Post-processing of Silicone Sealing Strips

The post-processing of silicone sealing strips refers to the series of treatments carried out after extrusion molding and initial vulcanization in order to meet specific requirements for dimension, function, appearance, and performance.

These steps are critical, as they directly determine the final quality and usability of the product.

Below are the major post-processing operations for silicone sealing strips, which can be categorized into several groups:

1. Cutting and Length-sizing

The most basic and common post-processing step, aimed at cutting extruded continuous strips into specified lengths.

• Mechanical Cutting: Uses rotary blades or punching dies for length sizing. High efficiency, suitable for large-volume standard parts.

Laser Cutting: Non-contact cutting using a laser beam. Advantages: Extremely high precision (±0.1 mm), no edge stress, capable of cutting complex cross-sections, no tool wear.

Applications: High-precision seals for electronics and medical devices.

Waterjet Cutting: Uses ultra-high-pressure water jets for cutting. Advantages: No heat-affected zone, smooth cut surfaces, suitable for thick-walled or large sealing strips.

2. Surface Treatment and Finishing

This step improves the surface properties of sealing strips to meet appearance, tactile, or functional requirements.

• Deburring and Flash Removal: Eliminates excess flash and burrs from extrusion and vulcanization.Cryogenic Deflashing: Parts are cooled to below -80℃, making flash brittle, then blasted with high-speed media (e.g., plastic pellets) to remove it. Highly effective for complex profiles and intricate parts, leaving no knife marks and ensuring high quality.

• Mechanical Trimming: Knife blades or grinding wheels are used. Lower cost, but may leave marks and requires skilled operators.

Surface Coating / Flocking: Flocking: Electrostatic application of short fibers (nylon, polyester) onto the surface. Widely used in automotive door and window seals, reducing friction and noise while improving luxury feel and closing sound quality.

Spraying: Application of PTFE (Teflon) or other low-friction coatings to enhance wear resistance and reduce drag.

Surface Activation Treatments: Since silicone has low surface energy and is chemically inert, treatments are needed to improve adhesion. Plasma Treatment: Effectively increases surface energy, making silicone easier to bond with adhesives.

Flame Treatment: A fast and cost-effective method often used to enhance bonding between silicone and plastic parts.

3. Functionalization and Assembly

These processes add extra functionality or assemble strips into more complex components.

• Joint Bonding: Ends of extruded strips are bonded to form closed-loop O-rings or other custom gasket shapes. Methods include specialized adhesives or hot splicing.

• Adhesive Backing: Attaching double-sided adhesive tapes (e.g., VHB, 3M) to the back of strips for easy installation—“peel and stick.” Very common in electronics, appliances, and construction.

• Insert Embedding / Overmolding: Embedding metal or plastic frames into the strip to increase structural strength and dimensional stability. Common in automotive window channels and building curtain wall seals.

• Functional Modifications: While not traditional “machining,” some post-treatments enhance material functionality: Conductivity: Adding conductive fillers for EMI/RFI shielding gaskets.

• Antistatic: Preventing electrostatic buildup.

• Antimicrobial: Incorporating antimicrobial agents for medical or food-grade products.

4. Heat Treatment and Secondary Vulcanization

• Secondary Vulcanization (Post-cure): Purpose: Heating the strip in an oven at specific temperatures (usually 200–250℃) for several hours.

• Effect: Completely removes residual peroxide by-products and volatile compounds, significantly improving compression set resistance, heat resistance, and stability, while eliminating odors. Essential for medical- and food-grade products.

5. Quality Inspection and Packaging

The final stage to ensure product quality before shipment.

• Dimensional Inspection: Using calipers, projectors, or laser measuring instruments to ensure tolerances.

• Performance Testing: Appearance Check: Inspecting for impurities, bubbles, scratches, or contamination.

• Functional Testing: Compression force, rebound resilience, water-tightness, etc.

Packaging: Options include reels, coils, or straight-cut strips.

Release film or talcum powder is used to prevent sticking.

For high-cleanliness applications (medical, electronics), anti-static bags or vacuum packaging are used.

Summary Table of Key Post-processing Steps

Conclusion

The post-processing of silicone sealing strips is a refined and highly application-specific process. Depending on the end use—automotive, medical, electronics, or construction—different combinations of processes are selected. Among them, laser cutting, cryogenic deflashing, flocking, adhesive backing, and secondary vulcanization are the most critical and widely used operations.