Specific requirements for the raw materials of silicone rubber and the production of silicone rubber products

1. Requirements for Extrusion-Grade Silicone Compounds

Plasticity range: 200～280; Die swell controlled at 10%～25%
Reinforcing filler: Fumed nano silica is preferred. Precipitated silica contains high moisture and tends to cause foaming during hot-air vulcanization, not recommended for high-end food-grade tubing.
Structure control agent: Hydroxyl silicone oil is the first choice for platinum-cured systems. Hexamethyldisilazane is commonly used in peroxide-cured grades.

Food grade (coffee machine water & steam tubing): Platinum addition curing system

Dicumyl peroxide (DCBP) is prohibited, as it generates small molecular substances that migrate under high-temperature steam, causing unpleasant odor.

Di-tert-butyl peroxide (DBPH) is only applicable for non-food-contact structural parts.
General industrial extruded strips/cable materials: DCBP curing system for continuous hot-air vulcanization.

Anti-scorch property: No premature curing under screw shearing and heating inside the barrel.
Low volatile content: Low moisture and low cyclic siloxanes to avoid pinholes and internal bubbles.
Good surface forming performance: Resists sharkskin, bamboo defect and melt fracture during high-speed extrusion for smooth surface.
Consistent batches: Stable hardness, plasticity and shrinkage rate for long-term dimensional consistency.
Low fouling: Non-stick to screws and less carbon accumulation during continuous mass production.

Tensile strength ≥7.0 MPa; Tear strength ≥15 kN/m; Elongation at break ≥400%

Operating temperature: -60～180℃, short-term resistance up to 200℃ under steam

Compression set (175℃ × 22h) ≤35% (critical index for sealing tubing)

Smooth inner and outer surfaces; free of sharkskin, scratches, pits, bubbles, pinholes, impurities and color difference.
No twisting, uneven wall thickness or bamboo-shaped deformation; transparent tubing free of haze and crystal spots.
Clean cutting surface; no delamination for co-extruded multi-layer tubing.

ID / OD standard tolerance: ±0.10～±0.15 mm; Precision food tubing: ±0.08 mm
Uniform wall thickness, eccentricity ≤8% (critical for pressure-bearing coffee tubing to prevent rupture)
Post-vulcanization shrinkage: 0.8%～1.3%; Shrinkage compensation must be considered in die design.

Process: Platinum curing + post-curing

Recommended post-curing: 200℃, 4～6 hours, to remove low-molecular D4/D6 cyclic siloxanes, eliminate odor and reduce migration.
Compliance Standards

China: GB 4806.11; Export markets: FDA 21CFR177.2600, LFGB
Sensory requirement: Odor-free. No off-flavor or contamination to coffee after exposure to hot water and steam.
Medium resistance: Resist hot water and saturated steam; No hardening, cracking or bleeding after long-term thermal cycling.

Thermal cycling resistance: No hardening, cracking or rapid elasticity degradation under repeated temperature cycles (-40℃ ↔180℃).
Burst pressure meets design requirements without slow leakage.
Aging resistance: Resists yellowing and cracking under long-term humidity and ozone exposure.
Good resilience: No permanent deformation after repeated bending during assembly.

Low inner surface friction & low absorption, less scale and coffee grease adhesion, easy cleaning.

Main vulcanization method: Continuous hot-air vulcanization tunnel, temperature range 180～320℃
Compounded silicone should be fully cooled and matured with constant-temperature storage; hot compound cannot be extruded directly.
Feed continuously with long silicone strips. Fragmented feeding easily entraps air and forms bubbles.
Stable traction speed; speed fluctuation directly creates bamboo-shaped dimensional defects.