The physical properties of silicone rubber sealing rings are closely related to their vulcanization process parameters. Vulcanization temperature, vulcanization time, vulcanization pressure, and the selection and dosage of vulcanizing agent all affect the progress of the vulcanization reaction and the crosslinking density, thereby altering key properties of the sealing ring such as hardness, elasticity, tensile strength, abrasion resistance, and aging resistance.
Vulcanization temperature is the primary parameter affecting the physical properties of silicone rubber sealing rings. During vulcanization, the temperature directly determines the rate of the vulcanization reaction and the crosslinking density. If the temperature is too low, the vulcanization reaction is slow, the crosslinking density is insufficient, resulting in low hardness, poor elasticity, and tensile strength and abrasion resistance failing to meet design requirements. If the temperature is too high, over-vulcanization may occur, causing crosslinking bonds to break, making the material brittle, abnormally increasing hardness, and significantly reducing elasticity and toughness. Aging resistance will also decrease due to excessive degradation of molecular chains. Therefore, selecting an appropriate vulcanization temperature to ensure the crosslinking reaction proceeds at the optimal rate is fundamental to obtaining ideal physical properties.
Vulcanization time also has a profound impact on the physical properties of the sealing ring. If the vulcanization time is too short, the cross-linking reaction will not be fully completed, resulting in a low cross-linking density in the sealing ring, unstable physical properties, and a tendency for under-vulcanization, manifested as low hardness, insufficient elasticity, and easy deformation. If the vulcanization time is too long, it may lead to over-vulcanization, excessively high cross-linking density, hardening and brittleness of the material, and decreased tear resistance and fatigue resistance. Therefore, precisely controlling the vulcanization time to achieve the optimal balance point for the cross-linking reaction is crucial to ensuring the stability of the sealing ring's physical properties.
Vulcanization pressure also plays a significant role in the vulcanization process of silicone rubber sealing rings. Appropriate vulcanization pressure ensures uniform filling of the mold with the rubber compound, avoiding the generation of air bubbles and defects, while promoting uniform cross-linking reaction and improving the consistency of the sealing ring's physical properties. Too low a pressure may lead to insufficient filling of the rubber compound, unstable sealing ring dimensions, and uneven physical properties; too high a pressure may cause excessive flow of the rubber compound, resulting in shape loss or internal stress concentration, affecting the long-term performance of the sealing ring.
The selection and dosage of the vulcanizing agent have a decisive impact on the physical properties of the sealing ring. Different types of vulcanizing agents have different cross-linking mechanisms and reactivity. For example, peroxide vulcanization systems are suitable for high-temperature vulcanization, forming stable C-C cross-linking bonds and improving the heat resistance and chemical corrosion resistance of the sealing ring. Platinum vulcanization systems, on the other hand, are suitable for low-temperature, rapid vulcanization, forming uniform Si-C cross-linking bonds and improving the elasticity and transparency of the sealing ring. The amount of vulcanizing agent used also needs precise control. Insufficient dosage will result in low cross-linking density and substandard physical properties; excessive dosage may lead to over-vulcanization, damaging the performance of the sealing ring.
The coordinated control of vulcanization process parameters is crucial to the physical properties of the sealing ring. In actual production, the vulcanization temperature, time, pressure, and the selection and dosage of the vulcanizing agent must be comprehensively adjusted according to the type of silicone rubber, the structure and size of the sealing ring, and the application requirements to achieve the best cross-linking effect. For example, for thick-walled sealing rings, a low-temperature, long-time vulcanization process is required to avoid internal under-vulcanization and external over-vulcanization; for high-precision sealing rings, the vulcanization pressure and mold temperature uniformity must be strictly controlled to ensure dimensional stability and consistency of physical properties.
Post-curing is also an important step in improving the physical properties of silicone rubber sealing rings. Through secondary curing, residual stress inside the sealing ring can be further eliminated, the cross-linked structure can be stabilized, and the hardness, elasticity, and heat resistance can be improved. At the same time, low molecular weight compounds can be removed, improving the appearance and odor of the sealing ring.
