Experience and Insights on Producing Bubble-Free Silicone Hoses

Achieving a bubble-free silicone hose is a systematic process involving raw materials, mixing, extrusion, vulcanization, and environmental control. Air bubbles can severely affect sealing performance, mechanical strength, and overall appearance. Below is a detailed breakdown of the main causes and effective solutions at each stage of production.

1. Raw Materials and Mixing Process

Causes of Bubbles:

• Moisture in silicone base material or curing agent (especially peroxides).

• Excess volatile components in raw materials.

• Improper mixing that traps air within the compound.

• Poor storage conditions causing moisture absorption.

Solutions:

• Pre-drying treatment: Before use, preheat silicone base material and curing agent in an oven at 70–80°C for 2–4 hours to remove moisture and volatiles. This is the most critical and effective step.

• Optimize mixing process: Ensure sufficient mixing time for uniform dispersion and use a vacuum kneader to eliminate trapped air during compounding.

• Proper storage: Keep materials sealed in a cool, dry place and follow the "first in, first out" rule to avoid prolonged air exposure.

2. Extrusion and Molding Process

Causes of Bubbles:

• Incorrect temperature settings in the extruder, especially if the feed zone temperature is too high, causing premature softening and trapped air.

• Poor die design with dead zones that lead to material stagnation and bubble formation.

• Insufficient extrusion pressure failing to compress and discharge trapped air.

Solutions:

• Optimize temperature profile: Adopt a “low-to-high” temperature curve. Keep the rear feed zone cooler to prevent premature curing, while the front and die zones should be hotter to ensure good plasticization and flow.

• Improve die design: Use streamlined conical channels and add venting holes where appropriate to allow gas discharge.

• Adopt vacuum extrusion: The most effective equipment upgrade. A vacuum vent at the plasticizing section removes air and volatiles during extrusion, ensuring bubble-free hose surfaces.

3. Vulcanization Process

Causes of Bubbles:

• Too rapid temperature rise during vulcanization causes the surface to cure first, trapping gases inside.

• Insufficient vulcanization pressure allows gas expansion within the product.

Solutions:

• Stepwise heating: Especially important for thick-walled hoses. Start with preheating at 100–120°C to allow gases to escape, then gradually raise to the final curing temperature (160–200°C) for full vulcanization.

• Ensure adequate pressure: In molding, maintain sufficient closing pressure; in hot air vulcanization, ensure adequate internal air pressure or mandrel support to prevent expansion.

4. Environmental and Operational Factors

Causes of Bubbles:

• High humidity in the production environment.

• Improper feeding operations introducing air into the compound.

Solutions:

• Environmental control: Maintain low humidity in the workshop and ensure consistent temperature.

• Operator training: Reinforce correct feeding and handling practices to minimize air entrapment.

Conclusion

Producing bubble-free silicone hoses requires a holistic approach covering raw materials, equipment, process control, and operator training. By systematically addressing each stage, manufacturers can significantly enhance product quality, reduce defects, and improve production efficiency.

A combination of vacuum mixing, optimized extrusion design, controlled vulcanization, and stable environmental conditions forms the foundation for achieving superior silicone hose performance with perfect sealing and appearance.