The three essential process parameters for rubber vulcanization are temperature, time, and pressure. Among them, vulcanization temperature has the most significant influence on product performance, while research on vulcanization pressure is relatively scarce.
Vulcanization pressure is the pressure per unit area applied to rubber compound during vulcanization. Except for some fabric-reinforced products and sponge rubber, most rubber items require appropriate pressure during vulcanization.
Vulcanization pressure is critical to ensure dimensional accuracy, structural density, physical and mechanical properties, smooth surface, and sealing performance of rubber products. Its main roles are:
1. Preventing air bubbles and improving compactness.
2. Driving compound flow to fully fill the mold cavity.
3. Enhancing adhesion between rubber and inserts (such as cord fabric) and flex resistance.
4. Improving overall physical and mechanical properties.
Factors to consider
1. Rubber compound formulation
2. Plasticity of the compound
3. Mold structure (compression, transfer, injection molding, etc.)
4. Vulcanization equipment type
5. Product structural features
1. Lower pressure for soft compounds (below 50 Shore A), higher for hard ones.
2. Lower pressure for thin products, higher for thick products.
3. Lower pressure for simple structures, higher for complex structures.
4. Higher pressure for high mechanical requirements.
5. Lower pressure at higher vulcanization temperatures.
1. Compression/transfer molding: 10–20 MPa; injection molding: 0–150 MPa.
2. Higher pressure increases static stiffness and reduces shrinkage. Domestic manufacturers usually adjust stiffness by hardness, while foreign producers prefer adjusting vulcanization pressure.
3. Shrinkage reaches zero at 83 MPa and turns negative with further pressure increase.
4. In molding, cavity pressure first rises, then falls and levels off.
5. Higher pressure improves 300% modulus and tensile strength, but reduces elongation, tear strength and compression set.
6. For damping rubber products, injection pressure is over twice that of compression molding, with better compression set at the same static stiffness.
