Rubber injection molding is a processing technology in which compounded rubber is injected into a closed mold through an injection molding machine to achieve vulcanization and shaping. The process combines screw plasticizing with plunger injection, allowing the rubber compound to complete the crosslinking reaction inside a heated mold. With a cavity pressure of 100–150 MPa, the process enables the production of high-precision, void-free parts, making it suitable for manufacturing precision components such as automotive seals and medical rubber stoppers. Its technical advantages include highly uniform heating of the compound, excellent product density, and superior mold-filling capability.
Process Principle
Based on the crosslinking characteristics of thermosetting polymers, the process includes three stages:
- Plasticizing stage:
The screw shears and plasticizes the compound at 70–90°C, achieving partial pre-crosslinking. - Injection stage:
The plunger injects the rubber into a 160–200°C mold under 120–200 MPa pressure. - Vulcanization stage:
Chemical crosslinking is completed under holding pressure, with time adjusted according to product thickness.
The mold is designed with a multi-gate system and overflow channels to ensure complete filling of complex cavities. Compared with traditional compression molding, cycle time is reduced by 40–60%, making this process ideal for high-precision rubber products with complex geometries.
Characteristics in Industrial Applications
- Temperature gradient controlled within ±1.5°C, eliminating scorch and under-cure defects
- Cavity pressure distribution uniformity up to 95%, with dimensional tolerances of ±0.02 mm
- Material utilization exceeds 98%, reducing flash by 80% compared with compression molding
- High automation capability enabling unmanned continuous production
Rubber injection molding completes the vulcanization during the injection phase, resulting in improved product performance.
Application Fields
The process mainly covers two product categories:
General molded products:
O-rings, dust boots, and other standardized components
Engineered precision parts:
- Automotive: turbocharger hoses, new-energy battery sealing components
- Electronics: connector sealing rings, vibration-damping pads
- Medical: syringe plungers, artificial-organ sealing valves
It is particularly suitable for composite products containing metal inserts, offering high positional accuracy. It can also produce micro-sized precision rubber components.
Process Parameters
Key control indicators form a three-parameter system:
- Temperature parameters:
Barrel zones controlled at 50–120°C; mold temperature maintained at 160 ± 5°C - Pressure parameters:
Injection pressure 120–200 MPa, back pressure 0.5–1.5 MPa - Time parameters:
Injection time 3–15 seconds; vulcanization time increases proportionally with part thickness
The essence of this process is to use a rubber injection molding machine to force compounded rubber into a closed vulcanization mold and form the product through pressurized vulcanization. Its technical strengths include uniform heating, high product density, and excellent mold-filling behavior. The correct technical term in English is “injection molding of rubber,” with “rubber injection” being an alternative name.
Equipment Configuration
A typical rubber injection molding system consists of five major modules:
- Injection unit:
Three-stage screw design with an L/D ratio of 18:1 - Clamping unit:
Two-plate hydraulic system with clamping force of 200–5000 tons - Temperature control system:
Oil-circulation mold-temperature controller with ±1°C accuracy - Hydraulic system:
Proportional servo control with 50 ms response time - Control system:
Integrated PLC and HMI, capable of storing 200 process recipes
Advanced machines are equipped with in-mold pressure sensors and infrared temperature measurement devices for real-time monitoring of the molding process.
