What is the relationship between the vulcanization temperature and pressure of the sealing ring?

In the vulcanization process of the sealing ring, the vulcanization temperature and pressure interact with each other and restrict each other, jointly determining the vulcanization effect and the performance of the sealing ring. The specific relationship is as follows:

I. Synergistic Mechanism

Accelerate the sulfurization process

Temperature governs the reaction rate: For every 10°C increase in sulfurization temperature, the reaction rate approximately increases by 1.5-2 times (following the van't Hoff rule). High temperature provides activation energy for the cross-linking bond formation.

Pressure promotes heat conduction: High pressure enhances the thermal contact between the rubber material and the mold, reducing temperature gradients and ensuring uniform sulfurization of thick-walled sealing rings (such as O-rings). For example, during the sulfurization of natural rubber automotive tires, high pressure can shorten the sulfurization time and improve the sulfurization efficiency.

Improve sealing performance

Pressure eliminates air bubbles: During sulfurization, the moisture, volatile substances, and sulfurization hydrogen gas in the rubber material escape under high temperature. If the pressure is insufficient, it will lead to an increase in porosity, reducing the sealing performance. High pressure (such as 2-5 MPa) can inhibit bubble formation and improve the compactness of the rubber material.

Temperature optimizes the cross-linking structure: Appropriate temperature (such as 143-150°C for natural rubber) can generate polysulfide cross-linking bonds, enhancing the elasticity and resilience of the sealing ring; excessive temperature may form monosulfide bonds, resulting in increased hardness but decreased sealing performance.

II. Dynamic Constraint Relationship

Temperature-Pressure Balance

High pressure suppresses the adverse effects of high temperature: High temperature is prone to cause rubber molecular chain cracking (sulfurization reversion), but high pressure can counteract the risk of thermal degradation by shortening the sulfurization time (such as raising the temperature to 180°C and combining with high pressure).

Low pressure requires low-temperature compensation: For thin-walled sealing rings (such as diaphragms), low pressure (such as atmospheric pressure) sulfurization requires a lower temperature (such as 100-120°C) to avoid scorching, while extending the sulfurization time to ensure the cross-linking degree.

Matching of process parameters

Thick-walled products: A "low-temperature long time + high pressure" strategy is required. For example, when sulfurizing thick rubber sealing rings, gradually heating to 150°C and maintaining high pressure (such as 10-20 MPa) can prevent insufficient sulfurization inside.

Thin-walled products: Use a "high temperature short time + low pressure" strategy. For example, when vulcanizing silicone rubber sealing rings at 200°C, low pressure (such as 0.5-1 MPa) can meet the requirements for compactness while shortening the production cycle.

III. Impact on Sealing Ring Performance

Physical and mechanical properties

Tensile strength and elongation at break: Increased pressure can increase the cross-linking density, enhancing tensile strength (such as when the pressure increases from 1.6 MPa to 2.5 MPa, the tensile strength increases by approximately 20%), but the elongation at break may decrease (as excessive cross-linking restricts molecular chain sliding).

Tear strength: Sealing rings with a higher proportion of polysulfide bonds have higher tear strength, but high pressure promotes the formation of monosulfide bonds, resulting in a decrease in tear strength (such as when the pressure increases from 2 MPa to 5 MPa, the tear strength decreases by approximately 15%).

Durability and reliability

Compression permanent deformation: High pressure can reduce the compression permanent deformation of the vulcanized rubber (such as when the pressure increases from 1 MPa to 3 MPa, the deformation rate decreases by 30%), improving the lifespan of the sealing ring in dynamic conditions.

Flexibility: Appropriate pressure (such as 2-3 MPa) can enhance the adhesion between rubber and the reinforcing material, preventing the sealing ring from delaminating during repeated bending.

IV. Practical Application Cases

Automobile engine sealing ring: Use the "160°C + 8 MPa" process. High pressure ensures full sulfurization of the thick-walled part, and high temperature promotes rapid cross-linking, meeting the requirements for high-temperature and oil-resistant sealing.

Medical device silicone sealing ring: Sulfurize at 200°C without pressure, taking advantage of the high thermal stability of silicone rubber, achieving a sealing performance with no air bubbles and high transparency by precisely controlling the temperature.

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