Rubber and Plastic Extrusion Process Industry Knowledge
The rubber and plastic extrusion process is a continuous, high-efficiency molding method. Its core principle involves forcing material through a die with a specific cross-section using a screw or plunger, resulting in a continuous profile (such as sealing strips, pipes, or wire/cable sheathing).
Below is the core framework of this process:
1. Core Process Flow
Feeding: Adding compounded rubber granules or powder into the extruder hopper, which enters the barrel via gravity or forced feeding.
Plasticizing/Compounding: Under the action of the rotating screw and heated barrel, the material undergoes solid conveying, melting, and shear mixing to achieve a uniform plastic state.
Extrusion: The plasticized melt is pushed forward by the screw and passes through the machine head and die at a certain pressure and speed.
Die Forming: The molten material flows through the die gap of a specific shape to initially form the continuous profile cross-section. This is the most critical step determining product shape accuracy.
Sizing & Cooling: The high-temperature, soft extrudate enters a cooling water tank or vacuum calibration table, rapidly cooling and solidifying to maintain shape stability (Note: Rubber typically requires subsequent vulcanization, while plastics are directly cooled and shaped).
Haul-off & Cutting: A puller draws the product at a matched speed, followed by cutting to length or winding by a coiler.
2. Key Equipment: Extruders
Single-Screw Extruder: Simple structure, low cost, easy operation. Suitable for most thermoplastics and general rubber products (e.g., pipes, sheets, profiles).
Twin-Screw Extruder: Excellent mixing performance, self-cleaning ability. Ideal for modified plastics, compounding, and processes requiring high shear.
Cold Feed vs. Hot Feed (Rubber Specific):
Hot Feed:Rubber must be pre-warmed and softened on a mill before feeding. High energy consumption; gradually being phased out.
Cold Feed:Room-temperature rubber is fed directly into the machine. The barrel features grooves or pins for more uniform plasticizing. This is the mainstream standard for modern rubber extrusion.
3. Common Defects & Control (Troubleshooting)
Melt Fracture / Shark Skin: Surface roughness or irregularities caused by excessively fast exit velocity or poor die design. Mitigated by reducing screw speed or increasing die gap.
Dimensional Fluctuation: Inconsistent thickness, usually due to unstable feeding, significant temperature fluctuations, or mismatched haul-off speed. Requires checking the feeding system and temperature control precision.
Bubbles / Voids: Raw material moisture or poor venting. Requires drying raw materials or checking the vacuum venting device.
Warping / Deformation: Uneven cooling or high internal stress. Requires optimizing cooling water temperature and sizing molds.
4. Industry Technology Trends
Precision Extrusion: Utilizing laser diameter gauges and closed-loop control systems to achieve micron-level tolerance control (commonly used for medical catheters and precision automotive sealing strips).
Online Monitoring & Intelligent Control: Using sensors to monitor melt pressure, temperature, and torque in real-time, combined with AI algorithms to optimize process parameters.
Multi-material Co-extrusion: Combining two or more different materials (e.g., rigid substrate + soft sealing layer) in a single pass to enhance functionality and reduce assembly steps.