liquid silicone rubber overmold with plastic, metal or glass, or two different LSR color, handness or silicone materials etc.

liquid silicone rubber for overmolding silicone membraneRubber To Metal Bonding

Horizontal LSR Injection Machines and Mold Designs
Horizontal Liquid Silicone Rubber Injection Machines, like plastic injection mold, which easier to achieve automated production.

Horizontal Liquid Silicone Rubber Machine

Silicone Injection Molding manufacturing process
Horizontal Liquid Silicone Rubber Machine

Notes:  Common compression machines also can converted into LSR machines only change materials feeding systems, which only produce some LSR products & parts as not high tolerance demands of sizes or designs, like baby care products, packaging products or cosmetics etc. This kind LSR molding is cheap, similar to silicone rubber compression molding or rubber tranfer molding
LSR Injection Molding Designs, is something like plastic injection molding with or without hot runner systems. LSR injection molding with shut-off valves, also called cold runner systems, which can save liquid silicone rubber materials and labor cost, also have good LSR product's surface (small injection gate). Liquid Silicone Rubber Injection molding without shut-off valves, like silicone injection molding, also called hot runner LSR & direct gate liquid silicone rubber injection molding, which can save some mold cost but bigger injection gate (not good lsr product's surface)

Liquid Silicone Rubber Mold with Hot Runner

Liquid Silicone Runner Injection Mold without shut-off valve & needle valve, also called hot runner systems LSR injection mould, which designed for big lsr silicone molded products like liquid silicon bottle & cups shapes, not high precision liquid silicone parts, or like liquid silicone pour-into only for samples or low-volume production, in aim to save liquid silicone mold-making cost.
LSR Injection Molding Hot Runner
Silicone Injection Molding Needle Valve Cold Flow Channel

Converted LSR Silicone Mold By Compression Machines

Compression machines also can converted into liquid silicone molded machines only add LSR material feeding systems, which only produce some LSR products & parts as not high tolerance demands of sizes or designs, like baby care products, packaging products or cosmetics etc.
Converted Liquid Silicone Mold
This kind LSR molding is cheap, similar to silicone rubber compression molding or rubber tranfer & injection molding.
Notes: This kinds of LSR Silicone Mold, called false LSR mold or false silicone injection mold, as have many "sequela" like: short mold life, rough design & sizes tolerance
be restricted by mold structure, and also can't produce complicated-design lsr silicone products.

Converted LSR Silicone Molded Methods
Liquid Silicone Rubber Mold Design for Manual Liquid Silicone Materials Feeding
Solid liquid (manual)
Liquid Silicone Rubber Tranfer Molding & Silicone Injection Mold
LSR hot runner
Cold Runner Systems for Converted Liquid Silicone Rubber Mold
Liquid Injection Molding


Liquid Silicone Runner Injection Mould

Liquid silicone rubber injection molding is the most precise, efficient, and safest and manufacturing process, the products by LSR injection molding with mini parting line and no and less silicone rubber burrs


Wall Thickness:

Because liquid silicone material doesn’t sink like plastic, so it’s  wall thickness does not have to be uniform. The wall thickness can be as thin as possible with silicone molding, can down to 0.127mm.

 liquid silicone rubber bellows

Tolerance and Molded Part Shrinkage:

 Part shrinkage will effect tolerance of products directly. The shrinkage variations of liquid silicone can be little compared to plastic material, so the tolerance of LSR can be much closer. sizes tolerance can less +/- 0.02mm.

liquid silicone injection molded LSR seal

It occurs during molding and post curing or unit fully cross-linked.

It depends on different materials. Typical shrinkage is between 1% and 5%.

Varies by the manufacture and product range from 0.25 per inch.


Optical Properties:

Liquid silicone is optically clear and have higher surface finishes compared to typical glass, and is widely used as optical lens. Some silicone refractive index can equal that of glass (1.53). what’s more, the silicone optical lens are UV aging, can operate at high temperatures, and have wider spectrum of transmission compared to acrylic and polycarbonate.
Optically Clear Liquid Silicone


Radiu and Fillets:

Radiu and fillets not only can improve a product’s appearance but also increase it’s tear strength.


Surface Finish:

Surface finish can match the mold texture. Surface finish can be dull, shiny, or include part identification marks. Surface finish has a direct bearing on the coefficient of friction.

Usually, textured surfaces provide better part releases than polished surfaces when molding.

Liquid Silicone Injection Molding for silicone menstrual cup

Draft Angles:

Draft angels are not required for silicone parts but for plastic part.



Undercuts is available on de-formable products. The products can be stretched to remove from cores without any deforms. Some times, we will add release agent to assist in expanding products to remove from cores. Note: usually, undercuts do not require expensive slides for the mold.


Parting Lines and Gate Location:

Liquid silicone are flexible, have small parting line, and can make the parting line at a suitable location compared to solid silicone and plastic parts.

LSR Products Surface Finishes

PM-F0: non-cosmetic, finish to protolab's discretion
PM-F1: low-cosmetic, most toolmarks removed
SPI-C1: 600 grit stone, 10-12 Ra
PM-T1: SPI-C1 + light bead blast
PM-T2: SPI-C1 + medium bead blast
SPI-A2: grade #2 diamond buff, 1-2 Ra

LSR Flow/Sulfur Analysis

1.The vulcanization chemistry of liquid silicone rubber requires a certain reaction time.
2.Ideal flow, within diameter 2mm, 170cm, and flow distance is more than 100cm.
3.Excessive mold temperatures will cause vulcanization, which cause the flow to be blocked.

LSR Common Problems and Solutions

Too low temperature and too short
Channel pollution
Increase temperature and prolong the time
Clean molding tubes and accelerate feed rate
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