Introduction
Custom rubber seals can be manufactured through various molding processes, including Liquid Silicone Rubber (LSR) Injection Molding, Rubber Extrusion, Rubber Overmolding, and Rubber Compression Molding. Each process is suited for different types of products, and the most appropriate method should be chosen based on factors such as product shape, production volume, material performance requirements, and cost considerations.
This article will focus on the Rubber Extrusion process, which is particularly ideal for producing continuous rubber products with specific cross-sectional profiles. It is widely used in applications like seals and tubing.
What Is the Rubber Extrusion Process?
Rubber extrusion is a continuous manufacturing process in which rubber compounds are heated, pressurized, and then forced through a shaped die to produce products with a consistent cross-sectional profile. Unlike injection molding, extrusion is more suitable for producing long, continuous components in large quantities.
Characteristics: Why Rubber Extrusion?
Unlike injection molding, extrusion is better suited for producing high-volume, long-length rubber products such as hoses, weatherstrips, cable jackets, and custom profiles.
- Continuous production: Supports virtually unlimited lengths of tubing, rods, films, cords, and complex profiles.
- High throughput: A single-screw extruder can produce up to 90 tons per year, compared to around 30 tons per year from an injection molding machine with the same screw diameter.
- Versatile applications: Extrusion can be used for mixing, coloring, compounding, reinforcing, and shaping a wide range of rubber products.
- Lower investment, faster turnaround: Switching dies and auxiliary equipment enables quick product changes at minimal cost.
Related reading: Key Molding Processes of Silicone Rubber Sealing Rings
Rubber Extrusion vs. LSR Injection Molding vs. Rubber Overmolding vs. Rubber Compression Molding
| Process | Applicable Product Shape | Material Characteristics | Process Features | Typical Applications |
| LSR Injection Molding | Precision, complex 3D shapes | High transparency, conductivity, flame retardancy | High automation, high precision, suitable for mass production | Medical, baby products, electronic seals |
| Rubber Extrusion | Long, continuous profiles with consistent cross-section | Sealing, waterproof | Ideal for continuous production, cost-effective | Seals, tubing, cable sheaths |
| Rubber Overmolding | Rubber and metal/plastic composite parts | Combination of dissimilar materials | Strong bonding of rubber with dissimilar materials, enhancing structural performance | Industrial buttons, grips, plug housings |
| Rubber Compression Molding | Simple or moderately complex parts | Various rubber materials | Suitable for small batch production with quick mold development | O-rings, gaskets, seals |
Typical Applications
- Automotive: Door and window seals, tubing, shock absorbers, under-hood insulation
- Construction: Weatherstrips, expansion joint covers, façade gaskets
- Electronics: Cable sleeves, insulation tubes, connector grommets
- Medical: Silicone medical tubing, fluid transfer lines, peristaltic pump hoses
- General Industry: Anti-vibration mounts, belt covers, sealing systems
- Home & DIY: Window insulation strips, flooring edge trims, gap fillers
Recommended reading: What Is EPDM Seal and Gasket?
Core Equipment in the Extrusion Line
1. Extruder
The heart of the process. The extruder melts and conveys rubber material forward. Equipment ranges from traditional plunger types to advanced cold-feed screw extruders—including pin-barrel and vented twin-screw models. Precision screw extruders now enable high-speed output with tight dimensional tolerances, making them suitable for complex composite applications (e.g., radial tire layers).
2. Die (Mold)
Custom-engineered dies define the final cross-sectional shape of the product. Precision die design is critical to ensure dimensional stability and surface quality.
3. Cooling Systems
Includes water troughs, air coolers, or spray chambers to quickly cool and stabilize extruded profiles.
4. Haul-off Units
Maintain consistent pull speed to ensure dimensional accuracy and process stability.
5. Cutting / Winding Systems
Extruded rubber is either cut to length or spooled, depending on the product type.
6. Curing / Vulcanization Equipment (Optional)
For many rubber products, post-extrusion curing is essential to enhance elasticity, durability, and chemical resistance. Hydraulic vulcanizers are now favored over mechanical types due to greater efficiency and stability.
If you’re looking for a reliable partner for custom extruded silicone products, consider working with a full-service provider that covers everything from design and mold development to extrusion and post-processing. Feel free to contact us!
Key Stages of the Rubber Extrusion Process
Rubber is typically supplied in pellet or block form and may consist of natural rubber, synthetic rubber, or blends. Additives such as vulcanizing agents, plasticizers, fillers, and colorants are included as needed. Below are key stages of silicone extrusion process:
1. Compounding
Raw elastomers are mixed with additives to achieve the desired properties. For silicone products, high consistency rubber (HCR) or liquid silicone rubber (LSR) is often used.
2. Feeding & Plasticizing
Rubber is fed into a screw extruder, where it is heated and sheared to reach a flowable state. Precise temperature control is essential to prevent thermal degradation, especially for silicone.
3. Shaping Through the Die
The molten rubber passes through a custom-designed die that defines the product’s cross-sectional profile. Die accuracy is crucial for product quality.
4. Cooling & Sizing
The extrudate is rapidly cooled using water or air systems to stabilize its shape. Cooling rate must be carefully managed to prevent internal stress.
5. Haul-Off & Cutting
The cooled product is pulled at a synchronized speed and either cut to length or wound into rolls.
6. Curing / Vulcanization
Depending on the compound, the extrusion process may be followed by continuous vulcanization (CV) using hot air tunnels, salt baths, or microwave systems. This step enhances and stabilizes the product’s mechanical and thermal properties.
More reading: Rubber Split Grommets
Technical Control Points
To ensure consistent quality and performance, the following parameters must be tightly controlled:
- Material formulation: Match rubber base and additives to end-use requirements
- Temperature control: Maintain ideal barrel zone temperatures to prevent degradation or poor flowability
- Die precision: Surface finish and tolerance directly affect geometry and appearance
- Cooling rate: Excessive speed can cause stress; too slow reduces efficiency
- Haul-off synchronization: Must match extrusion rate to avoid stretching or buckling
Advanced Extrusion Technologies
Vibration-Assisted Extrusion
Also known as vibration extrusion, this method introduces controlled mechanical vibrations during processing. It improves melt flow, reduces die swell, and enhances surface finish and mechanical properties.
Though still emerging, it holds potential for high-precision elastomer processing. Industrial use in silicone rubber extrusion remains limited, but active R&D may unlock broader adoption.
Reactive Extrusion
Allows chemical reactions (e.g., dynamic vulcanization, grafting) to occur during processing, enabling enhanced material properties.
Microcellular Foam Extrusion
Generates lightweight, insulating materials with a fine-pore structure. Common in footwear, packaging, and interior parts.
Co-Extrusion
Combines two or more materials from separate extruders into layered or multi-component profiles. Often used in multilayer films, cables, and high-performance gaskets. Also applied in cost reduction via internal recycling.
Precision Extrusion
A tightly controlled process achieving high dimensional accuracy and uniform material distribution at the microstructural level. By maintaining stable conditions for melt pressure, flow rate, and temperature, it delivers tolerances 50% tighter than standard methods. Used in:
- Medical-grade tubing
- Biaxially oriented films
- Optical fiber coating
- Photographic and projection films
- High-precision foam components
- Hazardous material containment
Success depends on stable equipment and precise parameter control, often requiring specialized precision extruders.
For industries requiring high-precision sealing profiles, partnering with an experienced silicone extrusion manufacturer is key to ensuring material performance and dimensional accuracy.
Conclusion
Rubber extrusion offers a reliable and efficient solution for producing consistent, high-quality rubber components. With ongoing advancements in precision and automation, it continues to support a wide range of industrial applications while helping manufacturers meet performance, cost, and scalability demands in today’s competitive environment.
