Are you evaluating silicone options for your next product or application? At Milosilicone, we know that selecting the proper silicone compound—whether Liquid Silicone Rubber (LSR), High‑Consistency Rubber (HCR), or Room‑Temperature Vulcanizing Silicone (RTV)—can make or break your design’s performance, manufacturability, and cost. In this in‑depth guide, we’ll explore the unique properties, processing requirements, and ideal use cases for each material, helping you make an informed decision that aligns with your production goals and end‑use requirements.
What Makes LSR, HCR, and RTV Different?
Silicone elastomers share a common backbone of silicon‑oxygen (Si–O) chains, but their processing methods and formulations vary widely:
- LSR (Liquid Silicone Rubber): A two‑component, platinum‑cured system that flows like a liquid at room temperature. LSR is metered and mixed in high‑precision machinery, then injection molded into complex parts.
- HCR (High‑Consistency Rubber): A standard silicone rubber supplied as a solid, gum‑like sheet. HCR requires masticating, calendaring, and extruding on rubber mills and presses. It’s cured in heated molds or compression presses.
- RTV (Room‑Temperature Vulcanizing Silicone): A one‑component or two‑component system that cures at ambient temperature—often via moisture in the air or a catalyst. RTV is typically brushed, poured, or dispensed as an adhesive or sealant.
Each silicone type offers distinct advantages—and limitations—depending on your application’s scale, geometry, regulatory needs, and production volume.
Liquid Silicone Rubber (LSR): Automation Meets Precision
Key Characteristics
- Flowable at Room Temperature: LSR begins as two separate fluids (base and catalyst) that are automatically mixed in precise ratios.
- Injection Molding Capability: Enables shot‑to‑shot consistency, thin‑wall sections (down to 0.2 mm), and intricate geometries—including undercuts and overmolds.
- Low Scrap Rates: Automated metering and continuous mixing minimize material waste.
- Biocompatibility & Purity: Platinum‑cured LSR grades meet medical (ISO 10993), food‑grade, and electronics (UL94 V‑0) standards.
Ideal Applications
- Medical Devices: Catheters, seals, diaphragms, and infant‑care products requiring sterilizability and biocompatibility.
- Electronics & Automotive: Keypads, connectors, seals exposed to high temperatures, vibration, and harsh chemicals.
- Consumer Goods: Overmolds on toothbrushes, kitchen utensils, and wearable devices for superior grip and durability.
Processing Considerations
- Equipment Investment: Requires specialized injection molding machines with heated barrels, precision shot dosing, and cold‑runner systems.
- Cleanroom Capability: For medical applications, LSR molding often takes place in ISO 7 or better environments—an offering at Milosilicone.
- Cycle Times: Rapid cure rates (10–60 seconds) allow high throughput but demand precise thermal control.
High‑Consistency Rubber (HCR): Rugged and Scalable
Key Characteristics
- Solid, Gum‑Like Form: Similar to traditional rubbers, delivered on rolls or slabs.
- Molding Versatility: Processed on rubber mills, extruders, or compression/transfer molding presses.
- High Tear Strength & Compression Set Resistance: Excellent for heavy‑duty seals, gaskets, and industrial bellows.
- Broad Temperature Range: Operates from −60 °C to +250 °C continuously.
Ideal Applications
- Industrial Seals & Gaskets: Hydraulic and pneumatic seals in heavy machinery, oil and gas equipment.
- Large‑Format Components: Bellows, expansion joints, and vibration mounts that exceed LSR’s injection‑molded size limits.
- Batch Production: Medium to high volumes where tolerances of ±0.2 mm are acceptable.
Processing Considerations
- Labor‑Intensive Mixing: HCR must be compounded on two‑roll mills or internal mixers to incorporate fillers, pigments, and curing agents.
- Longer Cure Times: Typical mold cure cycles range from 3 to 15 minutes, depending on wall thickness and mold temperature.
- Higher Scrap & Setup Costs: Manual handling and larger batch sizes can lead to increased material waste and longer startup times.
Room‑Temperature Vulcanizing Silicone (RTV): Convenience and Versatility
Key Characteristics
- Ambient Cure: Cures at room temperature without external heat—usually via moisture (one‑component) or added catalyst (two‑component).
- Excellent Adhesion: Bonds to metal, glass, plastics, and previously cured silicone.
- Sealing & Coating Performance: Remains flexible and gap‑filling, with weather and UV resistance.
Ideal Applications
- Sealants & Adhesives: Window glazing, electronics potting, and household caulks.
- Coatings & Encapsulants: Protective dielectric coatings for circuits and sensors.
- Prototyping & Small Runs: Quick turnaround when mold investment is not justified.
Processing Considerations
- Limited Mechanical Strength: RTV silicones typically have lower tensile and tear strength compared to LSR or HCR.
- Longer Cure Schedules: Full cure can take 24–72 hours, depending on humidity and thickness.
- Surface Finish Requirements: RTV may require masking or tooling to achieve a uniform bead or thin film.
Choosing the Right Silicone for Your Project
When weighing LSR vs. HCR vs. RTV, consider these decision factors:
| Criterion | LSR | HCR | RTV |
|---|---|---|---|
| Volume | High (>10k parts/yr) | Medium to high | Low to medium |
| Geometry Complexity | Very high | Medium | Low to medium |
| Tooling Investment | High | Moderate | Low |
| Mechanical Properties | Excellent | Excellent | Moderate |
| Cure Speed | Seconds–minutes | Minutes | Hours–days |
| Cleanroom Compatibility | Easy | Challenging | Easy |
| Environmental Resistance | Excellent | Excellent | Good |
At Milosilicone, we offer all three technologies under one roof, ensuring you get the ideal material and process for your specific requirements.
Partner with Milosilicone for Expert Silicone Solutions
Whether you’re launching a medical device requiring tight tolerances and biocompatibility, designing industrial seals that must withstand extreme pressures, or prototyping custom adhesives for electronics, Milosilicone is your go‑to supplier and manufacturer. Our turnkey capabilities include:
- Design & Material Selection: We help you pick the right silicone grade, durometer, and additives.
- Tooling & Molding: From precision LSR injection to HCR compression molding, we maintain ISO‑certified cleanrooms and advanced press lines.
- Quality & Compliance: Every batch undergoes full inspection—mechanical testing, dimensional analysis, and regulatory validation (FDA, CE).
- Scalable Production: We support low‑volume prototyping through high‑volume runs, adapting processes for cost and efficiency.
Let’s discuss your project needs and determine whether LSR, HCR, or RTV silicone is the best solution. Contact Milosilicone today for a no‑obligation consultation and discover how our expertise can accelerate your time to market.