Liquid silicone rubber (LSR) and solid silicone rubber represent two of the most commonly used types of silicone rubbers. Both offer a unique set of properties and advantages that make them suitable for different applications. This article will examine the key differences between LSR and solid silicone to help you determine which material is better suited for your needs.
What is Liquid Silicone Rubber (LSR)?
Liquid silicone rubber (LSR) is a two-component silicone that is supplied in ready-to-use liquid form. LSR consists of a silicone polymer mixed with a platinum-based catalyst that causes it to cure into a rubber-like elastomer.
Some key properties of LSR include:
High tear strength and flexibility
Excellent heat and cold resistance
Good dielectric properties and chemical resistance
Fast cure times allowing high-volume production
Ability to mold intricate, detailed parts
Low compression set and high stability
The liquid nature of LSR makes it ideal for high-volume injection molding of detailed, complex parts. Common applications of liquid silicone rubber include:
Seals, gaskets, and o-rings
Electrical insulation and connectors
Medical devices and implants
Automotive components
Consumer electronics
Precision molded parts
LSR offers versatility and can be customized to achieve different levels of hardness, from very soft gels to medium durometers. The rapid cure times of just seconds also enable automated production.
What is Solid Silicone Rubber?
Solid silicone rubber refers to silicones provided in pre-formed sheets, extrusions or other solid shapes rather than a liquid form. It consists of silicone polymers that are catalyzed and cured into solid elastomers.
Key properties of solid silicone rubber include:
High temperature resistance up to 500°F
Low compression set and high elasticity
Resistance to weathering, ozone, and UV light
Good electrical insulation properties
Excellent chemical and moisture resistance
Ability to withstand extreme environments
The non-flowing nature of solid silicone makes it suitable for applications where preformed shapes are needed. Typical uses of solid silicone rubber include:
Gaskets, seals, and insulation
Rollers and wheels
Connectors and spacers
Flooring and surface protection
High temperature tubing, hoses, and ducts
Food contact applications
Solid silicone can be fabricated by extrusion, molding, or calendering to produce various profiles, sheets, and shapes. The material is also available in a range of hardness levels.
Key Differences Between LSR and Solid Silicone
While both LSR and solid silicone offer useful properties, there are some key differences between the two materials:
1. Form
The most obvious difference is that LSR is a viscous liquid that can be injection molded, while solid silicone is a non-flowing solid that can be extruded or molded into set shapes.
2. Production Method
LSR allows high-volume automated production by injection molding. Solid silicone parts tend to be manually fabricated or molded in lower volumes.
3. Part Complexity
The pourable nature of LSR enables intricate parts with fine details to be replicated consistently. Solid silicone is limited to less complex geometries.
4. Cure Process
LSR cures rapidly within seconds after injection into molds. Solid silicone requires longer oven-curing during fabrication.
5. Strength and Tear Resistance
LSR typically has higher tensile strength and tear resistance than solid silicone rubber.
6. Temperature Resistance
Solid silicone generally has better high temperature capabilities up to 500°F compared to LSR.
7. Compression Set
LSR has lower compression set and higher ability to retain its original shape after compression.
8. Cost
LSR molds are expensive to manufacture initially but allow lower part costs in high volumes. Solid silicone fabrication has lower startup costs but higher per part costs.
Choosing Between LSR and Solid Silicone
Deciding between liquid silicone rubber and solid silicone depends primarily on your application requirements, production needs, and cost considerations.
LSR is ideal when you need:
Intricate molded parts and fine details
High-volume automated production
Superior physical properties like tensile and tear strength
Low compression set and stability over time
Solid silicone rubber works best when you require:
Simpler extruded profiles or molded shapes
Lower volume or manual production
High temperature performance above 400°F
Lower per-part cost in small quantities
LSR is suited for:
Molded gaskets, seals, o-rings
Medical devices and components
Electrical connectors and insulators
Precision consumer product parts
Solid silicone is preferred for:
Gaskets and seals cut from sheeting
Rollers, tubing, hoses
High temperature insulation and shields
Ducting, spacers, bumpers
Your production volume is also a key factor. LSR injection molding offers advantages for large production runs, while solid silicone may be more economical for smaller batches or prototypes.
Consider both the technical needs and economics of your application before deciding between liquid or solid silicone rubber. Partnering with an experienced silicone manufacturer can help you determine the optimal material and process to meet your specific requirements.
LSR Molding vs. Solid Silicone Fabrication
The production processes used for LSR and solid silicone parts also differ significantly:
LSR Molding
Uses multi-cavity injection molds
Automated, high-volume production
Rapid cycle times as low as 10-30 seconds
Consistent, flash-free complex parts
Requires high initial mold cost
Lower material cost at high volumes
Solid Silicone Fabrication
Manual or hydraulic presses for molding
Extrusion and calendering to make sheets/profiles
Lower volumes, more labor-intensive
Simpler part geometries
Lower startup costs for tools and dies
Higher material cost per part
For LSR, the initial investment is in precision injection molds that allow low-scrap automated production. This results in lower costs at higher volumes.
Solid silicone fabrication involves lower initial tooling costs but more manual processes. This leads to higher overall part costs except at very low volumes where initial mold costs are prohibitive.
LSR and Solid Silicone Properties Compared
The table below compares some typical physical properties between LSR and solid silicone rubber:
| Property | LSR | Solid Silicone |
|---|---|---|
| Hardness Range | 10 Shore A to 80 Shore A | 20 Shore A to 90 Shore A |
| Tensile Strength | Up to 11 MPa | Up to 10 MPa |
| Elongation at Break | 300% to 800% | 100% to 800% |
| Tear Strength | 15-35 kN/m | 10-25 kN/m |
| Compression Set | Down to 15% | Typically 25-50% |
| Operating Temperature | -55°C to 200°C | -60°C to 250°C |
As seen above, LSR generally provides higher tensile strength, elongation, tear resistance, and lower compression set capabilities compared to solid silicone. However, solid silicone can handle slightly higher operating temperatures.
Silicone Rubber Applications and Uses
The unique properties of both solid and liquid silicone rubber make them suitable for the following typical applications:
LSR uses:
O-rings, seals, and gaskets
Precision molded parts like valves, connectors, and nozzles
Healthcare components like catheters, tubes, and masks
Automotive sensors, membranes, and boots
Electronics assembly, thermal pads, and insulation
LED light housings, lenses, and encapsulants
Solid silicone applications:
Gaskets, seals, washers, spacers
Robotic end-effectors, grippers, wheels, rollers
High temperature hoses, ducts, tubing
Electrical insulation, thermal protection
Anti-vibration pads, shock absorbers
Food contact approved parts
Silicone rubber combines useful properties like temperature resistance, flexibility, sealing capabilities, chemical stability, and electrical insulation. This versatility allows liquid or solid silicone to serve critical roles across a wide range of industrial and consumer products.
Key Takeaways on LSR and Solid Silicone
Liquid silicone rubber (LSR) is a two-part silicone that injection molds into complex precision parts.
Solid silicone rubber comes in preformed shapes like sheets, tubes, and extrusions.
LSR offers higher strength and tear resistance while solid silicone has better high heat capabilities.
LSR enables high volume production of intricate detailed parts.
Solid silicone allows lower startup costs for simpler geometries and prototypes.
Consider technical requirements, manufacturing needs, and economics when choosing between the two materials.
Both liquid and solid silicones are widely used for seals, electrical insulation, automotive and consumer applications.
Finding the Right Silicone Partner
We hope this overview has helped illustrate the capabilities and differences between liquid silicone rubber and solid silicone materials. To take full advantage of their benefits, it’s important to work with an experienced silicone manufacturer for your project.
Our engineers have expertise in designing optimal LSR injection molds and fabricating solid silicone components that exceed expectations. We stay on top of the latest advancements in materials, manufacturing processes, and quality systems. Leverage our knowledge and capabilities to achieve parts with exceptional performance, quality, and value.
Contact us today to discuss your specific application requirements. We’ll help determine the ideal silicone solution to meet your needs.
